org.apache.flink.streaming.runtime.io

Class MultipleFuturesAvailabilityHelper

java.lang.Object

org.apache.flink.streaming.runtime.io.MultipleFuturesAvailabilityHelper

@Internal
public class MultipleFuturesAvailabilityHelper
extends Object

This class is semi-thread safe. Only method 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 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 CompletableFuture.thenRun(Runnable) only if it has not already been done.

Note 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).

Constructor Summary

Constructors

Constructor and Description
MultipleFuturesAvailabilityHelper(int size)

Method Summary

Modifier and Type	Method and Description
void	anyOf(int idx, CompletableFuture<?> availabilityFuture) Combine availabilityFuture using anyOf logic with other previously registered futures.
CompletableFuture<?>	getAvailableFuture()
void	resetToUnAvailable()

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

MultipleFuturesAvailabilityHelper

public MultipleFuturesAvailabilityHelper(int size)

Method Detail

getAvailableFuture

public CompletableFuture<?> getAvailableFuture()

Returns:

combined future using anyOf logic

resetToUnAvailable

public void resetToUnAvailable()

anyOf

public void anyOf(int idx,
                  CompletableFuture<?> availabilityFuture)

Combine availabilityFuture using anyOf logic with other previously registered futures.