#5840

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Build # #5840

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ben-manes

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style polish

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/caffeine/src/main/java/com/github/benmanes/caffeine/cache/BoundedLocalCache.java

/*
 * Copyright 2014 Ben Manes. All Rights Reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.github.benmanes.caffeine.cache;

import static com.github.benmanes.caffeine.cache.Async.ASYNC_EXPIRY;
import static com.github.benmanes.caffeine.cache.Caffeine.calculateHashMapCapacity;
import static com.github.benmanes.caffeine.cache.Caffeine.ceilingPowerOfTwo;
import static com.github.benmanes.caffeine.cache.Caffeine.requireArgument;
import static com.github.benmanes.caffeine.cache.Caffeine.requireState;
import static com.github.benmanes.caffeine.cache.Caffeine.toNanosSaturated;
import static com.github.benmanes.caffeine.cache.Caffeine.toUnchecked;
import static com.github.benmanes.caffeine.cache.LocalLoadingCache.newBulkMappingFunction;
import static com.github.benmanes.caffeine.cache.LocalLoadingCache.newMappingFunction;
import static com.github.benmanes.caffeine.cache.Node.PROBATION;
import static com.github.benmanes.caffeine.cache.Node.PROTECTED;
import static com.github.benmanes.caffeine.cache.Node.WINDOW;
import static java.lang.invoke.ConstantBootstraps.fieldVarHandle;
import static java.util.Locale.US;
import static java.util.Objects.requireNonNull;
import static java.util.Spliterator.DISTINCT;
import static java.util.Spliterator.IMMUTABLE;
import static java.util.Spliterator.NONNULL;
import static java.util.Spliterator.ORDERED;

import java.io.InvalidObjectException;
import java.io.ObjectInputStream;
import java.io.Serializable;
import java.lang.System.Logger;
import java.lang.System.Logger.Level;
import java.lang.invoke.MethodHandles;
import java.lang.invoke.VarHandle;
import java.lang.ref.ReferenceQueue;
import java.lang.ref.WeakReference;
import java.time.Duration;
import java.util.AbstractCollection;
import java.util.AbstractSet;
import java.util.ArrayDeque;
import java.util.Collection;
import java.util.Collections;
import java.util.Comparator;
import java.util.Deque;
import java.util.HashMap;
import java.util.IdentityHashMap;
import java.util.Iterator;
import java.util.LinkedHashMap;
import java.util.Map;
import java.util.NoSuchElementException;
import java.util.Objects;
import java.util.Optional;
import java.util.OptionalInt;
import java.util.OptionalLong;
import java.util.Set;
import java.util.Spliterator;
import java.util.Spliterators;
import java.util.concurrent.CancellationException;
import java.util.concurrent.CompletableFuture;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;
import java.util.concurrent.Executor;
import java.util.concurrent.ForkJoinPool;
import java.util.concurrent.ThreadLocalRandom;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.TimeoutException;
import java.util.concurrent.locks.ReentrantLock;
import java.util.function.BiConsumer;
import java.util.function.BiFunction;
import java.util.function.Consumer;
import java.util.function.Function;
import java.util.function.Predicate;
import java.util.stream.Stream;
import java.util.stream.StreamSupport;

import org.jspecify.annotations.NonNull;
import org.jspecify.annotations.Nullable;

import com.github.benmanes.caffeine.cache.Async.AsyncExpiry;
import com.github.benmanes.caffeine.cache.LinkedDeque.PeekingIterator;
import com.github.benmanes.caffeine.cache.Policy.CacheEntry;
import com.github.benmanes.caffeine.cache.References.InternalReference;
import com.github.benmanes.caffeine.cache.stats.StatsCounter;
import com.google.errorprone.annotations.CanIgnoreReturnValue;
import com.google.errorprone.annotations.Var;
import com.google.errorprone.annotations.concurrent.GuardedBy;

/**
 * An in-memory cache implementation that supports full concurrency of retrievals, a high expected
 * concurrency for updates, and multiple ways to bound the cache.
 * <p>
 * This class is abstract and code generated subclasses provide the complete implementation for a
 * particular configuration. This is to ensure that only the fields and execution paths necessary
 * for a given configuration are used.
 *
 * @author ben.manes@gmail.com (Ben Manes)
 * @param <K> the type of keys maintained by this cache
 * @param <V> the type of mapped values
 */
@SuppressWarnings({"RedundantSuppression", "ResultOfMethodCallIgnored", "serial", "unused"})
abstract class BoundedLocalCache<K, V> extends BLCHeader.DrainStatusRef
    implements LocalCache<K, V> {

  /*
   * This class performs a best-effort bounding of a ConcurrentHashMap using a page-replacement
   * algorithm to determine which entries to evict when the capacity is exceeded.
   *
   * Concurrency:
   * ------------
   * The page replacement algorithms are kept eventually consistent with the map. An update to the
   * map and recording of reads may not be immediately reflected in the policy's data structures.
   * These structures are guarded by a lock, and operations are applied in batches to avoid lock
   * contention. The penalty of applying the batches is spread across threads, so that the amortized
   * cost is slightly higher than performing just the ConcurrentHashMap operation [1].
   *
   * A memento of the reads and writes that were performed on the map is recorded in buffers. These
   * buffers are drained at the first opportunity after a write or when a read buffer is full. The
   * reads are offered to a buffer that will reject additions if contended on or if it is full. Due
   * to the concurrent nature of the read and write operations, a strict policy ordering is not
   * possible, but it may be observably strict when single-threaded. The buffers are drained
   * asynchronously to minimize the request latency and uses a state machine to determine when to
   * schedule this work on an executor.
   *
   * Due to a lack of a strict ordering guarantee, a task can be executed out-of-order, such as a
   * removal followed by its addition. The state of the entry is encoded using the key field to
   * avoid additional memory usage. An entry is "alive" if it is in both the hash table and the page
   * replacement policy. It is "retired" if it is not in the hash table and is pending removal from
   * the page replacement policy. Finally, an entry transitions to the "dead" state when it is
   * neither in the hash table nor the page replacement policy. Both the retired and dead states are
   * represented by a sentinel key that should not be used for map operations.
   *
   * Eviction:
   * ---------
   * Maximum size is implemented using the Window TinyLfu policy [2] due to its high hit rate, O(1)
   * time complexity, and small footprint. A new entry starts in the admission window and remains
   * there as long as it has high temporal locality (recency). Eventually an entry will slip from
   * the window into the main space. If the main space is already full, then a historic frequency
   * filter determines whether to evict the newly admitted entry or the victim entry chosen by the
   * eviction policy. This process ensures that the entries in the window were very recently used,
   * while entries in the main space are accessed very frequently and remain moderately recent. The
   * windowing allows the policy to have a high hit rate when entries exhibit a bursty access
   * pattern, while the filter ensures that popular items are retained. The admission window uses
   * LRU and the main space uses Segmented LRU.
   *
   * The optimal size of the window vs. main spaces is workload dependent [3]. A large admission
   * window is favored by recency-biased workloads, while a small one favors frequency-biased
   * workloads. When the window is too small, then recent arrivals are prematurely evicted, but when
   * it is too large, then they pollute the cache and force the eviction of more popular entries.
   * The optimal configuration is dynamically determined by using hill climbing to walk the hit
   * rate curve. For modestly sized caches this samples the hit rate and adjusts the window size
   * in the direction that is improving, decaying the step until the climber converges and
   * restarting when a large change indicates that the workload altered. Tiny caches allow the
   * sample period to grow as its step decays to avoid getting stuck at a poor configuration.
   * Larger caches instead compare the regions' hit densities within a single sample, which is
   * immune to the hit rate swings of a phasey workload, and take a proportional step towards the
   * balance point. As that signal only observes the hits that the current split earns, a region
   * that earns almost nothing cannot measure what a different split would, so those samples are
   * never trusted to hold position: the climber probes out of the blind state by hit rate,
   * accepts the new position if the density signal validates it, and otherwise undoes the probe
   * with exponentially longer pauses between attempts.
   *
   * The historic usage is retained in a compact popularity sketch, which uses hashing to
   * probabilistically estimate an item's frequency. This exposes a flaw where an adversary could
   * use hash flooding [4] to artificially raise the frequency of the main space's victim and cause
   * all candidates to be rejected. In the worst case, by exploiting hash collisions, an attacker
   * could cause the cache to never hit and hold only worthless items, resulting in a
   * denial-of-service attack against the underlying resource. This is mitigated by introducing
   * jitter, allowing candidates that are at least moderately popular to have a small, random chance
   * of being admitted. This causes the victim to be evicted, but in a way that marginally impacts
   * the hit rate.
   *
   * Expiration:
   * -----------
   * Expiration is implemented in O(1) time complexity. The time-to-idle policy uses an access-order
   * queue, the time-to-live policy uses a write-order queue, and variable expiration uses a
   * hierarchical timer wheel [5]. The queuing policies allow for peeking at the oldest entry to
   * determine if it has expired. If it has not, then the younger entries must not have expired
   * either. If a maximum size is set, then expiration will share the queues, minimizing the
   * per-entry footprint. The timer wheel based policy uses hashing and cascading in a manner that
   * amortizes the penalty of sorting to achieve a similar algorithmic cost.
   *
   * The expiration updates are applied in a best effort fashion. The reordering of variable or
   * access-order expiration may be discarded by the read buffer if it is full or contended.
   * Similarly, recording the touch for expiration to extend its lifetime may be ignored for an
   * entry if the last update was within a short time window. This is done to avoid overwhelming the
   * write buffer and to avoid false sharing on reads due to modifying the access time. The
   * write-order scan compensates by moving a stale-positioned head to the back of the queue when
   * its timestamp is fresher than the tail, so subsequent passes can resume from the next-oldest
   * entry. The access-order scan does not, because those queues are also the eviction order, so a
   * lost reorder defers reaping the entries behind its head until that head is read again or
   * expires.
   *
   * [1] BP-Wrapper: A Framework Making Any Replacement Algorithms (Almost) Lock Contention Free
   * https://web.njit.edu/~dingxn/papers/BP-Wrapper.pdf
   * [2] TinyLFU: A Highly Efficient Cache Admission Policy
   * https://dl.acm.org/citation.cfm?id=3149371
   * [3] Adaptive Software Cache Management
   * https://dl.acm.org/citation.cfm?id=3274816
   * [4] Denial of Service via Algorithmic Complexity Attack
   * https://www.usenix.org/legacy/events/sec03/tech/full_papers/crosby/crosby.pdf
   * [5] Hashed and Hierarchical Timing Wheels
   * http://www.cs.columbia.edu/~nahum/w6998/papers/ton97-timing-wheels.pdf
   */

  static final Logger logger = System.getLogger(BoundedLocalCache.class.getName());

  /** The number of CPUs */
  static final int NCPU = Runtime.getRuntime().availableProcessors();
  /** The initial capacity of the write buffer. */
  static final int WRITE_BUFFER_MIN = 4;
  /** The maximum capacity of the write buffer. */
  static final int WRITE_BUFFER_MAX = 128 * ceilingPowerOfTwo(NCPU);
  /** The maximum weighted capacity of the map. */
  static final long MAXIMUM_CAPACITY = Long.MAX_VALUE - Integer.MAX_VALUE;
  /** The initial percent of the maximum weighted capacity dedicated to the main space. */
  static final double PERCENT_MAIN = 0.99d;
  /** The percent of the maximum weighted capacity dedicated to the main's protected space. */
  static final double PERCENT_MAIN_PROTECTED = 0.80d;
  /** The minimum popularity for allowing randomized admission. */
  static final int ADMIT_HASHDOS_THRESHOLD = 6;
  /** The maximum number of entries that can be transferred between queues. */
  static final int QUEUE_TRANSFER_THRESHOLD = 1_000;
  /** The number of expirations per policy after which a maintenance cycle defers the rest. */
  static final int EXPIRATION_THRESHOLD = 1_000;
  /** The maximum number of collected references that can be drained per maintenance cycle. */
  static final int REFERENCE_THRESHOLD = 1_000;
  /** The maximum time window between touches for expiration updates. */
  static final long EXPIRE_TOLERANCE = TimeUnit.SECONDS.toNanos(1);
  /** The maximum duration before an entry expires. */
  static final long MAXIMUM_EXPIRY = (Long.MAX_VALUE >> 1); // 150 years
  /** The duration to wait on the eviction lock before warning of a possible misuse. */
  static final long WARN_AFTER_LOCK_WAIT_NANOS = TimeUnit.SECONDS.toNanos(30);
  /** The number of retries before computing to validate the entry's integrity; pow2 modulus. */
  static final int MAX_PUT_SPIN_WAIT_ATTEMPTS = 1024 - 1;
  /** The handle for the in-flight refresh operations. */
  static final VarHandle REFRESHES = fieldVarHandle(MethodHandles.lookup(),
      "refreshes", VarHandle.class, BoundedLocalCache.class, ConcurrentMap.class);

  final @Nullable RemovalListener<K, V> evictionListener;
  final @Nullable AsyncCacheLoader<K, V> cacheLoader;

  final MpscGrowableArrayQueue<Runnable> writeBuffer;
  final ConcurrentHashMap<Object, Node<K, V>> data;
  final PerformCleanupTask drainBuffersTask;
  final Consumer<Node<K, V>> accessPolicy;
  final NodeFactory<K, V> nodeFactory;
  final ReentrantLock evictionLock;
  final Weigher<K, V> weigher;
  final Executor executor;

  final boolean isWeighted;
  final boolean isAsync;

  volatile Buffer<Node<K, V>> readBuffer;

  @Nullable Set<K> keySet;
  @Nullable Collection<V> values;
  @Nullable Set<Entry<K, V>> entrySet;
  volatile @Nullable ConcurrentMap<Object, CompletableFuture<?>> refreshes;

  /** Creates an instance based on the builder's configuration. */
  @SuppressWarnings("GuardedBy")
  protected BoundedLocalCache(Caffeine<K, V> builder,
      @Nullable AsyncCacheLoader<K, V> cacheLoader, boolean isAsync) {
    this.isAsync = isAsync;
    this.cacheLoader = cacheLoader;
    executor = builder.getExecutor();
    isWeighted = builder.isWeighted();
    evictionLock = new ReentrantLock();
    weigher = builder.getWeigher(isAsync);
    drainBuffersTask = new PerformCleanupTask(this);
    nodeFactory = NodeFactory.newFactory(builder, isAsync);
    evictionListener = builder.getEvictionListener(isAsync);
    data = new ConcurrentHashMap<>(builder.getInitialCapacity());
    writeBuffer = new MpscGrowableArrayQueue<>(WRITE_BUFFER_MIN, WRITE_BUFFER_MAX);
    boolean tracksAccess = evicts() || collectKeys() || collectValues() || expiresAfterAccess();
    readBuffer = (tracksAccess && !fastpath()) ? new BoundedBuffer<>() : Buffer.disabled();
    accessPolicy = (evicts() || expiresAfterAccess())
        ? node -> onAccess(node, Access.HIT)
        : node -> {};

    if (evicts()) {
      setMaximumSize(builder.getMaximum());
    }
  }

  /** Ensures that the node is alive during the map operation. */
  void requireIsAlive(Object key, Node<?, ?> node) {
    if (!node.isAlive()) {
      throw new IllegalStateException(brokenEqualityMessage(key, node));
    }
  }

  /** Logs if the node cannot be found in the map but is still alive. */
  void logIfAlive(Node<?, ?> node) {
    if (node.isAlive()) {
      String message = brokenEqualityMessage(node.getKeyReference(), node);
      logger.log(Level.ERROR, message, new IllegalStateException());
    }
  }

  /** Returns the formatted broken equality error message. */
  String brokenEqualityMessage(Object key, Node<?, ?> node) {
    return String.format(US, "An invalid state was detected, occurring when the key's equals or "
        + "hashCode was modified while residing in the cache. This violation of the Map "
        + "contract can lead to non-deterministic behavior (key: %s, key type: %s, "
        + "node type: %s, cache type: %s).", key, key.getClass().getName(),
        node.getClass().getSimpleName(), getClass().getSimpleName());
  }

  /* --------------- Shared --------------- */

  @Override
  public boolean isAsync() {
    return isAsync;
  }

  /** Returns if the node's value is currently being computed asynchronously. */
  final boolean isComputingAsync(@Nullable V value) {
    return isAsync && !Async.isReady((CompletableFuture<?>) value);
  }

  @GuardedBy("evictionLock")
  protected AccessOrderDeque<Node<K, V>> accessOrderWindowDeque() {
    throw new UnsupportedOperationException();
  }

  @GuardedBy("evictionLock")
  protected AccessOrderDeque<Node<K, V>> accessOrderProbationDeque() {
    throw new UnsupportedOperationException();
  }

  @GuardedBy("evictionLock")
  protected AccessOrderDeque<Node<K, V>> accessOrderProtectedDeque() {
    throw new UnsupportedOperationException();
  }

  @GuardedBy("evictionLock")
  protected WriteOrderDeque<Node<K, V>> writeOrderDeque() {
    throw new UnsupportedOperationException();
  }

  @Override
  public final Executor executor() {
    return executor;
  }

  @Override
  public ConcurrentMap<Object, CompletableFuture<?>> refreshes() {
    @Var var pending = refreshes;
    if (pending == null) {
      pending = new ConcurrentHashMap<>();
      if (!REFRESHES.compareAndSet(this, null, pending)) {
        pending = requireNonNull(refreshes);
      }
    }
    return pending;
  }

  /** Invalidate the in-flight refresh. */
  @SuppressWarnings("RedundantCollectionOperation")
  void discardRefresh(Object keyReference) {
    var pending = refreshes;
    if ((pending != null) && pending.containsKey(keyReference)) {
      pending.remove(keyReference);
    }
  }

  @Override
  public Object referenceKey(K key) {
    return nodeFactory.newLookupKey(key);
  }

  @Override
  public boolean isPendingEviction(K key) {
    Node<K, V> node = data.get(nodeFactory.newLookupKey(key));
    if (node == null) {
      return false;
    }
    boolean expired = hasExpired(node, expirationTicker().read());
    V value = node.getValue();
    return (value == null) || (expired && !isComputingAsync(value));
  }

  /* --------------- Stats Support --------------- */

  @Override
  public boolean isRecordingStats() {
    return false;
  }

  @Override
  public StatsCounter statsCounter() {
    return StatsCounter.disabledStatsCounter();
  }

  @Override
  public Ticker statsTicker() {
    return Ticker.disabledTicker();
  }

  /* --------------- Removal Listener Support --------------- */

  @Override
  public @Nullable RemovalListener<K, V> removalListener() {
    return null;
  }

  @Override
  public void notifyRemoval(@Nullable K key, @Nullable V value, RemovalCause cause) {
    var removalListener = removalListener();
    if (removalListener == null) {
      return;
    }
    Runnable task = () -> {
      try {
        removalListener.onRemoval(key, value, cause);
      } catch (Throwable t) {
        if (t instanceof InterruptedException) {
          Thread.currentThread().interrupt();
        }
        logger.log(Level.WARNING, "Exception thrown by removal listener", t);
      }
    };
    try {
      executor.execute(task);
    } catch (Throwable t) {
      logger.log(Level.ERROR, "Exception thrown when submitting removal listener", t);
      task.run();
    }
  }

  /* --------------- Eviction Listener Support --------------- */

  void notifyEviction(@Nullable K key, @Nullable V value, RemovalCause cause) {
    if (evictionListener == null) {
      return;
    }
    try {
      evictionListener.onRemoval(key, value, cause);
    } catch (Throwable t) {
      if (t instanceof InterruptedException) {
        Thread.currentThread().interrupt();
      }
      logger.log(Level.WARNING, "Exception thrown by eviction listener", t);
    }
  }

  /* --------------- Reference Support --------------- */

  @Override
  public boolean collectKeys() {
    return false;
  }

  /** Returns if the values are weak or soft reference garbage collected. */
  protected boolean collectValues() {
    return false;
  }

  @SuppressWarnings({"DataFlowIssue", "NullAway"})
  protected ReferenceQueue<K> keyReferenceQueue() {
    return null;
  }

  @SuppressWarnings({"DataFlowIssue", "NullAway"})
  protected ReferenceQueue<V> valueReferenceQueue() {
    return null;
  }

  /* --------------- Expiration Support --------------- */

  /** Returns the {@link Pacer} used to schedule the maintenance task. */
  protected @Nullable Pacer pacer() {
    return null;
  }

  /** Returns if the cache expires entries by any of its policies. */
  final boolean expires() {
    return expiresAfterAccess() || expiresAfterWrite() || expiresVariable();
  }

  /** Returns if a read may extend when the entry expires. */
  final boolean expiresAfterRead() {
    return expiresAfterAccess() || expiresVariable();
  }

  /** Returns if the cache expires entries after a variable time threshold. */
  protected boolean expiresVariable() {
    return false;
  }

  /** Returns if the cache expires entries after an access time threshold. */
  protected boolean expiresAfterAccess() {
    return false;
  }

  /** Returns how long after the last access to an entry the map will retain that entry. */
  protected long expiresAfterAccessNanos() {
    throw new UnsupportedOperationException();
  }

  protected void setExpiresAfterAccessNanos(long expireAfterAccessNanos) {
    throw new UnsupportedOperationException();
  }

  /** Returns if the cache expires entries after a write time threshold. */
  protected boolean expiresAfterWrite() {
    return false;
  }

  /** Returns how long after the last write to an entry the map will retain that entry. */
  protected long expiresAfterWriteNanos() {
    throw new UnsupportedOperationException();
  }

  protected void setExpiresAfterWriteNanos(long expireAfterWriteNanos) {
    throw new UnsupportedOperationException();
  }

  /** Returns if the cache refreshes entries after a write time threshold. */
  protected boolean refreshAfterWrite() {
    return false;
  }

  /** Returns how long after the last write an entry becomes a candidate for refresh. */
  protected long refreshAfterWriteNanos() {
    throw new UnsupportedOperationException();
  }

  protected void setRefreshAfterWriteNanos(long refreshAfterWriteNanos) {
    throw new UnsupportedOperationException();
  }

  @Override
  @SuppressWarnings({"DataFlowIssue", "NullAway"})
  public Expiry<K, V> expiry() {
    return null;
  }

  /** Returns the {@link Ticker} used by this cache for expiration. */
  public Ticker expirationTicker() {
    return Ticker.disabledTicker();
  }

  protected TimerWheel<K, V> timerWheel() {
    throw new UnsupportedOperationException();
  }

