#19908

Committed 16 Jul 2025 07:54PM UTC coverage: 88.593% (+0.07%) from 88.528%

Build # #19908

Build Type

push

github

Committed by

ejona86

Commit Message

Revert "xds: Convert CdsLb to XdsDepManager"

This reverts commit 297ab05ef.

b/430347751 shows multiple concerning behaviors in the xDS stack with
the new A74 config update model. XdsDepManager and CdsLB2 still seem to
be working correctly, but the change is exacerbated issues in other
parts of the stack, like RingHashConfig not having equals fixed in
a8de9f07ab.

Revert only for the v1.74.x release, leaving it on master.

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/../rls/src/main/java/io/grpc/rls/CachingRlsLbClient.java

/*
 * Copyright 2020 The gRPC Authors
 *
 * 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 io.grpc.rls;

import static com.google.common.base.Preconditions.checkNotNull;
import static com.google.common.base.Preconditions.checkState;

import com.google.common.annotations.VisibleForTesting;
import com.google.common.base.Converter;
import com.google.common.base.MoreObjects;
import com.google.common.base.MoreObjects.ToStringHelper;
import com.google.common.base.Ticker;
import com.google.common.util.concurrent.Futures;
import com.google.common.util.concurrent.ListenableFuture;
import com.google.common.util.concurrent.MoreExecutors;
import com.google.common.util.concurrent.SettableFuture;
import com.google.errorprone.annotations.CheckReturnValue;
import com.google.errorprone.annotations.concurrent.GuardedBy;
import io.grpc.ChannelLogger;
import io.grpc.ChannelLogger.ChannelLogLevel;
import io.grpc.ConnectivityState;
import io.grpc.LoadBalancer.Helper;
import io.grpc.LoadBalancer.PickResult;
import io.grpc.LoadBalancer.PickSubchannelArgs;
import io.grpc.LoadBalancer.ResolvedAddresses;
import io.grpc.LoadBalancer.SubchannelPicker;
import io.grpc.LongCounterMetricInstrument;
import io.grpc.LongGaugeMetricInstrument;
import io.grpc.ManagedChannel;
import io.grpc.ManagedChannelBuilder;
import io.grpc.Metadata;
import io.grpc.MetricInstrumentRegistry;
import io.grpc.MetricRecorder.BatchCallback;
import io.grpc.MetricRecorder.BatchRecorder;
import io.grpc.MetricRecorder.Registration;
import io.grpc.Status;
import io.grpc.internal.BackoffPolicy;
import io.grpc.internal.ExponentialBackoffPolicy;
import io.grpc.lookup.v1.RouteLookupServiceGrpc;
import io.grpc.lookup.v1.RouteLookupServiceGrpc.RouteLookupServiceStub;
import io.grpc.rls.ChildLoadBalancerHelper.ChildLoadBalancerHelperProvider;
import io.grpc.rls.LbPolicyConfiguration.ChildLbStatusListener;
import io.grpc.rls.LbPolicyConfiguration.ChildPolicyWrapper;
import io.grpc.rls.LbPolicyConfiguration.RefCountedChildPolicyWrapperFactory;
import io.grpc.rls.LruCache.EvictionListener;
import io.grpc.rls.LruCache.EvictionType;
import io.grpc.rls.RlsProtoConverters.RouteLookupResponseConverter;
import io.grpc.rls.RlsProtoData.RouteLookupConfig;
import io.grpc.rls.RlsProtoData.RouteLookupRequest;
import io.grpc.rls.RlsProtoData.RouteLookupResponse;
import io.grpc.stub.StreamObserver;
import io.grpc.util.ForwardingLoadBalancerHelper;
import java.net.URI;
import java.net.URISyntaxException;
import java.util.Arrays;
import java.util.Collections;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.UUID;
import java.util.concurrent.Future;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.TimeUnit;
import javax.annotation.Nullable;
import javax.annotation.concurrent.ThreadSafe;

/**
 * A CachingRlsLbClient is a core implementation of RLS loadbalancer supports dynamic request
 * routing by fetching the decision from route lookup server. Every single request is routed by
 * the server's decision. To reduce the performance penalty, {@link LruCache} is used.
 */
@ThreadSafe
final class CachingRlsLbClient {

  private static final Converter<RouteLookupRequest, io.grpc.lookup.v1.RouteLookupRequest>
      REQUEST_CONVERTER = new RlsProtoConverters.RouteLookupRequestConverter().reverse();
  private static final Converter<RouteLookupResponse, io.grpc.lookup.v1.RouteLookupResponse>
      RESPONSE_CONVERTER = new RouteLookupResponseConverter().reverse();
  public static final long MIN_EVICTION_TIME_DELTA_NANOS = TimeUnit.SECONDS.toNanos(5);
  public static final int BYTES_PER_CHAR = 2;
  public static final int STRING_OVERHEAD_BYTES = 38;
  /** Minimum bytes for a Java Object. */
  public static final int OBJ_OVERHEAD_B = 16;

  private static final LongCounterMetricInstrument DEFAULT_TARGET_PICKS_COUNTER;
  private static final LongCounterMetricInstrument TARGET_PICKS_COUNTER;
  private static final LongCounterMetricInstrument FAILED_PICKS_COUNTER;
  private static final LongGaugeMetricInstrument CACHE_ENTRIES_GAUGE;
  private static final LongGaugeMetricInstrument CACHE_SIZE_GAUGE;
  private final Registration gaugeRegistration;
  private final String metricsInstanceUuid = UUID.randomUUID().toString();

