/*
* Copyright 2009 David Jurgens
*
* This file is part of the S-Space package and is covered under the terms and
* conditions therein.
*
* The S-Space package is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2 as published
* by the Free Software Foundation and distributed hereunder to you.
*
* THIS SOFTWARE IS PROVIDED "AS IS" AND NO REPRESENTATIONS OR WARRANTIES,
* EXPRESS OR IMPLIED ARE MADE. BY WAY OF EXAMPLE, BUT NOT LIMITATION, WE MAKE
* NO REPRESENTATIONS OR WARRANTIES OF MERCHANT- ABILITY OR FITNESS FOR ANY
* PARTICULAR PURPOSE OR THAT THE USE OF THE LICENSED SOFTWARE OR DOCUMENTATION
* WILL NOT INFRINGE ANY THIRD PARTY PATENTS, COPYRIGHTS, TRADEMARKS OR OTHER
* RIGHTS.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
//package edu.ucla.sspace.util;
import java.util.ArrayDeque;
import java.util.Queue;
import java.util.concurrent.BlockingQueue;
/**
* A daemon thread that continuously dequeues {@code Runnable} instances from a
* queue and executes them. This class is intended to be used with a {@link
* java.util.concurrent.Semaphore Semaphore}, whereby work is added the to the
* queue and the semaphore indicates when processing has finished.
*
* @author David Jurgens
*/
public class WorkerThread extends Thread {
/**
* A static variable to indicate which instance of the class the current
* thread is in its name.
*/
private static int threadInstanceCount;
/**
* The queue from which work items will be taken
*/
private final BlockingQueue<Runnable> workQueue;
/**
* An internal queue that holds thread-local tasks. This queue is intended
* to hold multiple tasks to avoid thread contention on the work queue.
*/
private final Queue<Runnable> internalQueue;
/**
* The number of items that should be queued to run by this thread at once.
*/
private final int threadLocalItems;
/**
* Creates a thread that continuously dequeues from the {@code workQueue} at
* once and excutes each item.
*/
public WorkerThread(BlockingQueue<Runnable> workQueue) {
this(workQueue, 1);
}
/**
* Creates a thread that continuously dequeues {@code threadLocalItems} from
* {@code workQueue} at once and excutes them sequentially.
*
* @param threadLocalItems the number of items this thread should dequeue
* from the work queue at one time. Setting this value too high can
* result in a loss of concurrency; setting it too low can result in
* high contention on the work queue if the time per task is also
* low.
*/
public WorkerThread(BlockingQueue<Runnable> workQueue,
int threadLocalItems) {
this.workQueue = workQueue;
this.threadLocalItems = threadLocalItems;
internalQueue = new ArrayDeque<Runnable>();
setDaemon(true);
synchronized(WorkerThread.class) {
setName("WorkerThread-" + (threadInstanceCount++));
}
}
/**
* Continuously dequeues {@code Runnable} instances from the work queue and
* execute them.
*/
public void run() {
Runnable r = null;
while (true) {
// Try to drain the maximum capacity of thread-local items, checking
// whether any were available
if (workQueue.drainTo(internalQueue, threadLocalItems) == 0) {
// block until a work item is available
try {
internalQueue.offer(workQueue.take());
} catch (InterruptedException ie) {
throw new Error(ie);
}
}
// Execute all of the thread-local items
while ((r = internalQueue.poll()) != null)
r.run();
}
}
}
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