  /* --------------- Eviction Support --------------- */

  /** Returns if the cache evicts entries due to a maximum size or weight threshold. */
  protected boolean evicts() {
    return false;
  }

  /** Returns if entries may be assigned different weights. */
  protected boolean isWeighted() {
    return isWeighted && (weigher != Weigher.singletonWeigher());
  }

  protected FrequencySketch frequencySketch() {
    throw new UnsupportedOperationException();
  }

  @GuardedBy("evictionLock")
  protected WindowClimber climber() {
    throw new UnsupportedOperationException();
  }

  /** Returns if an access to an entry can skip notifying the eviction policy. */
  protected boolean fastpath() {
    return false;
  }

  /** Returns the maximum weighted size. */
  protected long maximum() {
    throw new UnsupportedOperationException();
  }

  /** Returns the maximum weighted size. */
  protected long maximumAcquire() {
    throw new UnsupportedOperationException();
  }

  /** Returns the maximum weighted size of the window space. */
  protected long windowMaximum() {
    throw new UnsupportedOperationException();
  }

  /** Returns the maximum weighted size of the main's protected space. */
  protected long mainProtectedMaximum() {
    throw new UnsupportedOperationException();
  }

  @GuardedBy("evictionLock")
  protected void setMaximum(long maximum) {
    throw new UnsupportedOperationException();
  }

  @GuardedBy("evictionLock")
  protected void setWindowMaximum(long maximum) {
    throw new UnsupportedOperationException();
  }

  @GuardedBy("evictionLock")
  protected void setMainProtectedMaximum(long maximum) {
    throw new UnsupportedOperationException();
  }

  /** Returns the combined weight of the values in the cache (may be negative). */
  protected long weightedSize() {
    throw new UnsupportedOperationException();
  }

  /** Returns the combined weight of the values in the cache (may be negative). */
  protected long weightedSizeAcquire() {
    throw new UnsupportedOperationException();
  }

  /** Returns the uncorrected combined weight of the values in the window space. */
  protected long windowWeightedSize() {
    throw new UnsupportedOperationException();
  }

  /** Returns the uncorrected combined weight of the values in the main's protected space. */
  protected long mainProtectedWeightedSize() {
    throw new UnsupportedOperationException();
  }

  @GuardedBy("evictionLock")
  protected void setWeightedSize(long weightedSize) {
    throw new UnsupportedOperationException();
  }

  @GuardedBy("evictionLock")
  protected void setWindowWeightedSize(long weightedSize) {
    throw new UnsupportedOperationException();
  }

  @GuardedBy("evictionLock")
  protected void setMainProtectedWeightedSize(long weightedSize) {
    throw new UnsupportedOperationException();
  }

  /**
   * Sets the maximum weighted size of the cache. The caller may need to perform a maintenance cycle
   * to eagerly evicts entries until the cache shrinks to the appropriate size.
   */
  @GuardedBy("evictionLock")
  @SuppressWarnings({"ConstantValue", "Varifier"})
  void setMaximumSize(long maximum) {
    long max = Math.min(maximum, MAXIMUM_CAPACITY);
    if (max == maximum()) {
      return;
    }

    long window = max - (long) (PERCENT_MAIN * max);
    long mainProtected = (long) (PERCENT_MAIN_PROTECTED * (max - window));

    setMaximum(max);
    setWindowMaximum(window);
    setMainProtectedMaximum(mainProtected);

    if (climber() != null) {
      // null during the super constructor's initial sizing; the generated constructor replays this
      climber().resized(maximum());
    }

    if ((frequencySketch() != null) && !isWeighted() && (weightedSize() >= (max >>> 1))) {
      // Lazily initialize when close to the maximum size
      frequencySketch().ensureCapacity(max);
      recordReads();
    }
  }

  /** Evicts entries if the cache exceeds the maximum. */
  @GuardedBy("evictionLock")
  void evictEntries(long now) {
    if (!evicts()) {
      return;
    }
    var candidate = evictFromWindow();
    evictFromMain(candidate, now);
  }

  /**
   * Evicts entries from the window space into the main space while the window size exceeds a
   * maximum, transferring at most a bounded number of entries per maintenance cycle.
   *
   * @return the first candidate promoted into the probation space
   */
  @GuardedBy("evictionLock")
  @Nullable Node<K, V> evictFromWindow() {
    @Var Node<K, V> first = null;
    @Var int remaining = QUEUE_TRANSFER_THRESHOLD;
    @Var Node<K, V> node = accessOrderWindowDeque().peekFirst();
    while (windowWeightedSize() > windowMaximum()) {
      // The pending operations will adjust the size to reflect the correct weight
      if (node == null) {
        break;
      }
      if (remaining == 0) {
        // A resize can leave the window arbitrarily oversized, so the transfer is bounded per
        // maintenance cycle and re-armed to drain the backlog across cycles
        setDrainStatusOpaque(PROCESSING_TO_REQUIRED);
        break;
      }

      Node<K, V> next = node.getNextInAccessOrder();
      long weight = node.getPolicyWeight();
      if (weight != 0) {
        transfer(node, weight, WINDOW, PROBATION);
        if (first == null) {
          first = node;
        }
        remaining--;
      }
      node = next;
    }

    return first;
  }

  /**
   * Evicts entries from the main space if the cache exceeds the maximum capacity. The main space
   * determines whether admitting an entry (coming from the window space) is preferable to retaining
   * the eviction policy's victim. This decision is made using a frequency filter so that the
   * least frequently used entry is removed.
   * <p>
   * The window space's candidates were previously promoted to the probation space at its MRU
   * position and the eviction policy's victim starts at the LRU position. The candidates are
   * evaluated in promotion order while an eviction is required, and if exhausted then additional
   * entries are retrieved from the window space. Likewise, if the victim selection exhausts the
   * probation space then additional entries are retrieved from the protected space. The queues are
   * consumed in LRU order and the evicted entry is the one with a lower relative frequency, where
   * the preference is to retain the main space's victims versus the window space's candidates on a
   * tie.
   *
   * @param candidate the first candidate promoted into the probation space
   * @param now the current time, in nanoseconds
   */
  @GuardedBy("evictionLock")
  void evictFromMain(@Var @Nullable Node<K, V> candidate, long now) {
    @Var int victimQueue = PROBATION;
    @Var int candidateQueue = PROBATION;
    @Var Node<K, V> victim = accessOrderProbationDeque().peekFirst();
    while (weightedSize() > maximum()) {
      // Search the admission window for additional candidates
      if ((candidate == null) && (candidateQueue == PROBATION)) {
        candidate = accessOrderWindowDeque().peekFirst();
        candidateQueue = WINDOW;
      }

      // Try evicting from the protected and window queues
      if ((candidate == null) && (victim == null)) {
        if (victimQueue == PROBATION) {
          victim = accessOrderProtectedDeque().peekFirst();
          victimQueue = PROTECTED;
          continue;
        } else if (victimQueue == PROTECTED) {
          victim = accessOrderWindowDeque().peekFirst();
          victimQueue = WINDOW;
          continue;
        }

        // The pending operations will adjust the size to reflect the correct weight
        break;
      }

      // Skip over entries with zero weight
      if ((victim != null) && (victim.getPolicyWeight() == 0)) {
        victim = victim.getNextInAccessOrder();
        continue;
      } else if ((candidate != null) && (candidate.getPolicyWeight() == 0)) {
        candidate = candidate.getNextInAccessOrder();
        continue;
      }

      // Evict immediately if only one of the entries is present
      if (victim == null) {
        requireNonNull(candidate);
        candidate = evictAndAdvance(candidate, now, RemovalCause.SIZE);
        continue;
      } else if (candidate == null) {
        victim = evictAndAdvance(victim, now, RemovalCause.SIZE);
        continue;
      }

      // Evict immediately if both selected the same entry
      if (candidate == victim) {
        victim = evictAndAdvance(victim, now, RemovalCause.SIZE);
        candidate = null;
        continue;
      }

      // Evict immediately if an entry was collected
      var victimKeyRef = victim.getKeyReferenceOrNull();
      var candidateKeyRef = candidate.getKeyReferenceOrNull();
      if (victimKeyRef == null) {
        victim = evictAndAdvance(victim, now, RemovalCause.COLLECTED);
        continue;
      } else if (candidateKeyRef == null) {
        candidate = evictAndAdvance(candidate, now, RemovalCause.COLLECTED);
        continue;
      }

      // Evict immediately if an entry was removed
      if (!victim.isAlive()) {
        victim = evictAndAdvance(victim, now, RemovalCause.SIZE);
        continue;
      } else if (!candidate.isAlive()) {
        candidate = evictAndAdvance(candidate, now, RemovalCause.SIZE);
        continue;
      }

      // Evict immediately if the candidate's weight exceeds the maximum
      if (candidate.getPolicyWeight() > maximum()) {
        candidate = evictAndAdvance(candidate, now, RemovalCause.SIZE);
        continue;
      }

      // Evict the entry with the lowest frequency
      if (admit(candidateKeyRef, victimKeyRef)) {
        victim = evictAndAdvance(victim, now, RemovalCause.SIZE);
        candidate = candidate.getNextInAccessOrder();
      } else {
        candidate = evictAndAdvance(candidate, now, RemovalCause.SIZE);
      }
    }
  }

  /** Evicts the entry and returns its successor, or {@code null} if it was the last. */
  @GuardedBy("evictionLock")
  @Nullable Node<K, V> evictAndAdvance(Node<K, V> node, long now, RemovalCause cause) {
    Node<K, V> next = node.getNextInAccessOrder();
    evictEntry(node, cause, now);
    return next;
  }

  /**
   * Determines if the candidate should be accepted into the main space, as determined by its
   * frequency relative to the victim. A small amount of randomness is used to protect against hash
   * collision attacks, where the victim's frequency is artificially raised so that no new entries
   * are admitted.
   *
   * @param candidateKeyRef the keyRef for the entry being proposed for long term retention
   * @param victimKeyRef the keyRef for the entry chosen by the eviction policy for replacement
   * @return if the candidate should be admitted and the victim ejected
   */
  @GuardedBy("evictionLock")
  boolean admit(Object candidateKeyRef, Object victimKeyRef) {
    int candidateFreq = frequencySketch().frequency(candidateKeyRef);
    int victimFreq = frequencySketch().frequency(victimKeyRef);
    if (candidateFreq > victimFreq) {
      return true;
    } else if (candidateFreq >= ADMIT_HASHDOS_THRESHOLD) {
      // The maximum frequency is 15 and halved to 7 after a reset to age the history. An attack
      // exploits that a hot candidate is rejected in favor of a hot victim. The threshold of a warm
      // candidate reduces the number of random acceptances to minimize the impact on the hit rate.
      int random = ThreadLocalRandom.current().nextInt();
      return ((random & 127) == 0);
    }
    return false;
  }

  /** Expires entries that have expired by access, write, or variable. */
  @GuardedBy("evictionLock")
  void expireEntries(long now) {
    expireAfterAccessEntries(now);
    expireAfterWriteEntries(now);
    expireVariableEntries(now);

    Pacer pacer = pacer();
    if (pacer != null) {
      long delay = getExpirationDelay(now);
      if (delay == Long.MAX_VALUE) {
        pacer.cancel();
      } else {
        pacer.schedule(executor, drainBuffersTask, now, delay);
      }
    }
  }

  /** Expires entries in the access-order queue. */
  @GuardedBy("evictionLock")
  void expireAfterAccessEntries(long now) {
    if (!expiresAfterAccess()) {
      return;
    }

    @Var int remaining = EXPIRATION_THRESHOLD;
    remaining = expireAfterAccessEntries(now, WINDOW, accessOrderWindowDeque(), remaining);
    if (evicts()) {
      remaining = expireAfterAccessEntries(
          now, PROBATION, accessOrderProbationDeque(), remaining);
      remaining = expireAfterAccessEntries(
          now, PROTECTED, accessOrderProtectedDeque(), remaining);
    }
    if (remaining == 0) {
      setDrainStatusOpaque(PROCESSING_TO_REQUIRED);
    }
  }

  /**
   * Expires entries in an access-order queue, up to the {@code remaining} budget, and returns the
   * unused budget. When exhausted the caller re-arms maintenance to process the backlog.
   */
  @GuardedBy("evictionLock")
  int expireAfterAccessEntries(long now, int queueType,
      AccessOrderDeque<Node<K, V>> accessOrderDeque, @Var int remaining) {
    var head = accessOrderDeque.peekFirst();
    if (head == null) {
      return remaining;
    }
    long duration = expiresAfterAccessNanos();
    var last = requireNonNull(accessOrderDeque.peekLast());
    for (var node = head; (node != null) && (remaining > 0);) {
      var next = (node == last) ? null : node.getNextInAccessOrder();
      if ((now - node.getAccessTime()) < duration) {
        if (isComputingAsync(node.getValue())) {
          accessOrderDeque.moveToBack(node);
          node = next;
          continue;
        }
        return remaining;
      }
      evictEntry(node, RemovalCause.EXPIRED, now);
      remaining--;

      // Reentrant maintenance can unlink or move any entry, so the scan resumes from the head and
      // stops if the captured tail that ends the walk left the deque
      node = (node == last) ? null : accessOrderDeque.peekFirst();
      boolean bounded = (last.getQueueType() == queueType) && accessOrderDeque.contains(last);
      if ((node != null) && !bounded) {
        return 0;
      }
    }
    return remaining;
  }

  /** Expires entries on the write-order queue. */
  @GuardedBy("evictionLock")
  void expireAfterWriteEntries(long now) {
    if (!expiresAfterWrite()) {
      return;
    }

    var head = writeOrderDeque().peekFirst();
    if (head == null) {
      return;
    }
    long duration = expiresAfterWriteNanos();
    @Var int remaining = EXPIRATION_THRESHOLD;
    var last = requireNonNull(writeOrderDeque().peekLast());
    for (var node = head; (node != null) && (remaining > 0);) {
      var next = (node == last) ? null : node.getNextInWriteOrder();
      if ((now - node.getWriteTime()) < duration) {
        boolean stalePosition = ((last.getWriteTime() - node.getWriteTime()) < 0);
        if (stalePosition || isComputingAsync(node.getValue())) {
          writeOrderDeque().moveToBack(node);
          node = next;
          continue;
        }
        return;
      }
      evictEntry(node, RemovalCause.EXPIRED, now);
      remaining--;

      // Reentrant maintenance can unlink or move any entry, so the scan resumes from the head and
      // stops if the captured tail that ends the walk left the deque
      node = (node == last) ? null : writeOrderDeque().peekFirst();
      if ((node != null) && !writeOrderDeque().contains(last)) {
        remaining = 0;
        break;
      }
    }
    if (remaining == 0) {
      setDrainStatusOpaque(PROCESSING_TO_REQUIRED);
    }
  }

  /** Expires entries in the timer wheel. */
  @GuardedBy("evictionLock")
  void expireVariableEntries(long now) {
    if (expiresVariable() && (timerWheel().advance(this, now, EXPIRATION_THRESHOLD) == 0)) {
      setDrainStatusOpaque(PROCESSING_TO_REQUIRED);
    }
  }

  /** Returns the duration until the next item expires, or {@link Long#MAX_VALUE} if none. */
  @GuardedBy("evictionLock")
  long getExpirationDelay(long now) {
    @Var long delay = Long.MAX_VALUE;
    if (expiresAfterAccess()) {
      @Var Node<K, V> node = accessOrderWindowDeque().peekFirst();
      if (node != null) {
        long age = Math.max(0, now - node.getAccessTime());
        delay = Math.min(delay, expiresAfterAccessNanos() - age);
      }
      if (evicts()) {
        node = accessOrderProbationDeque().peekFirst();
        if (node != null) {
          long age = Math.max(0, now - node.getAccessTime());
          delay = Math.min(delay, expiresAfterAccessNanos() - age);
        }
        node = accessOrderProtectedDeque().peekFirst();
        if (node != null) {
          long age = Math.max(0, now - node.getAccessTime());
          delay = Math.min(delay, expiresAfterAccessNanos() - age);
        }
      }
    }
    if (expiresAfterWrite()) {
      Node<K, V> node = writeOrderDeque().peekFirst();
      if (node != null) {
        long age = Math.max(0, now - node.getWriteTime());
        delay = Math.min(delay, expiresAfterWriteNanos() - age);
      }
    }
    if (expiresVariable()) {
      delay = Math.min(delay, timerWheel().getExpirationDelay(now));
    }
    return delay;
  }

  /** Returns if the entry has expired. The caller must exempt an in-flight asynchronous load. */
  @SuppressWarnings("ShortCircuitBoolean")
  boolean hasExpired(Node<K, V> node, long now) {
    if (!expires()) {
      return false;
    }
    boolean expired =
        (expiresAfterAccess() && (now - node.getAccessTime() >= expiresAfterAccessNanos()))
        | (expiresAfterWrite() && (now - node.getWriteTime() >= expiresAfterWriteNanos()))
        | (expiresVariable() && (now - node.getVariableTime() >= 0));
    VarHandle.loadLoadFence();
    return expired;
  }

  /**
   * Attempts to evict the entry based on the given removal cause. A removal may be ignored if the
   * entry was updated and is no longer eligible for eviction.
   *
   * @param node the entry to evict
   * @param cause the reason to evict
   * @param now the current time, used only if expiring
   * @return if the entry was evicted
   */
  @GuardedBy("evictionLock")
  @SuppressWarnings({"GuardedByChecker", "SynchronizationOnLocalVariableOrMethodParameter"})
  boolean evictEntry(Node<K, V> node, RemovalCause cause, long now) {
    K key = node.getKey();
    var ctx = new EvictContext<V>();
    var keyReference = node.getKeyReference();

    data.computeIfPresent(keyReference, (k, n) -> {
      if (n != node) {
        return n;
      }
      synchronized (node) {
        ctx.value = node.getValue();
        boolean expired = hasExpired(node, now);
        boolean computing = isComputingAsync(ctx.value);
        if ((key == null) || (ctx.value == null)) {
          ctx.cause = RemovalCause.COLLECTED;
        } else if (cause == RemovalCause.COLLECTED) {
          ctx.resurrect = true;
          return node;
        } else if (expired && !computing) {
          ctx.cause = RemovalCause.EXPIRED;
        } else {
          ctx.cause = cause;
        }

        if (ctx.cause == RemovalCause.EXPIRED) {
          if (!expired) {
            ctx.resurrect = true;
            return node;
          } else if (computing) {
            long sentinel = (now + ASYNC_EXPIRY);
            setVariableTime(node, sentinel);
            setAccessTime(node, sentinel);
            setWriteTime(node, sentinel);
            ctx.resurrect = true;
            return node;
          }
        } else if (ctx.cause == RemovalCause.SIZE) {
          int weight = node.getWeight();
          if (weight == 0) {
            ctx.resurrect = true;
            return node;
          }
        }

        notifyEviction(key, ctx.value, ctx.cause);
        discardRefresh(keyReference);
        ctx.removed = true;
        node.retire();
        return null;
      }
    });

    // The entry is no longer eligible for eviction
    if (ctx.resurrect) {
      return false;
    }

    // If the eviction fails due to a concurrent removal of the victim, that removal may cancel out
    // the addition that triggered this eviction. The victim is eagerly unlinked and the size
    // decremented before the removal task so that if an eviction is still required then a new
    // victim will be chosen for removal.
    unlink(node);

    synchronized (node) {
      logIfAlive(node);
      makeDead(node);
    }

    if (ctx.removed) {
      var removeCause = requireNonNull(ctx.cause);
      statsCounter().recordEviction(node.getWeight(), removeCause);
      notifyRemoval(key, ctx.value, removeCause);
    }

    return true;
  }

  /** Adapts the eviction policy to towards the optimal recency / frequency configuration. */
  @GuardedBy("evictionLock")
  @SuppressWarnings("UnnecessaryReturnStatement")
  void climb() {
    if (!evicts()) {
      return;
    }

    if (frequencySketch().isNotInitialized()) {
      climber().resetSample();
    } else if (weightedSize() >= (maximum() >>> 1)) {
      climber().determineAdjustment(maximum(), windowMaximum(),
          mainProtectedMaximum(), frequencySketch().sampleSize);
    } else {
      climber().discardSample(maximum(), frequencySketch().sampleSize);
    }

    demoteFromMainProtected();
    long amount = climber().adjustment();
    if (amount == 0) {
      return;
    } else if (amount > 0) {
      increaseWindow();
    } else {
      decreaseWindow();
    }
  }

  /**
   * Increases the size of the admission window by shrinking the portion allocated to the main
   * space. As the main space is partitioned into probation and protected regions (80% / 20%), for
   * simplicity only the protected is reduced. If the regions exceed their maximums, this may cause
   * protected items to be demoted to the probation region and probation items to be demoted to the
   * admission window.
   */
  @GuardedBy("evictionLock")
  void increaseWindow() {
    if (mainProtectedMaximum() == 0) {
      return;
    }

    @SuppressWarnings("MathClampLong")
    @Var long quota = Math.min(climber().adjustment(), mainProtectedMaximum());
    setMainProtectedMaximum(mainProtectedMaximum() - quota);
    setWindowMaximum(windowMaximum() + quota);
    demoteFromMainProtected();

    for (int i = 0; i < QUEUE_TRANSFER_THRESHOLD; i++) {
      @Var Node<K, V> candidate = accessOrderProbationDeque().peekFirst();
      @Var boolean probation = true;
      if ((candidate == null) || (quota < candidate.getPolicyWeight())) {
        candidate = accessOrderProtectedDeque().peekFirst();
        probation = false;
      }
      if (candidate == null) {
        break;
      }

      long weight = candidate.getPolicyWeight();
      if (quota < weight) {
        break;
      }

      quota -= weight;
      transfer(candidate, weight, probation ? PROBATION : PROTECTED, WINDOW);
    }

    setMainProtectedMaximum(mainProtectedMaximum() + quota);
    setWindowMaximum(windowMaximum() - quota);
    climber().carryOver(quota);
  }

  /** Decreases the size of the admission window and increases the main's protected region. */
  @GuardedBy("evictionLock")
  void decreaseWindow() {
    if (windowMaximum() <= 1) {
      return;
    }

    @SuppressWarnings("MathClampLong")
    @Var long quota = Math.min(-climber().adjustment(), Math.max(0, windowMaximum() - 1));
    setMainProtectedMaximum(mainProtectedMaximum() + quota);
    setWindowMaximum(windowMaximum() - quota);