  // All cache status changes (pending, backoff, success) must be under this lock
  private final Object lock = new Object();
  // LRU cache based on access order (BACKOFF and actual data will be here)
  @GuardedBy("lock")
  private final RlsAsyncLruCache linkedHashLruCache;
  private final Future<?> periodicCleaner;
  // any RPC on the fly will cached in this map
  @GuardedBy("lock")
  private final Map<RouteLookupRequest, PendingCacheEntry> pendingCallCache = new HashMap<>();

  private final ScheduledExecutorService scheduledExecutorService;
  private final Ticker ticker;
  private final Throttler throttler;

  private final LbPolicyConfiguration lbPolicyConfig;
  private final BackoffPolicy.Provider backoffProvider;
  private final long maxAgeNanos;
  private final long staleAgeNanos;
  private final long callTimeoutNanos;

  private final RlsLbHelper helper;
  private final ManagedChannel rlsChannel;
  private final RouteLookupServiceStub rlsStub;
  private final RlsPicker rlsPicker;
  private final ResolvedAddressFactory childLbResolvedAddressFactory;
  @GuardedBy("lock")
  private final RefCountedChildPolicyWrapperFactory refCountedChildPolicyWrapperFactory;
  private final ChannelLogger logger;

  static {
    MetricInstrumentRegistry metricInstrumentRegistry
        = MetricInstrumentRegistry.getDefaultRegistry();
    DEFAULT_TARGET_PICKS_COUNTER = metricInstrumentRegistry.registerLongCounter(
        "grpc.lb.rls.default_target_picks",
        "EXPERIMENTAL. Number of LB picks sent to the default target", "{pick}",
        Arrays.asList("grpc.target", "grpc.lb.rls.server_target",
            "grpc.lb.rls.data_plane_target", "grpc.lb.pick_result"), Collections.emptyList(),
        false);
    TARGET_PICKS_COUNTER = metricInstrumentRegistry.registerLongCounter("grpc.lb.rls.target_picks",
        "EXPERIMENTAL. Number of LB picks sent to each RLS target. Note that if the default "
            + "target is also returned by the RLS server, RPCs sent to that target from the cache "
            + "will be counted in this metric, not in grpc.rls.default_target_picks.", "{pick}",
        Arrays.asList("grpc.target", "grpc.lb.rls.server_target", "grpc.lb.rls.data_plane_target",
            "grpc.lb.pick_result"), Collections.emptyList(),
        false);
    FAILED_PICKS_COUNTER = metricInstrumentRegistry.registerLongCounter("grpc.lb.rls.failed_picks",
        "EXPERIMENTAL. Number of LB picks failed due to either a failed RLS request or the "
            + "RLS channel being throttled", "{pick}",
        Arrays.asList("grpc.target", "grpc.lb.rls.server_target"),
        Collections.emptyList(), false);
    CACHE_ENTRIES_GAUGE = metricInstrumentRegistry.registerLongGauge("grpc.lb.rls.cache_entries",
        "EXPERIMENTAL. Number of entries in the RLS cache", "{entry}",
        Arrays.asList("grpc.target", "grpc.lb.rls.server_target", "grpc.lb.rls.instance_uuid"),
        Collections.emptyList(), false);
    CACHE_SIZE_GAUGE = metricInstrumentRegistry.registerLongGauge("grpc.lb.rls.cache_size",
        "EXPERIMENTAL. The current size of the RLS cache", "By",
        Arrays.asList("grpc.target", "grpc.lb.rls.server_target", "grpc.lb.rls.instance_uuid"),
        Collections.emptyList(), false);
  }

