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DeferredFutureTask.java
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DeferredFutureTask.java
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/*
* Copyright 2013-2017 Ray Tsang
*
* Licensed 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.jdeferred;
import java.util.concurrent.Callable;
import java.util.concurrent.CancellationException;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.FutureTask;
import org.jdeferred.DeferredManager.StartPolicy;
import org.jdeferred.impl.DeferredObject;
/**
* FutureTask can wrap around {@link Callable} and {@link Runnable}.
* In these two cases, a new {@link Deferred} object will be created.
* This class will override {@link FutureTask#done} to trigger the
* appropriate {@link Deferred} actions.
*
* Note, type used for {@link Deferred#reject(Object)} is always {@link Throwable}.
*
* When the task is completed successfully, {@link Deferred#resolve(Object)} will be called.
* When a task is canceled, {@link Deferred#reject(Object)} will be called with an instance of {@link CancellationException}
* If any Exception occured, {@link Deferred#reject(Object)} will be called with the Exception instance.
*
* @author Ray Tsang
*
* @param <D> Type used for {@link Deferred#resolve(Object)}
* @param <P> Type used for {@link Deferred#notify(Object)}
*/
public class DeferredFutureTask<D, P> extends FutureTask<D> {
protected final Deferred<D, Throwable, P> deferred;
protected final StartPolicy startPolicy;
private Object taskDelegate;
private CancellationHandler cancellationHandler;
/**
* Creates a new {@code DeferredFutureTask} with the given task.
* The given task may implement the {@code CancellationHandler} interface.
*
* @param task the task to be executed. Must not be null.
*/
public DeferredFutureTask(Callable<D> task) {
this(task, null);
}
/**
* Creates a new {@code DeferredFutureTask} with the given task.
* The given task may implement the {@code CancellationHandler} interface.
*
* @param task the task to be executed. Must not be null.
*/
public DeferredFutureTask(Runnable task) {
this(task, null);
}
/**
* Creates a new {@code DeferredFutureTask} with the given task.
* The given task may implement the {@code CancellationHandler} interface.
*
* @param task the task to be executed. Must not be null.
*/
public DeferredFutureTask(DeferredCallable<D, P> task) {
this(task, null);
}
/**
* Creates a new {@code DeferredFutureTask} with the given task.
* The given task may implement the {@code CancellationHandler} interface.
*
* @param task the task to be executed. Must not be null.
*/
public DeferredFutureTask(DeferredRunnable<P> task) {
this(task, null);
}
/**
* Creates a new {@code DeferredFutureTask} with the given task and a explicit {@code CancellationHandler}
* The given {@code cancellationHandler} has precedence over the given task if the task implements the {@code CancellationHandler} interface.
*
* @param task the task to be executed. Must not be null.
* @param cancellationHandler the {@code CancellationHandler} to invoke during onCancel. May be null.
*/
public DeferredFutureTask(Callable<D> task, CancellationHandler cancellationHandler) {
super(task);
this.taskDelegate = task;
this.cancellationHandler = cancellationHandler;
this.deferred = new DeferredObject<D, Throwable, P>();
this.startPolicy = StartPolicy.DEFAULT;
}
/**
* Creates a new {@code DeferredFutureTask} with the given task and a explicit {@code CancellationHandler}
* The given {@code cancellationHandler} has precedence over the given task if the task implements the {@code CancellationHandler} interface.
*
* @param task the task to be executed. Must not be null.
* @param cancellationHandler the {@code CancellationHandler} to invoke during onCancel. May be null.
*/
public DeferredFutureTask(Runnable task, CancellationHandler cancellationHandler) {
super(task, null);
this.taskDelegate = task;
this.cancellationHandler = cancellationHandler;
this.deferred = new DeferredObject<D, Throwable, P>();
this.startPolicy = StartPolicy.DEFAULT;
}
/**
* Creates a new {@code DeferredFutureTask} with the given task and a explicit {@code CancellationHandler}
* The given {@code cancellationHandler} has precedence over the given task if the task implements the {@code CancellationHandler} interface.
*
* @param task the task to be executed. Must not be null.
* @param cancellationHandler the {@code CancellationHandler} to invoke during onCancel. May be null.
*/
public DeferredFutureTask(DeferredCallable<D, P> task, CancellationHandler cancellationHandler) {
super(task);
this.taskDelegate = task;
this.cancellationHandler = cancellationHandler;
this.deferred = task.getDeferred();
this.startPolicy = task.getStartPolicy();
}
/**
* Creates a new {@code DeferredFutureTask} with the given task and a explicit {@code CancellationHandler}
* The given {@code cancellationHandler} has precedence over the given task if the task implements the {@code CancellationHandler} interface.
*
* @param task the task to be executed. Must not be null.
* @param cancellationHandler the {@code CancellationHandler} to invoke during onCancel. May be null.
*/
@SuppressWarnings("unchecked")
public DeferredFutureTask(DeferredRunnable<P> task, CancellationHandler cancellationHandler) {
super(task, null);
this.taskDelegate = task;
this.cancellationHandler = cancellationHandler;
this.deferred = (Deferred<D, Throwable, P>) task.getDeferred();
this.startPolicy = task.getStartPolicy();
}
public Promise<D, Throwable, P> promise() {
return deferred.promise();
}
@Override
protected void done() {
if (isCancelled()) {
deferred.reject(new CancellationException());
cleanup();
return;
}
try {
deferred.resolve(get());
} catch (InterruptedException e) {
// TODO: should cleanup be called here?
cleanup();
} catch (ExecutionException e) {
try {
deferred.reject(e.getCause());
} finally {
cleanup();
}
} catch (Throwable t) {
// TODO: this exception will be lost. Handle it via global ExceptionHandler?
t.printStackTrace();
}
}
/**
* Performs resource cleanup upon interruption or cancellation of the underlying task.
* This method gives precedence to {@code cancellationHandler} it not null, otherwise
* it invokes the underlying task's {@code onCancel()} if it implements the {@code CancellationHandler} interface.
*/
protected void cleanup() {
// TODO: handle any exceptions that may occur during cleanup via global ExceptionHandler?
if (cancellationHandler != null) {
cancellationHandler.onCancel();
} else if (taskDelegate instanceof CancellationHandler) {
((CancellationHandler) taskDelegate).onCancel();
}
}
public StartPolicy getStartPolicy() {
return startPolicy;
}
}