    @Var int remaining = QUEUE_TRANSFER_THRESHOLD;
    @Var Node<K, V> candidate = accessOrderWindowDeque().peekFirst();
    while ((candidate != null) && (remaining > 0)) {
      Node<K, V> next = candidate.getNextInAccessOrder();
      long weight = candidate.getPolicyWeight();
      if (weight != 0) {
        if (quota < weight) {
          break;
        }
        quota -= weight;
        transfer(candidate, weight, WINDOW, PROBATION);
        remaining--;
      }
      candidate = next;
    }

    setMainProtectedMaximum(mainProtectedMaximum() - quota);
    setWindowMaximum(windowMaximum() + quota);
    climber().carryOver(-quota);
  }

  /** Transfers the nodes from the protected to the probation region if it exceeds the maximum. */
  @GuardedBy("evictionLock")
  void demoteFromMainProtected() {
    long mainProtectedMaximum = mainProtectedMaximum();
    @Var int remaining = QUEUE_TRANSFER_THRESHOLD;
    while (mainProtectedWeightedSize() > mainProtectedMaximum) {
      Node<K, V> demoted = accessOrderProtectedDeque().peekFirst();
      if (demoted == null) {
        break;
      }
      if (remaining == 0) {
        setDrainStatusOpaque(PROCESSING_TO_REQUIRED);
        break;
      }
      transfer(demoted, demoted.getPolicyWeight(), PROTECTED, PROBATION);
      remaining--;
    }
  }

  /**
   * Moves the node into another region of the eviction policy, adjusting the weighted size of each
   * region that tracks its own.
   */
  @GuardedBy("evictionLock")
  void transfer(Node<K, V> node, long weight, int from, int to) {
    if (from == WINDOW) {
      setWindowWeightedSize(windowWeightedSize() - weight);
      accessOrderWindowDeque().remove(node);
    } else if (from == PROBATION) {
      accessOrderProbationDeque().remove(node);
    } else {
      setMainProtectedWeightedSize(mainProtectedWeightedSize() - weight);
      accessOrderProtectedDeque().remove(node);
    }

    if (to == WINDOW) {
      setWindowWeightedSize(windowWeightedSize() + weight);
      accessOrderWindowDeque().offerLast(node);
      node.makeWindow();
    } else if (to == PROBATION) {
      accessOrderProbationDeque().offerLast(node);
      node.makeMainProbation();
    } else {
      setMainProtectedWeightedSize(mainProtectedWeightedSize() + weight);
      accessOrderProtectedDeque().offerLast(node);
      node.makeMainProtected();
    }
  }

  /**
   * Performs the post-processing work required after a read.
   *
   * @param node the entry in the page replacement policy
   * @param now the current time, in nanoseconds
   * @param recordHit if the hit count should be incremented
   * @return the refreshed value if immediately loaded, else null
   */
  @Nullable V afterRead(Node<K, V> node, long now, boolean recordHit) {
    if (recordHit) {
      statsCounter().recordHits(1);
    }

    boolean delayable = (readBuffer.offer(node) != Buffer.FULL);
    if (shouldDrainBuffers(delayable)) {
      scheduleDrainBuffers();
    }
    return refreshIfNeeded(node, now);
  }

  /** Enables the read buffer (disabled if fastpath until the frequency sketch is initialized). */
  @GuardedBy("evictionLock")
  void recordReads() {
    if (readBuffer == Buffer.<Node<K, V>>disabled()) {
      readBuffer = new BoundedBuffer<>();
    }
  }

  /**
   * Asynchronously refreshes the entry if eligible.
   *
   * @param node the entry in the cache to refresh
   * @param now the current time, in nanoseconds
   * @return the refreshed value if immediately loaded, else null
   */
  @SuppressWarnings("FutureReturnValueIgnored")
  @Nullable V refreshIfNeeded(Node<K, V> node, long now) {
    if (!refreshAfterWrite()) {
      return null;
    }

    K key;
    V oldValue;
    long writeTime = node.getWriteTime();
    long refreshWriteTime = markRefreshing(writeTime);
    ConcurrentMap<Object, CompletableFuture<?>> refreshes;
    if (((now - writeTime) > refreshAfterWriteNanos())
        && ((key = node.getKey()) != null) && ((oldValue = node.getValue()) != null)
        && !isComputingAsync(oldValue) && !isRefreshing(writeTime)
        && !(refreshes = refreshes()).containsKey(node.getKeyReference())
        && node.isAlive() && node.casWriteTime(writeTime, refreshWriteTime)) {
      long startTime;
      var keyReference = referenceKey(key);
      CompletableFuture<? extends @Nullable V> refreshFuture;
      @SuppressWarnings({"unchecked", "Varifier"})
      @Nullable V[] reloading = (@Nullable V[]) new Object[1];
      try {
        // The registration is published before the loader is called, so the loader runs outside
        // the refresh map's bin
        var pending = new LocalLoadingCache.PendingRefresh();
        var registered = refreshes.computeIfAbsent(keyReference, k -> {
          if (!node.isAlive() || (node.getWriteTime() != refreshWriteTime)) {
            return null;
          }
          // no-op if the future's completion state was modified (e.g. obtrude methods)
          @SuppressWarnings("unchecked")
          V value = isAsync ? Async.getIfReady((CompletableFuture<V>) oldValue) : oldValue;
          reloading[0] = value;
          return (value == null) ? null : pending;
        });
        if (registered != pending) {
          return null;
        }
        try {
          startTime = statsTicker().read();
          requireNonNull(cacheLoader);
          var refresh = cacheLoader.asyncReload(key, requireNonNull(reloading[0]), executor);
          refreshFuture = requireNonNull(refresh, "Null future");
        } catch (Throwable e) {
          pending.withdraw(refreshes, keyReference, e);
          if (e instanceof InterruptedException) {
            Thread.currentThread().interrupt();
          }
          logger.log(Level.WARNING, "Exception thrown when submitting refresh task", e);
          return null;
        }
        pending.publish(refreshes, keyReference, refreshFuture);
      } finally {
        node.casWriteTime(refreshWriteTime, writeTime);
      }

      var refreshed = refreshFuture.handle((newValue, error) -> {
        long loadTime = statsTicker().read() - startTime;
        if (error != null) {
          if (!(error instanceof CancellationException) && !(error instanceof TimeoutException)) {
            logger.log(Level.WARNING, "Exception thrown during refresh", error);
          }
          refreshes.remove(keyReference, refreshFuture);
          statsCounter().recordLoadFailure(loadTime);
          return null;
        }

        @SuppressWarnings("unchecked")
        V value = (isAsync && (newValue != null)) ? (V) refreshFuture : newValue;
        @Nullable RemovalCause[] cause = new RemovalCause[1];
        var hints = new RemapHints();
        hints.quietly = true;
        V result;
        try {
          result = compute(key, (K k, @Nullable V currentValue) -> {
            // Keep the refresh registered until the write clears it to avoid readers from
            // prematurely scheduling another reload
            boolean owned = (refreshes.get(keyReference) == refreshFuture);
            if (currentValue == null) {
              // If the entry is absent then drop this refresh, unless a successor owns the
              // registration, and maybe notify the listener
              if (value != null) {
                cause[0] = RemovalCause.EXPLICIT;
              }
              hints.preserveRefresh = !owned;
              return null;
            }
            if ((currentValue == oldValue) && node.isAlive()
                && (writeTimeOf(node) == writeTime) && owned) {
              // If the entry was not modified while in-flight (no ABA) then replace, refreshing the
              // metadata even when the reloaded value is the same instance
              return value;
            }
            // Otherwise the refresh is discarded. The rejection installs nothing, so the entry's
            // timestamps are preserved rather than restarted at the completion time. A
            // same-instance reload is not a value change, so it is not notified. When a successor
            // refresh owns the registration, leave it intact so this by-key discard cannot steal
            // its token.
            boolean sameInstance = (currentValue == value)
                || (isAsync && (newValue == Async.getIfReady((CompletableFuture<?>) currentValue)));
            if ((value != null) && !sameInstance) {
              cause[0] = RemovalCause.REPLACED;
            }
            hints.preserveTimestamps = true;
            hints.preserveRefresh = !owned;
            return currentValue;
          }, expiry(), /* recordLoad= */ false, hints);
        } catch (Throwable t) {
          logger.log(Level.WARNING, "Exception thrown during refresh", t);
          refreshes.remove(keyReference, refreshFuture);
          statsCounter().recordLoadFailure(loadTime);
          return null;
        }

        if (cause[0] != null) {
          notifyRemoval(key, value, cause[0]);
        }
        if (newValue == null) {
          statsCounter().recordLoadFailure(loadTime);
        } else {
          statsCounter().recordLoadSuccess(loadTime);
        }
        return result;
      });
      return Async.getIfReady(refreshed);
    }

    return null;
  }

  /**
   * Returns the expiration time for the entry after being created.
   *
   * @param key the key of the entry that was created
   * @param value the value of the entry that was created
   * @param expiry the calculator for the expiration time
   * @param now the current time, in nanoseconds
   * @return the expiration time
   */
  long expireAfterCreate(K key, V value, @Nullable Expiry<? super K, ? super V> expiry, long now) {
    if (expiresVariable()) {
      requireNonNull(expiry);
      long duration = Math.max(0L, expiry.expireAfterCreate(key, value, now));
      return expiresAt(now, duration);
    }
    return 0L;
  }

  /**
   * Returns the expiration time for the entry after being updated.
   *
   * @param node the entry in the page replacement policy
   * @param key the key of the entry that was updated
   * @param value the value of the entry that was updated
   * @param expiry the calculator for the expiration time
   * @param now the current time, in nanoseconds
   * @return the expiration time
   */
  long expireAfterUpdate(Node<K, V> node, K key, V value,
      @Nullable Expiry<? super K, ? super V> expiry, long now) {
    if (expiresVariable()) {
      requireNonNull(expiry);
      long currentDuration = Math.max(0L, node.getVariableTime() - now);
      long duration = Math.max(0L, expiry.expireAfterUpdate(key, value, now, currentDuration));
      return expiresAt(now, duration);
    }
    return 0L;
  }

  /**
   * Returns the access time for the entry after a read.
   *
   * @param node the entry in the page replacement policy
   * @param key the key of the entry that was read
   * @param value the value of the entry that was read
   * @param expiry the calculator for the expiration time
   * @param now the current time, in nanoseconds
   * @return the expiration time
   */
  long expireAfterRead(Node<K, V> node, K key, V value, Expiry<K, V> expiry, long now) {
    if (expiresVariable()) {
      long variableTime = node.getVariableTime();
      long currentDuration = Math.max(0L, variableTime - now);
      if (isAsync && (currentDuration > MAXIMUM_EXPIRY)) {
        // expireAfterCreate has not yet set the duration after completion
        return variableTime;
      }
      long duration = Math.max(0L, expiry.expireAfterRead(key, value, now, currentDuration));
      return expiresAt(now, duration);
    }
    return 0L;
  }

  /**
   * Attempts to update the access time for the entry after a read.
   *
   * @param node the entry in the page replacement policy
   * @param key the key of the entry that was read
   * @param value the value of the entry that was read
   * @param expiry the calculator for the expiration time
   * @param now the current time, in nanoseconds
   */
  void tryExpireAfterRead(Node<K, V> node, K key, V value, Expiry<K, V> expiry, long now) {
    if (!expiresVariable()) {
      return;
    }

    long variableTime = node.getVariableTime();
    long currentDuration = Math.max(0L, variableTime - now);
    if (isAsync && (currentDuration > MAXIMUM_EXPIRY)) {
      // expireAfterCreate has not yet set the duration after completion
      return;
    }

    long tolerance = EXPIRE_TOLERANCE;
    long duration = Math.max(0L, expiry.expireAfterRead(key, value, now, currentDuration));
    long expirationTime = expiresAt(now, duration);
    long extension = expirationTime - variableTime;
    if ((extension != 0)
        && ((duration <= tolerance) || (extension < 0) || (extension > tolerance))) {
      VarHandle.loadLoadFence();
      if (node.getValue() == value) {
        node.casVariableTime(variableTime, expirationTime);
      }
    }
  }

  void setAccessTime(Node<K, V> node, long now) {
    if (!expiresAfterAccess()) {
      return;
    }
    long tolerance = EXPIRE_TOLERANCE;
    long accessTime = node.getAccessTime();
    if ((expiresAfterAccessNanos() <= tolerance) || (Math.abs(now - accessTime) > tolerance)) {
      node.setAccessTime(now);
    }
  }

  void setWriteTime(Node<K, V> node, long now) {
    if (expiresAfterWrite() || refreshAfterWrite()) {
      // The write time reserves its low bit to mark that a refresh is in flight, so a recorded time
      // is always even and an age must be measured against an evenly truncated clock
      node.setWriteTime(toWriteTime(now));
    }
  }

  void setVariableTime(Node<K, V> node, long expirationTime) {
    if (expiresVariable()) {
      node.setVariableTime(expirationTime);
    }
  }

  /** Returns if the entry's expiration is still deferred to its value's completion. */
  boolean isExpirationDeferred(Node<K, V> node, long now) {
    return expiresVariable() && ((node.getVariableTime() - now) > MAXIMUM_EXPIRY);
  }

  /** Returns if the entry's write time would exceed the minimum expiration reorder threshold. */
  boolean exceedsWriteTimeTolerance(Node<K, V> node, long varTime, long now) {
    long variableTime = node.getVariableTime();
    long writeTime = node.getWriteTime();
    long tolerance = EXPIRE_TOLERANCE;
    return
        (expiresAfterWrite()
            && ((expiresAfterWriteNanos() <= tolerance) || (Math.abs(now - writeTime) > tolerance)))
        || (refreshAfterWrite()
            && ((refreshAfterWriteNanos() <= tolerance) || (Math.abs(now - writeTime) > tolerance)))
        || (expiresVariable() && (Math.abs(varTime - variableTime) > tolerance));
  }

  /** Returns the expiration time for a duration. */
  long expiresAt(long now, long duration) {
    return isAsync ? (now + duration) : (now + Math.min(duration, MAXIMUM_EXPIRY));
  }

  /** Returns the time to record on the entry. */
  long expirationTimeFor(@Nullable V value, long now) {
    return isComputingAsync(value) ? (now + ASYNC_EXPIRY) : now;
  }

  /** Returns the time truncated to the write time's granularity. */
  static long toWriteTime(long time) {
    return (time & ~1L);
  }

  /** Returns the entry's write time, with the refresh marker removed. */
  static long writeTimeOf(Node<?, ?> node) {
    return toWriteTime(node.getWriteTime());
  }

  /** Returns if a refresh is in flight for the entry that recorded this write time. */
  static boolean isRefreshing(long writeTime) {
    return ((writeTime & 1L) != 0L);
  }

  /** Returns the write time marked as having a refresh in flight. */
  static long markRefreshing(long writeTime) {
    return (writeTime | 1L);
  }

  /**
   * Performs the post-processing work required after a write.
   *
   * @param task the pending operation to be applied
   */
  void afterWrite(Runnable task) {
    if (writeBuffer.offer(task)) {
      scheduleAfterWrite();
      return;
    }

    // In scenarios where the writing threads cannot make progress then they attempt to provide
    // assistance by performing the eviction work directly. This can resolve cases where the
    // maintenance task is scheduled but not running. That might occur due to all of the executor's
    // threads being busy (perhaps writing into this cache), the write rate greatly exceeds the
    // consuming rate, priority inversion, or if the executor silently discarded the maintenance
    // task. Unfortunately this cannot resolve when the eviction is blocked waiting on a long-
    // running computation due to an eviction listener, the victim is being computed on by a writer,
    // or the victim residing in the same hash bin as a computing entry. In those cases a warning is
    // logged to encourage the application to decouple these computations from the map operations.
    lock();
    try {
      maintenance(task);
    } catch (RuntimeException e) {
      logger.log(Level.ERROR, "Exception thrown when performing the maintenance task", e);
    } finally {
      evictionLock.unlock();
    }
    rescheduleCleanUpIfIncomplete();
  }

  /** Acquires the eviction lock. */
  void lock() {
    @Var long remainingNanos = WARN_AFTER_LOCK_WAIT_NANOS;
    long end = System.nanoTime() + remainingNanos;
    @Var boolean interrupted = false;
    try {
      for (;;) {
        try {
          if (evictionLock.tryLock(remainingNanos, TimeUnit.NANOSECONDS)) {
            return;
          }
          logger.log(Level.WARNING, "The cache is experiencing excessive wait times for acquiring "
              + "the eviction lock. This may indicate that a long-running computation has halted "
              + "eviction when trying to remove the victim entry. Consider using AsyncCache to "
              + "decouple the computation from the map operation.", new TimeoutException());
          evictionLock.lock();
          return;
        } catch (InterruptedException e) {
          remainingNanos = end - System.nanoTime();
          interrupted = true;
        }
      }
    } finally {
      if (interrupted) {
        Thread.currentThread().interrupt();
      }
    }
  }

  /**
   * Conditionally schedules the asynchronous maintenance task after a write operation. If the
   * task status was IDLE or REQUIRED then the maintenance task is scheduled immediately. If it
   * is already processing then it is set to transition to REQUIRED upon completion so that a new
   * execution is triggered by the next operation.
   */
  void scheduleAfterWrite() {
    @Var int drainStatus = drainStatusOpaque();
    for (;;) {
      switch (drainStatus) {
        case IDLE:
          if (casDrainStatus(IDLE, REQUIRED)) {
            scheduleDrainBuffers();
            return;
          }
          drainStatus = drainStatusAcquire();
          continue;
        case REQUIRED:
          scheduleDrainBuffers();
          return;
        case PROCESSING_TO_IDLE:
          if (casDrainStatus(PROCESSING_TO_IDLE, PROCESSING_TO_REQUIRED)) {
            return;
          }
          drainStatus = drainStatusAcquire();
          continue;
        case PROCESSING_TO_REQUIRED:
          return;
        default:
          throw new IllegalStateException("Invalid drain status: " + drainStatus);
      }
    }
  }

  /**
   * Attempts to schedule an asynchronous task to apply the pending operations to the page
   * replacement policy. If the executor rejects the task then it is run directly.
   */
  void scheduleDrainBuffers() {
    if (drainStatusOpaque() >= PROCESSING_TO_IDLE) {
      return;
    }
    if (evictionLock.tryLock()) {
      try {
        int drainStatus = drainStatusOpaque();
        if (drainStatus >= PROCESSING_TO_IDLE) {
          return;
        }
        setDrainStatusRelease(PROCESSING_TO_IDLE);
        executor.execute(drainBuffersTask);
      } catch (Throwable t) {
        logger.log(Level.WARNING, "Exception thrown when submitting maintenance task", t);
        maintenance(/* ignored */ null);
      } finally {
        evictionLock.unlock();
      }
    }
  }

  /** Returns whether a thread waits for the eviction lock and this thread does not hold it. */
  boolean isEvictionLockAwaited() {
    return !evictionLock.isHeldByCurrentThread() && evictionLock.hasQueuedThreads();
  }

  @Override
  public void cleanUp() {
    try {
      performCleanUp(/* ignored */ null);
    } catch (RuntimeException e) {
      logger.log(Level.ERROR, "Exception thrown when performing the maintenance task", e);
    }
  }

  /**
   * Performs the maintenance work, blocking until the lock is acquired.
   *
   * @param task an additional pending task to run, or {@code null} if not present
   */
  void performCleanUp(@Nullable Runnable task) {
    evictionLock.lock();
    try {
      maintenance(task);
    } finally {
      evictionLock.unlock();
    }
    rescheduleCleanUpIfIncomplete();
  }

  /**
   * If there remains pending operations that were not handled by the prior clean up then try to
   * schedule an asynchronous maintenance task. This may occur due to a concurrent write after the
   * maintenance work had started or if the amortized threshold of work per clean up was reached.
   */
  @SuppressWarnings("resource")
  void rescheduleCleanUpIfIncomplete() {
    if (drainStatusOpaque() != REQUIRED) {
      return;
    }

    // An immediate scheduling cannot be performed on a custom executor because it may use a
    // caller-runs policy. This could cause the caller's penalty to exceed the amortized threshold,
    // e.g. repeated concurrent writes could result in a retry loop.
    if (executor == ForkJoinPool.commonPool()) {
      scheduleDrainBuffers();
      return;
    }

    // If a scheduler was configured then the maintenance can be deferred onto the custom executor
    // and run in the near future. Otherwise, it will be handled due to other cache activity.
    var pacer = pacer();
    if ((pacer != null) && !pacer.isScheduled() && evictionLock.tryLock()) {
      try {
        if ((drainStatusOpaque() == REQUIRED) && !pacer.isScheduled()) {
          pacer.schedule(executor, drainBuffersTask, expirationTicker().read(), Pacer.TOLERANCE);
        }
      } finally {
        evictionLock.unlock();
      }
    }
  }

  /**
   * Performs the pending maintenance work and sets the state flags during processing to avoid
   * excess scheduling attempts. The read buffer, write buffer, and reference queues are drained,
   * followed by expiration, and size-based eviction.
   *
   * @param task an additional pending task to run, or {@code null} if not present
   */
  @GuardedBy("evictionLock")
  void maintenance(@Nullable Runnable task) {
    setDrainStatusRelease(PROCESSING_TO_IDLE);

    try {
      try {
        drainReadBuffer();
        drainWriteBuffer();
      } finally {
        if (task != null) {
          task.run();
        }
      }

      drainKeyReferences();
      drainValueReferences();

      long now = expirationTicker().read();
      expireEntries(now);
      evictEntries(now);

      climb();
    } finally {
      if ((drainStatusOpaque() != PROCESSING_TO_IDLE)
          || !casDrainStatus(PROCESSING_TO_IDLE, IDLE)) {
        setDrainStatusOpaque(REQUIRED);
      }
    }
  }

  /** Drains the weak key references queue. */
  @GuardedBy("evictionLock")
  void drainKeyReferences() {
    if (!collectKeys()) {
      return;
    }
    for (int i = 0; i <= REFERENCE_THRESHOLD; i++) {
      var keyRef = keyReferenceQueue().poll();
      if (keyRef == null) {
        return;
      }
      Node<K, V> node = data.get(keyRef);
      if (node != null) {
        evictEntry(node, RemovalCause.COLLECTED, 0L);
      }
    }
    setDrainStatusOpaque(PROCESSING_TO_REQUIRED);
  }

