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

package io.soluble.pjb.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:

 * 
 * ThreadPool pool = new ThreadPool("MyThreadPool", 20);

 * pool.start(new YourRunnable());

 * 
 *
 * @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);
    }
}