[GitHub] [flink] TsReaper commented on a change in pull request #12073: [FLINK-17735][streaming] Add specialized collecting iterator

[GitBox <gi...@apache.org>]

TsReaper commented on a change in pull request #12073:
URL: https://github.com/apache/flink/pull/12073#discussion_r426216888



##########
File path: flink-streaming-java/src/main/java/org/apache/flink/streaming/api/operators/collect/CollectResultFetcher.java
##########
@@ -0,0 +1,343 @@
+/*
+ * 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.streaming.api.operators.collect;
+
+import org.apache.flink.annotation.VisibleForTesting;
+import org.apache.flink.api.common.JobExecutionResult;
+import org.apache.flink.api.common.JobStatus;
+import org.apache.flink.api.common.accumulators.SerializedListAccumulator;
+import org.apache.flink.api.common.typeutils.TypeSerializer;
+import org.apache.flink.api.common.typeutils.base.array.BytePrimitiveArraySerializer;
+import org.apache.flink.api.java.tuple.Tuple2;
+import org.apache.flink.core.execution.JobClient;
+import org.apache.flink.runtime.jobgraph.OperatorID;
+import org.apache.flink.runtime.operators.coordination.CoordinationRequestGateway;
+import org.apache.flink.util.Preconditions;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import javax.annotation.Nullable;
+
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.LinkedList;
+import java.util.List;
+import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.ExecutionException;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.TimeoutException;
+
+/**
+ * A fetcher which fetches query results from sink and provides exactly-once semantics.
+ */
+public class CollectResultFetcher<T> {
+
+	private static final int DEFAULT_RETRY_MILLIS = 100;
+	private static final long DEFAULT_ACCUMULATOR_GET_MILLIS = 10000;
+
+	private static final Logger LOG = LoggerFactory.getLogger(CollectResultFetcher.class);
+
+	private final CompletableFuture<OperatorID> operatorIdFuture;
+	private final String accumulatorName;
+	private final int retryMillis;
+
+	private ResultBuffer buffer;
+
+	private JobClient jobClient;
+	private boolean terminated;
+	private boolean closed;
+
+	public CollectResultFetcher(
+			CompletableFuture<OperatorID> operatorIdFuture,
+			TypeSerializer<T> serializer,
+			String accumulatorName) {
+		this(
+			operatorIdFuture,
+			serializer,
+			accumulatorName,
+			DEFAULT_RETRY_MILLIS);
+	}
+
+	@VisibleForTesting
+	public CollectResultFetcher(
+			CompletableFuture<OperatorID> operatorIdFuture,
+			TypeSerializer<T> serializer,
+			String accumulatorName,
+			int retryMillis) {
+		this.operatorIdFuture = operatorIdFuture;
+		this.accumulatorName = accumulatorName;
+		this.retryMillis = retryMillis;
+
+		this.buffer = new ResultBuffer(serializer);
+
+		this.terminated = false;
+	}
+
+	public void setJobClient(JobClient jobClient) {
+		Preconditions.checkArgument(
+			jobClient instanceof CoordinationRequestGateway,
+			"Job client must be a CoordinationRequestGateway. This is a bug.");
+		this.jobClient = jobClient;
+	}
+
+	@SuppressWarnings("unchecked")
+	public T next() {
+		if (closed) {
+			return null;
+		}
+
+		T res = buffer.next();
+		if (res != null) {
+			// we still have user-visible results, just use them
+			return res;
+		} else if (terminated) {
+			// no user-visible results, but job has terminated, we have to return
+			return null;
+		}
+
+		// we're going to fetch some more
+		while (true) {
+			if (isJobTerminated()) {
+				// job terminated, read results from accumulator
+				terminated = true;
+				Tuple2<Long, CollectCoordinationResponse> accResults = getAccumulatorResults();
+				if (accResults != null) {
+					buffer.dealWithResponse(accResults.f1, accResults.f0);
+				}
+				buffer.complete();
+			} else {
+				// job still running, try to fetch some results
+				CollectCoordinationResponse<T> response;
+				try {
+					response = sendRequest(buffer.version, buffer.offset);
+				} catch (Exception e) {
+					LOG.warn("An exception occurs when fetching query results", e);
+					sleepBeforeRetry();
+					continue;
+				}
+				buffer.dealWithResponse(response);
+			}
+
+			// try to return results after fetching
+			res = buffer.next();
+			if (res != null) {
+				// ok, we have results this time
+				return res;
+			} else if (terminated) {
+				// still no results, but job has terminated, we have to return
+				return null;
+			} else {
+				// still no results, but job is still running, retry
+				sleepBeforeRetry();
+			}
+		}
+	}
+
+	public void close() {
+		if (closed) {
+			return;
+		}
+
+		cancelJob();
+		closed = true;
+	}
+
+	@Override
+	protected void finalize() throws Throwable {
+		// in case that user neither reads all data nor closes the iterator
+		close();
+	}
+
+	@SuppressWarnings("unchecked")