  /** Drains the weak / soft value references queue. */
  @GuardedBy("evictionLock")
  void drainValueReferences() {
    if (!collectValues()) {
      return;
    }
    for (int i = 0; i <= REFERENCE_THRESHOLD; i++) {
      var valueRef = valueReferenceQueue().poll();
      if (valueRef == null) {
        return;
      }
      @SuppressWarnings("unchecked")
      var ref = (InternalReference<V>) valueRef;
      Node<K, V> node = data.get(ref.getKeyReference());
      if ((node != null) && (valueRef == node.getValueReference())) {
        evictEntry(node, RemovalCause.COLLECTED, 0L);
      }
    }
    setDrainStatusOpaque(PROCESSING_TO_REQUIRED);
  }

  /** Drains the read buffer. */
  @GuardedBy("evictionLock")
  void drainReadBuffer() {
    readBuffer.drainTo(accessPolicy);
  }

  /**
   * Updates the node's location in the page replacement policy and credits the access.
   * <p>
   * A quiet access reorders but does not record the usage with the admission filter or the adaptive
   * climber's sample, as an asynchronous cache's load completion finalizes the entry's weight
   * rather than conveying a usage; counting it once per load skews the admission frequencies and
   * misattributes window hits.
   */
  @GuardedBy("evictionLock")
  void onAccess(Node<K, V> node, Access access) {
    if (evicts()) {
      var keyRef = node.getKeyReferenceOrNull();
      if ((keyRef == null) || !node.isAlive()) {
        return;
      }
      if (access.recordsUsage()) {
        frequencySketch().increment(keyRef);
      }
      boolean inWindow = node.inWindow();
      boolean inProbation = !inWindow && node.inMainProbation();
      if (inWindow) {
        reorder(accessOrderWindowDeque(), node);
      } else if (inProbation) {
        reorderProbation(node);
      } else {
        reorder(accessOrderProtectedDeque(), node);
      }
      if (access.recordsHit() && (node.getPolicyWeight() != 0)) {
        // a zero-weight entry (an in-flight async load, a pinned entry) earns hits with no
        // capacity, so it must not steer the sizing; the sketch still observes the key
        climber().recordHit(inWindow, inProbation);
      }
    } else if (expiresAfterAccess()) {
      reorder(accessOrderWindowDeque(), node);
    }
    if (expiresVariable()) {
      timerWheel().reschedule(node);
    }
  }

  /** Promote the node from probation to protected on an access. */
  @GuardedBy("evictionLock")
  void reorderProbation(Node<K, V> node) {
    if (!accessOrderProbationDeque().contains(node)) {
      // Ignore stale accesses for an entry that is no longer present
      return;
    } else if (node.getPolicyWeight() > mainProtectedMaximum()) {
      reorder(accessOrderProbationDeque(), node);
      return;
    }

    // If the protected space exceeds its maximum, the LRU items are demoted to the probation space.
    // This is deferred to the adaption phase at the end of the maintenance cycle.
    transfer(node, node.getPolicyWeight(), PROBATION, PROTECTED);
  }

  /** Updates the node's location in the policy's deque, unless it is no longer linked. */
  static <K, V> void reorder(LinkedDeque<Node<K, V>> deque, Node<K, V> node) {
    // An entry may be scheduled for reordering despite having been removed. This can occur when the
    // entry was concurrently read while a writer was removing it. If the entry is no longer linked
    // then it does not need to be processed.
    if (deque.contains(node)) {
      deque.moveToBack(node);
    }
  }

  /** Drains the write buffer. */
  @GuardedBy("evictionLock")
  void drainWriteBuffer() {
    for (int i = 0; i <= WRITE_BUFFER_MAX; i++) {
      Runnable task = writeBuffer.relaxedPoll();
      if (task == null) {
        return;
      }
      task.run();
    }
    setDrainStatusOpaque(PROCESSING_TO_REQUIRED);
  }

  /** Removes the node from the policy's queues. */
  @GuardedBy("evictionLock")
  void unlink(Node<K, V> node) {
    if (node.inWindow() && (evicts() || expiresAfterAccess())) {
      accessOrderWindowDeque().remove(node);
    } else if (evicts()) {
      if (node.inMainProbation()) {
        accessOrderProbationDeque().remove(node);
      } else {
        accessOrderProtectedDeque().remove(node);
      }
    }
    if (expiresAfterWrite()) {
      writeOrderDeque().remove(node);
    } else if (expiresVariable()) {
      timerWheel().deschedule(node);
    }
  }

  /**
   * Atomically transitions the node to the <code>dead</code> state and decrements the
   * <code>weightedSize</code>.
   *
   * @param node the entry in the page replacement policy
   */
  @GuardedBy("evictionLock")
  @SuppressWarnings("SynchronizationOnLocalVariableOrMethodParameter")
  void makeDead(Node<K, V> node) {
    synchronized (node) {
      if (node.isDead()) {
        return;
      }
      if (evicts()) {
        // The node's policy weight may be out of sync due to a pending update waiting to be
        // processed. At this point the node's weight is finalized, so the weight can be safely
        // taken from the node's perspective and the sizes will be adjusted correctly.
        if (node.inWindow()) {
          setWindowWeightedSize(windowWeightedSize() - node.getWeight());
        } else if (node.inMainProtected()) {
          setMainProtectedWeightedSize(mainProtectedWeightedSize() - node.getWeight());
        }
        setWeightedSize(weightedSize() - node.getWeight());
      }
      node.die();
    }
  }

  /** Adds the node to the page replacement policy. */
  final class AddTask implements Runnable {
    final Node<K, V> node;
    final int weight;

    AddTask(Node<K, V> node, int weight) {
      this.weight = weight;
      this.node = node;
    }

    @Override
    @GuardedBy("evictionLock")
    public void run() {
      if (evicts()) {
        setWeightedSize(weightedSize() + weight);
        setWindowWeightedSize(windowWeightedSize() + weight);
        node.setPolicyWeight(node.getPolicyWeight() + weight);

        long maximum = maximum();
        if (weightedSize() >= (maximum >>> 1)) {
          if (weightedSize() > MAXIMUM_CAPACITY) {
            evictEntries(expirationTicker().read());
          } else {
            // Lazily initialize when close to the maximum
            long capacity = isWeighted() ? data.mappingCount() : maximum;
            frequencySketch().ensureCapacity(capacity);
            recordReads();
          }
        }

        climber().recordMiss();
      }

      // ignore out-of-order write operations
      boolean isAlive;
      synchronized (node) {
        isAlive = node.isAlive();
      }
      if (isAlive) {
        if (expiresAfterWrite()) {
          writeOrderDeque().offerLast(node);
        }
        if (expiresVariable()) {
          timerWheel().schedule(node);
        }
        if (evicts()) {
          var keyRef = node.getKeyReferenceOrNull();
          if ((keyRef != null) && node.isAlive()) {
            frequencySketch().increment(keyRef);
          }
          if (weight > windowMaximum()) {
            accessOrderWindowDeque().offerFirst(node);
          } else {
            accessOrderWindowDeque().offerLast(node);
          }
          if (weight > maximum()) {
            evictEntry(node, RemovalCause.SIZE, expirationTicker().read());
          }
        } else if (expiresAfterAccess()) {
          accessOrderWindowDeque().offerLast(node);
        }
      }
    }
  }

  /** Removes a node from the page replacement policy. */
  final class RemovalTask implements Runnable {
    final Node<K, V> node;

    RemovalTask(Node<K, V> node) {
      this.node = node;
    }

    @Override
    @GuardedBy("evictionLock")
    public void run() {
      // add may not have been processed yet
      unlink(node);
      makeDead(node);
    }
  }

  /** Updates the weighted size. */
  final class UpdateTask implements Runnable {
    final int weightDifference;
    final Node<K, V> node;
    final Access access;

    public UpdateTask(Node<K, V> node, int weightDifference) {
      this(node, weightDifference, Access.HIT);
    }

    public UpdateTask(Node<K, V> node, int weightDifference, Access access) {
      this.weightDifference = weightDifference;
      this.access = access;
      this.node = node;
    }

    @Override
    @GuardedBy("evictionLock")
    public void run() {
      if (expiresAfterWrite()) {
        reorder(writeOrderDeque(), node);
      } else if (expiresVariable()) {
        timerWheel().reschedule(node);
      }
      if (evicts()) {
        if (access.recordsMiss()) {
          climber().recordMiss();
        }
        long oldWeightedSize = node.getPolicyWeight();
        node.setPolicyWeight(oldWeightedSize + weightDifference);
        if (node.inWindow()) {
          setWindowWeightedSize(windowWeightedSize() + weightDifference);
          if (node.getPolicyWeight() > maximum()) {
            evictEntry(node, RemovalCause.SIZE, expirationTicker().read());
          } else if (node.getPolicyWeight() <= windowMaximum()) {
            onAccess(node, access);
          } else if (accessOrderWindowDeque().contains(node)) {
            accessOrderWindowDeque().moveToFront(node);
          }
        } else if (node.inMainProbation()) {
          if (node.getPolicyWeight() <= maximum()) {
            onAccess(node, access);
          } else {
            evictEntry(node, RemovalCause.SIZE, expirationTicker().read());
          }
        } else {
          setMainProtectedWeightedSize(mainProtectedWeightedSize() + weightDifference);
          if (node.getPolicyWeight() <= maximum()) {
            onAccess(node, access);
          } else {
            evictEntry(node, RemovalCause.SIZE, expirationTicker().read());
          }
        }

        setWeightedSize(weightedSize() + weightDifference);
        if (weightedSize() > MAXIMUM_CAPACITY) {
          evictEntries(expirationTicker().read());
        }
      } else if (expiresAfterAccess()) {
        onAccess(node, access);
      }
    }
  }

  /** What an access records beyond the reorder. */
  enum Access {
    HIT(/* usage= */ true, /* hit= */ true, /* miss= */ false),
    RELOAD(/* usage= */ true, /* hit= */ false, /* miss= */ true),
    QUIET(/* usage= */ false, /* hit= */ false, /* miss= */ false);

    private final boolean hit;
    private final boolean miss;
    private final boolean usage;

    Access(boolean usage, boolean hit, boolean miss) {
      this.usage = usage;
      this.hit = hit;
      this.miss = miss;
    }

    /** Returns whether the admission filter observes the key. */
    boolean recordsUsage() {
      return usage;
    }

    /** Returns whether the climber's sample earns a hit. */
    boolean recordsHit() {
      return hit;
    }

    /** Returns whether the climber's sample takes the miss an insertion would have recorded. */
    boolean recordsMiss() {
      return miss;
    }
  }

  /* --------------- Concurrent Map Support --------------- */

  @Override
  public boolean isEmpty() {
    return data.isEmpty();
  }

  @Override
  public int size() {
    return data.size();
  }

  @Override
  public long estimatedSize() {
    return data.mappingCount();
  }

  @Override
  public void clear() {
    // Discard all pending refreshes
    var pending = refreshes;
    if (pending != null) {
      pending.clear();
    }

    Deque<Node<K, V>> entries;
    evictionLock.lock();
    try {
      // Discard all pending reads
      readBuffer.drainTo(e -> {});

      // Apply the pending writes
      for (var task = writeBuffer.relaxedPoll(); task != null; task = writeBuffer.relaxedPoll()) {
        task.run();
      }

      // Cancel the scheduled cleanup
      Pacer pacer = pacer();
      if (pacer != null) {
        pacer.cancel();
      }

      // Discard all entries, falling back to one-by-one to avoid excessive lock hold times
      long now = expirationTicker().read();
      int threshold = (WRITE_BUFFER_MAX / 2);
      entries = new ArrayDeque<>(data.values());
      while (writeBuffer.size() < threshold) {
        var node = entries.pollFirst();
        if (node == null) {
          break;
        }
        removeNode(node, now);
      }

      // A submitted task that ran while this thread waited for the lock deferred to it
      if (drainStatusOpaque() >= PROCESSING_TO_IDLE) {
        setDrainStatusRelease(REQUIRED);
      }
    } finally {
      evictionLock.unlock();
    }

    // Remove any stragglers if released early to more aggressively flush incoming writes
    @Var boolean cleanUp = false;
    for (var node : entries) {
      var key = node.getKey();
      if (key == null) {
        cleanUp = true;
      } else {
        remove(key);
      }
    }
    if (collectKeys() && cleanUp) {
      cleanUp();
    } else {
      rescheduleCleanUpIfIncomplete();
    }
  }

  @GuardedBy("evictionLock")
  @SuppressWarnings({"GuardedByChecker", "SynchronizationOnLocalVariableOrMethodParameter"})
  void removeNode(Node<K, V> node, long now) {
    K key = node.getKey();
    var ctx = new EvictContext<V>();
    var keyReference = node.getKeyReference();

    data.computeIfPresent(keyReference, (k, n) -> {
      if (n != node) {
        return n;
      }
      synchronized (node) {
        ctx.value = node.getValue();
        ctx.oldWeight = node.getWeight();

        if ((key == null) || (ctx.value == null)) {
          ctx.cause = RemovalCause.COLLECTED;
        } else if (hasExpired(node, now) && !isComputingAsync(ctx.value)) {
          ctx.cause = RemovalCause.EXPIRED;
        } else {
          ctx.cause = RemovalCause.EXPLICIT;
        }

        if (ctx.cause.wasEvicted()) {
          notifyEviction(key, ctx.value, ctx.cause);
        }

        discardRefresh(k);
        node.retire();
        return null;
      }
    });

    unlink(node);

    synchronized (node) {
      logIfAlive(node);
      makeDead(node);
    }

    if (ctx.cause != null) {
      if (ctx.cause.wasEvicted()) {
        statsCounter().recordEviction(ctx.oldWeight, ctx.cause);
      }
      notifyRemoval(key, ctx.value, ctx.cause);
    }
  }

  @Override
  public boolean containsKey(@Nullable Object key) {
    requireNonNull(key);

    Node<K, V> node = data.get(nodeFactory.newLookupKey(key));
    if (node == null) {
      return false;
    }
    boolean expired = hasExpired(node, expirationTicker().read());
    V value = node.getValue();
    if ((value == null) || (expired && !isComputingAsync(value))) {
      scheduleDrainBuffers();
      return false;
    }
    return true;
  }

  @Override
  public boolean containsValue(@Nullable Object value) {
    requireNonNull(value);

    long now = expirationTicker().read();
    for (Node<K, V> node : data.values()) {
      boolean expired = hasExpired(node, now);
      V nodeValue = node.getValue();
      if ((node.getKey() == null) || (nodeValue == null)
          || (expired && !isComputingAsync(nodeValue))) {
        scheduleDrainBuffers();
      } else if (node.isAlive() && node.containsValue(value)) {
        return true;
      }
    }
    return false;
  }

  @Override
  public @Nullable V get(@Nullable Object key) {
    requireNonNull(key);
    return getIfPresent(key, /* recordStats= */ false);
  }

  @Override
  public @Nullable V getIfPresent(Object key, boolean recordStats) {
    Node<K, V> node = data.get(nodeFactory.newLookupKey(key));
    if (node == null) {
      if (recordStats) {
        statsCounter().recordMisses(1);
      }
      if (drainStatusOpaque() == REQUIRED) {
        scheduleDrainBuffers();
      }
      return null;
    }

    long now = expirationTicker().read();
    boolean expired = hasExpired(node, now);
    V value = node.getValue();
    if ((value == null) || (expired && !isComputingAsync(value))) {
      if (recordStats) {
        statsCounter().recordMisses(1);
      }
      scheduleDrainBuffers();
      return null;
    }

    if (expiresAfterRead() && !isComputingAsync(value)) {
      @SuppressWarnings("unchecked")
      var castedKey = (K) key;
      setAccessTime(node, now);
      tryExpireAfterRead(node, castedKey, value, expiry(), now);
    }
    V refreshed = afterRead(node, now, recordStats);
    return (refreshed == null) ? value : refreshed;
  }

  @Override
  public @Nullable V getIfPresentQuietly(Object key) {
    Node<K, V> node = data.get(nodeFactory.newLookupKey(key));
    if (node == null) {
      return null;
    }
    boolean expired = hasExpired(node, expirationTicker().read());
    V value = node.getValue();
    if ((value == null) || (expired && !isComputingAsync(value))) {
      return null;
    }
    return value;
  }

  /**
   * Returns the key associated with the mapping in this cache, or {@code null} if there is none.
   *
   * @param key the key whose canonical instance is to be returned
   * @return the key used by the mapping, or {@code null} if this cache does not contain a mapping
   *         for the key
   * @throws NullPointerException if the specified key is null
   */
  public @Nullable K getKey(K key) {
    Node<K, V> node = data.get(nodeFactory.newLookupKey(key));
    if (node == null) {
      if (drainStatusOpaque() == REQUIRED) {
        scheduleDrainBuffers();
      }
      return null;
    }
    afterRead(node, /* now= */ 0L, /* recordHit= */ false);
    return node.getKey();
  }

  @Override
  public int getAllPresent(Map<K, @Nullable V> result, boolean retainAbsent) {
    @Var int absent = 0;
    @Var boolean drain = false;
    int uniqueKeys = result.size();
    long now = expirationTicker().read();
    for (var iter = result.entrySet().iterator(); iter.hasNext();) {
      var entry = iter.next();
      Node<K, V> node = data.get(nodeFactory.newLookupKey(entry.getKey()));
      if (node != null) {
        boolean expired = hasExpired(node, now);
        V value = node.getValue();
        if ((value != null) && !expired) {
          setAccessTime(node, now);
          tryExpireAfterRead(node, entry.getKey(), value, expiry(), now);
          V refreshed = afterRead(node, now, /* recordHit= */ false);
          entry.setValue((refreshed == null) ? value : refreshed);
          continue;
        }
        drain = true;
      }
      absent++;
      if (!retainAbsent) {
        iter.remove();
      }
    }
    if (drain) {
      scheduleDrainBuffers();
    }
    statsCounter().recordHits(uniqueKeys - absent);
    statsCounter().recordMisses(absent);
    return absent;
  }

  @Override
  public void putAll(Map<? extends K, ? extends V> map) {
    map.forEach(this::put);
  }

  @Override
  public @Nullable V put(K key, V value) {
    return put(key, value, expiry(), /* onlyIfAbsent= */ false);
  }

  @Override
  public @Nullable V putIfAbsent(K key, V value) {
    return put(key, value, expiry(), /* onlyIfAbsent= */ true);
  }

  /**
   * Adds a node to the policy and the data store. If an existing node is found, then its value is
   * updated if allowed.
   *
   * @param key key with which the specified value is to be associated
   * @param value value to be associated with the specified key
   * @param expiry the calculator for the write expiration time
   * @param onlyIfAbsent a write is performed only if the key is not already associated with a value
   * @return the prior value in or null if no mapping was found
   */
  @SuppressWarnings("SynchronizationOnLocalVariableOrMethodParameter")
  @Nullable V put(K key, V value, Expiry<K, V> expiry, boolean onlyIfAbsent) {
    requireNonNull(key);
    requireNonNull(value);

    @Var int newWeight = -1;
    @Var Object keyRef = null;
    @Var Node<K, V> node = null;
    Object lookupKey = nodeFactory.newLookupKey(key);
    for (int attempts = 1; ; attempts++) {
      @Var Node<K, V> prior = data.get(lookupKey);
      if (prior == null) {
        if (node == null) {
          if (newWeight < 0) {
            newWeight = weigher.weigh(key, value);
          }
          long now = expirationTicker().read();
          keyRef = nodeFactory.newReferenceKey(key, keyReferenceQueue());
          node = nodeFactory.newNode(keyRef, value, valueReferenceQueue(), newWeight, now);
          long expirationTime = expirationTimeFor(value, now);
          setVariableTime(node, expireAfterCreate(key, value, expiry, now));
          setAccessTime(node, expirationTime);
          setWriteTime(node, expirationTime);
        }
        var newNode = node;
        var newKeyRef = requireNonNull(keyRef);
        prior = (cacheLoader == null)
            ? data.putIfAbsent(newKeyRef, newNode)
            : data.computeIfAbsent(newKeyRef, k -> {
                discardRefresh(k);
                return newNode;
              });
        if ((prior == null) || (prior == node)) {
          afterWrite(new AddTask(node, newWeight));
          return null;
        }
      }
      if (onlyIfAbsent) {
        // An optimistic fast path to avoid unnecessary locking
        long now = expirationTicker().read();
        boolean expired = hasExpired(prior, now);
        V currentValue = prior.getValue();
        if ((currentValue != null) && (!expired || isComputingAsync(currentValue))) {
          if (!isComputingAsync(currentValue)) {
            tryExpireAfterRead(prior, key, currentValue, expiry, now);
            setAccessTime(prior, now);
          }
          afterRead(prior, now, /* recordHit= */ false);
          return currentValue;
        }
      }

      // A read may race with the entry's removal, so that after the entry is acquired it may no
      // longer be usable. A retry will reread from the map and either find an absent mapping, a
      // new entry, or a stale entry.
      if (!prior.isAlive()) {
        // A reread of the stale entry may occur if the state transition occurred but the map
        // removal was delayed by a context switch, so that this thread spin waits until resolved.
        if ((attempts & MAX_PUT_SPIN_WAIT_ATTEMPTS) != 0) {
          Thread.onSpinWait();
          continue;
        }

