org.apache.flink.streaming.runtime.io.MultipleFuturesAvailabilityHelper Maven / Gradle / Ivy
/*
* 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.runtime.io;
import org.apache.flink.annotation.Internal;
import java.util.concurrent.CompletableFuture;
import static org.apache.flink.util.concurrent.FutureUtils.assertNoException;
/**
* This class is semi-thread safe. Only method {@link #notifyCompletion()} is allowed to be executed
* from an outside of the task thread.
*
* It solves a problem of a potential memory leak as described in FLINK-25728. In short we have
* to ensure, that if there is one input (future) that rarely (or never) completes, that such future
* would not prevent previously returned combined futures (like {@link
* CompletableFuture#anyOf(CompletableFuture[])} from being garbage collected. Additionally, we
* don't want to accumulate more and more completion stages on such rarely completed future, so we
* are registering {@link CompletableFuture#thenRun(Runnable)} only if it has not already been done.
*
*
Note {@link #resetToUnAvailable()} doesn't de register previously registered futures. If
* future was registered in the past, but for whatever reason now it is not, such future can still
* complete the newly created future.
*
*
It might be no longer needed after upgrading to JDK9
* (https://bugs.openjdk.java.net/browse/JDK-8160402).
*/
@Internal
public class MultipleFuturesAvailabilityHelper {
private final CompletableFuture[] futuresToCombine;
private volatile CompletableFuture availableFuture = new CompletableFuture<>();
public MultipleFuturesAvailabilityHelper(int size) {
futuresToCombine = new CompletableFuture[size];
}
/** @return combined future using anyOf logic */
public CompletableFuture getAvailableFuture() {
return availableFuture;
}
public void resetToUnAvailable() {
if (availableFuture.isDone()) {
availableFuture = new CompletableFuture<>();
}
}
private void notifyCompletion() {
availableFuture.complete(null);
}
/**
* Combine {@code availabilityFuture} using anyOf logic with other previously registered
* futures.
*/
public void anyOf(final int idx, CompletableFuture availabilityFuture) {
if (futuresToCombine[idx] == null || futuresToCombine[idx].isDone()) {
futuresToCombine[idx] = availabilityFuture;
assertNoException(availabilityFuture.thenRun(this::notifyCompletion));
}
}
}