如何使用固定数量的线程使用未绑定的可排序队列？

Question

请假设以下内容:

public static void main(String[] args) {
    ThreadPoolExecutor pool = new ThreadPoolExecutor(0, 5, 1L, TimeUnit.SECONDS, new PriorityBlockingQueue<Runnable>());
    DashboardHtmlExport d = new DashboardHtmlExport();
    for (int i = 0; i < 40; i++) {
        System.out.println("Submitting: " + i);
        try {
            Thread.sleep(cooldown);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        pool.submit(d.new A(i));
    }
}

private class A implements Runnable, Comparable<A> {
    private int order;

    public A(int order) {
        this.order = order;
    }

    public void run() {
        try {
            Thread.sleep(busyTime);
        } catch (InterruptedException e) {
            System.out.println(e.getMessage());
        }
        System.out.println(new Date());
    }

    public int compareTo(A o) {
        return Integer.valueOf(o.order).compareTo(Integer.valueOf(order));
    }
}

这产生了以下错误:

Submitting: 0
Submitting: 1
Exception in thread "main" java.lang.ClassCastException: java.util.concurrent.FutureTask cannot be cast to java.lang.Comparable
    at java.util.PriorityQueue.siftUpComparable(PriorityQueue.java:578)
    at java.util.PriorityQueue.siftUp(PriorityQueue.java:574)
    at java.util.PriorityQueue.offer(PriorityQueue.java:274)
    at java.util.concurrent.PriorityBlockingQueue.offer(PriorityBlockingQueue.java:164)
    at java.util.concurrent.ThreadPoolExecutor.execute(ThreadPoolExecutor.java:653)
    at java.util.concurrent.AbstractExecutorService.submit(AbstractExecutorService.java:78)
    at com.skycomm.cth.pages.test.DashboardHtmlExport.main(DashboardHtmlExport.java:133)
Tue Jul 10 23:48:45 GMT+02:00 2012

为什么会这样？

这只有在工作busyTime的较少的cooldown时间.意味着队列无法处理超过2个提交的任务!!

基本上我正在尝试做的是拥有一个UNBOUND大小的池,并且可以通过比较或比较来排序.我只能使用a 来实现UNBOUND队列,LinkedBlockingQueue但这当然不可排序!

谢谢.

Answer 1

ThreadPoolExecutor RunnableFuture使用newTaskFor()方法将您提交的Runnable转换为a ,并将此RunnableFuture添加到队列中.因此,如果要使用PriorityQueue,则应覆盖该newTaskFor()方法以确保RunnableFuture其创建的实例具有可比性.

或者您也可以使用该execute()方法而不是submit()方法来绕过任务创建.