  private CachingRlsLbClient(Builder builder) {
    helper = new RlsLbHelper(checkNotNull(builder.helper, "helper"));
    scheduledExecutorService = helper.getScheduledExecutorService();
    lbPolicyConfig = checkNotNull(builder.lbPolicyConfig, "lbPolicyConfig");
    RouteLookupConfig rlsConfig = lbPolicyConfig.getRouteLookupConfig();
    maxAgeNanos = rlsConfig.maxAgeInNanos();
    staleAgeNanos = rlsConfig.staleAgeInNanos();
    callTimeoutNanos = rlsConfig.lookupServiceTimeoutInNanos();
    ticker = checkNotNull(builder.ticker, "ticker");
    throttler = checkNotNull(builder.throttler, "throttler");
    linkedHashLruCache =
        new RlsAsyncLruCache(
            rlsConfig.cacheSizeBytes(),
            new AutoCleaningEvictionListener(builder.evictionListener),
            ticker,
            helper);
    periodicCleaner =
        scheduledExecutorService.scheduleAtFixedRate(this::periodicClean, 1, 1, TimeUnit.MINUTES);
    logger = helper.getChannelLogger();
    String serverHost = null;
    try {
      serverHost = new URI(null, helper.getAuthority(), null, null, null).getHost();
    } catch (URISyntaxException ignore) {
      // handled by the following null check
    }
    if (serverHost == null) {
      logger.log(
          ChannelLogLevel.DEBUG, "Can not get hostname from authority: {0}", helper.getAuthority());
      serverHost = helper.getAuthority();
    }
    RlsRequestFactory requestFactory = new RlsRequestFactory(
        lbPolicyConfig.getRouteLookupConfig(), serverHost);
    rlsPicker = new RlsPicker(requestFactory, rlsConfig.lookupService());
    // It is safe to use helper.getUnsafeChannelCredentials() because the client authenticates the
    // RLS server using the same authority as the backends, even though the RLS server’s addresses
    // will be looked up differently than the backends; overrideAuthority(helper.getAuthority()) is
    // called to impose the authority security restrictions.
    ManagedChannelBuilder<?> rlsChannelBuilder = helper.createResolvingOobChannelBuilder(
        rlsConfig.lookupService(), helper.getUnsafeChannelCredentials());
    rlsChannelBuilder.overrideAuthority(helper.getAuthority());
    Map<String, ?> routeLookupChannelServiceConfig =
        lbPolicyConfig.getRouteLookupChannelServiceConfig();
    if (routeLookupChannelServiceConfig != null) {
      logger.log(
          ChannelLogLevel.DEBUG,
          "RLS channel service config: {0}",
          routeLookupChannelServiceConfig);
      rlsChannelBuilder.defaultServiceConfig(routeLookupChannelServiceConfig);
      rlsChannelBuilder.disableServiceConfigLookUp();
    }
    rlsChannel = rlsChannelBuilder.build();
    rlsStub = RouteLookupServiceGrpc.newStub(rlsChannel);
    childLbResolvedAddressFactory =
        checkNotNull(builder.resolvedAddressFactory, "resolvedAddressFactory");
    backoffProvider = builder.backoffProvider;
    ChildLoadBalancerHelperProvider childLbHelperProvider =
        new ChildLoadBalancerHelperProvider(helper, new SubchannelStateManagerImpl(), rlsPicker);
    refCountedChildPolicyWrapperFactory =
        new RefCountedChildPolicyWrapperFactory(
            lbPolicyConfig.getLoadBalancingPolicy(), childLbResolvedAddressFactory,
            childLbHelperProvider,
            new BackoffRefreshListener());

    gaugeRegistration = helper.getMetricRecorder()
        .registerBatchCallback(new BatchCallback() {
          @Override
          public void accept(BatchRecorder recorder) {
            int estimatedSize;
            long estimatedSizeBytes;
            synchronized (lock) {
              estimatedSize = linkedHashLruCache.estimatedSize();
              estimatedSizeBytes = linkedHashLruCache.estimatedSizeBytes();
            }
            recorder.recordLongGauge(CACHE_ENTRIES_GAUGE, estimatedSize,
                Arrays.asList(helper.getChannelTarget(), rlsConfig.lookupService(),
                    metricsInstanceUuid), Collections.emptyList());
            recorder.recordLongGauge(CACHE_SIZE_GAUGE, estimatedSizeBytes,
                Arrays.asList(helper.getChannelTarget(), rlsConfig.lookupService(),
                    metricsInstanceUuid), Collections.emptyList());
          }
        }, CACHE_ENTRIES_GAUGE, CACHE_SIZE_GAUGE);

    logger.log(ChannelLogLevel.DEBUG, "CachingRlsLbClient created");
  }

  void init() {
    synchronized (lock) {
      refCountedChildPolicyWrapperFactory.init();
    }
  }

  /**
   * Convert the status to UNAVAILABLE and enhance the error message.
   * @param status status as provided by server
   * @param serverName Used for error description
   * @return Transformed status
   */
  static Status convertRlsServerStatus(Status status, String serverName) {
    return Status.UNAVAILABLE.withCause(status.getCause()).withDescription(
        String.format("Unable to retrieve RLS targets from RLS server %s.  "
                + "RLS server returned: %s: %s",
            serverName, status.getCode(), status.getDescription()));
  }

  private void periodicClean() {
    synchronized (lock) {
      linkedHashLruCache.cleanupExpiredEntries();
    }
  }

  /** Populates async cache entry for new request. */
  @GuardedBy("lock")
  private CachedRouteLookupResponse asyncRlsCall(
      RouteLookupRequest request, @Nullable BackoffPolicy backoffPolicy) {
    if (throttler.shouldThrottle()) {
      logger.log(ChannelLogLevel.DEBUG, "[RLS Entry {0}] Throttled RouteLookup", request);
      // Cache updated, but no need to call updateBalancingState because no RPCs were queued waiting
      // on this result
      return CachedRouteLookupResponse.backoffEntry(createBackOffEntry(
          request, Status.RESOURCE_EXHAUSTED.withDescription("RLS throttled"), backoffPolicy));
    }
    final SettableFuture<RouteLookupResponse> response = SettableFuture.create();
    io.grpc.lookup.v1.RouteLookupRequest routeLookupRequest = REQUEST_CONVERTER.convert(request);
    logger.log(ChannelLogLevel.DEBUG,
        "[RLS Entry {0}] Starting RouteLookup: {1}", request, routeLookupRequest);
    rlsStub.withDeadlineAfter(callTimeoutNanos, TimeUnit.NANOSECONDS)
        .routeLookup(
            routeLookupRequest,
            new StreamObserver<io.grpc.lookup.v1.RouteLookupResponse>() {
              @Override
              public void onNext(io.grpc.lookup.v1.RouteLookupResponse value) {
                logger.log(ChannelLogLevel.DEBUG,
                    "[RLS Entry {0}] RouteLookup succeeded: {1}", request, value);
                response.set(RESPONSE_CONVERTER.reverse().convert(value));
              }