        // If the spin wait attempts are exhausted then fallback to a map computation in order to
        // deschedule this thread until the entry's removal completes. If the key was modified
        // while in the map so that its equals or hashCode changed then the contents may be
        // corrupted, where the cache holds an evicted (dead) entry that could not be removed.
        // That is a violation of the Map contract, so we check that the mapping is in the "alive"
        // state while in the computation.
        data.computeIfPresent(lookupKey, (k, n) -> {
          requireIsAlive(key, n);
          return n;
        });
        continue;
      }

      long now;
      V oldValue;
      long varTime;
      int oldWeight;
      @Var boolean expired = false;
      @Var boolean mayUpdate = true;
      @Var boolean exceedsTolerance = false;
      if (newWeight < 0) {
        newWeight = weigher.weigh(key, value);
      }
      synchronized (prior) {
        if (!prior.isAlive()) {
          continue;
        }
        oldValue = prior.getValue();
        oldWeight = prior.getWeight();
        now = expirationTicker().read();
        if (oldValue == null) {
          varTime = expireAfterCreate(key, value, expiry, now);
          notifyEviction(key, null, RemovalCause.COLLECTED);
        } else if (hasExpired(prior, now) && !isComputingAsync(oldValue)) {
          expired = true;
          varTime = expireAfterCreate(key, value, expiry, now);
          notifyEviction(key, oldValue, RemovalCause.EXPIRED);
        } else if (onlyIfAbsent) {
          mayUpdate = false;
          varTime = expireAfterRead(prior, key, oldValue, expiry, now);
        } else {
          varTime = expireAfterUpdate(prior, key, value, expiry, now);
        }

        long expirationTime = expirationTimeFor(mayUpdate ? value : oldValue, now);
        if (mayUpdate) {
          exceedsTolerance = exceedsWriteTimeTolerance(prior, varTime, expirationTime);
          prior.setValue(value, valueReferenceQueue());
          prior.setWeight(newWeight);
          if (expired || (oldValue == null) || exceedsTolerance) {
            setWriteTime(prior, expirationTime);
          }

          discardRefresh(lookupKey);
        }

        setVariableTime(prior, varTime);
        setAccessTime(prior, expirationTime);
      }

      if (expired) {
        statsCounter().recordEviction(oldWeight, RemovalCause.EXPIRED);
        notifyRemoval(key, oldValue, RemovalCause.EXPIRED);
      } else if (oldValue == null) {
        statsCounter().recordEviction(oldWeight, RemovalCause.COLLECTED);
        notifyRemoval(key, /* value= */ null, RemovalCause.COLLECTED);
      } else if (mayUpdate) {
        notifyOnReplace(key, oldValue, value);
      }

      int weightedDifference = mayUpdate ? (newWeight - oldWeight) : 0;
      if ((oldValue == null) || (weightedDifference != 0) || expired) {
        var access = (expired || (oldValue == null)) ? Access.RELOAD : Access.HIT;
        afterWrite(new UpdateTask(prior, weightedDifference, access));
      } else if (!onlyIfAbsent && exceedsTolerance) {
        afterWrite(new UpdateTask(prior, weightedDifference));
      } else {
        afterRead(prior, now, /* recordHit= */ false);
      }

      return expired ? null : oldValue;
    }
  }

  @Override
  @SuppressWarnings("SynchronizationOnLocalVariableOrMethodParameter")
  public @Nullable V remove(@Nullable Object key) {
    requireNonNull(key);

    var ctx = new RemoveContext<K, V>();
    Object lookupKey = nodeFactory.newLookupKey(key);
    data.compute(lookupKey, (k, n) -> {
      if (n == null) {
        discardRefresh(k);
        return null;
      }
      synchronized (n) {
        requireIsAlive(key, n);
        ctx.oldKey = n.getKey();
        ctx.oldValue = n.getValue();
        ctx.oldWeight = n.getWeight();
        RemovalCause actualCause;
        if ((ctx.oldKey == null) || (ctx.oldValue == null)) {
          actualCause = RemovalCause.COLLECTED;
        } else if (hasExpired(n, expirationTicker().read()) && !isComputingAsync(ctx.oldValue)) {
          actualCause = RemovalCause.EXPIRED;
        } else {
          actualCause = RemovalCause.EXPLICIT;
        }
        if (actualCause.wasEvicted()) {
          notifyEviction(ctx.oldKey, ctx.oldValue, actualCause);
        }
        ctx.cause = actualCause;
        discardRefresh(k);
        ctx.node = n;
        n.retire();
        return null;
      }
    });

    if (ctx.cause != null) {
      afterWrite(new RemovalTask(requireNonNull(ctx.node)));
      if (ctx.cause.wasEvicted()) {
        statsCounter().recordEviction(ctx.oldWeight, ctx.cause);
      }
      notifyRemoval(ctx.oldKey, ctx.oldValue, ctx.cause);
    }
    return (ctx.cause == RemovalCause.EXPLICIT) ? ctx.oldValue : null;
  }

  @Override
  @SuppressWarnings("SynchronizationOnLocalVariableOrMethodParameter")
  public boolean remove(@Nullable Object key, @Nullable Object value) {
    requireNonNull(key);
    if (value == null) {
      return false;
    }

    var ctx = new RemoveContext<K, V>();
    Object lookupKey = nodeFactory.newLookupKey(key);
    data.computeIfPresent(lookupKey, (kR, node) -> {
      synchronized (node) {
        requireIsAlive(key, node);
        ctx.oldKey = node.getKey();
        ctx.oldValue = node.getValue();
        ctx.oldWeight = node.getWeight();
        if ((ctx.oldKey == null) || (ctx.oldValue == null)) {
          ctx.cause = RemovalCause.COLLECTED;
        } else if (hasExpired(node, expirationTicker().read()) && !isComputingAsync(ctx.oldValue)) {
          ctx.cause = RemovalCause.EXPIRED;
        } else if (node.containsValue(value)) {
          ctx.cause = RemovalCause.EXPLICIT;
        } else {
          return node;
        }
        if (ctx.cause.wasEvicted()) {
          notifyEviction(ctx.oldKey, ctx.oldValue, ctx.cause);
        }
        discardRefresh(kR);
        ctx.node = node;
        node.retire();
        return null;
      }
    });

    if (ctx.node == null) {
      return false;
    }
    var removeCause = requireNonNull(ctx.cause);
    afterWrite(new RemovalTask(ctx.node));
    if (removeCause.wasEvicted()) {
      statsCounter().recordEviction(ctx.oldWeight, removeCause);
    }
    notifyRemoval(ctx.oldKey, ctx.oldValue, removeCause);

    return (removeCause == RemovalCause.EXPLICIT);
  }

  @Override
  @SuppressWarnings("SynchronizationOnLocalVariableOrMethodParameter")
  public @Nullable V replace(K key, V value) {
    requireNonNull(key);
    requireNonNull(value);
    var ctx = new ReplaceContext<K, V>();
    int weight = weigher.weigh(key, value);
    Node<K, V> node = data.computeIfPresent(nodeFactory.newLookupKey(key), (k, n) -> {
      synchronized (n) {
        requireIsAlive(key, n);
        ctx.nodeKey = n.getKey();
        ctx.oldValue = n.getValue();
        ctx.oldWeight = n.getWeight();
        if ((ctx.nodeKey == null) || (ctx.oldValue == null)
            || (hasExpired(n, ctx.now = expirationTicker().read())
                && !isComputingAsync(ctx.oldValue))) {
          ctx.oldValue = null;
          ctx.garbage = true;
          return n;
        }

        long varTime = expireAfterUpdate(n, key, value, expiry(), ctx.now);
        n.setValue(value, valueReferenceQueue());
        n.setWeight(weight);

        long expirationTime = expirationTimeFor(value, ctx.now);
        ctx.exceedsTolerance = exceedsWriteTimeTolerance(n, varTime, expirationTime);
        if (ctx.exceedsTolerance) {
          setWriteTime(n, expirationTime);
        }
        setAccessTime(n, expirationTime);
        setVariableTime(n, varTime);
        discardRefresh(k);
        return n;
      }
    });

    if ((node == null) || (ctx.nodeKey == null) || (ctx.oldValue == null)) {
      if (ctx.garbage) {
        scheduleDrainBuffers();
      }
      return null;
    }

    int weightedDifference = (weight - ctx.oldWeight);
    if (ctx.exceedsTolerance || (weightedDifference != 0)) {
      afterWrite(new UpdateTask(node, weightedDifference));
    } else {
      afterRead(node, ctx.now, /* recordHit= */ false);
    }

    notifyOnReplace(ctx.nodeKey, ctx.oldValue, value);
    return ctx.oldValue;
  }

  @Override
  @SuppressWarnings("SynchronizationOnLocalVariableOrMethodParameter")
  public boolean replace(K key, V oldValue, V newValue,
      boolean shouldDiscardRefresh, boolean quietly) {
    requireNonNull(key);
    requireNonNull(oldValue);
    requireNonNull(newValue);
    var ctx = new ReplaceContext<K, V>();
    int weight = weigher.weigh(key, newValue);
    Node<K, V> node = data.computeIfPresent(nodeFactory.newLookupKey(key), (k, n) -> {
      synchronized (n) {
        requireIsAlive(key, n);
        ctx.nodeKey = n.getKey();
        ctx.oldValue = n.getValue();
        ctx.oldWeight = n.getWeight();
        if ((ctx.nodeKey == null) || (ctx.oldValue == null)
            || (hasExpired(n, ctx.now = expirationTicker().read())
                && !isComputingAsync(ctx.oldValue))) {
          ctx.oldValue = null;
          ctx.garbage = true;
          return n;
        } else if (!n.containsValue(oldValue)) {
          ctx.oldValue = null;
          return n;
        }

        // A completion finalizes only what the insertion deferred. Its caller reads the future's
        // readiness before the write, so a value that becomes available in between is evaluated by
        // the insertion, and evaluating it again would charge that creation as an update.
        long varTime = (quietly && !isExpirationDeferred(n, ctx.now))
            ? n.getVariableTime()
            : expireAfterUpdate(n, key, newValue, expiry(), ctx.now);
        n.setValue(newValue, valueReferenceQueue());
        n.setWeight(weight);

        long expirationTime = expirationTimeFor(newValue, ctx.now);
        ctx.exceedsTolerance = exceedsWriteTimeTolerance(n, varTime, expirationTime);
        if (ctx.exceedsTolerance) {
          setWriteTime(n, expirationTime);
        }
        setAccessTime(n, expirationTime);
        setVariableTime(n, varTime);

        if (shouldDiscardRefresh) {
          discardRefresh(k);
        }
      }
      return n;
    });

    if ((node == null) || (ctx.nodeKey == null) || (ctx.oldValue == null)) {
      if (ctx.garbage) {
        scheduleDrainBuffers();
      }
      return false;
    }

    int weightedDifference = (weight - ctx.oldWeight);
    if (ctx.exceedsTolerance || (weightedDifference != 0)) {
      afterWrite(new UpdateTask(node, weightedDifference, quietly ? Access.QUIET : Access.HIT));
    } else if (!quietly) {
      afterRead(node, ctx.now, /* recordHit= */ false);
    }

    notifyOnReplace(ctx.nodeKey, ctx.oldValue, newValue);
    return true;
  }

  @Override
  public void replaceAll(BiFunction<? super K, ? super V, ? extends V> function) {
    requireNonNull(function);

    BiFunction<K, @Nullable V, V> remappingFunction = (key, oldValue) ->
        requireNonNull(function.apply(key, requireNonNull(oldValue)));
    for (K key : keySet()) {
      Object lookupKey = nodeFactory.newLookupKey(key);
      remap(key, lookupKey, remappingFunction, expiry(),
          new ComputeContext<>(), /* computeIfAbsent= */ false);
    }
  }

  @Override
  public @Nullable V computeIfAbsent(K key,
      @Var Function<? super K, ? extends @Nullable V> mappingFunction,
      boolean recordStats, boolean recordLoad) {
    requireNonNull(key);
    requireNonNull(mappingFunction);

    // An optimistic fast path to avoid unnecessary locking
    Node<K, V> node = data.get(nodeFactory.newLookupKey(key));
    if (node != null) {
      long now = expirationTicker().read();
      boolean expired = hasExpired(node, now);
      V value = node.getValue();
      if ((value != null) && (!expired || isComputingAsync(value))) {
        if (expiresAfterRead() && !isComputingAsync(value)) {
          tryExpireAfterRead(node, key, value, expiry(), now);
          setAccessTime(node, now);
        }
        var refreshed = afterRead(node, now, /* recordHit= */ recordStats);
        return (refreshed == null) ? value : refreshed;
      }
    }
    if (recordStats) {
      mappingFunction = statsAware(mappingFunction, recordLoad);
    }
    Object keyRef = nodeFactory.newReferenceKey(key, keyReferenceQueue());
    return doComputeIfAbsent(key, keyRef, mappingFunction, new ComputeContext<>(), recordStats);
  }

  /** Returns the current value from a computeIfAbsent invocation. */
  @SuppressWarnings("SynchronizationOnLocalVariableOrMethodParameter")
  @Nullable V doComputeIfAbsent(K key, Object keyRef,
      Function<? super K, ? extends @Nullable V> mappingFunction,
      ComputeContext<K, V> ctx, boolean recordStats) {
    Node<K, V> node = data.compute(keyRef, (k, n) -> {
      if (n == null) {
        ctx.newValue = mappingFunction.apply(key);
        if (ctx.newValue == null) {
          discardRefresh(k);
          return null;
        }
        ctx.now = expirationTicker().read();
        ctx.newWeight = weigher.weigh(key, ctx.newValue);
        var created = nodeFactory.newNode(k, ctx.newValue,
            valueReferenceQueue(), ctx.newWeight, ctx.now);
        long expirationTime = expirationTimeFor(ctx.newValue, ctx.now);
        setVariableTime(created, expireAfterCreate(key, ctx.newValue, expiry(), ctx.now));
        setAccessTime(created, expirationTime);
        setWriteTime(created, expirationTime);
        discardRefresh(k);
        return created;
      }

      synchronized (n) {
        requireIsAlive(key, n);
        ctx.nodeKey = n.getKey();
        ctx.oldValue = n.getValue();
        ctx.oldWeight = n.getWeight();
        RemovalCause actualCause;
        if ((ctx.nodeKey == null) || (ctx.oldValue == null)) {
          actualCause = RemovalCause.COLLECTED;
        } else if (hasExpired(n, ctx.now = expirationTicker().read())
            && !isComputingAsync(ctx.oldValue)) {
          actualCause = RemovalCause.EXPIRED;
        } else {
          return n;
        }

        ctx.cause = actualCause;
        notifyEviction(ctx.nodeKey, ctx.oldValue, actualCause);

        try {
          ctx.newValue = mappingFunction.apply(key);
          if (ctx.newValue == null) {
            discardRefresh(k);
            ctx.removed = n;
            n.retire();
            return null;
          }
          ctx.now = expirationTicker().read();
          ctx.newWeight = weigher.weigh(key, ctx.newValue);
          long varTime = expireAfterCreate(key, ctx.newValue, expiry(), ctx.now);

          n.setValue(ctx.newValue, valueReferenceQueue());
          n.setWeight(ctx.newWeight);

          long expirationTime = expirationTimeFor(ctx.newValue, ctx.now);
          setAccessTime(n, expirationTime);
          setWriteTime(n, expirationTime);
          setVariableTime(n, varTime);
          discardRefresh(k);
          return n;
        } catch (Throwable e) {
          ctx.newValue = null;
          discardRefresh(k);
          ctx.exception = e;
          ctx.removed = n;
          n.retire();
          return null;
        }
      }
    });

    if (ctx.cause != null) {
      statsCounter().recordEviction(ctx.oldWeight, ctx.cause);
      notifyRemoval(ctx.nodeKey, ctx.oldValue, ctx.cause);
    }
    if (node == null) {
      if (ctx.removed != null) {
        afterWrite(new RemovalTask(ctx.removed));
      }
      if (ctx.exception != null) {
        throw toUnchecked(ctx.exception);
      }
      return null;
    }
    if ((ctx.oldValue != null) && (ctx.newValue == null)) {
      if (!isComputingAsync(ctx.oldValue)) {
        tryExpireAfterRead(node, key, ctx.oldValue, expiry(), ctx.now);
        setAccessTime(node, ctx.now);
      }

      var refreshed = afterRead(node, ctx.now, /* recordHit= */ recordStats);
      return (refreshed == null) ? ctx.oldValue : refreshed;
    }
    if ((ctx.oldValue == null) && (ctx.cause == null)) {
      afterWrite(new AddTask(node, ctx.newWeight));
    } else {
      int weightedDifference = (ctx.newWeight - ctx.oldWeight);
      afterWrite(new UpdateTask(node, weightedDifference, Access.RELOAD));
    }

    return ctx.newValue;
  }

  @Override
  public @Nullable V computeIfPresent(K key,
      BiFunction<? super K, ? super V, ? extends @Nullable V> remappingFunction) {
    requireNonNull(key);
    requireNonNull(remappingFunction);

    // An optimistic fast path to avoid unnecessary locking
    Object lookupKey = nodeFactory.newLookupKey(key);
    var node = data.get(lookupKey);
    if (node == null) {
      return null;
    }
    boolean expired = hasExpired(node, expirationTicker().read());
    V value = node.getValue();
    if ((value == null) || expired) {
      scheduleDrainBuffers();
      return null;
    }

    @SuppressWarnings("NullAway")
    BiFunction<? super K, ? super @Nullable V, ? extends @Nullable V> statsAwareRemappingFunction =
        statsAware(remappingFunction, /* recordLoad= */ true);
    return remap(key, lookupKey, statsAwareRemappingFunction,
        expiry(), new ComputeContext<>(), /* computeIfAbsent= */ false);
  }

  @Override
  public @Nullable V compute(K key,
      BiFunction<? super K, ? super @Nullable V, ? extends @Nullable V> remappingFunction,
      @Nullable Expiry<? super K, ? super V> expiry, boolean recordLoad,
      @Nullable RemapHints hints) {
    requireNonNull(key);
    requireNonNull(remappingFunction);

    Object keyRef = nodeFactory.newReferenceKey(key, keyReferenceQueue());
    var ctx = new ComputeContext<K, V>();
    ctx.hints = hints;
    return remap(key, keyRef, statsAware(remappingFunction, recordLoad),
        expiry, ctx, /* computeIfAbsent= */ true);
  }

  @Override
  public @Nullable V merge(K key, V value,
      BiFunction<? super V, ? super V, ? extends @Nullable V> remappingFunction) {
    requireNonNull(key);
    requireNonNull(value);
    requireNonNull(remappingFunction);

    Object keyRef = nodeFactory.newReferenceKey(key, keyReferenceQueue());
    BiFunction<? super V, ? super V, ? extends @Nullable V> f = statsAware(remappingFunction);
    return remap(key, keyRef,
        (k, oldValue) -> (oldValue == null) ? value : f.apply(oldValue, value), expiry(),
        new ComputeContext<>(), /* computeIfAbsent= */ true);
  }

  /**
   * Attempts to compute a mapping for the specified key and its current mapped value (or
   * {@code null} if there is no current mapping).
   * <p>
   * An entry that has expired or been reference collected is evicted and the computation continues
   * as if the entry had not been present. This method does not pre-screen and does not wrap the
   * remappingFunction to be statistics aware.
   *
   * @param key key with which the specified value is to be associated
   * @param keyRef the key to associate with or a lookup only key if not {@code computeIfAbsent}
   * @param remappingFunction the function to compute a value
   * @param expiry the calculator for the expiration time
   * @param ctx the mutable context for passing state to and from the compute lambda
   * @param computeIfAbsent if an absent entry can be computed
   * @return the new value associated with the specified key, or null if none
   */
  @SuppressWarnings({"StatementWithEmptyBody", "SynchronizationOnLocalVariableOrMethodParameter"})
  @Nullable V remap(K key, Object keyRef,
      BiFunction<? super K, ? super @Nullable V, ? extends @Nullable V> remappingFunction,
      @Nullable Expiry<? super K, ? super V> expiry,
      ComputeContext<K, V> ctx, boolean computeIfAbsent) {
    Node<K, V> node = data.compute(keyRef, (kr, n) -> {
      if (n == null) {
        if (!computeIfAbsent) {
          return null;
        }
        ctx.newValue = remappingFunction.apply(key, null);
        if (ctx.newValue == null) {
          // A stale refresh whose entry is absent leaves a successor's registration intact
          if ((ctx.hints == null) || !ctx.hints.preserveRefresh) {
            discardRefresh(kr);
          }
          return null;
        }
        try {
          ctx.now = expirationTicker().read();
          ctx.newWeight = weigher.weigh(key, ctx.newValue);
          long varTime = expireAfterCreate(key, ctx.newValue, expiry, ctx.now);
          var created = nodeFactory.newNode(keyRef, ctx.newValue,
              valueReferenceQueue(), ctx.newWeight, ctx.now);

          long expirationTime = expirationTimeFor(ctx.newValue, ctx.now);
          setAccessTime(created, expirationTime);
          setWriteTime(created, expirationTime);
          setVariableTime(created, varTime);
          return created;
        } finally {
          discardRefresh(kr);
        }
      }

      synchronized (n) {
        requireIsAlive(key, n);
        ctx.nodeKey = n.getKey();
        ctx.oldValue = n.getValue();
        ctx.oldWeight = n.getWeight();
        if ((ctx.nodeKey == null) || (ctx.oldValue == null)) {
          ctx.cause = RemovalCause.COLLECTED;
        } else if (hasExpired(n, expirationTicker().read()) && !isComputingAsync(ctx.oldValue)) {
          ctx.cause = RemovalCause.EXPIRED;
        }
        if (ctx.cause != null) {
          notifyEviction(ctx.nodeKey, ctx.oldValue, ctx.cause);
          if (!computeIfAbsent) {
            discardRefresh(kr);
            ctx.removed = n;
            n.retire();
            return null;
          }
        }

        boolean wasEvicted = (ctx.cause != null);
        try {
          ctx.newValue = remappingFunction.apply(key,
              (ctx.cause == null) ? ctx.oldValue : null);

          if (ctx.newValue == null) {
            if (ctx.cause == null) {
              ctx.cause = RemovalCause.EXPLICIT;
            }
            // A stale refresh whose entry was evicted leaves a successor's registration intact
            if ((ctx.hints == null) || !ctx.hints.preserveRefresh) {
              discardRefresh(kr);
            }
            ctx.removed = n;
            n.retire();
            return null;
          }

