ThreadPool.java

/*-*- mode: Java; tab-width:8 -*-*/

package php.java.bridge;

/*
 * Copyright (C) 2003-2007 Jost Boekemeier
 *
 * Permission is hereby granted, free of charge, to any person obtaining a
 * copy of this software and associated documentation files (the "Software"),
 * to deal in the Software without restriction, including without limitation
 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
 * and/or sell copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
 * THE COPYRIGHT HOLDER(S) OR AUTHOR(S) BE LIABLE FOR ANY CLAIM, DAMAGES OR
 * OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
 * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
 * OTHER DEALINGS IN THE SOFTWARE.
 */

import java.util.Iterator;
import java.util.LinkedList;

/**
 * A standard thread pool, accepts runnables and runs them in a thread environment.
 * Example:<br>
 * <code>
 * ThreadPool pool = new ThreadPool("MyThreadPool", 20);<br>
 * pool.start(new YourRunnable());<br>
 * </code>
 *@author jostb
 */
public class ThreadPool {
    private String name;
    private int threads = 0, idles = 0, poolMaxSize, poolReserve;
    private LinkedList runnables = new LinkedList();
    private LinkedList threadList = new LinkedList();

    /**
     * Threads continue to pull runnables and run them in the thread
     * environment.
     */
    protected class Delegate extends Thread {
	protected boolean terminate = false;

	public Delegate(String name) { super(name); }
	public Delegate(ThreadGroup group, String name) { super(group, name); }
	protected void terminate() {}
	protected void end() {}
	protected void createThread(String name) { startNewThread(name); }
	
	public void run() {
	    try {
		while(!terminate) { getNextRunnable().run(); end(); }
	    } catch (InterruptedException e) {
		    /*ignore*/
	    }catch (Throwable t) { 
	           Util.printStackTrace(t); createThread(getName()); 
	    } finally { terminate(); }
	}
    }
    protected Delegate createDelegate(String name) {
        return new Delegate(name);
    }
    protected void startNewThread(String name) {
        Delegate d = createDelegate(name);
        threadList.add(d);
	d.start();
    }
    protected synchronized boolean checkReserve() {
      return threads-idles < poolReserve;
    }
    /*
     * Helper: Pull a runnable off the list of runnables. If there's
     * no work, sleep the thread until we receive a notify.
     */
    private synchronized Runnable getNextRunnable() throws InterruptedException {
	while(runnables.isEmpty()) {
	    idles++; wait(); idles--;
	}
	return (Runnable)runnables.removeFirst();
    }

    /**
     * Push a runnable to the list of runnables. The notify will fail
     * if all threads are busy. Since the pool contains at least one
     * thread, it will pull the runnable off the list when it becomes
     * available.
     * @param r - The runnable
     */
    public synchronized void start(Runnable r) {
	runnables.add(r);
	if(idles==0 && threads < poolMaxSize) {
	    threads++;
	    startNewThread(name+"#"+String.valueOf(threads));
	}
	else
	    notify();
    }
    
    protected void init(String name, int poolMaxSize) {
	this.name = name;
    	this.poolMaxSize = poolMaxSize;
    	this.poolReserve = (poolMaxSize>>>2)*3;
    }
    
    /** Terminate all threads in the pool. */
    public void destroy() {
	    for (Iterator ii = threadList.iterator(); ii.hasNext(); ) {
		    Delegate d = (Delegate) ii.next();
		    d.terminate = true;
		    d.interrupt();
	    }
    }
    /**
     * Creates a new thread pool.
     * @param name - The name of the pool threads.
     * @param poolMaxSize - The max. number of threads, must be >= 1.
     */
    public ThreadPool (String name, int poolMaxSize) {
	if(poolMaxSize<1) throw new IllegalArgumentException("poolMaxSize must be >0");
        init(name, poolMaxSize);
    }
}