#20365

Committed 27 Jul 2026 06:04AM UTC coverage: 89.199% (+0.07%) from 89.125%

Build # #20365

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push

github

Committed by

web-flow

Commit Message

core: Implement LB Delay Observability (Proposal A121) (#12807)

This PR implements **Attempt-Level RPC Delay Observability** across the core channel transport, built-in load balancers, xDS policies, and the OpenTelemetry telemetry plugin, aligned with [gRPC Proposal A121](https://github.com/grpc/proposal/pull/556).

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86.0

/../api/src/main/java/io/grpc/ClientStreamTracer.java

/*
 * Copyright 2017 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;

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

import com.google.common.base.MoreObjects;

/**
 * {@link StreamTracer} for the client-side.
 *
 * <p>This class is thread-safe.
 */
@ExperimentalApi("https://github.com/grpc/grpc-java/issues/2861")
public abstract class ClientStreamTracer extends StreamTracer {
  /**
   * Indicates how long the call was delayed, in nanoseconds, due to waiting for name resolution
   * result. If the call option is not set, the call did not experience name resolution delay.
   */
  public static final CallOptions.Key<Long> NAME_RESOLUTION_DELAYED =
      CallOptions.Key.create("io.grpc.ClientStreamTracer.NAME_RESOLUTION_DELAYED");

  /**
   * The stream is being created on a ready transport.
   *
   * @param headers the mutable initial metadata. Modifications to it will be sent to the socket but
   *     not be seen by client interceptors and the application.
   *
   * @since 1.40.0
   */
  public void streamCreated(@Grpc.TransportAttr Attributes transportAttrs, Metadata headers) {
  }

  /**
   * Name resolution is completed and the connection starts getting established. This method is only
   * invoked on the streams that encounter such delay.
   *
   * </p>gRPC buffers the client call if the remote address and configurations, e.g. timeouts and
   * retry policy, are not ready. Asynchronously gRPC internally does the name resolution to get
   * this information. The streams that are processed immediately on ready transports by the time
   * the RPC comes do not go through the pending process, thus this callback will not be invoked.
   */
  public void createPendingStream() {
  }

  /**
   * Called when an attempt-level delay segment (such as waiting for a load balancing pick or
   * connection establishment) starts.
   *
   * <p>This method is invoked synchronously on the attempt thread. Implementations should start
   * internal timers or child tracing spans (named strictly {@code "Attempt Delay"}) carrying the
   * canonical {@code grpc.delay_type} attribute.
   *
   * @param delayType canonical low-cardinality label categorizing the delay (e.g., "connecting")
   * @param delayReason high-cardinality diagnostic string describing granular runtime conditions
   * @since 1.82.0
   */
  public void recordAttemptDelayStart(String delayType, String delayReason) {
  }

  /**
   * Called when an attempt-level delay reason changes while the overall delay type remains
   * constant (for example, when a priority load balancing policy fails over between tiers).
   *
   * <p>Implementations should record structured events (such as {@code "Delay state transition"})
   * on the active delay span without recreating the span or resetting cumulative timers.
   *
   * @param delayReason updated high-cardinality diagnostic string describing new conditions
   * @since 1.82.0
   */
  public void recordAttemptDelayReasonChanged(String delayReason) {
  }

  /**
   * Called when an attempt-level delay segment ends upon successful pick or stream creation.
   *
   * <p>Implementations should simultaneously close active child tracing spans and record elapsed
   * duration to the {@code grpc.client.attempt.delay.duration} histogram.
   *
   * @since 1.82.0
   */
  public void recordAttemptDelayEnd() {
  }

  /**
   * Headers has been sent to the socket.
   */
  public void outboundHeaders() {
  }

  /**
   * Headers has been received from the server.
   */
  public void inboundHeaders() {
  }

  /**
   * Headers has been received from the server. This method does not pass ownership to {@code
   * headers}, so implementations must not access the metadata after returning. Modifications to the
   * metadata within this method will be seen by interceptors and the application.
   *
   * @param headers the received header metadata
   */
  public void inboundHeaders(Metadata headers) {
    inboundHeaders();
  }

  /**
   * Trailing metadata has been received from the server. This method does not pass ownership to
   * {@code trailers}, so implementations must not access the metadata after returning.
   * Modifications to the metadata within this method will be seen by interceptors and the
   * application.
   *
   * @param trailers the received trailing metadata
   * @since 1.17.0
   */
  public void inboundTrailers(Metadata trailers) {
  }

  /**
   * Information providing context to the call became available.
   */
  @Internal
  public void addOptionalLabel(String key, String value) {
  }