          // If the caller flagged a same-instance return as a no-op (e.g., a refresh was rejected
          // and should not touch the entry), skip the metadata updates below.
          if ((ctx.hints != null) && ctx.hints.preserveTimestamps
              && (ctx.newValue == ctx.oldValue) && (ctx.cause == null)) {
            // Skip for query-style callers whose no-op path must leave any in-flight refresh intact
            if (!ctx.hints.preserveRefresh) {
              discardRefresh(kr);
            }
            ctx.unmodified = true;
            return n;
          }

          long varTime;
          ctx.newWeight = weigher.weigh(key, ctx.newValue);
          ctx.now = expirationTicker().read();
          if (ctx.cause == null) {
            if (ctx.newValue != ctx.oldValue) {
              ctx.cause = RemovalCause.REPLACED;
            }
            varTime = expireAfterUpdate(n, key, ctx.newValue, expiry, ctx.now);
          } else {
            varTime = expireAfterCreate(key, ctx.newValue, expiry, ctx.now);
          }

          if (ctx.newValue != ctx.oldValue) {
            n.setValue(ctx.newValue, valueReferenceQueue());
          }
          n.setWeight(ctx.newWeight);

          long expirationTime = expirationTimeFor(ctx.newValue, ctx.now);
          ctx.exceedsTolerance = exceedsWriteTimeTolerance(n, varTime, expirationTime);
          if (((ctx.cause != null) && ctx.cause.wasEvicted()) || ctx.exceedsTolerance) {
            setWriteTime(n, expirationTime);
          }
          setAccessTime(n, expirationTime);
          setVariableTime(n, varTime);
          discardRefresh(kr);
          return n;
        } catch (Throwable e) {
          if ((ctx.hints == null) || !ctx.hints.preserveRefresh) {
            discardRefresh(kr);
          }
          if (!wasEvicted) {
            throw e;
          }
          ctx.newValue = null;
          ctx.exception = e;
          ctx.removed = n;
          n.retire();
          return null;
        }
      }
    });

    if (ctx.cause != null) {
      if (ctx.cause == RemovalCause.REPLACED) {
        requireNonNull(ctx.newValue);
        notifyOnReplace(key, ctx.oldValue, ctx.newValue);
      } else {
        if (ctx.cause.wasEvicted()) {
          statsCounter().recordEviction(ctx.oldWeight, ctx.cause);
        }
        notifyRemoval(ctx.nodeKey, ctx.oldValue, ctx.cause);
      }
    }

    if (ctx.removed != null) {
      afterWrite(new RemovalTask(ctx.removed));
    } else if (node == null) {
      // absent and not computable
    } else if (ctx.unmodified) {
      // caller flagged a same-instance return as a no-op
    } else if ((ctx.oldValue == null) && (ctx.cause == null)) {
      afterWrite(new AddTask(node, ctx.newWeight));
    } else {
      int weightedDifference = ctx.newWeight - ctx.oldWeight;
      boolean quietly = (ctx.hints != null) && ctx.hints.quietly;
      boolean reload = (ctx.cause != null) && ctx.cause.wasEvicted();
      if (ctx.exceedsTolerance || (weightedDifference != 0) || (evicts() && !quietly && reload)) {
        var access = quietly ? Access.QUIET : (reload ? Access.RELOAD : Access.HIT);
        afterWrite(new UpdateTask(node, weightedDifference, access));
      } else {
        if (!quietly) {
          afterRead(node, ctx.now, /* recordHit= */ false);
        }
        if (reload) {
          scheduleDrainBuffers();
        }
      }
    }

    if (ctx.exception != null) {
      throw toUnchecked(ctx.exception);
    }
    return ctx.newValue;
  }

  @Override
  public void forEach(BiConsumer<? super K, ? super V> action) {
    requireNonNull(action);

    for (var iterator = new EntryIterator<>(this); iterator.hasNext();) {
      action.accept(requireNonNull(iterator.key), requireNonNull(iterator.value));
      iterator.advance();
    }
  }

  @Override
  public Set<K> keySet() {
    Set<K> ks = keySet;
    return (ks == null) ? (keySet = new KeySetView<>(this)) : ks;
  }

  @Override
  public Collection<V> values() {
    Collection<V> vs = values;
    return (vs == null) ? (values = new ValuesView<>(this)) : vs;
  }

  @Override
  public Set<Entry<K, V>> entrySet() {
    Set<Entry<K, V>> es = entrySet;
    return (es == null) ? (entrySet = new EntrySetView<>(this)) : es;
  }

  /**
   * Object equality requires reflexive, symmetric, transitive, and consistency properties. Of
   * these, symmetry and consistency require further clarification for how they are upheld.
   * <p>
   * The <i>consistency</i> property between invocations requires that the results are the same if
   * there are no modifications to the information used. Therefore, usages should expect that this
   * operation may return misleading results if either the maps or the data held by them is modified
   * during the execution of this method. This characteristic allows for comparing the map sizes and
   * assuming stable mappings, as done by {@link java.util.AbstractMap}-based maps.
   * <p>
   * The <i>symmetric</i> property requires that the result is the same for all implementations of
   * {@link Map#equals(Object)}. That contract is defined in terms of the stable mappings provided
   * by {@link #entrySet()}, meaning that the {@link #size()} optimization forces that the count is
   * consistent with the mappings when used for an equality check.
   * <p>
   * The cache's {@link #size()} method may include entries that have expired or have been reference
   * collected, but have not yet been removed from the backing map. An iteration over the map may
   * trigger the removal of these dead entries when skipped over during traversal. To ensure
   * consistency and symmetry, usages should call {@link #cleanUp()} before this method while no
   * other concurrent operations are being performed on this cache. This is not done implicitly by
   * {@link #size()} as many usages assume it to be instantaneous and lock-free. As a postcondition
   * the iteration count is verified against the prescreened {@link #size()} so that a concurrent
   * maintenance pass that drops dead entries during traversal is detected and reported as not
   * equal, rather than silently returning {@code true} on the surviving subset.
   */
  @Override
  public boolean equals(@Nullable Object o) {
    if (o == this) {
      return true;
    } else if (!(o instanceof Map)) {
      return false;
    }

    var map = (Map<?, ?>) o;
    int expectedSize = size();
    if (map.size() != expectedSize) {
      return false;
    }

    try {
      @Var int count = 0;
      long now = expirationTicker().read();
      for (var node : data.values()) {
        boolean expired = hasExpired(node, now);
        K key = node.getKey();
        V value = node.getValue();
        if ((key == null) || (value == null) || !node.isAlive()
            || (expired && !isComputingAsync(value))) {
          scheduleDrainBuffers();
          return false;
        } else {
          var val = map.get(key);
          if ((val == null) || ((val != value) && !val.equals(value))) {
            return false;
          }
        }
        count++;
      }
      return (count == expectedSize);
    } catch (ClassCastException | NullPointerException ignored) {
      return false;
    }
  }

  @Override
  public int hashCode() {
    @Var int hash = 0;
    @Var boolean drain = false;
    long now = expirationTicker().read();
    for (var node : data.values()) {
      boolean expired = hasExpired(node, now);
      K key = node.getKey();
      V value = node.getValue();
      if ((key == null) || (value == null) || !node.isAlive()
          || (expired && !isComputingAsync(value))) {
        drain = true;
      } else {
        hash += key.hashCode() ^ value.hashCode();
      }
    }
    if (drain) {
      scheduleDrainBuffers();
    }
    return hash;
  }

  @Override
  public String toString() {
    @Var boolean drain = false;
    long now = expirationTicker().read();
    var result = new StringBuilder().append('{');
    for (var node : data.values()) {
      boolean expired = hasExpired(node, now);
      K key = node.getKey();
      V value = node.getValue();
      if ((key == null) || (value == null) || !node.isAlive()
          || (expired && !isComputingAsync(value))) {
        drain = true;
      } else {
        if (result.length() != 1) {
          result.append(',').append(' ');
        }
        result.append((key == this) ? "(this Map)" : key);
        result.append('=');
        result.append((value == this) ? "(this Map)" : value);
      }
    }
    if (drain) {
      scheduleDrainBuffers();
    }
    return result.append('}').toString();
  }

  /**
   * Returns the computed result from the ordered traversal of the cache entries.
   *
   * @param hottest the coldest or hottest iteration order
   * @param transformer a function that unwraps the value
   * @param mappingFunction the mapping function to compute a value
   * @return the computed value
   */
  @SuppressWarnings("GuardedByChecker")
  <T extends @Nullable Object> T evictionOrder(boolean hottest,
      Function<@Nullable V, @Nullable V> transformer,
      Function<Stream<CacheEntry<K, V>>, T> mappingFunction) {
    Comparator<Node<K, V>> comparator = Comparator.comparingInt(node -> {
      var keyRef = node.getKeyReferenceOrNull();
      return ((keyRef == null) || !node.isAlive()) ? 0 : frequencySketch().frequency(keyRef);
    });
    Iterable<Node<K, V>> iterable;
    if (hottest) {
      iterable = () -> {
        var secondary = PeekingIterator.comparing(
            accessOrderProbationDeque().descendingIterator(),
            accessOrderWindowDeque().descendingIterator(), comparator);
        return PeekingIterator.concat(
            accessOrderProtectedDeque().descendingIterator(), secondary);
      };
    } else {
      iterable = () -> {
        var primary = PeekingIterator.comparing(
            accessOrderWindowDeque().iterator(), accessOrderProbationDeque().iterator(),
            comparator.reversed());
        return PeekingIterator.concat(primary, accessOrderProtectedDeque().iterator());
      };
    }
    return snapshot(iterable, transformer, mappingFunction);
  }

  /**
   * Returns the computed result from the ordered traversal of the cache entries.
   *
   * @param oldest the youngest or oldest iteration order
   * @param transformer a function that unwraps the value
   * @param mappingFunction the mapping function to compute a value
   * @return the computed value
   */
  @SuppressWarnings("GuardedByChecker")
  <T extends @Nullable Object> T expireAfterAccessOrder(boolean oldest,
      Function<@Nullable V, @Nullable V> transformer,
      Function<Stream<CacheEntry<K, V>>, T> mappingFunction) {
    Iterable<Node<K, V>> iterable;
    if (evicts()) {
      iterable = () -> {
        @Var Comparator<Node<K, V>> comparator = (n1, n2) ->
            Long.signum(n1.getAccessTime() - n2.getAccessTime());
        PeekingIterator<Node<K, V>> first;
        PeekingIterator<Node<K, V>> second;
        PeekingIterator<Node<K, V>> third;
        if (oldest) {
          comparator = comparator.reversed();
          first = accessOrderWindowDeque().iterator();
          second = accessOrderProbationDeque().iterator();
          third = accessOrderProtectedDeque().iterator();
        } else {
          first = accessOrderWindowDeque().descendingIterator();
          second = accessOrderProbationDeque().descendingIterator();
          third = accessOrderProtectedDeque().descendingIterator();
        }
        return PeekingIterator.comparing(
            PeekingIterator.comparing(first, second, comparator), third, comparator);
      };
    } else {
      iterable = oldest
          ? accessOrderWindowDeque()
          : accessOrderWindowDeque()::descendingIterator;
    }
    return snapshot(iterable, transformer, mappingFunction);
  }

  /**
   * Returns the computed result from the ordered traversal of the cache entries.
   *
   * @param iterable the supplier of the entries in the cache
   * @param transformer a function that unwraps the value
   * @param mappingFunction the mapping function to compute a value
   * @return the computed value
   */
  @SuppressWarnings("MathClampLong")
  <T extends @Nullable Object> T snapshot(Iterable<Node<K, V>> iterable,
      Function<@Nullable V, @Nullable V> transformer,
      Function<Stream<CacheEntry<K, V>>, T> mappingFunction) {
    requireNonNull(mappingFunction);
    requireNonNull(transformer);
    requireNonNull(iterable);

    evictionLock.lock();
    try {
      maintenance(/* ignored */ null);

      // Obtain the iterator as late as possible for modification count checking
      try (var stream = StreamSupport.stream(Spliterators.spliteratorUnknownSize(
           iterable.iterator(), DISTINCT | ORDERED | NONNULL | IMMUTABLE), /* parallel= */ false)) {
        boolean[] open = { true };
        return mappingFunction.apply(stream.onClose(() -> open[0] = false)
            .peek(ignored -> requireState(open[0], "stream has already been closed"))
            .map(node -> nodeToCacheEntry(node, transformer,
                (int) Math.max(0L, Math.min(node.getPolicyWeight(), Integer.MAX_VALUE))))
            .filter(Objects::nonNull));
      }
    } finally {
      evictionLock.unlock();
      rescheduleCleanUpIfIncomplete();
    }
  }

  /**
   * Returns an entry for the given node if it can be used externally, else null. The weight is
   * the caller's best-effort reading and the timestamps are read after the value, so either may
   * belong to a concurrent update.
   */
  @Nullable CacheEntry<K, V> nodeToCacheEntry(
      Node<K, V> node, Function<@Nullable V, @Nullable V> transformer, int weight) {
    long now = expirationTicker().read();
    boolean expired = hasExpired(node, now);
    V rawValue = node.getValue();
    if (rawValue == null) {
      return null;
    }
    V value = transformer.apply(rawValue);
    K key = node.getKey();
    if ((key == null) || (value == null) || !node.isAlive() || expired) {
      return null;
    }

    @Var long expiresAfter = Long.MAX_VALUE;
    if (expiresAfterAccess()) {
      expiresAfter = Math.min(expiresAfter,
          expiresAfterAccessNanos() - Math.max(0L, now - node.getAccessTime()));
    }
    if (expiresAfterWrite()) {
      expiresAfter = Math.min(expiresAfter,
          expiresAfterWriteNanos() - Math.max(0L, toWriteTime(now) - writeTimeOf(node)));
    }
    if (expiresVariable()) {
      expiresAfter = node.getVariableTime() - now;
    }

    long refreshableAfter = refreshAfterWrite()
        ? refreshAfterWriteNanos() - Math.max(0L, now - writeTimeOf(node))
        : Long.MAX_VALUE;
    return SnapshotEntry.forEntry(key, value, now,
        isWeighted ? weight : 1, now + expiresAfter, now + refreshableAfter);
  }

  /** Creates a serialization proxy based on the common configuration shared by all cache types. */
  static <K, V> SerializationProxy<K, V> makeSerializationProxy(BoundedLocalCache<?, ?> cache) {
    var proxy = new SerializationProxy<K, V>();
    proxy.weakKeys = cache.collectKeys();
    proxy.weakValues = cache.nodeFactory.weakValues();
    proxy.softValues = cache.nodeFactory.softValues();
    proxy.isRecordingStats = cache.isRecordingStats();
    proxy.evictionListener = cache.evictionListener;
    proxy.removalListener = cache.removalListener();
    proxy.ticker = cache.expirationTicker();
    if (cache.expiresAfterAccess()) {
      proxy.expiresAfterAccessNanos = cache.expiresAfterAccessNanos();
    }
    if (cache.expiresAfterWrite()) {
      proxy.expiresAfterWriteNanos = cache.expiresAfterWriteNanos();
    }
    if (cache.expiresVariable()) {
      proxy.expiry = cache.expiry();
    }
    if (cache.refreshAfterWrite()) {
      proxy.refreshAfterWriteNanos = cache.refreshAfterWriteNanos();
    }
    if (cache.evicts()) {
      if (cache.isWeighted) {
        proxy.weigher = cache.weigher;
        proxy.maximumWeight = cache.maximumAcquire();
      } else {
        proxy.maximumSize = cache.maximumAcquire();
      }
    }
    proxy.cacheLoader = cache.cacheLoader;
    proxy.async = cache.isAsync;
    return proxy;
  }

  /** Mutable context for passing state between a lambda and the caller. */
  static final class EvictContext<V> {
    @Nullable RemovalCause cause;
    @Nullable V value;
    boolean resurrect;
    boolean removed;
    int oldWeight;
  }

  /** Mutable context for passing state between a lambda and the caller. */
  static final class RemoveContext<K, V> {
    @Nullable K oldKey;
    @Nullable V oldValue;
    @Nullable Node<K, V> node;
    @Nullable RemovalCause cause;
    int oldWeight;
  }

  /** Mutable context for passing state between a lambda and the caller. */
  static final class ReplaceContext<K, V> {
    @Nullable K nodeKey;
    @Nullable V oldValue;

    long now;
    int oldWeight;
    boolean garbage;
    boolean exceedsTolerance;
  }

  /** Mutable context for passing state between a lambda and the caller. */
  static final class ComputeContext<K, V> {
    @Nullable K nodeKey;
    @Nullable V oldValue;
    @Nullable V newValue;
    @Nullable RemapHints hints;
    @Nullable Node<K, V> removed;
    @Nullable RemovalCause cause;
    @Nullable Throwable exception;

    long now;
    int oldWeight;
    int newWeight;
    boolean unmodified;
    boolean exceedsTolerance;
  }

  /** A function that produces an unmodifiable map up to the limit in stream order. */
  static final class SizeLimiter<K, V> implements Function<Stream<CacheEntry<K, V>>, Map<K, V>> {
    private final int expectedSize;
    private final long limit;

    SizeLimiter(int expectedSize, long limit) {
      requireArgument(limit >= 0, "limit cannot be negative: %s", limit);
      this.expectedSize = expectedSize;
      this.limit = limit;
    }

    @Override
    public Map<K, V> apply(Stream<CacheEntry<K, V>> stream) {
      var map = new LinkedHashMap<K, V>(calculateHashMapCapacity(expectedSize));
      stream.limit(limit).forEach(entry -> map.put(entry.getKey(), entry.getValue()));
      return Collections.unmodifiableMap(map);
    }
  }

  /** A function that produces an unmodifiable map up to the weighted limit in stream order. */
  static final class WeightLimiter<K, V> implements Function<Stream<CacheEntry<K, V>>, Map<K, V>> {
    private final long weightLimit;

    long weightedSize;

    WeightLimiter(long weightLimit) {
      requireArgument(weightLimit >= 0, "weight limit cannot be negative: %s", weightLimit);
      this.weightLimit = weightLimit;
    }

    @Override
    public Map<K, V> apply(Stream<CacheEntry<K, V>> stream) {
      var map = new LinkedHashMap<K, V>();
      stream.takeWhile(entry -> {
        weightedSize += entry.weight();
        if (weightedSize < 0) {
          weightedSize = Long.MAX_VALUE;
        }
        return (weightedSize <= weightLimit);
      }).forEach(entry -> map.put(entry.getKey(), entry.getValue()));
      return Collections.unmodifiableMap(map);
    }
  }

  /** An adapter to safely externalize the keys. */
  static final class KeySetView<K, V> extends AbstractSet<K> {
    final BoundedLocalCache<K, V> cache;

    KeySetView(BoundedLocalCache<K, V> cache) {
      this.cache = requireNonNull(cache);
    }

    @Override
    public int size() {
      return cache.size();
    }

    @Override
    public void clear() {
      cache.clear();
    }

    @Override
    @SuppressWarnings("SuspiciousMethodCalls")
    public boolean contains(@Nullable Object o) {
      return cache.containsKey(o);
    }

    @Override
    public boolean containsAll(Collection<?> collection) {
      requireNonNull(collection);
      if (collection != this) {
        for (Object o : collection) {
          if ((o == null) || !contains(o)) {
            return false;
          }
        }
      }
      return true;
    }

    @Override
    public boolean removeAll(Collection<?> collection) {
      requireNonNull(collection);
      @Var boolean modified = false;
      if (cache.collectKeys() || ((collection instanceof Set<?>) && (collection.size() > size()))) {
        for (K key : this) {
          if (collection.contains(key)) {
            modified |= remove(key);
          }
        }
      } else {
        for (var item : collection) {
          modified |= (item != null) && remove(item);
        }
      }
      return modified;
    }

    @Override
    public boolean remove(@Nullable Object o) {
      return (cache.remove(o) != null);
    }

    @Override
    public boolean removeIf(Predicate<? super K> filter) {
      requireNonNull(filter);
      @Var boolean modified = false;
      for (K key : this) {
        if (filter.test(key) && remove(key)) {
          modified = true;
        }
      }
      return modified;
    }

    @Override
    public boolean retainAll(Collection<?> collection) {
      requireNonNull(collection);
      @Var boolean modified = false;
      for (K key : this) {
        if (!collection.contains(key) && remove(key)) {
          modified = true;
        }
      }
      return modified;
    }

    @Override
    public Iterator<K> iterator() {
      return new KeyIterator<>(cache);
    }

    @Override
    public Spliterator<K> spliterator() {
      return new KeySpliterator<>(cache);
    }
  }

  /** An adapter to safely externalize the key iterator. */
  static final class KeyIterator<K, V> implements Iterator<K> {
    final EntryIterator<K, V> iterator;

    KeyIterator(BoundedLocalCache<K, V> cache) {
      this.iterator = new EntryIterator<>(cache);
    }

    @Override
    public boolean hasNext() {
      return iterator.hasNext();
    }

    @Override
    public K next() {
      return iterator.nextKey();
    }

    @Override
    public void remove() {
      iterator.remove();
    }
  }

  /** An adapter to safely externalize the key spliterator. */
  static final class KeySpliterator<K, V> implements Spliterator<K> {
    final Spliterator<Node<K, V>> spliterator;
    final BoundedLocalCache<K, V> cache;

    KeySpliterator(BoundedLocalCache<K, V> cache) {
      this(cache, cache.data.values().spliterator());
    }

    KeySpliterator(BoundedLocalCache<K, V> cache, Spliterator<Node<K, V>> spliterator) {
      this.spliterator = requireNonNull(spliterator);
      this.cache = requireNonNull(cache);
    }

    @Override
    public void forEachRemaining(Consumer<? super K> action) {
      requireNonNull(action);
      Consumer<Node<K, V>> consumer = node -> {
        long now = cache.expirationTicker().read();
        boolean expired = cache.hasExpired(node, now);
        K key = node.getKey();
        V value = node.getValue();
        if ((key == null) || (value == null) || (expired && !cache.isComputingAsync(value))) {
          cache.scheduleDrainBuffers();
        } else if (node.isAlive()) {
          action.accept(key);
        }
      };
      spliterator.forEachRemaining(consumer);
    }

    @Override
    public boolean tryAdvance(Consumer<? super K> action) {
      requireNonNull(action);
      boolean[] advanced = { false };
      Consumer<Node<K, V>> consumer = node -> {
        long now = cache.expirationTicker().read();
        boolean expired = cache.hasExpired(node, now);
        K key = node.getKey();
        V value = node.getValue();
        if ((key == null) || (value == null) || (expired && !cache.isComputingAsync(value))) {
          cache.scheduleDrainBuffers();
        } else if (node.isAlive()) {
          action.accept(key);
          advanced[0] = true;
        }
      };
      while (spliterator.tryAdvance(consumer)) {
        if (advanced[0]) {
          return true;
        }
      }
      return false;
    }

    @Override
    public @Nullable Spliterator<K> trySplit() {
      Spliterator<Node<K, V>> split = spliterator.trySplit();
      return (split == null) ? null : new KeySpliterator<>(cache, split);
    }

    @Override
    public long estimateSize() {
      return spliterator.estimateSize();
    }

    @Override
    public int characteristics() {
      return DISTINCT | CONCURRENT | NONNULL;
    }
  }

  /** An adapter to safely externalize the values. */
  static final class ValuesView<K, V> extends AbstractCollection<V> {
    final BoundedLocalCache<K, V> cache;

    ValuesView(BoundedLocalCache<K, V> cache) {
      this.cache = requireNonNull(cache);
    }

    @Override
    public int size() {
      return cache.size();
    }

    @Override
    public void clear() {
      cache.clear();
    }

    @Override
    @SuppressWarnings("SuspiciousMethodCalls")
    public boolean contains(@Nullable Object o) {
      return cache.containsValue(o);
    }

