/*
* 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.geode.internal.util.concurrent;
import java.util.concurrent.CancellationException;
import java.util.concurrent.Future;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.TimeoutException;
import org.apache.geode.CancelCriterion;
import org.apache.geode.internal.i18n.LocalizedStrings;
/**
* Represents a Future without a background thread. Instead of a Runnable that will set the value,
* some known thread will set the value in the future by calling the set method. Also supports the
* case where the "future is now" when the value is known at construction time.
*
* Cancelling this future sets the state to cancelled and causes threads waiting on get to proceed
* with a CancellationException.
*
*/
public class FutureResult implements Future {
private final StoppableCountDownLatch latch;
private Object value;
private volatile boolean isCancelled = false;
/** Creates a new instance of FutureResult */
public FutureResult(CancelCriterion crit) {
this.latch = new StoppableCountDownLatch(crit, 1);
}
/** Creates a new instance of FutureResult with the value available immediately */
public FutureResult(Object value) {
this.value = value;
this.latch = null;
}
public boolean cancel(boolean mayInterruptIfRunning) {
if (this.isCancelled)
return false; // already cancelled
this.isCancelled = true;
if (this.latch != null)
this.latch.countDown();
return true;
}
public Object get() throws InterruptedException {
if (Thread.interrupted())
throw new InterruptedException(); // check in case latch is null
if (this.isCancelled) {
throw new CancellationException(
LocalizedStrings.FutureResult_FUTURE_WAS_CANCELLED.toLocalizedString());
}
if (this.latch != null)
this.latch.await();
if (this.isCancelled) {
throw new CancellationException(
LocalizedStrings.FutureResult_FUTURE_WAS_CANCELLED.toLocalizedString());
}
return this.value;
}
public Object get(long timeout, TimeUnit unit) throws InterruptedException, TimeoutException {
if (Thread.interrupted())
throw new InterruptedException(); // check in case latch is null
if (this.isCancelled) {
throw new CancellationException(
LocalizedStrings.FutureResult_FUTURE_WAS_CANCELLED.toLocalizedString());
}
if (this.latch != null) {
if (!this.latch.await(unit.toMillis(timeout))) {
throw new TimeoutException();
}
}
return this.value;
}
public boolean isCancelled() {
return this.isCancelled;
}
public boolean isDone() {
return this.latch == null || this.latch.getCount() == 0L || this.isCancelled;
}
public void set(Object value) {
this.value = value;
if (this.latch != null)
this.latch.countDown();
}
}