ThreadPool.java

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package cedar.jetweb.util;

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

public class ThreadPool extends Thread {
    protected String name = "anonymous";
    protected int maxThreads = 4;
    protected long interval = 10000;

    protected LinkedList<Thread> waitingThreads = new LinkedList<Thread>();
    protected LinkedList<Thread> runningThreads = new LinkedList<Thread>();

    protected volatile boolean running;


    public ThreadPool() {}

    public ThreadPool(String n, int max, long inter) {
    name = n;
    maxThreads = max;
    interval = inter;
    System.out.println("Creating Thread Pool \""+name+"\" with max threads = "+maxThreads+
               " and interval "+interval+" ms");
    }

    public void add(Thread t) {
    System.out.println("ThreadPool "+name+": adding thread");
    waitingThreads.add(t);
    System.out.println(" "+waitingThreads.size()+" threads now waiting");
    }

    @SuppressWarnings("unchecked")
    public void run() {
    running = true;
    while (running) {
        // Remove threads that have finished.
        LinkedList<Thread> tempRunningThreads = (LinkedList<Thread>)runningThreads.clone();
        Iterator<Thread> iter = runningThreads.iterator();
        while (iter.hasNext()) {
        Thread t = (Thread) iter.next();
        if (!t.isAlive()) tempRunningThreads.remove(t); // ??? Safe?
        }
        runningThreads = tempRunningThreads;

        // Add threads from waitingThreads to runningThreads and start them,
        // until all slots filled.
        iter = waitingThreads.iterator();
        tempRunningThreads = (LinkedList<Thread>)runningThreads.clone();
        LinkedList<Thread> tempWaitingThreads = (LinkedList<Thread>) waitingThreads.clone();
        while (iter.hasNext() && maxThreads-tempRunningThreads.size() > 0) {
        Thread t = iter.next();
        tempWaitingThreads.remove(t);
        tempRunningThreads.add(t);
        t.start();
        System.out.println("ThreadPool "+name+" starting a thread, "+
                   tempWaitingThreads.size()+" still waiting.");
        }
        runningThreads = tempRunningThreads;
        waitingThreads = tempWaitingThreads;

        // Sleep for interval ms before checking again.
        try {
        this.sleep(interval);
        } catch (InterruptedException e) {}
    }
    }

    public void halt() {
    running = false;
    }

}

Generated Wed Jan 17 09:14:27 GMT 2007