Coordinates threads for multi-threaded operations
/* Copyright (C) 2005-2008 by Peter Eastman
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. */
import java.util.concurrent.atomic.*;
import java.util.*;
/**
* This class coordinates threads for multi-threaded operations. The execution model
* provided by this class is a single "task" (e.g. tracing a ray through a single pixel)
* which must be executed many times. The task is parameterized by a single index
* (e.g. the column containing the pixel).
* <p>
* To use this class, pass it an object which implements the Task interface. It
* automatically creates an appropriate number of threads based on the number of
* available processors. When you call run(), the task is repeatedly executed by
* the worker threads, with the index running
* over the desired range. You may invoke run() any number of times (e.g. once
* for each row of the image). Finally, call finish() to clean up the worker threads.
*/
public class ThreadManager
{
private int numIndices;
private AtomicInteger nextIndex;
private Thread thread[];
private HashSet<Thread> waitingThreads;
private Task task;
private Object controller;
private boolean controllerWaiting;
/**
* Create a new uninitialized ThreadManager. You must invoke setNumIndices() and setTask()
* to initialize it before calling run().
*/
public ThreadManager()
{
this(0, null);
}
/**
* Create a new ThreadManager.
*
* @param numIndices the number of values the index should take on (from 0 to numIndices-1)
* @param task the task to perform
*/
public ThreadManager(int numIndices, Task task)
{
this.numIndices = numIndices;
this.task = task;
nextIndex = new AtomicInteger(numIndices);
controller = new Object();
controllerWaiting = false;
waitingThreads = new HashSet<Thread>();
}
/**
* Create and start the worker threads. This is invoked the first time run() is called.
*/
private void createThreads()
{
// Create a worker thread for each processor.
thread = new Thread [Runtime.getRuntime().availableProcessors()];
for (int i = 0; i < thread.length; i++)
{
thread[i] = new Thread("Worker thread "+(i+1)) {
public void run()
{
// Repeatedly perform the task until we are finished.
while (true)
{
try
{
int index = nextIndex();
task.execute(index);
}
catch (InterruptedException ex)
{
task.cleanup();
return;
}
catch (Exception ex)
{
cancel();
ex.printStackTrace();
}
}
}
};
thread[i].start();
}
}
/**
* Set the number of values the index should take on. This must be invoked from the same
* thread that instantiated the ThreadManager and that calls run().
*/
public void setNumIndices(int numIndices)
{
this.numIndices = numIndices;
nextIndex.set(numIndices);
}
/**
* Set the Task to be executed by the worker threads. If another Task has already been set,
* that one is discarded immediately and cleanup() will never be invoked on in. This method
* must be invoked from the same thread that instantiated the ThreadManager and that calls run().
*/
public void setTask(Task task)
{
this.task = task;
}
/**
* Perform the task the specified number of times. This method blocks until all
* occurrences of the task are completed. If the current thread is interrupted
* while this method is in progress, all of the worker threads will be interrupted
* and disposed of.
*/
public void run()
{
controllerWaiting = false;
nextIndex.set(0);
waitingThreads.clear();
if (thread == null)
createThreads();
// Notify all the worker threads, then wait for them to finish.
synchronized (this)
{
notifyAll();
}
synchronized (controller)
{
try
{
controllerWaiting = true;
controller.wait();
}
catch (InterruptedException ex)
{
finish();
}
}
}
/**
* Cancel a run which is in progress. Calling this method does not interrupt any tasks that
* are currently executing, but it prevents any more from being started until the next time
* run() is called.
*/
public void cancel()
{
nextIndex.set(numIndices);
}
/**
* Dispose of all the worker threads. Once this has been called, do not call run() again.
*/
public void finish()
{
if (thread != null)
for (int i = 0; i < thread.length; i++)
thread[i].interrupt();
}
private int nextIndex() throws InterruptedException
{
int index;
while ((index = nextIndex.getAndIncrement()) >= numIndices)
{
// Wait until run() is called again.
synchronized (this)
{
waitingThreads.add(Thread.currentThread());
if (waitingThreads.size() == thread.length)
{
while (!controllerWaiting)
wait(1);
synchronized (controller)
{
controller.notify();
}
}
wait();
}
}
return index;
}
/**
* This interface defines a task to be performed by the worker threads.
*/
public static interface Task
{
/**
* Execute the task for the specified index.
*/
public void execute(int index);
/**
* This is called once from each worker thread when finish() is called. It gives a chance
* to do any necessary cleanup.
*/
public void cleanup();
}
}
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