Created SettableListenableFuture with tests
A SettableListenableFuture implementation of Spring's ListenableFuture The class is inspired by Google Guava’s com.google.common.util.concurrent.SettableFuture, but this implementation uses ReentrantReadWriteLock and CountDownLatch internally to handle thread synchronization. Issue: SPR-11614
This commit is contained in:
Mattias Severson
committed by
Rossen Stoyanchev
Rossen Stoyanchev
parent
0dc6082b01
commit
38b525aa9e
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/*
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* Copyright 2002-2014 the original author or authors.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package org.springframework.util.concurrent;
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import org.springframework.util.Assert;
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import java.util.concurrent.CancellationException;
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import java.util.concurrent.CountDownLatch;
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import java.util.concurrent.ExecutionException;
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import java.util.concurrent.Future;
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import java.util.concurrent.TimeUnit;
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import java.util.concurrent.TimeoutException;
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import java.util.concurrent.locks.ReadWriteLock;
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import java.util.concurrent.locks.ReentrantReadWriteLock;
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/**
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* A {@link ListenableFuture} whose value can be set by the {@link #set(Object)} or
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* {@link #setException(Throwable)}. It may also be cancelled.
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*
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* <p>Inspired by {@code com.google.common.util.concurrent.SettableFuture}.
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*
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* @author Mattias Severson
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* @since 4.1
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*/
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public class SettableListenableFuture<T> implements ListenableFuture<T> {
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private final SettableFuture<T> settableFuture = new SettableFuture<T>();
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private final ListenableFutureCallbackRegistry<T> registry = new ListenableFutureCallbackRegistry<T>();
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/**
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* Set the value of this future. This method will return {@code true} if
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* the value was set successfully, or {@code false} if the future has already
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* been set or cancelled.
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*
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* @param value the value that will be set.
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* @return {@code true} if the value was successfully set, else {@code false}.
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*/
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public boolean set(T value) {
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boolean setValue = this.settableFuture.setValue(value);
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if (setValue) {
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this.registry.success(value);
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}
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return setValue;
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}
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/**
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* Set the exception of this future. This method will return {@code true} if
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* the exception was set successfully, or {@code false} if the future has already
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* been set or cancelled.
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* @param exception the value that will be set.
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* @return {@code true} if the exception was successfully set, else {@code false}.
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*/
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public boolean setException(Throwable exception) {
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Assert.notNull(exception, "exception must not be null");
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boolean setException = this.settableFuture.setThrowable(exception);
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if (setException) {
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this.registry.failure(exception);
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}
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return setException;
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}
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@Override
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public void addCallback(ListenableFutureCallback<? super T> callback) {
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this.registry.addCallback(callback);
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}
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@Override
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public boolean cancel(boolean mayInterruptIfRunning) {
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boolean cancelled = this.settableFuture.cancel(mayInterruptIfRunning);
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if (cancelled && mayInterruptIfRunning) {
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interruptTask();
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}
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return cancelled;
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}
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@Override
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public boolean isCancelled() {
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return this.settableFuture.isCancelled();
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}
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@Override
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public boolean isDone() {
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return this.settableFuture.isDone();
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}
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/**
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* Retrieve the value.
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* <p>Will return the value if it has been set by calling {@link #set(Object)}, throw
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* an {@link ExecutionException} if the {@link #setException(Throwable)} has been
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* called, throw a {@link CancellationException} if the future has been cancelled, or
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* throw an {@link IllegalStateException} if neither a value, nor an exception has
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* been set.
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* @return The value associated with this future.
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*/
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@Override
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public T get() throws InterruptedException, ExecutionException {
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return this.settableFuture.get();
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}
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/**
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* Retrieve the value.
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* <p>Will return the value if it has been by calling {@link #set(Object)}, throw an
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* {@link ExecutionException} if the {@link #setException(Throwable)}
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* has been called, throw a {@link java.util.concurrent.CancellationException} if the
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* future has been cancelled.
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* @param timeout the maximum time to wait.
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* @param unit the time unit of the timeout argument.
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* @return The value associated with this future.
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*/
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@Override
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public T get(long timeout, TimeUnit unit) throws InterruptedException, ExecutionException, TimeoutException {
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return this.settableFuture.get(timeout, unit);
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}
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/**
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* Subclasses can override this method to implement interruption of the future's
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* computation. The method is invoked automatically by a successful call to
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* {@link #cancel(boolean) cancel(true)}.
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*
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* <p>The default implementation does nothing.
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*/
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protected void interruptTask() {
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}
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/**
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* Helper class that keeps track of the state of this future.
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* @param <T> The type of value to be set.
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*/
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private static class SettableFuture<T> implements Future<T> {
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private final ReadWriteLock lock = new ReentrantReadWriteLock(true);
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private final CountDownLatch latch = new CountDownLatch(1);
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private T value;
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private Throwable throwable;
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private State state = State.INITIALIZED;
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@Override
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public T get() throws ExecutionException, InterruptedException {
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this.latch.await();
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this.lock.readLock().lock();
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try {
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return getValue();
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}
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finally {
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this.lock.readLock().unlock();
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}
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}
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@Override
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public T get(long timeout, TimeUnit unit) throws InterruptedException, ExecutionException, TimeoutException {
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if (this.latch.await(timeout, unit)) {
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this.lock.readLock().lock();
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try {
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return getValue();
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}
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finally {
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this.lock.readLock().unlock();
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}
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}
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else {
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throw new TimeoutException();
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}
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}
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private T getValue() throws ExecutionException {
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switch (this.state) {
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case COMPLETED:
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if (this.throwable != null) {
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throw new ExecutionException(this.throwable);
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}
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else {
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return this.value;
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}
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case CANCELLED:
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throw new CancellationException("Future has been cancelled.");
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default:
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throw new IllegalStateException("Invalid state: " + this.state);
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}
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}
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@Override
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public boolean isDone() {
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this.lock.readLock().lock();
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try {
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switch (this.state) {
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case COMPLETED:
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case CANCELLED:
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return true;
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default:
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return false;
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}
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}
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finally {
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this.lock.readLock().unlock();
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}
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}
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@Override
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public boolean cancel(boolean mayInterruptIfRunning) {
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this.lock.writeLock().lock();
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try {
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if (this.state.equals(State.INITIALIZED)) {
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this.state = State.CANCELLED;
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this.latch.countDown();
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return true;
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}
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}
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finally {
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this.lock.writeLock().unlock();
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}
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return false;
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}
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@Override
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public boolean isCancelled() {
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this.lock.readLock().lock();
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try {
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return this.state.equals(State.CANCELLED);
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}
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finally {
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this.lock.readLock().unlock();
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}
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}
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boolean setValue(T value) {
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this.lock.writeLock().lock();
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try {
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if (this.state.equals(State.INITIALIZED)) {
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this.value = value;
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this.state = State.COMPLETED;
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this.latch.countDown();
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return true;
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}
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}
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finally {
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this.lock.writeLock().unlock();
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}
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return false;
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}
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Throwable getThrowable() {
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return this.throwable;
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}
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boolean setThrowable(Throwable throwable) {
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this.lock.writeLock().lock();
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try {
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if (this.state.equals(State.INITIALIZED)) {
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this.throwable = throwable;
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this.state = State.COMPLETED;
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this.latch.countDown();
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return true;
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}
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}
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finally {
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this.lock.writeLock().unlock();
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}
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return false;
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}
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private enum State {INITIALIZED, COMPLETED, CANCELLED}
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}
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}
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