  /**
   * Factory class for {@link ClientStreamTracer}.
   */
  public abstract static class Factory {
    /**
     * Creates a {@link ClientStreamTracer} for a new client stream.  This is called inside the
     * transport when it's creating the stream.
     *
     * @param info information about the stream
     * @param headers the mutable headers of the stream. It can be safely mutated within this
     *        method.  Changes made to it will be sent by the stream.  It should not be saved
     *        because it is not safe for read or write after the method returns.
     *
     * @since 1.20.0
     */
    public ClientStreamTracer newClientStreamTracer(StreamInfo info, Metadata headers) {
      throw new UnsupportedOperationException("Not implemented");
    }
  }

  /**
   * Information about a stream.
   *
   * <p>Note this class doesn't override {@code equals()} and {@code hashCode}, as is the case for
   * {@link CallOptions}.
   *
   * @since 1.20.0
   */
  @ExperimentalApi("https://github.com/grpc/grpc-java/issues/2861")
  public static final class StreamInfo {
    private final CallOptions callOptions;
    private final int previousAttempts;
    private final boolean isTransparentRetry;
    private final boolean isHedging;

    StreamInfo(
        CallOptions callOptions, int previousAttempts, boolean isTransparentRetry,
        boolean isHedging) {
      this.callOptions = checkNotNull(callOptions, "callOptions");
      this.previousAttempts = previousAttempts;
      this.isTransparentRetry = isTransparentRetry;
      this.isHedging = isHedging;
    }

    /**
     * Returns the effective CallOptions of the call.
     */
    public CallOptions getCallOptions() {
      return callOptions;
    }

    /**
     * Returns the number of preceding attempts for the RPC.
     *
     * @since 1.40.0
     */
    public int getPreviousAttempts() {
      return previousAttempts;
    }

    /**
     * Whether the stream is a transparent retry.
     *
     * @since 1.40.0
     */
    public boolean isTransparentRetry() {
      return isTransparentRetry;
    }

    /**
     * Whether the stream is hedging.
     *
     * @since 1.74.0
     */
    public boolean isHedging() {
      return isHedging;
    }

    /**
     * Converts this StreamInfo into a new Builder.
     *
     * @since 1.21.0
     */
    public Builder toBuilder() {
      return new Builder()
          .setCallOptions(callOptions)
          .setPreviousAttempts(previousAttempts)
          .setIsTransparentRetry(isTransparentRetry)
          .setIsHedging(isHedging);

    }

    /**
     * Creates an empty Builder.
     *
     * @since 1.21.0
     */
    public static Builder newBuilder() {
      return new Builder();
    }

    @Override
    public String toString() {
      return MoreObjects.toStringHelper(this)
          .add("callOptions", callOptions)
          .add("previousAttempts", previousAttempts)
          .add("isTransparentRetry", isTransparentRetry)
          .add("isHedging", isHedging)
          .toString();
    }

    /**
     * Builds {@link StreamInfo} objects.
     *
     * @since 1.21.0
     */
    public static final class Builder {
      private CallOptions callOptions = CallOptions.DEFAULT;
      private int previousAttempts;
      private boolean isTransparentRetry;
      private boolean isHedging;

      Builder() {
      }

      /**
       * Sets the effective CallOptions of the call.  This field is optional.
       */
      public Builder setCallOptions(CallOptions callOptions) {
        this.callOptions = checkNotNull(callOptions, "callOptions cannot be null");
        return this;
      }

      /**
       * Set the number of preceding attempts of the RPC.
       *
       * @since 1.40.0
       */
      public Builder setPreviousAttempts(int previousAttempts) {
        this.previousAttempts = previousAttempts;
        return this;
      }

      /**
       * Sets whether the stream is a transparent retry.
       *
       * @since 1.40.0
       */
      public Builder setIsTransparentRetry(boolean isTransparentRetry) {
        this.isTransparentRetry = isTransparentRetry;
        return this;
      }

      /**
       * Sets whether the stream is hedging.
       *
       * @since 1.74.0
       */
      public Builder setIsHedging(boolean isHedging) {
        this.isHedging = isHedging;
        return this;
      }

      /**
       * Builds a new StreamInfo.
       */
      public StreamInfo build() {
        return new StreamInfo(callOptions, previousAttempts, isTransparentRetry, isHedging);
      }
    }
  }
}

