WorkQueue.java

import java.util.concurrent.LinkedBlockingQueue;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;

public class WorkQueue {
	private static final int numThreads = 10;
	private static WorkQueue instance = null;
	private final ThreadPoolExecutor workers;
	
	/**
	 * Dummy object used to send messages from queue to main
	 */
	public static Object messenger = new Object();
	
	private WorkQueue() {
		workers = new ThreadPoolExecutor(numThreads, numThreads, 0, TimeUnit.MILLISECONDS, new LinkedBlockingQueue<Runnable>());
	}

	public static WorkQueue getInstance() {
		if (instance == null) {
			synchronized (WorkQueue.class) {
				if (instance == null) {
					instance = new WorkQueue();
				}
			}
		}
		return instance;
	}

	public void execute(Runnable r) {
		workers.execute(r);
	}

	public void shutdown() {
		workers.shutdown();
		// notify the main thread when work queue is shutting down
		synchronized (messenger) {
			messenger.notifyAll();
		}
	}
	
	public boolean isShutdown() {
		return workers.isShutdown();
	}
	
	public int getActiveCount() {
		return workers.getActiveCount();
	}
	
	public long getTaskCount() {
		return workers.getTaskCount();
	}
	
	/**
	 * Blocks until work queue is shutdown
	 */
	public void awaitShutdown() {
		while (!workers.isShutdown()) {
			synchronized (messenger) {
				try {
					messenger.wait();
				} catch (InterruptedException e) {
				}
			}
			Thread.yield();
		}
	}
}