Introduce global checkpoint listeners #32696
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| /* | ||
| * Licensed to Elasticsearch under one or more contributor | ||
| * license agreements. See the NOTICE file distributed with | ||
| * this work for additional information regarding copyright | ||
| * ownership. Elasticsearch licenses this file to you 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. | ||
| */ | ||
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| package org.elasticsearch.index.shard; | ||
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| import org.apache.logging.log4j.Logger; | ||
| import org.apache.logging.log4j.message.ParameterizedMessage; | ||
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| import java.io.Closeable; | ||
| import java.io.IOException; | ||
| import java.util.ArrayList; | ||
| import java.util.List; | ||
| import java.util.Objects; | ||
| import java.util.concurrent.Executor; | ||
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| import static org.elasticsearch.index.seqno.SequenceNumbers.NO_OPS_PERFORMED; | ||
| import static org.elasticsearch.index.seqno.SequenceNumbers.UNASSIGNED_SEQ_NO; | ||
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| /** | ||
| * Represents a collection of global checkpoint listeners. This collection can be added to, and all listeners present at the time of an | ||
| * update will be notified together. All listeners will be notified when the shard is closed. | ||
| */ | ||
| public class GlobalCheckpointListeners implements Closeable { | ||
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| /** | ||
| * A global checkpoint listener consisting of a callback that is notified when the global checkpoint is updated or the shard is closed. | ||
| */ | ||
| @FunctionalInterface | ||
| public interface GlobalCheckpointListener { | ||
| /** | ||
| * Callback when the global checkpoint is updated or the shard is closed. If the shard is closed, the value of the global checkpoint | ||
| * will be set to {@link org.elasticsearch.index.seqno.SequenceNumbers#UNASSIGNED_SEQ_NO} and the exception will be non-null. If the | ||
| * global checkpoint is updated, the exception will be null. | ||
| * | ||
| * @param globalCheckpoint the updated global checkpoint | ||
| * @param e if non-null, the shard is closed | ||
| */ | ||
| void accept(long globalCheckpoint, IndexShardClosedException e); | ||
| } | ||
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| // guarded by this | ||
| private boolean closed; | ||
| private volatile List<GlobalCheckpointListener> listeners; | ||
| private long lastKnownGlobalCheckpoint = UNASSIGNED_SEQ_NO; | ||
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| private final ShardId shardId; | ||
| private final Executor executor; | ||
| private final Logger logger; | ||
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| /** | ||
| * Construct a global checkpoint listeners collection. | ||
| * | ||
| * @param shardId the shard ID on which global checkpoint updates can be listened to | ||
| * @param executor the executor for listener notifications | ||
| * @param logger a shard-level logger | ||
| */ | ||
| GlobalCheckpointListeners( | ||
| final ShardId shardId, | ||
| final Executor executor, | ||
| final Logger logger) { | ||
| this.shardId = Objects.requireNonNull(shardId); | ||
| this.executor = Objects.requireNonNull(executor); | ||
| this.logger = Objects.requireNonNull(logger); | ||
| } | ||
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| /** | ||
| * Add a global checkpoint listener. If the global checkpoint is above the current global checkpoint known to the listener then the | ||
| * listener will be asynchronously notified on the executor used to construct this collection of global checkpoint listeners. If the | ||
| * shard is closed then the listener will be asynchronously notified on the executor used to construct this collection of global | ||
| * checkpoint listeners. The listener will only be notified of at most one event, either the global checkpoint is updated or the shard | ||
| * is closed. A listener must re-register after one of these events to receive subsequent events. | ||
| * | ||
| * @param currentGlobalCheckpoint the current global checkpoint known to the listener | ||
| * @param listener the listener | ||
| */ | ||
| synchronized void add(final long currentGlobalCheckpoint, final GlobalCheckpointListener listener) { | ||
| if (closed) { | ||
| executor.execute(() -> notifyListener(listener, UNASSIGNED_SEQ_NO, new IndexShardClosedException(shardId))); | ||
| return; | ||
| } | ||
| if (lastKnownGlobalCheckpoint > currentGlobalCheckpoint) { | ||
| // notify directly | ||
| executor.execute(() -> notifyListener(listener, lastKnownGlobalCheckpoint, null)); | ||
| return; | ||
| } else { | ||
| if (listeners == null) { | ||
| listeners = new ArrayList<>(); | ||
| } | ||
| listeners.add(listener); | ||
| } | ||
| } | ||
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| @Override | ||
| public synchronized void close() throws IOException { | ||
| closed = true; | ||
| notifyListeners(UNASSIGNED_SEQ_NO, new IndexShardClosedException(shardId)); | ||
| } | ||
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| synchronized int pendingListeners() { | ||
| return listeners == null ? 0 : listeners.size(); | ||
| } | ||
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| /** | ||
| * Invoke to notify all registered listeners of an updated global checkpoint. | ||
| * | ||
| * @param globalCheckpoint the updated global checkpoint | ||
| */ | ||
| synchronized void globalCheckpointUpdated(final long globalCheckpoint) { | ||
| assert globalCheckpoint >= NO_OPS_PERFORMED; | ||
| assert globalCheckpoint > lastKnownGlobalCheckpoint | ||
| : "updated global checkpoint [" + globalCheckpoint + "]" | ||
| + " is not more than the last known global checkpoint [" + lastKnownGlobalCheckpoint + "]"; | ||
| lastKnownGlobalCheckpoint = globalCheckpoint; | ||
|
Contributor
There was a problem hiding this comment. I think this has to be synchronized to avoid race conditions with add. Say an add method already sampled the I may be missing something here, but my point is that this is too complex IMO. I don't see why we can't just make this a simple fully synchronized method. The listeners are call on executor anyway. |
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| notifyListeners(globalCheckpoint, null); | ||
| } | ||
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| private void notifyListeners(final long globalCheckpoint, final IndexShardClosedException e) { | ||
|
Contributor
There was a problem hiding this comment. for simplicity, let's move this under the mutex everywhere (and add |
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| assert Thread.holdsLock(this); | ||
| assert (globalCheckpoint == UNASSIGNED_SEQ_NO && e != null) || (globalCheckpoint >= NO_OPS_PERFORMED && e == null); | ||
| if (listeners != null) { | ||
| // capture the current listeners | ||
| final List<GlobalCheckpointListener> currentListeners = listeners; | ||
| listeners = null; | ||
| if (currentListeners != null) { | ||
| executor.execute(() -> { | ||
| for (final GlobalCheckpointListener listener : currentListeners) { | ||
| notifyListener(listener, globalCheckpoint, e); | ||
| } | ||
| }); | ||
| } | ||
| } | ||
| } | ||
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| private void notifyListener(final GlobalCheckpointListener listener, final long globalCheckpoint, final IndexShardClosedException e) { | ||
| try { | ||
| listener.accept(globalCheckpoint, e); | ||
| } catch (final Exception caught) { | ||
| if (globalCheckpoint != UNASSIGNED_SEQ_NO) { | ||
| logger.warn( | ||
| new ParameterizedMessage( | ||
| "error notifying global checkpoint listener of updated global checkpoint [{}]", | ||
| globalCheckpoint), | ||
| caught); | ||
| } else { | ||
| logger.warn("error notifying global checkpoint listener of closed shard", caught); | ||
| } | ||
| } | ||
| } | ||
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| } | ||
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Nit: I wonder if we should have an onFailure method here for all kind of failures and send the IndexShardClosedException down that route. The down side is of course that people wouldn't be able to pass a method references, but the method won't need to start with if (e != null) etc.
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I prefer to use a functional interface for enabling the use of lambda expressions.