              @Override
              public void onError(Throwable t) {
                logger.log(ChannelLogLevel.DEBUG,
                    "[RLS Entry {0}] RouteLookup failed: {1}", request, t);
                response.setException(t);
                throttler.registerBackendResponse(true);
              }

              @Override
              public void onCompleted() {
                throttler.registerBackendResponse(false);
              }
            });
    return CachedRouteLookupResponse.pendingResponse(
        createPendingEntry(request, response, backoffPolicy));
  }

  /**
   * Returns async response of the {@code request}. The returned value can be in 3 different states;
   * cached, pending and backed-off due to error. The result remains same even if the status is
   * changed after the return.
   */
  @CheckReturnValue
  final CachedRouteLookupResponse get(final RouteLookupRequest request) {
    synchronized (lock) {
      final CacheEntry cacheEntry;
      cacheEntry = linkedHashLruCache.read(request);
      if (cacheEntry == null) {
        PendingCacheEntry pendingEntry = pendingCallCache.get(request);
        if (pendingEntry != null) {
          return CachedRouteLookupResponse.pendingResponse(pendingEntry);
        }
        return asyncRlsCall(request, /* backoffPolicy= */ null);
      }

      if (cacheEntry instanceof DataCacheEntry) {
        // cache hit, initiate async-refresh if entry is staled
        DataCacheEntry dataEntry = ((DataCacheEntry) cacheEntry);
        if (dataEntry.isStaled(ticker.read())) {
          dataEntry.maybeRefresh();
        }
        return CachedRouteLookupResponse.dataEntry((DataCacheEntry) cacheEntry);
      }
      return CachedRouteLookupResponse.backoffEntry((BackoffCacheEntry) cacheEntry);
    }
  }

  /** Performs any pending maintenance operations needed by the cache. */
  void close() {
    logger.log(ChannelLogLevel.DEBUG, "CachingRlsLbClient closed");
    synchronized (lock) {
      periodicCleaner.cancel(false);
      // all childPolicyWrapper will be returned via AutoCleaningEvictionListener
      linkedHashLruCache.close();
      // TODO(creamsoup) maybe cancel all pending requests
      pendingCallCache.clear();
      rlsChannel.shutdownNow();
      rlsPicker.close();
      gaugeRegistration.close();
    }
  }

  void requestConnection() {
    rlsChannel.getState(true);
  }

  @GuardedBy("lock")
  private PendingCacheEntry createPendingEntry(
      RouteLookupRequest request,
      ListenableFuture<RouteLookupResponse> pendingCall,
      @Nullable BackoffPolicy backoffPolicy) {
    PendingCacheEntry entry = new PendingCacheEntry(request, pendingCall, backoffPolicy);
    // Add the entry to the map before adding the Listener, because the listener removes the
    // entry from the map
    pendingCallCache.put(request, entry);
    // Beware that the listener can run immediately on the current thread
    pendingCall.addListener(() -> pendingRpcComplete(entry), MoreExecutors.directExecutor());
    return entry;
  }

  private void pendingRpcComplete(PendingCacheEntry entry) {
    synchronized (lock) {
      boolean clientClosed = pendingCallCache.remove(entry.request) == null;
      if (clientClosed) {
        return;
      }

      try {
        createDataEntry(entry.request, Futures.getDone(entry.pendingCall));
        // Cache updated. DataCacheEntry constructor indirectly calls updateBalancingState() to
        // reattempt picks when the child LB is done connecting
      } catch (Exception e) {
        createBackOffEntry(entry.request, Status.fromThrowable(e), entry.backoffPolicy);
        // Cache updated. updateBalancingState() to reattempt picks
        helper.triggerPendingRpcProcessing();
      }
    }
  }

  @GuardedBy("lock")
  private DataCacheEntry createDataEntry(
      RouteLookupRequest request, RouteLookupResponse routeLookupResponse) {
    logger.log(
        ChannelLogLevel.DEBUG,
        "[RLS Entry {0}] Transition to data cache: routeLookupResponse={1}",
        request, routeLookupResponse);
    DataCacheEntry entry = new DataCacheEntry(request, routeLookupResponse);
    // Constructor for DataCacheEntry causes updateBalancingState, but the picks can't happen until
    // this cache update because the lock is held
    linkedHashLruCache.cacheAndClean(request, entry);
    return entry;
  }

  @GuardedBy("lock")
  private BackoffCacheEntry createBackOffEntry(
      RouteLookupRequest request, Status status, @Nullable BackoffPolicy backoffPolicy) {
    if (backoffPolicy == null) {
      backoffPolicy = backoffProvider.get();
    }
    long delayNanos = backoffPolicy.nextBackoffNanos();
    logger.log(
        ChannelLogLevel.DEBUG,
        "[RLS Entry {0}] Transition to back off: status={1}, delayNanos={2}",
        request, status, delayNanos);
    BackoffCacheEntry entry = new BackoffCacheEntry(request, status, backoffPolicy);
    // Lock is held, so the task can't execute before the assignment
    entry.scheduledFuture = scheduledExecutorService.schedule(
        () -> refreshBackoffEntry(entry), delayNanos, TimeUnit.NANOSECONDS);
    linkedHashLruCache.cacheAndClean(request, entry);
    return entry;
  }