1	/*
2	* Copyright 2017 The gRPC Authors
3	*
4	* Licensed under the Apache License, Version 2.0 (the "License");
5	* you may not use this file except in compliance with the License.
6	* You may obtain a copy of the License at
7	*
8	* http://www.apache.org/licenses/LICENSE-2.0
9	*
10	* Unless required by applicable law or agreed to in writing, software
11	* distributed under the License is distributed on an "AS IS" BASIS,
12	* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13	* See the License for the specific language governing permissions and
14	* limitations under the License.
15	*/
16
17	package io.grpc;
18
19	import static com.google.common.base.Preconditions.checkNotNull;
20
21	import com.google.common.base.MoreObjects;
22
23	/**
24	* {@link StreamTracer} for the client-side.
25	*
26	* <p>This class is thread-safe.
27	*/
28	@ExperimentalApi("https://github.com/grpc/grpc-java/issues/2861")
29	public abstract class ClientStreamTracer extends StreamTracer {	1✔
30	/**
31	* Indicates how long the call was delayed, in nanoseconds, due to waiting for name resolution
32	* result. If the call option is not set, the call did not experience name resolution delay.
33	*/
34	public static final CallOptions.Key<Long> NAME_RESOLUTION_DELAYED =	1✔
35	CallOptions.Key.create("io.grpc.ClientStreamTracer.NAME_RESOLUTION_DELAYED");	1✔
36
37	/**
38	* The stream is being created on a ready transport.
39	*
40	* @param headers the mutable initial metadata. Modifications to it will be sent to the socket but
41	* not be seen by client interceptors and the application.
42	*
43	* @since 1.40.0
44	*/
45	public void streamCreated(@Grpc.TransportAttr Attributes transportAttrs, Metadata headers) {
46	}	1✔
47
48	/**
49	* Name resolution is completed and the connection starts getting established. This method is only
50	* invoked on the streams that encounter such delay.
51	*
52	* </p>gRPC buffers the client call if the remote address and configurations, e.g. timeouts and
53	* retry policy, are not ready. Asynchronously gRPC internally does the name resolution to get
54	* this information. The streams that are processed immediately on ready transports by the time
55	* the RPC comes do not go through the pending process, thus this callback will not be invoked.
56	*/
57	public void createPendingStream() {
58	}	1✔
59
60	/**
61	* Called when an attempt-level delay segment (such as waiting for a load balancing pick or
62	* connection establishment) starts.
63	*
64	* <p>This method is invoked synchronously on the attempt thread. Implementations should start
65	* internal timers or child tracing spans (named strictly {@code "Attempt Delay"}) carrying the
66	* canonical {@code grpc.delay_type} attribute.
67	*
68	* @param delayType canonical low-cardinality label categorizing the delay (e.g., "connecting")
69	* @param delayReason high-cardinality diagnostic string describing granular runtime conditions
70	* @since 1.82.0
71	*/
72	public void recordAttemptDelayStart(String delayType, String delayReason) {
73	}	1✔
74
75	/**
76	* Called when an attempt-level delay reason changes while the overall delay type remains
77	* constant (for example, when a priority load balancing policy fails over between tiers).
78	*
79	* <p>Implementations should record structured events (such as {@code "Delay state transition"})
80	* on the active delay span without recreating the span or resetting cumulative timers.
81	*
82	* @param delayReason updated high-cardinality diagnostic string describing new conditions
83	* @since 1.82.0
84	*/
85	public void recordAttemptDelayReasonChanged(String delayReason) {
86	}	1✔
87
88	/**
89	* Called when an attempt-level delay segment ends upon successful pick or stream creation.
90	*
91	* <p>Implementations should simultaneously close active child tracing spans and record elapsed
92	* duration to the {@code grpc.client.attempt.delay.duration} histogram.
93	*
94	* @since 1.82.0
95	*/
96	public void recordAttemptDelayEnd() {
97	}	1✔
98
99	/**
100	* Headers has been sent to the socket.
101	*/
102	public void outboundHeaders() {
103	}	1✔
104
105	/**
106	* Headers has been received from the server.
107	*/
108	public void inboundHeaders() {
109	}	1✔
110
111	/**
112	* Headers has been received from the server. This method does not pass ownership to {@code
113	* headers}, so implementations must not access the metadata after returning. Modifications to the
114	* metadata within this method will be seen by interceptors and the application.
115	*
116	* @param headers the received header metadata
117	*/
118	public void inboundHeaders(Metadata headers) {
119	inboundHeaders();	1✔
120	}	1✔
121
122	/**
123	* Trailing metadata has been received from the server. This method does not pass ownership to
124	* {@code trailers}, so implementations must not access the metadata after returning.
125	* Modifications to the metadata within this method will be seen by interceptors and the
