org.apache.flink.runtime.state.gemini.engine.snapshot.SnapshotCompletableFuture Maven / Gradle / Ivy

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/*
 * 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.state.gemini.engine.snapshot;

import org.apache.flink.annotation.VisibleForTesting;
import org.apache.flink.util.Preconditions;

import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.CompletableFuture;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.atomic.AtomicBoolean;
import java.util.concurrent.atomic.AtomicInteger;

/**
 * An implementation of {@link CompletableFuture} for snapshot. This future
 * includes multiple stages for the async part of the snapshot , which will
 * be executed in the order they added. The number of running tasks will be
 * 0 when a stage finishes, and then the next stage will be started if needed.
 * The future will complete when all stages are finished or an exception
 * happened in any stage. All stages must be added to the future before start
 * via {@link #addSnapshotStage(SnapshotStage)}.
 */
public class SnapshotCompletableFuture extends CompletableFuture {

	private final AtomicInteger runningTasks;

	private final AtomicBoolean endSnapshot;

	private SnapshotManager.PendingSnapshot pendingSnapshot;

	/**
	 * Snapshot stages to run in order.
	 */
	private List snapshotStages;

	/**
	 * Index of next stage in the {@link #snapshotStages}.
	 */
	private AtomicInteger nextStageIndex;

	private ExecutorService snapshotExecutor;

	public SnapshotCompletableFuture(ExecutorService snapshotExecutor) {
		this.snapshotExecutor = snapshotExecutor;
		this.runningTasks = new AtomicInteger(0);
		this.endSnapshot = new AtomicBoolean(false);
		this.snapshotStages = new ArrayList<>();
		this.nextStageIndex = new AtomicInteger(0);
	}

	public void incRunningTask() {
		runningTasks.incrementAndGet();
	}

	public void decRunningTask() {
		int left = runningTasks.decrementAndGet();
		Preconditions.checkState(left >= 0, "Number of left running tasks can't be negative.");
		if (left == 0) {
			// if the future has been cancelled or complete with exception, just return
			if (isCancelled() || isCompletedExceptionally()) {
				return;
			}

			// all stages finish with no exception, and just complete the future
			if (nextStageIndex.get() >= snapshotStages.size()) {
				complete(true);
				return;
			}

			// there are stages to run
			incRunningTask();
			int index = nextStageIndex.getAndAdd(1);
			runStage(snapshotStages.get(index));
			// there is no code to execute after this decRunningTask, and it's safe
			// to call decRunningTask recursively
			decRunningTask();
		}
	}

	public void setPendingSnapshot(SnapshotManager.PendingSnapshot pendingSnapshot) {
		this.pendingSnapshot = pendingSnapshot;
	}

	public SnapshotManager.PendingSnapshot getPendingSnapshot() {
		return this.pendingSnapshot;
	}

	public boolean isEndSnapshot() {
		return endSnapshot.get();
	}

	public void setEndSnapshot() {
		endSnapshot.set(true);
	}

	public void addSnapshotStage(SnapshotStage snapshotStage) {
		snapshotStages.add(snapshotStage);
	}

	public SnapshotStage getSnapshotStage(int index) {
		return index >= 0 && index < snapshotStages.size() ? snapshotStages.get(index) : null;
	}

	@VisibleForTesting
	List getSnapshotStageList() {
		return snapshotStages;
	}

	@VisibleForTesting
	int getNextStateIndex() {
		return nextStageIndex.get();
	}

	@VisibleForTesting
	int getRunningTasks() {
		return runningTasks.get();
	}

	private void runStage(SnapshotStage snapshotStage) {
		if (snapshotStage.isAsync()) {
			runAsyncStage(snapshotStage);
		} else {
			runSyncStage(snapshotStage);
		}
	}

	private void runSyncStage(SnapshotStage snapshotStage) {
		incRunningTask();
		try {
			snapshotStage.run();
		} catch (Exception e) {
			setEndSnapshot();
			completeExceptionally(e);
		} finally {
			decRunningTask();
		}
	}

	private void runAsyncStage(SnapshotStage snapshotStage) {
		incRunningTask();
		snapshotExecutor.submit(() -> {
			try {
				snapshotStage.run();
			} catch (Exception e) {
				setEndSnapshot();
				completeExceptionally(e);
			} finally {
				decRunningTask();
			}
		});
	}
 }