workqueue.java

java 进阶专用。

// HORRIBLE PROGRAM - uses busy-wait instead of Object.wait! - Page 204

import java.util.*;

public abstract class WorkQueue {
    private final List queue = new LinkedList();
    private boolean stopped = false;

    protected WorkQueue() { new WorkerThread().start(); }

    public final void enqueue(Object workItem) {
        synchronized (queue) { queue.add(workItem); }
    }
    public final void stop()  {
        synchronized (queue) { stopped = true; }
    }
    protected abstract void processItem(Object workItem)
        throws InterruptedException;
    private class WorkerThread extends Thread {
        public void run() {
            final Object QUEUE_IS_EMPTY = new Object();
            while (true) {  // Main loop
                Object workItem = QUEUE_IS_EMPTY;
                synchronized (queue) {
                    if (stopped)
                        return;
                    if (!queue.isEmpty())
                        workItem = queue.remove(0);
                }

                if (workItem != QUEUE_IS_EMPTY) {
                    try {
                        processItem(workItem);
                    } catch (InterruptedException e) {
                        return;
                    }
                }
            }
        }
    }
}