/*
* Mojito Distributed Hash Table (Mojito DHT)
* Copyright (C) 2006-2007 LimeWire LLC
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
*/
package org.limewire.mojito.concurrent;
import java.util.Collections;
import java.util.LinkedHashSet;
import java.util.Set;
import java.util.concurrent.CancellationException;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ScheduledFuture;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.TimeoutException;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.limewire.concurrent.OnewayExchanger;
import org.limewire.mojito.Context;
import org.limewire.mojito.exceptions.LockTimeoutException;
/**
* A cancellable asynchronous DHT task. This class provides a base implementation
* of {@link DHTFuture}, with methods to start and cancel a DHT task, query to see
* if the task is complete, and retrieve the result of the task. The result can only
* be retrieved when the computation has completed; the <code>get</code> method
* will block if the task has not yet completed. Once the task has completed,
* the computation cannot be restarted or cancelled.
*
* {@see java.util.concurrent.FutureTask}
*/
public class DHTFutureTask<T> implements Runnable, DHTFuture<T>, Cancellable {
private static final Log LOG = LogFactory.getLog(DHTFutureTask.class);
private final OnewayExchanger<T, ExecutionException> exchanger;
private final Set<DHTFutureListener<T>> listeners
= Collections.synchronizedSet(new LinkedHashSet<DHTFutureListener<T>>());
private final Context context;
private final DHTTask<T> task;
/**
* true if starting or started.
* LOCKING: exchanger
*/
private boolean taskIsActive;
private ScheduledFuture<?> watchdog = null;
public DHTFutureTask(final Context context, DHTTask<T> task) {
this.task = task;
this.context = context;
exchanger = new OnewayExchanger<T, ExecutionException>(true) {
@Override
public synchronized void setValue(T value) {
if (!isDone()) {
super.setValue(value);
killWatchdog();
internalDone();
}
}
@Override
public synchronized void setException(ExecutionException exception) {
if (!isDone()) {
super.setException(exception);
killWatchdog();
internalDone();
}
}
@Override
public synchronized boolean cancel() {
if (super.cancel()) {
killWatchdog();
internalDone();
return true;
}
return false;
}
};
}
public void run() {
try {
synchronized(exchanger) {
if (isDone()) {
return;
}
taskIsActive = true;
}
task.start(exchanger);
synchronized (exchanger) {
if (!isDone()) {
initWatchdog();
}
}
} catch (Throwable t) {
exchanger.setException(new ExecutionException(t));
}
}
/**
* Starts the Watchdog
*/
private void initWatchdog() {
Runnable r = new Runnable() {
public void run() {
boolean timeout = false;
synchronized (exchanger) {
if (!isDone()) {
if (LOG.isDebugEnabled()) {
LOG.debug("Watchdog is canceling " + task);
}
timeout = taskIsActive;
exchanger.setException(
new ExecutionException(
new LockTimeoutException(task.toString())));
}
}
if (timeout) {
task.cancel();
}
}
};
watchdog = context.getDHTExecutorService().schedule(
r, task.getWaitOnLockTimeout(), TimeUnit.MILLISECONDS);
}
/**
* Stops the Watchdog
*/
private void killWatchdog() {
synchronized (exchanger) {
if (watchdog != null) {
watchdog.cancel(true);
watchdog = null;
}
}
}
/**
* Protected method invoked when this task transitions to state isDone
* (whether normally or via cancellation). The default implementation
* does nothing. Subclasses may override this method to invoke completion
* callbacks or perform bookkeeping. Note that you can query status
* inside the implementation of this method to determine whether this
* task has been cancelled.
*/
protected void done() {
}
/**
* Calls done() and notifies all DHTFutureListeners
*/
private void internalDone() {
Runnable task = new Runnable() {
public void run() {
done();
// Notify the listeners on a different Thread
try {
T value = exchanger.get();
fireFutureResult(value);
} catch (ExecutionException e) {
fireExecutionException(e);
} catch (CancellationException e) {
fireCancellationException(e);
} catch (InterruptedException e) {
fireInterruptedException(e);
}
}
};
context.getDHTExecutorService().execute(task);
}
/*
* (non-Javadoc)
* @see org.limewire.mojito.concurrent.DHTFuture#addDHTFutureListener(org.limewire.mojito.concurrent.DHTFutureListener)
*/
public void addDHTFutureListener(final DHTFutureListener<T> listener) {
if (listener == null) {
throw new NullPointerException("DHTFutureListener is null");
}
boolean done = false;
synchronized (exchanger) {
done = isDone();
if (!done) {
listeners.add(listener);
}
}
if (done) {
Runnable r = new Runnable() {
public void run() {
try {
T value = exchanger.get();
listener.handleFutureSuccess(value);
} catch (ExecutionException e) {
listener.handleExecutionException(e);
} catch (CancellationException e) {
listener.handleCancellationException(e);
} catch (InterruptedException e) {
listener.handleInterruptedException(e);
}
}
};
context.getDHTExecutorService().execute(r);
}
}
/*
* (non-Javadoc)
* @see java.util.concurrent.Future#cancel(boolean)
*/
public boolean cancel(boolean mayInterruptIfRunning) {
boolean cancelTask = false;
synchronized (exchanger) {
if (!isDone()) {
if (!taskIsActive || mayInterruptIfRunning) {
exchanger.cancel();
cancelTask = taskIsActive;
}
}
}
if (cancelTask) {
task.cancel();
}
return cancelTask;
}
/*
* (non-Javadoc)
* @see java.util.concurrent.Future#isCancelled()
*/
public final boolean isCancelled() {
return exchanger.isCancelled();
}
/*
* (non-Javadoc)
* @see java.util.concurrent.Future#isDone()
*/
public final boolean isDone() {
return exchanger.isDone();
}
/*
* (non-Javadoc)
* @see java.util.concurrent.Future#get()
*/
public T get() throws InterruptedException, ExecutionException {
BlockingDHTFutureListener<T> listener = new BlockingDHTFutureListener<T>();
addDHTFutureListener(listener);
return listener.get();
}
/*
* (non-Javadoc)
* @see java.util.concurrent.Future#get(long, java.util.concurrent.TimeUnit)
*/
public T get(long timeout, TimeUnit unit)
throws InterruptedException, ExecutionException, TimeoutException {
BlockingDHTFutureListener<T> listener = new BlockingDHTFutureListener<T>();
addDHTFutureListener(listener);
return listener.get(timeout, unit);
}
/**
* Returns a copy of all listeners as an Array
*/
@SuppressWarnings("unchecked")
private DHTFutureListener<T>[] listeners() {
synchronized (listeners) {
return listeners.toArray(new DHTFutureListener[0]);
}
}
/**
* Fires a success event
*/
protected void fireFutureResult(T value) {
for (DHTFutureListener<T> l : listeners()) {
l.handleFutureSuccess(value);
}
}
/**
* Fires an ExecutionException event
*/
protected void fireExecutionException(ExecutionException e) {
for (DHTFutureListener<T> l : listeners()) {
l.handleExecutionException(e);
}
}
/**
* Fires an CancellationException event
*/
protected void fireCancellationException(CancellationException e) {
for (DHTFutureListener<T> l : listeners()) {
l.handleCancellationException(e);
}
}
/**
* Fires an InterruptedException event
*/
protected void fireInterruptedException(InterruptedException e) {
for (DHTFutureListener<T> l : listeners) {
l.handleInterruptedException(e);
}
}
}