zhijiangW commented on a change in pull request #11515: [FLINK-16744][task] implement channel state persistence for unaligned checkpoints URL: https://github.com/apache/flink/pull/11515#discussion_r402045285
########## File path: flink-runtime/src/main/java/org/apache/flink/runtime/checkpoint/channel/ChannelStateWriterImpl.java ########## @@ -0,0 +1,225 @@ +/* + * Licensed to the Apache Software Foundation (ASF) under one or more + * contributor license agreements. See the NOTICE file distributed with + * this work for additional information regarding copyright ownership. + * The ASF 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. + */ + +package org.apache.flink.runtime.checkpoint.channel; + +import org.apache.flink.annotation.Internal; +import org.apache.flink.runtime.checkpoint.CheckpointOptions; +import org.apache.flink.runtime.io.network.buffer.Buffer; +import org.apache.flink.runtime.state.CheckpointStorageWorkerView; +import org.apache.flink.runtime.state.CheckpointStreamFactory; +import org.apache.flink.util.Preconditions; + +import org.slf4j.Logger; +import org.slf4j.LoggerFactory; + +import javax.annotation.concurrent.ThreadSafe; + +import java.util.Map; +import java.util.concurrent.ArrayBlockingQueue; +import java.util.concurrent.BlockingQueue; +import java.util.concurrent.ConcurrentHashMap; + +import static org.apache.flink.runtime.checkpoint.channel.ChannelStateWriteRequest.completeInput; +import static org.apache.flink.runtime.checkpoint.channel.ChannelStateWriteRequest.completeOutput; +import static org.apache.flink.runtime.checkpoint.channel.ChannelStateWriteRequest.write; + +/** + * {@link ChannelStateWriter} implemented using + * {@link CheckpointStreamFactory.CheckpointStateOutputStream CheckpointStateOutputStreams}. Internally, it has + * <ul> + * <li>one stream per checkpoint; having multiple streams would mean more files written and more connections opened + * (and more latency on restore)</li> + * <li>one thread; having multiple threads means more connections, couples with the implementation and increases complexity</li> + * </ul> + */ +@Internal +@ThreadSafe +public class ChannelStateWriterImpl implements ChannelStateWriter { + + private static final Logger LOG = LoggerFactory.getLogger(ChannelStateWriterImpl.class); + private static final int DEFAULT_HANDOVER_CAPACITY = 10; + private static final int DEFAULT_MAX_CHECKPOINTS = 5; // currently, only single in-flight checkpoint is supported + + private class ProcessRequestsLoop implements Runnable { + private final ChannelStateWriteRequestProcessor requestProcessor; + + private ProcessRequestsLoop(int maxCheckpoints, CheckpointStorageWorkerView streamFactoryFactory, ChannelStateSerializer serializer) { + this.requestProcessor = new ChannelStateWriteRequestProcessor(maxCheckpoints, streamFactoryFactory, serializer); + } + + @Override + public void run() { + try { + loop(); + } catch (Exception ex) { + thrown = ex; + } finally { + handover.clear(); + requestProcessor.cleanup(thrown != null ? thrown : new RuntimeException("loop terminated, isRunning: " + isRunning)); + } + LOG.debug("loop terminated"); + } + + private void loop() throws Exception { + while (isRunning || !handover.isEmpty()) { + try { + requestProcessor.processRequest(handover.take()); + } catch (InterruptedException e) { + if (isRunning || !handover.isEmpty()) { + LOG.info("interrupted while waiting for an item (continue waiting)", e); + } else { + Thread.currentThread().interrupt(); + return; + } + } + } + } + } + + private final Thread asyncWriter; + private final BlockingQueue<ChannelStateWriteRequest> handover; + private final Map<Long, ChannelStateWriteResult> results; + private final int maxCheckpoints; + private volatile boolean isRunning; + private volatile Exception thrown; + + public ChannelStateWriterImpl(CheckpointStorageWorkerView streamFactoryFactory) { + this(streamFactoryFactory, DEFAULT_MAX_CHECKPOINTS); + } + + /** + * Creates a {@link ChannelStateWriterImpl} with {@link #DEFAULT_MAX_CHECKPOINTS} as {@link #maxCheckpoints}. + */ + ChannelStateWriterImpl(CheckpointStorageWorkerView streamFactoryFactory, int maxCheckpoints) { + this(streamFactoryFactory, DEFAULT_HANDOVER_CAPACITY, new ChannelStateSerializerImpl(), maxCheckpoints); + } + + /** + * Creates a {@link ChannelStateWriterImpl}. + * + * @param maxCheckpoints maximum number of checkpoints to be written currently or finished but not taken yet. + */ + ChannelStateWriterImpl( + CheckpointStorageWorkerView streamFactory, + int handoverCapacity, + ChannelStateSerializer serializer, + int maxCheckpoints) { + this.handover = new ArrayBlockingQueue<>(handoverCapacity); + this.results = new ConcurrentHashMap<>(maxCheckpoints); + this.maxCheckpoints = maxCheckpoints; + this.asyncWriter = new Thread(new ProcessRequestsLoop(maxCheckpoints, streamFactory, serializer)); + this.isRunning = true; + } + + @Override + public void start(long checkpointId, CheckpointOptions checkpointOptions) { + LOG.debug("start checkpoint {} ({})", checkpointId, checkpointOptions); + rethrow(); + Preconditions.checkState(isRunning && asyncWriter.isAlive(), "not running"); + ChannelStateWriteResult result = new ChannelStateWriteResult(); + ChannelStateWriteResult put = results.computeIfAbsent(checkpointId, id -> { + Preconditions.checkArgument(results.size() < maxCheckpoints, "results.size() > maxCheckpoints", results.size(), maxCheckpoints); + enqueue(new CheckpointStartRequest(checkpointId, result, checkpointOptions.getTargetLocation())); + return result; + }); + Preconditions.checkArgument(put == result, "result future already present for checkpoint id: " + checkpointId); + } + + @Override + public void addInputData(long checkpointId, InputChannelInfo info, int startSeqNum, Buffer... data) { + LOG.debug("add input data, checkpoint id: {}, channel: {}, startSeqNum: {}, num buffers: {}", + checkpointId, info, startSeqNum, data == null ? 0 : data.length); + enqueue(write(checkpointId, info, checkBufferType(data))); + } + + @Override + public void addOutputData(long checkpointId, ResultSubpartitionInfo info, int startSeqNum, Buffer... data) { + LOG.debug("add output data, checkpoint id: {}, channel: {}, startSeqNum: {}, num buffers: {}", + checkpointId, info, startSeqNum, data == null ? 0 : data.length); + enqueue(write(checkpointId, info, checkBufferType(data))); + } + + @Override + public void finishInput(long checkpointId) { + LOG.debug("finish input data, checkpoint id: {}", checkpointId); + enqueue(completeInput(checkpointId)); + } + + @Override + public void finishOutput(long checkpointId) { + LOG.debug("finish output data, checkpoint id: {}", checkpointId); + enqueue(completeOutput(checkpointId)); + } + + @Override + public ChannelStateWriteResult getWriteResult(long checkpointId) { + LOG.debug("requested write result, checkpoint id: {}", checkpointId); + ChannelStateWriteResult result = results.remove(checkpointId); + Preconditions.checkArgument(result != null, "channel state write result not found for checkpoint id " + checkpointId); + return result; + } + + public void open() { + Preconditions.checkState(isRunning); + asyncWriter.start(); + } + + @Override + public void close() { + isRunning = false; + results.clear(); + asyncWriter.interrupt(); + while (asyncWriter.isAlive()) { + try { + asyncWriter.join(); + } catch (InterruptedException e) { + if (!asyncWriter.isAlive()) { + Thread.currentThread().interrupt(); + } + LOG.debug("interrupted while waiting for the writer thread to die", e); + } + } + rethrow(); + } + + private void enqueue(ChannelStateWriteRequest request) { + rethrow(); + Preconditions.checkState(isRunning); + try { + handover.put(request); + } catch (InterruptedException e) { + throw new RuntimeException("Interrupted while trying to add new handover request", e); + } + } + + private void rethrow() { + if (thrown != null) { + throw new RuntimeException(thrown); // wrap to record current stack-trace + } + } + + private static Buffer[] checkBufferType(Buffer... data) { Review comment: Give some javadoc to explain why we do not support event data? 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