java - 在Java中指定任务顺序执行

Question

我搜索了很多，但找不到任何解决方案。我以这种方式使用 java 线程池:

ExecutorService c = Executors.newFixedThreadPool(3);
for (int i = 0; i < 10; ++i) {
  c.execute(new MyTask(i));
}

以这种方式，任务按顺序执行(如在队列中)。但我需要改变“选择下一个任务”策略。所以我想分配给每个任务指定优先级(它不是线程优先级)并执行与这些优先级相对应的任务。因此，当执行者完成另一个任务时，它会选择下一个任务作为具有最高优先级的任务。它描述了常见问题。也许有更简单的方法不考虑优先级。它选择最后添加的任务作为下一个执行而不是首先添加的任务。粗略地说FixedThreadPool使用FIFO策略。我可以使用后进先出策略吗？

Answer 1

您可以使用 PriorityBlockingQueue将 Queue 指定给 ThreadPoolExecutor。

public class PriorityExecutor extends ThreadPoolExecutor {

    public PriorityExecutor(int corePoolSize, int maximumPoolSize,
            long keepAliveTime, TimeUnit unit, BlockingQueue<Runnable> workQueue) {
        super(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue);
    }
    //Utitlity method to create thread pool easily
    public static ExecutorService newFixedThreadPool(int nThreads) {
        return new PriorityExecutor(nThreads, nThreads, 0L,
                TimeUnit.MILLISECONDS, new PriorityBlockingQueue<Runnable>());
    }
    //Submit with New comparable task 
    public Future<?> submit(Runnable task, int priority) {
        return super.submit(new ComparableFutureTask(task, null, priority));
    }
    //execute with New comparable task 
    public void execute(Runnable command, int priority) {
        super.execute(new ComparableFutureTask(command, null, priority));
    }
}

定义 ComparableFutureTask 以比较优先级。

class ComparableFutureTask<T> extends FutureTask<T>
        implements
            Comparable<ComparableFutureTask<T>> {

    volatile int priority = 0;

    public ComparableFutureTask(Runnable runnable, T result, int priority) {
        super(runnable, result);
        this.priority = priority;
    }
    public ComparableFutureTask(Callable<T> callable, int priority) {
        super(callable);
        this.priority = priority;
    }
    @Override
    public int compareTo(ComparableFutureTask<T> o) {
        return Integer.valueOf(priority).compareTo(o.priority);
    }
  }