  private void refreshBackoffEntry(BackoffCacheEntry entry) {
    synchronized (lock) {
      // This checks whether the task has been cancelled and prevents a second execution.
      if (!entry.scheduledFuture.cancel(false)) {
        // Future was previously cancelled
        return;
      }
      logger.log(ChannelLogLevel.DEBUG,
          "[RLS Entry {0}] Calling RLS for transition to pending", entry.request);
      linkedHashLruCache.invalidate(entry.request);
      asyncRlsCall(entry.request, entry.backoffPolicy);
    }
  }

  private static final class RlsLbHelper extends ForwardingLoadBalancerHelper {

    final Helper helper;
    private ConnectivityState state;
    private SubchannelPicker picker;

    RlsLbHelper(Helper helper) {
      this.helper = helper;
    }

    @Override
    protected Helper delegate() {
      return helper;
    }

    @Override
    public void updateBalancingState(ConnectivityState newState, SubchannelPicker newPicker) {
      state = newState;
      picker = newPicker;
      super.updateBalancingState(newState, newPicker);
    }

    void triggerPendingRpcProcessing() {
      checkState(state != null, "updateBalancingState hasn't yet been called");
      helper.getSynchronizationContext().execute(
          () -> super.updateBalancingState(state, picker));
    }
  }

  /**
   * Viewer class for cached {@link RouteLookupResponse} and associated {@link ChildPolicyWrapper}.
   */
  static final class CachedRouteLookupResponse {
    // Should only have 1 of following 3 cache entries
    @Nullable
    private final DataCacheEntry dataCacheEntry;
    @Nullable
    private final PendingCacheEntry pendingCacheEntry;
    @Nullable
    private final BackoffCacheEntry backoffCacheEntry;

    CachedRouteLookupResponse(
        DataCacheEntry dataCacheEntry,
        PendingCacheEntry pendingCacheEntry,
        BackoffCacheEntry backoffCacheEntry) {
      this.dataCacheEntry = dataCacheEntry;
      this.pendingCacheEntry = pendingCacheEntry;
      this.backoffCacheEntry = backoffCacheEntry;
      checkState((dataCacheEntry != null ^ pendingCacheEntry != null ^ backoffCacheEntry != null)
          && !(dataCacheEntry != null && pendingCacheEntry != null && backoffCacheEntry != null),
          "Expected only 1 cache entry value provided");
    }

    static CachedRouteLookupResponse pendingResponse(PendingCacheEntry pendingEntry) {
      return new CachedRouteLookupResponse(null, pendingEntry, null);
    }

    static CachedRouteLookupResponse backoffEntry(BackoffCacheEntry backoffEntry) {
      return new CachedRouteLookupResponse(null, null, backoffEntry);
    }

    static CachedRouteLookupResponse dataEntry(DataCacheEntry dataEntry) {
      return new CachedRouteLookupResponse(dataEntry, null, null);
    }

    boolean hasData() {
      return dataCacheEntry != null;
    }

    @Nullable
    ChildPolicyWrapper getChildPolicyWrapper() {
      if (!hasData()) {
        return null;
      }
      return dataCacheEntry.getChildPolicyWrapper();
    }

    @VisibleForTesting
    @Nullable
    ChildPolicyWrapper getChildPolicyWrapper(String target) {
      if (!hasData()) {
        return null;
      }
      return dataCacheEntry.getChildPolicyWrapper(target);
    }

    @Nullable
    String getHeaderData() {
      if (!hasData()) {
        return null;
      }
      return dataCacheEntry.getHeaderData();
    }

    boolean hasError() {
      return backoffCacheEntry != null;
    }

    boolean isPending() {
      return pendingCacheEntry != null;
    }

    @Nullable
    Status getStatus() {
      if (!hasError()) {
        return null;
      }
      return backoffCacheEntry.getStatus();
    }

    @Override
    public String toString() {
      ToStringHelper toStringHelper = MoreObjects.toStringHelper(this);
      if (dataCacheEntry != null) {
        toStringHelper.add("dataCacheEntry", dataCacheEntry);
      }
      if (pendingCacheEntry != null) {
        toStringHelper.add("pendingCacheEntry", pendingCacheEntry);
      }
      if (backoffCacheEntry != null) {
        toStringHelper.add("backoffCacheEntry", backoffCacheEntry);
      }
      return toStringHelper.toString();
    }
  }

  /** A pending cache entry when the async RouteLookup RPC is still on the fly. */
  static final class PendingCacheEntry {
    private final ListenableFuture<RouteLookupResponse> pendingCall;
    private final RouteLookupRequest request;
    @Nullable
    private final BackoffPolicy backoffPolicy;

    PendingCacheEntry(
        RouteLookupRequest request,
        ListenableFuture<RouteLookupResponse> pendingCall,
        @Nullable BackoffPolicy backoffPolicy) {
      this.request = checkNotNull(request, "request");
      this.pendingCall = checkNotNull(pendingCall, "pendingCall");
      this.backoffPolicy = backoffPolicy;
    }

    @Override
    public String toString() {
      return MoreObjects.toStringHelper(this)
          .add("request", request)
          .toString();
    }
  }