+	private CollectCoordinationResponse<T> sendRequest(
+			String version,
+			long offset) throws InterruptedException, ExecutionException {
+		checkJobClientConfigured();
+		CoordinationRequestGateway gateway = (CoordinationRequestGateway) jobClient;
+
+		OperatorID operatorId = operatorIdFuture.getNow(null);
+		Preconditions.checkNotNull(operatorId, "Unknown operator ID. This is a bug.");
+
+		CollectCoordinationRequest request = new CollectCoordinationRequest(version, offset);
+		return (CollectCoordinationResponse) gateway.sendCoordinationRequest(operatorId, request).get();
+	}
+
+	@Nullable
+	private Tuple2<Long, CollectCoordinationResponse> getAccumulatorResults() {
+		checkJobClientConfigured();
+
+		JobExecutionResult executionResult;
+		try {
+			// this timeout is sort of hack, see comments in isJobTerminated for explanation
+			executionResult = jobClient.getJobExecutionResult(getClass().getClassLoader()).get(
+				DEFAULT_ACCUMULATOR_GET_MILLIS, TimeUnit.MILLISECONDS);
+		} catch (InterruptedException | ExecutionException | TimeoutException e) {
+			throw new RuntimeException("Failed to fetch job execution result", e);
+		}
+
+		ArrayList<byte[]> accResults = executionResult.getAccumulatorResult(accumulatorName);
+		if (accResults == null) {
+			// job terminates abnormally
+			return null;
+		}
+
+		try {
+			List<byte[]> serializedResults =
+				SerializedListAccumulator.deserializeList(accResults, BytePrimitiveArraySerializer.INSTANCE);
+			byte[] serializedResult = serializedResults.get(0);
+			return CollectSinkFunction.deserializeAccumulatorResult(serializedResult);
+		} catch (ClassNotFoundException | IOException e) {
+			// this is impossible
+			throw new RuntimeException("Failed to deserialize accumulator results", e);
+		}
+	}
+
+	private boolean isJobTerminated() {
+		checkJobClientConfigured();
+
+		try {
+			JobStatus status = jobClient.getJobStatus().get();
+			return status.isGloballyTerminalState();
+		} catch (Exception e) {
+			// TODO
+			//  This is sort of hack.
+			//  Currently different execution environment will have different behaviors
+			//  when fetching a finished job status.
+			//  For example, standalone session cluster will return a normal FINISHED,
+			//  while mini cluster will throw IllegalStateException,
+			//  and yarn per job will throw ApplicationNotFoundException.
+			//  We have to assume that job has finished in this case.
+			//  Change this when these behaviors are unified.
+			LOG.warn("Failed to get job status so we assume that the job has terminated. Some data might be lost.", e);
+			return true;
+		}
+	}
+
+	private void cancelJob() {
+		checkJobClientConfigured();
+
+		if (!isJobTerminated()) {
+			jobClient.cancel();
+		}
+	}
+
+	private void sleepBeforeRetry() {
+		if (retryMillis <= 0) {
+			return;
+		}
+
+		try {
+			// TODO a more proper retry strategy?
+			Thread.sleep(retryMillis);
+		} catch (InterruptedException e) {
+			LOG.warn("Interrupted when sleeping before a retry", e);
+		}
+	}
+
+	private void checkJobClientConfigured() {
+		Preconditions.checkNotNull(jobClient, "Job client must be configured before first use.");
+	}
+
+	private class ResultBuffer {
+
+		private static final String INIT_VERSION = "";
+
+		private final LinkedList<T> buffer;
+		private final TypeSerializer<T> serializer;
+
+		private String version;
+		private long offset;
+		private long lastCheckpointedOffset;
+		private long userHead;
+		private long userTail;
+
+		private ResultBuffer(TypeSerializer<T> serializer) {
+			this.buffer = new LinkedList<>();
+			this.serializer = serializer;
+
+			this.version = INIT_VERSION;
+			this.offset = 0;
+			this.lastCheckpointedOffset = 0;
+			this.userHead = 0;
+			this.userTail = 0;
+		}
+
+		private T next() {
+			if (userHead == userTail) {
+				return null;
+			}
+			T ret = buffer.removeFirst();
+			userHead++;
+
+			sanityCheck();
+			return ret;
+		}
+
+		private void dealWithResponse(CollectCoordinationResponse<T> response) {
+			dealWithResponse(response, offset);
+		}
+
+		private void dealWithResponse(CollectCoordinationResponse<T> response, long responseOffset) {
+			String responseVersion = response.getVersion();
+			long responseLastCheckpointedOffset = response.getLastCheckpointedOffset();
+			List<T> results;
+			try {
+				results = response.getResults(serializer);
+			} catch (IOException e) {
+				LOG.warn("An exception occurs when deserializing query results. Some results might be lost.", e);
+				results = Collections.emptyList();
+			}
+
+			if (responseLastCheckpointedOffset > lastCheckpointedOffset) {

Review comment:
       It is impossible for `responseLastCheckpointedOffset` to be smaller than `lastCheckpointedOffset`, offsets are always non-decreasing.




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