问在Java中指定任务顺序执行
EN

Stack Overflow用户

提问于 2012-10-04 07:37:31

回答 2查看 6.9K关注 0票数 14

我已经搜索了很多，但找不到任何解决方案。我以这样的方式使用java线程池：

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

这样，任务就按顺序执行(就像在队列中一样)。但我需要改变“选择下一个任务”的策略。因此我希望为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任务。因此，当执行程序完成另一个任务时，它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。也许有一种更简单的方法，不考虑优先级。它选择最后添加的任务作为下一个要执行的任务，而不是第一个添加的任务。粗略地说，FixedThreadPool使用先进先出策略。例如，我可以使用后进先出策略吗？

multithreading

threadpool

threadpoolexecutor

java

回答 2

Stack Overflow用户

发布于 2012-10-04 07:52:31

您可以使用PriorityBlockingQueue指定要执行ThreadPoolExecutor的队列。

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));
    }
}

定义要按优先级进行比较的ComparableFutureTask。

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);
    }
  }

票数 12

Stack Overflow用户

发布于 2012-10-04 08:05:25

ThreadPoolExecutor构造函数接受BlockingQueue。您可以将queue作为PriorityBlockingQueue进行传递。它不会在排序时生成任何被授权者，您需要传递自定义比较器来维护顺序。

static BlockingQueue<Task> queue=new PriorityBlockingQueue<Task>(MAXPOOL,new TaskComparator());

static ThreadPoolExecutor threadpool = new ThreadPoolExecutor(30, MAXPOOL, 
        MAXPOOL, TimeUnit.SECONDS, (PriorityBlockingQueue) queue, new mThreadFactory());



class TaskComparator implements Comparator<Task>{
  public int compare(Task t1, Task t2){
    //write you own logic to compare two task.
  }
}