126	* application.
127	*
128	* @param trailers the received trailing metadata
129	* @since 1.17.0
130	*/
131	public void inboundTrailers(Metadata trailers) {
132	}	1✔
133
134	/**
135	* Information providing context to the call became available.
136	*/
137	@Internal
138	public void addOptionalLabel(String key, String value) {
139	}	1✔
140
141	/**
142	* Factory class for {@link ClientStreamTracer}.
143	*/
144	public abstract static class Factory {	1✔
145	/**
146	* Creates a {@link ClientStreamTracer} for a new client stream. This is called inside the
147	* transport when it's creating the stream.
148	*
149	* @param info information about the stream
150	* @param headers the mutable headers of the stream. It can be safely mutated within this
151	* method. Changes made to it will be sent by the stream. It should not be saved
152	* because it is not safe for read or write after the method returns.
153	*
154	* @since 1.20.0
155	*/
156	public ClientStreamTracer newClientStreamTracer(StreamInfo info, Metadata headers) {
157	throw new UnsupportedOperationException("Not implemented");	×
158	}
159	}
160
161	/**
162	* Information about a stream.
163	*
164	* <p>Note this class doesn't override {@code equals()} and {@code hashCode}, as is the case for
165	* {@link CallOptions}.
166	*
167	* @since 1.20.0
168	*/
169	@ExperimentalApi("https://github.com/grpc/grpc-java/issues/2861")
170	public static final class StreamInfo {
171	private final CallOptions callOptions;
172	private final int previousAttempts;
173	private final boolean isTransparentRetry;
174	private final boolean isHedging;
175
176	StreamInfo(
177	CallOptions callOptions, int previousAttempts, boolean isTransparentRetry,
178	boolean isHedging) {	1✔
179	this.callOptions = checkNotNull(callOptions, "callOptions");	1✔
180	this.previousAttempts = previousAttempts;	1✔
181	this.isTransparentRetry = isTransparentRetry;	1✔
182	this.isHedging = isHedging;	1✔
183	}	1✔
184
185	/**
186	* Returns the effective CallOptions of the call.
187	*/
188	public CallOptions getCallOptions() {
189	return callOptions;	1✔
190	}
191
192	/**
193	* Returns the number of preceding attempts for the RPC.
194	*
195	* @since 1.40.0
196	*/
197	public int getPreviousAttempts() {
198	return previousAttempts;	1✔
199	}
200
201	/**
202	* Whether the stream is a transparent retry.
203	*
204	* @since 1.40.0
205	*/
206	public boolean isTransparentRetry() {
207	return isTransparentRetry;	1✔
208	}
209
210	/**
211	* Whether the stream is hedging.
212	*
213	* @since 1.74.0
214	*/
215	public boolean isHedging() {
216	return isHedging;	1✔
217	}
218
219	/**
220	* Converts this StreamInfo into a new Builder.
221	*
222	* @since 1.21.0
223	*/
224	public Builder toBuilder() {
225	return new Builder()	1✔
226	.setCallOptions(callOptions)	1✔
227	.setPreviousAttempts(previousAttempts)	1✔
228	.setIsTransparentRetry(isTransparentRetry)	1✔
229	.setIsHedging(isHedging);	1✔
230
231	}
232
233	/**
234	* Creates an empty Builder.
235	*
236	* @since 1.21.0
237	*/
238	public static Builder newBuilder() {
239	return new Builder();	1✔
240	}
241
242	@Override
243	public String toString() {
244	return MoreObjects.toStringHelper(this)	×
245	.add("callOptions", callOptions)	×
246	.add("previousAttempts", previousAttempts)	×
247	.add("isTransparentRetry", isTransparentRetry)	×
248	.add("isHedging", isHedging)	×
249	.toString();	×
250	}
251
252	/**
253	* Builds {@link StreamInfo} objects.
254	*
255	* @since 1.21.0
256	*/
257	public static final class Builder {
258	private CallOptions callOptions = CallOptions.DEFAULT;	1✔
259	private int previousAttempts;
260	private boolean isTransparentRetry;
261	private boolean isHedging;
262
263	Builder() {	1✔
264	}	1✔
265
266	/**
267	* Sets the effective CallOptions of the call. This field is optional.
268	*/
269	public Builder setCallOptions(CallOptions callOptions) {
270	this.callOptions = checkNotNull(callOptions, "callOptions cannot be null");	1✔
271	return this;	1✔
272	}
273
274	/**
275	* Set the number of preceding attempts of the RPC.
276	*
277	* @since 1.40.0
278	*/
279	public Builder setPreviousAttempts(int previousAttempts) {
280	this.previousAttempts = previousAttempts;	1✔
281	return this;	1✔
282	}
283
284	/**
285	* Sets whether the stream is a transparent retry.
286	*
287	* @since 1.40.0
288	*/
289	public Builder setIsTransparentRetry(boolean isTransparentRetry) {
290	this.isTransparentRetry = isTransparentRetry;	1✔
291	return this;	1✔
292	}
293
294	/**
295	* Sets whether the stream is hedging.
296	*
297	* @since 1.74.0
298	*/
299	public Builder setIsHedging(boolean isHedging) {
300	this.isHedging = isHedging;	1✔
301	return this;	1✔
302	}
303
304	/**
305	* Builds a new StreamInfo.
306	*/
307	public StreamInfo build() {
308	return new StreamInfo(callOptions, previousAttempts, isTransparentRetry, isHedging);	1✔
309	}
310	}
311	}
312	}

grpc / grpc-java / #20365

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