  /** Common cache entry data for {@link RlsAsyncLruCache}. */
  abstract static class CacheEntry {

    protected final RouteLookupRequest request;

    CacheEntry(RouteLookupRequest request) {
      this.request = checkNotNull(request, "request");
    }

    abstract int getSizeBytes();

    abstract boolean isExpired(long now);

    abstract void cleanup();

    protected boolean isOldEnoughToBeEvicted(long now) {
      return true;
    }
  }

  /** Implementation of {@link CacheEntry} contains valid data. */
  final class DataCacheEntry extends CacheEntry {
    private final RouteLookupResponse response;
    private final long minEvictionTime;
    private final long expireTime;
    private final long staleTime;
    private final List<ChildPolicyWrapper> childPolicyWrappers;

    // GuardedBy CachingRlsLbClient.lock
    DataCacheEntry(RouteLookupRequest request, final RouteLookupResponse response) {
      super(request);
      this.response = checkNotNull(response, "response");
      checkState(!response.targets().isEmpty(), "No targets returned by RLS");
      childPolicyWrappers =
          refCountedChildPolicyWrapperFactory
              .createOrGet(response.targets());
      long now = ticker.read();
      minEvictionTime = now + MIN_EVICTION_TIME_DELTA_NANOS;
      expireTime = now + maxAgeNanos;
      staleTime = now + staleAgeNanos;
    }

    /**
     * Refreshes cache entry by creating {@link PendingCacheEntry}. When the {@code
     * PendingCacheEntry} received data from RLS server, it will replace the data entry if valid
     * data still exists. Flow looks like following.
     *
     * <pre>
     * Timeline                       | async refresh
     *                                V put new cache (entry2)
     * entry1: Pending | hasValue | staled  |
     * entry2:                        | OV* | pending | hasValue | staled |
     *
     * OV: old value
     * </pre>
     */
    void maybeRefresh() {
      synchronized (lock) { // Lock is already held, but ErrorProne can't tell
        if (pendingCallCache.containsKey(request)) {
          // pending already requested
          return;
        }
        logger.log(ChannelLogLevel.DEBUG,
            "[RLS Entry {0}] Cache entry is stale, refreshing", request);
        asyncRlsCall(request, /* backoffPolicy= */ null);
      }
    }

    @VisibleForTesting
    ChildPolicyWrapper getChildPolicyWrapper(String target) {
      for (ChildPolicyWrapper childPolicyWrapper : childPolicyWrappers) {
        if (childPolicyWrapper.getTarget().equals(target)) {
          return childPolicyWrapper;
        }
      }

      throw new RuntimeException("Target not found:" + target);
    }

    @Nullable
    ChildPolicyWrapper getChildPolicyWrapper() {
      for (ChildPolicyWrapper childPolicyWrapper : childPolicyWrappers) {
        if (childPolicyWrapper.getState() != ConnectivityState.TRANSIENT_FAILURE) {
          return childPolicyWrapper;
        }
      }
      return childPolicyWrappers.get(0);
    }

    String getHeaderData() {
      return response.getHeaderData();
    }

    // Assume UTF-16 (2 bytes) and overhead of a String object is 38 bytes
    int calcStringSize(String target) {
      return target.length() * BYTES_PER_CHAR + STRING_OVERHEAD_BYTES;
    }

    @Override
    int getSizeBytes() {
      int targetSize = 0;
      for (String target : response.targets()) {
        targetSize += calcStringSize(target);
      }
      return targetSize + calcStringSize(response.getHeaderData()) + OBJ_OVERHEAD_B // response size
          + Long.SIZE * 2 + OBJ_OVERHEAD_B; // Other fields
    }

    @Override
    boolean isExpired(long now) {
      return expireTime - now <= 0;
    }

    boolean isStaled(long now) {
      return staleTime - now <= 0;
    }

    @Override
    protected boolean isOldEnoughToBeEvicted(long now) {
      return minEvictionTime - now <= 0;
    }

    @Override
    void cleanup() {
      synchronized (lock) {
        for (ChildPolicyWrapper policyWrapper : childPolicyWrappers) {
          refCountedChildPolicyWrapperFactory.release(policyWrapper);
        }
      }
    }

    @Override
    public String toString() {
      return MoreObjects.toStringHelper(this)
          .add("request", request)
          .add("response", response)
          .add("expireTime", expireTime)
          .add("staleTime", staleTime)
          .add("childPolicyWrappers", childPolicyWrappers)
          .toString();
    }
  }

  /**
   * Implementation of {@link CacheEntry} contains error. This entry will transition to pending
   * status when the backoff time is expired.
   */
  private static final class BackoffCacheEntry extends CacheEntry {

    private final Status status;
    private final BackoffPolicy backoffPolicy;
    private Future<?> scheduledFuture;

    BackoffCacheEntry(RouteLookupRequest request, Status status, BackoffPolicy backoffPolicy) {
      super(request);
      this.status = checkNotNull(status, "status");
      this.backoffPolicy = checkNotNull(backoffPolicy, "backoffPolicy");
    }

    Status getStatus() {
      return status;
    }

    @Override
    int getSizeBytes() {
      return OBJ_OVERHEAD_B * 3 + Long.SIZE + 8; // 3 java objects, 1 long and a boolean
    }

    @Override
    boolean isExpired(long now) {
      return scheduledFuture.isDone();
    }