    @Override
    public boolean containsAll(Collection<?> collection) {
      requireNonNull(collection);
      if (collection != this) {
        for (Object o : collection) {
          if ((o == null) || !contains(o)) {
            return false;
          }
        }
      }
      return true;
    }

    @Override
    public boolean removeAll(Collection<?> collection) {
      requireNonNull(collection);
      @Var boolean modified = false;
      for (var iterator = new EntryIterator<>(cache); iterator.hasNext();) {
        var key = requireNonNull(iterator.key);
        var value = requireNonNull(iterator.value);
        if (collection.contains(value) && cache.remove(key, value)) {
          modified = true;
        }
        iterator.advance();
      }
      return modified;
    }

    @Override
    public boolean remove(@Nullable Object o) {
      if (o == null) {
        return false;
      }
      for (var iterator = new EntryIterator<>(cache); iterator.hasNext();) {
        var key = requireNonNull(iterator.key);
        var node = requireNonNull(iterator.next);
        var value = requireNonNull(iterator.value);
        if (node.containsValue(o) && cache.remove(key, value)) {
          return true;
        }
        iterator.advance();
      }
      return false;
    }

    @Override
    public boolean removeIf(Predicate<? super V> filter) {
      requireNonNull(filter);
      @Var boolean modified = false;
      for (var iterator = new EntryIterator<>(cache); iterator.hasNext();) {
        var value = requireNonNull(iterator.value);
        if (filter.test(value)) {
          var key = requireNonNull(iterator.key);
          modified |= cache.remove(key, value);
        }
        iterator.advance();
      }
      return modified;
    }

    @Override
    public boolean retainAll(Collection<?> collection) {
      requireNonNull(collection);
      @Var boolean modified = false;
      for (var iterator = new EntryIterator<>(cache); iterator.hasNext();) {
        var key = requireNonNull(iterator.key);
        var value = requireNonNull(iterator.value);
        if (!collection.contains(value) && cache.remove(key, value)) {
          modified = true;
        }
        iterator.advance();
      }
      return modified;
    }

    @Override
    public Iterator<V> iterator() {
      return new ValueIterator<>(cache);
    }

    @Override
    public Spliterator<V> spliterator() {
      return new ValueSpliterator<>(cache);
    }
  }

  /** An adapter to safely externalize the value iterator. */
  static final class ValueIterator<K, V> implements Iterator<V> {
    final EntryIterator<K, V> iterator;

    ValueIterator(BoundedLocalCache<K, V> cache) {
      this.iterator = new EntryIterator<>(cache);
    }

    @Override
    public boolean hasNext() {
      return iterator.hasNext();
    }

    @Override
    public V next() {
      return iterator.nextValue();
    }

    @Override
    public void remove() {
      iterator.remove();
    }
  }

  /** An adapter to safely externalize the value spliterator. */
  static final class ValueSpliterator<K, V> implements Spliterator<V> {
    final Spliterator<Node<K, V>> spliterator;
    final BoundedLocalCache<K, V> cache;

    ValueSpliterator(BoundedLocalCache<K, V> cache) {
      this(cache, cache.data.values().spliterator());
    }

    ValueSpliterator(BoundedLocalCache<K, V> cache, Spliterator<Node<K, V>> spliterator) {
      this.spliterator = requireNonNull(spliterator);
      this.cache = requireNonNull(cache);
    }

    @Override
    public void forEachRemaining(Consumer<? super V> action) {
      requireNonNull(action);
      Consumer<Node<K, V>> consumer = node -> {
        long now = cache.expirationTicker().read();
        boolean expired = cache.hasExpired(node, now);
        K key = node.getKey();
        V value = node.getValue();
        if ((key == null) || (value == null) || (expired && !cache.isComputingAsync(value))) {
          cache.scheduleDrainBuffers();
        } else if (node.isAlive()) {
          action.accept(value);
        }
      };
      spliterator.forEachRemaining(consumer);
    }

    @Override
    public boolean tryAdvance(Consumer<? super V> action) {
      requireNonNull(action);
      boolean[] advanced = { false };
      Consumer<Node<K, V>> consumer = node -> {
        long now = cache.expirationTicker().read();
        boolean expired = cache.hasExpired(node, now);
        K key = node.getKey();
        V value = node.getValue();
        if ((key == null) || (value == null) || (expired && !cache.isComputingAsync(value))) {
          cache.scheduleDrainBuffers();
        } else if (node.isAlive()) {
          action.accept(value);
          advanced[0] = true;
        }
      };
      while (spliterator.tryAdvance(consumer)) {
        if (advanced[0]) {
          return true;
        }
      }
      return false;
    }

    @Override
    public @Nullable Spliterator<V> trySplit() {
      Spliterator<Node<K, V>> split = spliterator.trySplit();
      return (split == null) ? null : new ValueSpliterator<>(cache, split);
    }

    @Override
    public long estimateSize() {
      return spliterator.estimateSize();
    }

    @Override
    public int characteristics() {
      return CONCURRENT | NONNULL;
    }
  }

  /** An adapter to safely externalize the entries. */
  static final class EntrySetView<K, V> extends AbstractSet<Entry<K, V>> {
    final BoundedLocalCache<K, V> cache;

    EntrySetView(BoundedLocalCache<K, V> cache) {
      this.cache = requireNonNull(cache);
    }

    @Override
    public int size() {
      return cache.size();
    }

    @Override
    public void clear() {
      cache.clear();
    }

    @Override
    public boolean contains(@Nullable Object o) {
      if (!(o instanceof Entry<?, ?>)) {
        return false;
      }
      var entry = (Entry<?, ?>) o;
      var key = entry.getKey();
      var value = entry.getValue();
      if ((key == null) || (value == null)) {
        return false;
      }
      Node<K, V> node = cache.data.get(cache.nodeFactory.newLookupKey(key));
      if (node == null) {
        return false;
      }
      boolean expired = cache.hasExpired(node, cache.expirationTicker().read());
      V nodeValue = node.getValue();
      return (nodeValue != null) && node.containsValue(value)
          && (!expired || cache.isComputingAsync(nodeValue));
    }

    @Override
    public boolean containsAll(Collection<?> collection) {
      requireNonNull(collection);
      if (collection != this) {
        for (Object o : collection) {
          if ((o == null) || !contains(o)) {
            return false;
          }
        }
      }
      return true;
    }

    @Override
    public boolean removeAll(Collection<?> collection) {
      requireNonNull(collection);
      @Var boolean modified = false;
      if (cache.collectKeys() || cache.collectValues()
          || ((collection instanceof Set<?>) && (collection.size() > size()))) {
        for (var entry : this) {
          if (collection.contains(entry)) {
            modified |= remove(entry);
          }
        }
      } else {
        for (var item : collection) {
          modified |= remove(item);
        }
      }
      return modified;
    }

    @Override
    @SuppressWarnings("SuspiciousMethodCalls")
    public boolean remove(@Nullable Object o) {
      if (!(o instanceof Entry<?, ?>)) {
        return false;
      }
      var entry = (Entry<?, ?>) o;
      var key = entry.getKey();
      return (key != null) && cache.remove(key, entry.getValue());
    }

    @Override
    public boolean removeIf(Predicate<? super Entry<K, V>> filter) {
      requireNonNull(filter);
      @Var boolean modified = false;
      for (var iterator = new EntryIterator<>(cache); iterator.hasNext();) {
        var key = requireNonNull(iterator.key);
        var value = requireNonNull(iterator.value);
        if (filter.test(Map.entry(key, value))) {
          modified |= cache.remove(key, value);
        }
        iterator.advance();
      }
      return modified;
    }

    @Override
    public boolean retainAll(Collection<?> collection) {
      requireNonNull(collection);
      @Var boolean modified = false;
      for (var entry : this) {
        if (!collection.contains(entry) && remove(entry)) {
          modified = true;
        }
      }
      return modified;
    }

    @Override
    public Iterator<Entry<K, V>> iterator() {
      return new EntryIterator<>(cache);
    }

    @Override
    public Spliterator<Entry<K, V>> spliterator() {
      return new EntrySpliterator<>(cache);
    }
  }

  /** An adapter to safely externalize the entry iterator. */
  static final class EntryIterator<K, V> implements Iterator<Entry<K, V>> {
    final BoundedLocalCache<K, V> cache;
    final Iterator<Node<K, V>> iterator;

    @Nullable K key;
    @Nullable V value;
    @Nullable K removalKey;
    @Nullable Node<K, V> next;

    EntryIterator(BoundedLocalCache<K, V> cache) {
      this.iterator = cache.data.values().iterator();
      this.cache = cache;
    }

    @Override
    public boolean hasNext() {
      if (next != null) {
        return true;
      }

      long now = cache.expirationTicker().read();
      while (iterator.hasNext()) {
        next = iterator.next();
        boolean expired = cache.hasExpired(next, now);
        value = next.getValue();
        key = next.getKey();

        boolean evictable = (key == null) || (value == null)
            || (expired && !cache.isComputingAsync(value));
        if (evictable || !next.isAlive()) {
          if (evictable) {
            cache.scheduleDrainBuffers();
          }
          advance();
          continue;
        }
        return true;
      }
      return false;
    }

    /** Invalidates the current position so that the iterator may compute the next position. */
    void advance() {
      value = null;
      next = null;
      key = null;
    }

    K nextKey() {
      if (!hasNext()) {
        throw new NoSuchElementException();
      }
      removalKey = key;
      advance();
      return requireNonNull(removalKey);
    }

    V nextValue() {
      if (!hasNext()) {
        throw new NoSuchElementException();
      }
      removalKey = key;
      V val = value;
      advance();
      return requireNonNull(val);
    }

    @Override
    public Entry<K, V> next() {
      if (!hasNext()) {
        throw new NoSuchElementException();
      }
      var entry = new WriteThroughEntry<K, @NonNull V>(
          cache, requireNonNull(key), requireNonNull(value));
      removalKey = key;
      advance();
      return entry;
    }

    @Override
    public void remove() {
      if (removalKey == null) {
        throw new IllegalStateException();
      }
      cache.remove(removalKey);
      removalKey = null;
    }
  }

  /** An adapter to safely externalize the entry spliterator. */
  static final class EntrySpliterator<K, V> implements Spliterator<Entry<K, V>> {
    final Spliterator<Node<K, V>> spliterator;
    final BoundedLocalCache<K, V> cache;

    EntrySpliterator(BoundedLocalCache<K, V> cache) {
      this(cache, cache.data.values().spliterator());
    }

    EntrySpliterator(BoundedLocalCache<K, V> cache, Spliterator<Node<K, V>> spliterator) {
      this.spliterator = requireNonNull(spliterator);
      this.cache = requireNonNull(cache);
    }

    @Override
    public void forEachRemaining(Consumer<? super Entry<K, V>> action) {
      requireNonNull(action);
      Consumer<Node<K, V>> consumer = node -> {
        long now = cache.expirationTicker().read();
        boolean expired = cache.hasExpired(node, now);
        K key = node.getKey();
        V value = node.getValue();
        if ((key == null) || (value == null) || (expired && !cache.isComputingAsync(value))) {
          cache.scheduleDrainBuffers();
        } else if (node.isAlive()) {
          action.accept(new WriteThroughEntry<>(cache, key, value));
        }
      };
      spliterator.forEachRemaining(consumer);
    }

    @Override
    public boolean tryAdvance(Consumer<? super Entry<K, V>> action) {
      requireNonNull(action);
      boolean[] advanced = { false };
      Consumer<Node<K, V>> consumer = node -> {
        long now = cache.expirationTicker().read();
        boolean expired = cache.hasExpired(node, now);
        K key = node.getKey();
        V value = node.getValue();
        if ((key == null) || (value == null) || (expired && !cache.isComputingAsync(value))) {
          cache.scheduleDrainBuffers();
        } else if (node.isAlive()) {
          action.accept(new WriteThroughEntry<>(cache, key, value));
          advanced[0] = true;
        }
      };
      while (spliterator.tryAdvance(consumer)) {
        if (advanced[0]) {
          return true;
        }
      }
      return false;
    }

    @Override
    public @Nullable Spliterator<Entry<K, V>> trySplit() {
      Spliterator<Node<K, V>> split = spliterator.trySplit();
      return (split == null) ? null : new EntrySpliterator<>(cache, split);
    }

    @Override
    public long estimateSize() {
      return spliterator.estimateSize();
    }

    @Override
    public int characteristics() {
      return DISTINCT | CONCURRENT | NONNULL;
    }
  }

  /** A reusable task that performs the maintenance work. */
  static final class PerformCleanupTask
      extends WeakReference<BoundedLocalCache<?, ?>> implements Runnable {

    PerformCleanupTask(BoundedLocalCache<?, ?> cache) {
      super(cache);
    }

    @Override
    public void run() {
      BoundedLocalCache<?, ?> cache = get();
      // A thread waiting for the lock performs the maintenance, so a copy need not queue behind it
      if ((cache != null) && !cache.isEvictionLockAwaited()) {
        try {
          cache.performCleanUp(/* ignored */ null);
        } catch (Throwable t) {
          logger.log(Level.ERROR, "Exception thrown when performing the maintenance task", t);
        }
      }
    }
    @Override public void clear() {}
    @Override public boolean enqueue() {
      return false;
    }
  }

  /* --------------- Manual Cache --------------- */

  static class BoundedLocalManualCache<K, V> implements LocalManualCache<K, V>, Serializable {
    private static final long serialVersionUID = 1;

    final BoundedLocalCache<K, V> cache;

    @Nullable Policy<K, V> policy;

    BoundedLocalManualCache(Caffeine<K, V> builder) {
      this(builder, null);
    }

    BoundedLocalManualCache(Caffeine<K, V> builder, @Nullable CacheLoader<? super K, V> loader) {
      cache = LocalCacheFactory.newBoundedLocalCache(builder, loader, /* isAsync= */ false);
    }

    @Override
    public final BoundedLocalCache<K, V> cache() {
      return cache;
    }

    @Override
    public final Policy<K, V> policy() {
      @Var var p = policy;
      if (p == null) {
        Function<@Nullable V, @Nullable V> identity = v -> v;
        p = new BoundedPolicy<>(cache, identity);
        policy = p;
      }
      return p;
    }

    private void readObject(ObjectInputStream stream) throws InvalidObjectException {
      throw new InvalidObjectException("Proxy required");
    }

    private Object writeReplace() {
      return makeSerializationProxy(cache);
    }
  }

  @SuppressWarnings({"NullableOptional",
    "OptionalAssignedToNull", "OptionalUsedAsFieldOrParameterType"})
  static final class BoundedPolicy<K, V> implements Policy<K, V> {
    final Function<@Nullable V, @Nullable V> transformer;
    final BoundedLocalCache<K, V> cache;

    @Nullable Optional<Eviction<K, V>> eviction;
    @Nullable Optional<FixedRefresh<K, V>> refreshes;
    @Nullable Optional<FixedExpiration<K, V>> afterWrite;
    @Nullable Optional<FixedExpiration<K, V>> afterAccess;
    @Nullable Optional<VarExpiration<K, V>> variable;

    BoundedPolicy(BoundedLocalCache<K, V> cache, Function<@Nullable V, @Nullable V> transformer) {
      this.transformer = transformer;
      this.cache = cache;
    }

    @Override public boolean isRecordingStats() {
      return cache.isRecordingStats();
    }
    @Override public @Nullable V getIfPresentQuietly(K key) {
      return transformer.apply(cache.getIfPresentQuietly(key));
    }
    @SuppressWarnings("GuardedByChecker")
    @Override public @Nullable CacheEntry<K, V> getEntryIfPresentQuietly(K key) {
      Node<K, V> node = cache.data.get(cache.nodeFactory.newLookupKey(key));
      return (node == null) ? null : cache.nodeToCacheEntry(node, transformer, node.getWeight());
    }
    @SuppressWarnings("Java9CollectionFactory")
    @Override public Map<K, CompletableFuture<V>> refreshes() {
      var refreshes = cache.refreshes;
      if ((refreshes == null) || refreshes.isEmpty()) {
        @SuppressWarnings({"ImmutableMapOf", "RedundantUnmodifiable"})
        Map<K, CompletableFuture<V>> emptyMap = Collections.unmodifiableMap(Collections.emptyMap());
        return emptyMap;
      } else if (cache.collectKeys()) {
        var inFlight = new IdentityHashMap<K, CompletableFuture<V>>(refreshes.size());
        for (var entry : refreshes.entrySet()) {
          @SuppressWarnings("unchecked")
          var key = ((InternalReference<K>) entry.getKey()).get();
          @SuppressWarnings("unchecked")
          var future = (CompletableFuture<V>) entry.getValue();
          if ((key != null) && !(future instanceof LocalLoadingCache.PendingRefresh)) {
            inFlight.put(key, future);
          }
        }
        return Collections.unmodifiableMap(inFlight);
      }
      @SuppressWarnings("unchecked")
      var castedRefreshes = (Map<K, CompletableFuture<V>>) (Object) refreshes;
      var inFlight = new HashMap<>(castedRefreshes);
      inFlight.values().removeIf(LocalLoadingCache.PendingRefresh.class::isInstance);
      return Collections.unmodifiableMap(inFlight);
    }
    @Override public Optional<Eviction<K, V>> eviction() {
      if (!cache.evicts()) {
        return Optional.empty();
      }
      var e = eviction;
      return (e == null) ? (eviction = Optional.of(new BoundedEviction())) : e;
    }
    @Override public Optional<FixedExpiration<K, V>> expireAfterAccess() {
      if (!cache.expiresAfterAccess()) {
        return Optional.empty();
      }
      var e = afterAccess;
      return (e == null)
          ? (afterAccess = Optional.of(new BoundedExpireAfterAccess()))
          : e;
    }
    @Override public Optional<FixedExpiration<K, V>> expireAfterWrite() {
      if (!cache.expiresAfterWrite()) {
        return Optional.empty();
      }
      var e = afterWrite;
      return (e == null)
          ? (afterWrite = Optional.of(new BoundedExpireAfterWrite()))
          : e;
    }
    @Override public Optional<VarExpiration<K, V>> expireVariably() {
      if (!cache.expiresVariable()) {
        return Optional.empty();
      }
      var e = variable;
      return (e == null)
          ? (variable = Optional.of(new BoundedVarExpiration()))
          : e;
    }
    @Override public Optional<FixedRefresh<K, V>> refreshAfterWrite() {
      if (!cache.refreshAfterWrite()) {
        return Optional.empty();
      }
      var r = refreshes;
      return (r == null)
          ? (refreshes = Optional.of(new BoundedRefreshAfterWrite()))
          : r;
    }

    final class BoundedEviction implements Eviction<K, V> {
      @Override public boolean isWeighted() {
        return cache.isWeighted;
      }
      @Override public OptionalInt weightOf(K key) {
        requireNonNull(key);
        if (!cache.isWeighted) {
          return OptionalInt.empty();
        }
        Node<K, V> node = cache.data.get(cache.nodeFactory.newLookupKey(key));
        if (node == null) {
          return OptionalInt.empty();
        }
        boolean expired = cache.hasExpired(node, cache.expirationTicker().read());
        if (expired) {
          return OptionalInt.empty();
        }
        synchronized (node) {
          V value = node.getValue();
          return ((value != null) && node.isAlive() && !cache.isComputingAsync(value))
              ? OptionalInt.of(node.getWeight())
              : OptionalInt.empty();
        }
      }
      @Override public OptionalLong weightedSize() {
        return cache.isWeighted
            ? OptionalLong.of(Math.max(0, cache.weightedSizeAcquire()))
            : OptionalLong.empty();
      }
      @Override public long getMaximum() {
        return cache.maximumAcquire();
      }
      @Override public void setMaximum(long maximum) {
        requireArgument(maximum >= 0, "maximum must not be negative");
        cache.evictionLock.lock();
        try {
          cache.setMaximumSize(maximum);
          cache.maintenance(/* ignored */ null);
        } finally {
          cache.evictionLock.unlock();
          cache.rescheduleCleanUpIfIncomplete();
        }
      }
      @Override public Map<K, V> coldest(int limit) {
        int expectedSize = Math.min(limit, cache.size());
        var limiter = new SizeLimiter<K, V>(expectedSize, limit);
        return cache.evictionOrder(/* hottest= */ false, transformer, limiter);
      }
      @Override public Map<K, V> coldestWeighted(long weightLimit) {
        var limiter = isWeighted()
            ? new WeightLimiter<K, V>(weightLimit)
            : new SizeLimiter<K, V>((int) Math.min(weightLimit, cache.size()), weightLimit);
        return cache.evictionOrder(/* hottest= */ false, transformer, limiter);
      }
      @Override
      public <T extends @Nullable Object> T coldest(
          Function<Stream<CacheEntry<K, V>>, T> mappingFunction) {
        requireNonNull(mappingFunction);
        return cache.evictionOrder(/* hottest= */ false, transformer, mappingFunction);
      }
      @Override public Map<K, V> hottest(int limit) {
        int expectedSize = Math.min(limit, cache.size());
        var limiter = new SizeLimiter<K, V>(expectedSize, limit);
        return cache.evictionOrder(/* hottest= */ true, transformer, limiter);
      }
      @Override public Map<K, V> hottestWeighted(long weightLimit) {
        var limiter = isWeighted()
            ? new WeightLimiter<K, V>(weightLimit)
            : new SizeLimiter<K, V>((int) Math.min(weightLimit, cache.size()), weightLimit);
        return cache.evictionOrder(/* hottest= */ true, transformer, limiter);
      }
      @Override
      public <T extends @Nullable Object> T hottest(
          Function<Stream<CacheEntry<K, V>>, T> mappingFunction) {
        requireNonNull(mappingFunction);
        return cache.evictionOrder(/* hottest= */ true, transformer, mappingFunction);
      }
    }