    @Override
    void cleanup() {
      scheduledFuture.cancel(false);
    }

    @Override
    public String toString() {
      return MoreObjects.toStringHelper(this)
          .add("request", request)
          .add("status", status)
          .toString();
    }
  }

  /** Returns a Builder for {@link CachingRlsLbClient}. */
  static Builder newBuilder() {
    return new Builder();
  }

  /** A Builder for {@link CachingRlsLbClient}. */
  static final class Builder {

    private Helper helper;
    private LbPolicyConfiguration lbPolicyConfig;
    private Throttler throttler = new HappyThrottler();
    private ResolvedAddressFactory resolvedAddressFactory;
    private Ticker ticker = Ticker.systemTicker();
    private EvictionListener<RouteLookupRequest, CacheEntry> evictionListener;
    private BackoffPolicy.Provider backoffProvider = new ExponentialBackoffPolicy.Provider();

    Builder setHelper(Helper helper) {
      this.helper = checkNotNull(helper, "helper");
      return this;
    }

    Builder setLbPolicyConfig(LbPolicyConfiguration lbPolicyConfig) {
      this.lbPolicyConfig = checkNotNull(lbPolicyConfig, "lbPolicyConfig");
      return this;
    }

    Builder setThrottler(Throttler throttler) {
      this.throttler = checkNotNull(throttler, "throttler");
      return this;
    }

    /**
     * Sets a factory to create {@link ResolvedAddresses} for child load balancer.
     */
    Builder setResolvedAddressesFactory(
        ResolvedAddressFactory resolvedAddressFactory) {
      this.resolvedAddressFactory =
          checkNotNull(resolvedAddressFactory, "resolvedAddressFactory");
      return this;
    }

    Builder setTicker(Ticker ticker) {
      this.ticker = checkNotNull(ticker, "ticker");
      return this;
    }

    Builder setEvictionListener(
        @Nullable EvictionListener<RouteLookupRequest, CacheEntry> evictionListener) {
      this.evictionListener = evictionListener;
      return this;
    }

    Builder setBackoffProvider(BackoffPolicy.Provider provider) {
      this.backoffProvider = checkNotNull(provider, "provider");
      return this;
    }

    CachingRlsLbClient build() {
      CachingRlsLbClient client = new CachingRlsLbClient(this);
      client.init();
      return client;
    }
  }

  /**
   * When any {@link CacheEntry} is evicted from {@link LruCache}, it performs {@link
   * CacheEntry#cleanup()} after original {@link EvictionListener} is finished.
   */
  private static final class AutoCleaningEvictionListener
      implements EvictionListener<RouteLookupRequest, CacheEntry> {

    private final EvictionListener<RouteLookupRequest, CacheEntry> delegate;

    AutoCleaningEvictionListener(
        @Nullable EvictionListener<RouteLookupRequest, CacheEntry> delegate) {
      this.delegate = delegate;
    }

    @Override
    public void onEviction(RouteLookupRequest key, CacheEntry value, EvictionType cause) {
      if (delegate != null) {
        delegate.onEviction(key, value, cause);
      }
      // performs cleanup after delegation
      value.cleanup();
    }
  }

  /** A Throttler never throttles. */
  private static final class HappyThrottler implements Throttler {

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

    @Override
    public void registerBackendResponse(boolean throttled) {
      // no-op
    }
  }

  /** Implementation of {@link LinkedHashLruCache} for RLS. */
  private static final class RlsAsyncLruCache
      extends LinkedHashLruCache<RouteLookupRequest, CacheEntry> {
    private final RlsLbHelper helper;

    RlsAsyncLruCache(long maxEstimatedSizeBytes,
        @Nullable EvictionListener<RouteLookupRequest, CacheEntry> evictionListener,
        Ticker ticker, RlsLbHelper helper) {
      super(maxEstimatedSizeBytes, evictionListener, ticker);
      this.helper = checkNotNull(helper, "helper");
    }

    @Override
    protected boolean isExpired(RouteLookupRequest key, CacheEntry value, long nowNanos) {
      return value.isExpired(nowNanos);
    }

    @Override
    protected int estimateSizeOf(RouteLookupRequest key, CacheEntry value) {
      return value.getSizeBytes();
    }

    @Override
    protected boolean shouldInvalidateEldestEntry(
        RouteLookupRequest eldestKey, CacheEntry eldestValue, long now) {
      if (!eldestValue.isOldEnoughToBeEvicted(now)) {
        return false;
      }

      // eldest entry should be evicted if size limit exceeded
      return this.estimatedSizeBytes() > this.estimatedMaxSizeBytes();
    }

    public CacheEntry cacheAndClean(RouteLookupRequest key, CacheEntry value) {
      CacheEntry newEntry = cache(key, value);

      // force cleanup if new entry pushed cache over max size (in bytes)
      if (fitToLimit()) {
        helper.triggerPendingRpcProcessing();
      }
      return newEntry;
    }
  }

  /**
   * LbStatusListener refreshes {@link BackoffCacheEntry} when lb state is changed to {@link
   * ConnectivityState#READY} from {@link ConnectivityState#TRANSIENT_FAILURE}.
   */
  private final class BackoffRefreshListener implements ChildLbStatusListener {

    @Nullable
    private ConnectivityState prevState = null;