    @SuppressWarnings("PreferJavaTimeOverload")
    final class BoundedExpireAfterAccess implements FixedExpiration<K, V> {
      @Override public OptionalLong ageOf(K key, TimeUnit unit) {
        requireNonNull(key);
        requireNonNull(unit);
        Object lookupKey = cache.nodeFactory.newLookupKey(key);
        Node<K, V> node = cache.data.get(lookupKey);
        if (node == null) {
          return OptionalLong.empty();
        }
        long now = cache.expirationTicker().read();
        boolean expired = cache.hasExpired(node, now);
        V value = node.getValue();
        if ((value == null) || expired || cache.isComputingAsync(value)) {
          return OptionalLong.empty();
        }
        long age = now - node.getAccessTime();
        return (age < 0)
            ? OptionalLong.empty()
            : OptionalLong.of(unit.convert(age, TimeUnit.NANOSECONDS));
      }
      @Override public long getExpiresAfter(TimeUnit unit) {
        return unit.convert(cache.expiresAfterAccessNanos(), TimeUnit.NANOSECONDS);
      }
      @Override public void setExpiresAfter(long duration, TimeUnit unit) {
        requireArgument(duration >= 0, "duration cannot be negative: %s %s", duration, unit);
        cache.setExpiresAfterAccessNanos(unit.toNanos(duration));
        cache.scheduleAfterWrite();
      }
      @Override public Map<K, V> oldest(int limit) {
        return oldest(new SizeLimiter<>(Math.min(limit, cache.size()), limit));
      }
      @Override public <T extends @Nullable Object> T oldest(
          Function<Stream<CacheEntry<K, V>>, T> mappingFunction) {
        return cache.expireAfterAccessOrder(/* oldest= */ true, transformer, mappingFunction);
      }
      @Override public Map<K, V> youngest(int limit) {
        return youngest(new SizeLimiter<>(Math.min(limit, cache.size()), limit));
      }
      @Override public <T extends @Nullable Object> T youngest(
          Function<Stream<CacheEntry<K, V>>, T> mappingFunction) {
        return cache.expireAfterAccessOrder(/* oldest= */ false, transformer, mappingFunction);
      }
    }

    @SuppressWarnings("PreferJavaTimeOverload")
    final class BoundedExpireAfterWrite implements FixedExpiration<K, V> {
      @Override public OptionalLong ageOf(K key, TimeUnit unit) {
        requireNonNull(key);
        requireNonNull(unit);
        Object lookupKey = cache.nodeFactory.newLookupKey(key);
        Node<K, V> node = cache.data.get(lookupKey);
        if (node == null) {
          return OptionalLong.empty();
        }
        long now = cache.expirationTicker().read();
        boolean expired = cache.hasExpired(node, now);
        V value = node.getValue();
        if ((value == null) || expired || cache.isComputingAsync(value)) {
          return OptionalLong.empty();
        }
        long age = toWriteTime(now) - writeTimeOf(node);
        return (age < 0)
            ? OptionalLong.empty()
            : OptionalLong.of(unit.convert(age, TimeUnit.NANOSECONDS));
      }
      @Override public long getExpiresAfter(TimeUnit unit) {
        return unit.convert(cache.expiresAfterWriteNanos(), TimeUnit.NANOSECONDS);
      }
      @Override public void setExpiresAfter(long duration, TimeUnit unit) {
        requireArgument(duration >= 0, "duration cannot be negative: %s %s", duration, unit);
        cache.setExpiresAfterWriteNanos(unit.toNanos(duration));
        cache.scheduleAfterWrite();
      }
      @Override public Map<K, V> oldest(int limit) {
        return oldest(new SizeLimiter<>(Math.min(limit, cache.size()), limit));
      }
      @SuppressWarnings("GuardedByChecker")
      @Override public <T extends @Nullable Object> T oldest(
          Function<Stream<CacheEntry<K, V>>, T> mappingFunction) {
        return cache.snapshot(cache.writeOrderDeque(), transformer, mappingFunction);
      }
      @Override public Map<K, V> youngest(int limit) {
        return youngest(new SizeLimiter<>(Math.min(limit, cache.size()), limit));
      }
      @SuppressWarnings("GuardedByChecker")
      @Override public <T extends @Nullable Object> T youngest(
          Function<Stream<CacheEntry<K, V>>, T> mappingFunction) {
        return cache.snapshot(cache.writeOrderDeque()::descendingIterator,
            transformer, mappingFunction);
      }
    }

    @SuppressWarnings("PreferJavaTimeOverload")
    final class BoundedVarExpiration implements VarExpiration<K, V> {
      @Override public OptionalLong getExpiresAfter(K key, TimeUnit unit) {
        requireNonNull(key);
        requireNonNull(unit);
        Object lookupKey = cache.nodeFactory.newLookupKey(key);
        Node<K, V> node = cache.data.get(lookupKey);
        if (node == null) {
          return OptionalLong.empty();
        }
        long now = cache.expirationTicker().read();
        boolean expired = cache.hasExpired(node, now);
        V value = node.getValue();
        if ((value == null) || expired || cache.isComputingAsync(value)) {
          return OptionalLong.empty();
        }
        long duration = node.getVariableTime() - now;
        return (cache.isAsync && (duration > MAXIMUM_EXPIRY))
            ? OptionalLong.empty()
            : OptionalLong.of(unit.convert(duration, TimeUnit.NANOSECONDS));
      }
      @Override public void setExpiresAfter(K key, long duration, TimeUnit unit) {
        requireNonNull(key);
        requireNonNull(unit);
        requireArgument(duration >= 0, "duration cannot be negative: %s %s", duration, unit);
        Object lookupKey = cache.nodeFactory.newLookupKey(key);
        Node<K, V> node = cache.data.get(lookupKey);
        if (node != null) {
          long extension;
          long durationNanos = TimeUnit.NANOSECONDS.convert(duration, unit);
          synchronized (node) {
            long now = cache.expirationTicker().read();
            V value = node.getValue();
            if ((value == null) || cache.isComputingAsync(value)
                || cache.hasExpired(node, now)) {
              return;
            }
            long expirationTime = now + Math.min(durationNanos, MAXIMUM_EXPIRY);
            extension = expirationTime - node.getVariableTime();
            node.setVariableTime(expirationTime);
          }
          if ((extension < 0) || (extension > EXPIRE_TOLERANCE)) {
            cache.afterWrite(cache.new UpdateTask(node, 0, Access.QUIET));
          }
        }
      }
      @Override public @Nullable V put(K key, V value, long duration, TimeUnit unit) {
        requireNonNull(unit);
        requireNonNull(value);
        requireArgument(duration >= 0, "duration cannot be negative: %s %s", duration, unit);
        return cache.isAsync
            ? putAsync(key, value, duration, unit)
            : putSync(key, value, duration, unit, /* onlyIfAbsent= */ false);
      }
      @Override public @Nullable V putIfAbsent(K key, V value, long duration, TimeUnit unit) {
        requireNonNull(unit);
        requireNonNull(value);
        requireArgument(duration >= 0, "duration cannot be negative: %s %s", duration, unit);
        return cache.isAsync
            ? putIfAbsentAsync(key, value, duration, unit)
            : putSync(key, value, duration, unit, /* onlyIfAbsent= */ true);
      }
      @Nullable V putSync(K key, V value, long duration, TimeUnit unit, boolean onlyIfAbsent) {
        var expiry = new FixedExpireAfterWrite<K, V>(duration, unit);
        return cache.put(key, value, expiry, onlyIfAbsent);
      }
      @SuppressWarnings("unchecked")
      @Nullable V putIfAbsentAsync(K key, V value, long duration, TimeUnit unit) {
        // Mirrors LocalAsyncCache.AsMapView#putIfAbsent(key, value), but the first probe reads a
        // present entry through the fixed duration, as putSync does, not the user's Expiry
        var expiry = (Expiry<K, V>) new AsyncExpiry<>(new FixedExpireAfterWrite<>(duration, unit));
        var asyncValue = (V) CompletableFuture.completedFuture(value);

        var probe = (CompletableFuture<V>) cache.put(
            key, asyncValue, expiry, /* onlyIfAbsent= */ true);
        V present = Async.getIfReady(probe);
        if ((probe == null) || (present != null)) {
          return present;
        }

        for (;;) {
          var priorFuture = (CompletableFuture<V>) cache.getIfPresentQuietly(key);
          if (priorFuture != null) {
            if (!priorFuture.isDone()) {
              Async.getWhenSuccessful(priorFuture);
              continue;
            }

            V prior = Async.getWhenSuccessful(priorFuture);
            if (prior != null) {
              return prior;
            }
          }

          boolean[] added = { false };
          var hints = new LocalCache.RemapHints();
          var computed = (CompletableFuture<V>) cache.compute(key, (K k, @Nullable V oldValue) -> {
            var oldValueFuture = (CompletableFuture<V>) oldValue;
            added[0] = (oldValueFuture == null)
                || (oldValueFuture.isDone() && (Async.getIfReady(oldValueFuture) == null));
            if (added[0]) {
              return asyncValue;
            }
            hints.preserveEntry();
            return oldValue;
          }, expiry, /* recordLoad= */ false, hints);

          if (added[0]) {
            return null;
          } else {
            V prior = Async.getWhenSuccessful(computed);
            if (prior != null) {
              return prior;
            }
          }
        }
      }
      @SuppressWarnings("unchecked")
      @Nullable V putAsync(K key, V value, long duration, TimeUnit unit) {
        var expiry = (Expiry<K, V>) new AsyncExpiry<>(new FixedExpireAfterWrite<>(duration, unit));
        var asyncValue = (V) CompletableFuture.completedFuture(value);

        var oldValueFuture = (CompletableFuture<V>) cache.put(
            key, asyncValue, expiry, /* onlyIfAbsent= */ false);
        return Async.getWhenSuccessful(oldValueFuture);
      }
      @Override public @Nullable V compute(K key,
          BiFunction<? super K, ? super @Nullable V, ? extends @Nullable V> remappingFunction,
          Duration duration) {
        requireNonNull(key);
        requireNonNull(duration);
        requireNonNull(remappingFunction);
        requireArgument(!duration.isNegative(), "duration cannot be negative: %s", duration);
        var expiry = new FixedExpireAfterWrite<K, V>(
            toNanosSaturated(duration), TimeUnit.NANOSECONDS);

        return cache.isAsync
            ? computeAsync(key, remappingFunction, expiry)
            : cache.compute(key, remappingFunction, expiry, /* recordLoad= */ true);
      }
      @Nullable V computeAsync(K key,
          BiFunction<? super K, ? super @Nullable V, ? extends @Nullable V> remappingFunction,
          Expiry<? super K, ? super V> expiry) {
        // Keep in sync with LocalAsyncCache.AsMapView#compute(key, remappingFunction)
        @SuppressWarnings("unchecked")
        var delegate = (LocalCache<K, CompletableFuture<V>>) cache;

        @SuppressWarnings({"unchecked", "Varifier"})
        @Nullable V[] newValue = (@Nullable V[]) new Object[1];
        for (;;) {
          Async.getWhenSuccessful(delegate.getIfPresentQuietly(key));

          var hints = new LocalCache.RemapHints();
          CompletableFuture<V> valueFuture = delegate.compute(
              key, (K k, @Nullable CompletableFuture<V> oldValueFuture) -> {
                if ((oldValueFuture != null) && !oldValueFuture.isDone()) {
                  hints.preserveEntry();
                  return oldValueFuture;
                }

                V oldValue = Async.getIfReady(oldValueFuture);
                BiFunction<? super K, ? super @Nullable V, ? extends @Nullable V> function =
                    delegate.statsAware(remappingFunction, /* recordLoad= */ true);
                newValue[0] = function.apply(key, oldValue);
                return (newValue[0] == null) ? null
                    : CompletableFuture.completedFuture(newValue[0]);
              }, new AsyncExpiry<>(expiry), /* recordLoad= */ false, hints);

          if (newValue[0] != null) {
            return newValue[0];
          } else if (valueFuture == null) {
            return null;
          }
        }
      }
      @Override public Map<K, V> oldest(int limit) {
        return oldest(new SizeLimiter<>(Math.min(limit, cache.size()), limit));
      }
      @Override public <T extends @Nullable Object> T oldest(
          Function<Stream<CacheEntry<K, V>>, T> mappingFunction) {
        return cache.snapshot(cache.timerWheel(), transformer, mappingFunction);
      }
      @Override public Map<K, V> youngest(int limit) {
        return youngest(new SizeLimiter<>(Math.min(limit, cache.size()), limit));
      }
      @Override public <T extends @Nullable Object> T youngest(
          Function<Stream<CacheEntry<K, V>>, T> mappingFunction) {
        return cache.snapshot(cache.timerWheel()::descendingIterator, transformer, mappingFunction);
      }
    }

    static final class FixedExpireAfterWrite<K, V> implements Expiry<K, V> {
      final long duration;
      final TimeUnit unit;

      FixedExpireAfterWrite(long duration, TimeUnit unit) {
        this.duration = duration;
        this.unit = unit;
      }
      @Override public long expireAfterCreate(K key, V value, long currentTime) {
        return unit.toNanos(duration);
      }
      @Override public long expireAfterUpdate(
          K key, V value, long currentTime, long currentDuration) {
        return unit.toNanos(duration);
      }
      @CanIgnoreReturnValue
      @Override public long expireAfterRead(
          K key, V value, long currentTime, long currentDuration) {
        return currentDuration;
      }
    }

    @SuppressWarnings("PreferJavaTimeOverload")
    final class BoundedRefreshAfterWrite implements FixedRefresh<K, V> {
      @Override public OptionalLong ageOf(K key, TimeUnit unit) {
        requireNonNull(key);
        requireNonNull(unit);
        Object lookupKey = cache.nodeFactory.newLookupKey(key);
        Node<K, V> node = cache.data.get(lookupKey);
        if (node == null) {
          return OptionalLong.empty();
        }
        long now = cache.expirationTicker().read();
        boolean expired = cache.hasExpired(node, now);
        V value = node.getValue();
        if ((value == null) || expired || cache.isComputingAsync(value)) {
          return OptionalLong.empty();
        }
        long age = toWriteTime(now) - writeTimeOf(node);
        return (age < 0)
            ? OptionalLong.empty()
            : OptionalLong.of(unit.convert(age, TimeUnit.NANOSECONDS));
      }
      @Override public long getRefreshesAfter(TimeUnit unit) {
        return unit.convert(cache.refreshAfterWriteNanos(), TimeUnit.NANOSECONDS);
      }
      @Override public void setRefreshesAfter(long duration, TimeUnit unit) {
        requireNonNull(unit);
        requireArgument(duration > 0, "duration must be positive: %s %s", duration, unit);
        cache.setRefreshAfterWriteNanos(unit.toNanos(duration));
        cache.scheduleAfterWrite();
      }
    }
  }

  /* --------------- Loading Cache --------------- */

  static final class BoundedLocalLoadingCache<K, V>
      extends BoundedLocalManualCache<K, V> implements LocalLoadingCache<K, V> {
    private static final long serialVersionUID = 1;

    final Function<K, @Nullable V> mappingFunction;
    final @Nullable Function<Set<? extends K>, Map<K, V>> bulkMappingFunction;

    BoundedLocalLoadingCache(Caffeine<K, V> builder, CacheLoader<? super K, V> loader) {
      super(builder, loader);
      requireNonNull(loader);
      mappingFunction = newMappingFunction(loader);
      bulkMappingFunction = newBulkMappingFunction(loader);
    }

    @Override
    @SuppressWarnings({"DataFlowIssue", "NullAway"})
    public AsyncCacheLoader<? super K, V> cacheLoader() {
      return cache.cacheLoader;
    }

    @Override
    public Function<K, @Nullable V> mappingFunction() {
      return mappingFunction;
    }

    @Override
    public @Nullable Function<Set<? extends K>, Map<K, V>> bulkMappingFunction() {
      return bulkMappingFunction;
    }

    private void readObject(ObjectInputStream stream) throws InvalidObjectException {
      throw new InvalidObjectException("Proxy required");
    }

    private Object writeReplace() {
      return makeSerializationProxy(cache);
    }
  }

  /* --------------- Async Cache --------------- */

  static final class BoundedLocalAsyncCache<K, V> implements LocalAsyncCache<K, V>, Serializable {
    private static final long serialVersionUID = 1;

    final BoundedLocalCache<K, CompletableFuture<V>> cache;

    @Nullable ConcurrentMap<K, CompletableFuture<V>> mapView;
    @Nullable CacheView<K, V> cacheView;
    @Nullable Policy<K, V> policy;

    @SuppressWarnings("unchecked")
    BoundedLocalAsyncCache(Caffeine<K, V> builder) {
      cache = (BoundedLocalCache<K, CompletableFuture<V>>) LocalCacheFactory
          .newBoundedLocalCache(builder, /* cacheLoader= */ null, /* isAsync= */ true);
    }

    @Override
    public BoundedLocalCache<K, CompletableFuture<V>> cache() {
      return cache;
    }

    @Override
    public ConcurrentMap<K, CompletableFuture<V>> asMap() {
      var mv = mapView;
      return (mv == null) ? (mapView = new AsyncAsMapView<>(this)) : mv;
    }

    @Override
    public Cache<K, V> synchronous() {
      var cv = cacheView;
      return (cv == null) ? (cacheView = new CacheView<>(this)) : cv;
    }

    @Override
    public Policy<K, V> policy() {
      @Var var p = policy;
      if (p == null) {
        @SuppressWarnings("unchecked")
        var castCache = (BoundedLocalCache<K, V>) cache;
        Function<CompletableFuture<V>, @Nullable V> transformer = Async::getIfReady;
        @SuppressWarnings("unchecked")
        var castTransformer = (Function<@Nullable V, @Nullable V>) transformer;
        p = new BoundedPolicy<>(castCache, castTransformer);
        policy = p;
      }
      return p;
    }

    private void readObject(ObjectInputStream stream) throws InvalidObjectException {
      throw new InvalidObjectException("Proxy required");
    }

    private Object writeReplace() {
      return makeSerializationProxy(cache);
    }
  }

  /* --------------- Async Loading Cache --------------- */

  static final class BoundedLocalAsyncLoadingCache<K, V>
      extends LocalAsyncLoadingCache<K, V> implements Serializable {
    private static final long serialVersionUID = 1;

    final BoundedLocalCache<K, CompletableFuture<V>> cache;

    @Nullable ConcurrentMap<K, CompletableFuture<V>> mapView;
    @Nullable Policy<K, V> policy;

    @SuppressWarnings("unchecked")
    BoundedLocalAsyncLoadingCache(Caffeine<K, V> builder, AsyncCacheLoader<? super K, V> loader) {
      super(loader);
      cache = (BoundedLocalCache<K, CompletableFuture<V>>) LocalCacheFactory
          .newBoundedLocalCache(builder, loader, /* isAsync= */ true);
    }

    @Override
    public BoundedLocalCache<K, CompletableFuture<V>> cache() {
      return cache;
    }

    @Override
    public ConcurrentMap<K, CompletableFuture<V>> asMap() {
      var mv = mapView;
      return (mv == null) ? (mapView = new AsyncAsMapView<>(this)) : mv;
    }

    @Override
    public Policy<K, V> policy() {
      @Var var p = policy;
      if (p == null) {
        @SuppressWarnings("unchecked")
        var castCache = (BoundedLocalCache<K, V>) cache;
        Function<CompletableFuture<V>, @Nullable V> transformer = Async::getIfReady;
        @SuppressWarnings("unchecked")
        var castTransformer = (Function<@Nullable V, @Nullable V>) transformer;
        p = new BoundedPolicy<>(castCache, castTransformer);
        policy = p;
      }
      return p;
    }

    private void readObject(ObjectInputStream stream) throws InvalidObjectException {
      throw new InvalidObjectException("Proxy required");
    }

    private Object writeReplace() {
      return makeSerializationProxy(cache);
    }
  }
}

/** The namespace for field padding through inheritance. */
@SuppressWarnings({"IdentifierName", "MultiVariableDeclaration"})
final class BLCHeader {

  private BLCHeader() {}

  @SuppressWarnings("unused")
  static class PadDrainStatus {
    byte p000, p001, p002, p003, p004, p005, p006, p007;
    byte p008, p009, p010, p011, p012, p013, p014, p015;
    byte p016, p017, p018, p019, p020, p021, p022, p023;
    byte p024, p025, p026, p027, p028, p029, p030, p031;
    byte p032, p033, p034, p035, p036, p037, p038, p039;
    byte p040, p041, p042, p043, p044, p045, p046, p047;
    byte p048, p049, p050, p051, p052, p053, p054, p055;
    byte p056, p057, p058, p059, p060, p061, p062, p063;
    byte p064, p065, p066, p067, p068, p069, p070, p071;
    byte p072, p073, p074, p075, p076, p077, p078, p079;
    byte p080, p081, p082, p083, p084, p085, p086, p087;
    byte p088, p089, p090, p091, p092, p093, p094, p095;
    byte p096, p097, p098, p099, p100, p101, p102, p103;
    byte p104, p105, p106, p107, p108, p109, p110, p111;
    byte p112, p113, p114, p115, p116, p117, p118, p119;
  }

  /** Enforces a memory layout to avoid false sharing by padding the drain status. */
  abstract static class DrainStatusRef extends PadDrainStatus {
    static final VarHandle DRAIN_STATUS = fieldVarHandle(MethodHandles.lookup(),
        "drainStatus", VarHandle.class, DrainStatusRef.class, int.class);

    /** A drain is not taking place. */
    static final int IDLE = 0;
    /** A drain is required due to a pending write modification. */
    static final int REQUIRED = 1;
    /** A drain is in progress and will transition to idle. */
    static final int PROCESSING_TO_IDLE = 2;
    /** A drain is in progress and will transition to required. */
    static final int PROCESSING_TO_REQUIRED = 3;

    /** The draining status of the buffers. */
    volatile int drainStatus = IDLE;

    /**
     * Returns whether maintenance work is needed.
     *
     * @param delayable if draining the read buffer can be delayed
     */
    @SuppressWarnings("StatementSwitchToExpressionSwitch")
    boolean shouldDrainBuffers(boolean delayable) {
      switch (drainStatusOpaque()) {
        case IDLE:
          return !delayable;
        case REQUIRED:
          return true;
        case PROCESSING_TO_IDLE:
        case PROCESSING_TO_REQUIRED:
          return false;
        default:
          throw new IllegalStateException("Invalid drain status: " + drainStatus);
      }
    }

    int drainStatusOpaque() {
      return (int) DRAIN_STATUS.getOpaque(this);
    }

    int drainStatusAcquire() {
      return (int) DRAIN_STATUS.getAcquire(this);
    }

    void setDrainStatusOpaque(int drainStatus) {
      DRAIN_STATUS.setOpaque(this, drainStatus);
    }

    void setDrainStatusRelease(int drainStatus) {
      DRAIN_STATUS.setRelease(this, drainStatus);
    }

    boolean casDrainStatus(int expect, int update) {
      return DRAIN_STATUS.compareAndSet(this, expect, update);
    }
  }
}

ben-manes / caffeine / #5840

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