    @Override
    public void onStatusChanged(ConnectivityState newState) {
      if (prevState == ConnectivityState.TRANSIENT_FAILURE
          && newState == ConnectivityState.READY) {
        logger.log(ChannelLogLevel.DEBUG, "Transitioning from TRANSIENT_FAILURE to READY");
        synchronized (lock) {
          for (CacheEntry value : linkedHashLruCache.values()) {
            if (value instanceof BackoffCacheEntry) {
              refreshBackoffEntry((BackoffCacheEntry) value);
            }
          }
        }
      }
      prevState = newState;
    }
  }

  /** A header will be added when RLS server respond with additional header data. */
  @VisibleForTesting
  static final Metadata.Key<String> RLS_DATA_KEY =
      Metadata.Key.of("X-Google-RLS-Data", Metadata.ASCII_STRING_MARSHALLER);

  final class RlsPicker extends SubchannelPicker {

    private final RlsRequestFactory requestFactory;
    private final String lookupService;

    RlsPicker(RlsRequestFactory requestFactory, String lookupService) {
      this.requestFactory = checkNotNull(requestFactory, "requestFactory");
      this.lookupService = checkNotNull(lookupService, "rlsConfig");
    }

    @Override
    public PickResult pickSubchannel(PickSubchannelArgs args) {
      String serviceName = args.getMethodDescriptor().getServiceName();
      String methodName = args.getMethodDescriptor().getBareMethodName();
      RouteLookupRequest request =
          requestFactory.create(serviceName, methodName, args.getHeaders());
      final CachedRouteLookupResponse response = CachingRlsLbClient.this.get(request);

      if (response.getHeaderData() != null && !response.getHeaderData().isEmpty()) {
        Metadata headers = args.getHeaders();
        headers.discardAll(RLS_DATA_KEY);
        headers.put(RLS_DATA_KEY, response.getHeaderData());
      }
      String defaultTarget = lbPolicyConfig.getRouteLookupConfig().defaultTarget();
      boolean hasFallback = defaultTarget != null && !defaultTarget.isEmpty();
      if (response.hasData()) {
        ChildPolicyWrapper childPolicyWrapper = response.getChildPolicyWrapper();
        SubchannelPicker picker =
            (childPolicyWrapper != null) ? childPolicyWrapper.getPicker() : null;
        if (picker == null) {
          return PickResult.withNoResult();
        }
        // Happy path
        PickResult pickResult = picker.pickSubchannel(args);
        if (pickResult.hasResult()) {
          helper.getMetricRecorder().addLongCounter(TARGET_PICKS_COUNTER, 1,
              Arrays.asList(helper.getChannelTarget(), lookupService,
                  childPolicyWrapper.getTarget(), determineMetricsPickResult(pickResult)),
              Collections.emptyList());
        }
        return pickResult;
      } else if (response.hasError()) {
        if (hasFallback) {
          return useFallback(args);
        }
        helper.getMetricRecorder().addLongCounter(FAILED_PICKS_COUNTER, 1,
            Arrays.asList(helper.getChannelTarget(), lookupService), Collections.emptyList());
        return PickResult.withError(
            convertRlsServerStatus(response.getStatus(),
                lbPolicyConfig.getRouteLookupConfig().lookupService()));
      } else {
        return PickResult.withNoResult();
      }
    }

    private ChildPolicyWrapper fallbackChildPolicyWrapper;

    /** Uses Subchannel connected to default target. */
    private PickResult useFallback(PickSubchannelArgs args) {
      // TODO(creamsoup) wait until lb is ready
      startFallbackChildPolicy();
      SubchannelPicker picker = fallbackChildPolicyWrapper.getPicker();
      if (picker == null) {
        return PickResult.withNoResult();
      }
      PickResult pickResult = picker.pickSubchannel(args);
      if (pickResult.hasResult()) {
        helper.getMetricRecorder().addLongCounter(DEFAULT_TARGET_PICKS_COUNTER, 1,
            Arrays.asList(helper.getChannelTarget(), lookupService,
                fallbackChildPolicyWrapper.getTarget(), determineMetricsPickResult(pickResult)),
            Collections.emptyList());
      }
      return pickResult;
    }

    private String determineMetricsPickResult(PickResult pickResult) {
      if (pickResult.getStatus().isOk()) {
        return "complete";
      } else if (pickResult.isDrop()) {
        return "drop";
      } else {
        return "fail";
      }
    }

    private void startFallbackChildPolicy() {
      String defaultTarget = lbPolicyConfig.getRouteLookupConfig().defaultTarget();
      synchronized (lock) {
        if (fallbackChildPolicyWrapper != null) {
          return;
        }
        logger.log(ChannelLogLevel.DEBUG, "starting fallback to {0}", defaultTarget);
        fallbackChildPolicyWrapper = refCountedChildPolicyWrapperFactory.createOrGet(defaultTarget);
      }
    }

    // GuardedBy CachingRlsLbClient.lock
    void close() {
      synchronized (lock) { // Lock is already held, but ErrorProne can't tell
        if (fallbackChildPolicyWrapper != null) {
          refCountedChildPolicyWrapperFactory.release(fallbackChildPolicyWrapper);
        }
      }
    }

    @Override
    public String toString() {
      return MoreObjects.toStringHelper(this)
          .add("target", lbPolicyConfig.getRouteLookupConfig().lookupService())
          .toString();
    }
  }

}

grpc / grpc-java / #19908

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