执行程序中的 Thread.join() 等效项[重复]

Question

我有一个新手问题。我有这个代码：

public class Main 
{

    public static void main(String[] args) throws InterruptedException 
    {
        // TODO Auto-generated method stub
        IntHolder aHolder=new IntHolder();
        aHolder.Number=0;

        IncrementorThread A= new IncrementorThread(1, aHolder);
        IncrementorThread B= new IncrementorThread(2, aHolder);
        IncrementorThread C= new IncrementorThread(3, aHolder);

        A.start();
        B.start();
        C.start();

        A.join();
        B.join();
        C.join();
        System.out.println("All threads completed...");

    }

}

这将等待所有线程完成。如果我像这样使用Executors：

public class Main 
{

    public static void main(String[] args) 
    {
        // TODO Auto-generated method stub
        IntHolder aHolder=new IntHolder();
        aHolder.number=0;

        IncrementalRunable A= new IncrementalRunable(1, aHolder);
        IncrementalRunable B= new IncrementalRunable(2, aHolder);
        IncrementalRunable C= new IncrementalRunable(3, aHolder);

        ExecutorService exec = Executors.newFixedThreadPool(3);
        exec.execute(A);
        exec.execute(B);
        exec.execute(C);
        //Don't know what to do here

        System.out.println("All threads completed...");
    }
}

如何暂停主线程以等待执行器中的所有线程完成，即所有线程完成工作后应打印“所有线程完成...”？

Answer 1

我们可以使用下面的代码来加入线程。

 executor.execute(new YouThread());

    try{     
         executor.shutdown();
         while (!executor.awaitTermination(24L, TimeUnit.HOURS)) {
             System.out.println("Not yet. Still waiting for termination");
         }                
    }catch(InterruptedException e){
        e.printStackTrace();
    }

Answer 2

尝试以这种方式使用线程池。

executor.shutdown();
executor.awaitTermination(MAX_PRIORITY, TimeUnit.HOURS);

Answer 3

executor.shutdown();
while (!executor.awaitTermination(24L, TimeUnit.HOURS)) {
    System.out.println("Not yet. Still waiting for termination");
}

使用shutdown() + awaitTermination() 组合。

编辑：

基于@Lital 的评论

List<Callable<Object>> calls = new ArrayList<Callable<Object>>();
calls.add(Executors.callable(new IncrementalRunable(1, aHolder)));
calls.add(Executors.callable(new IncrementalRunable(2, aHolder)));
calls.add(Executors.callable(new IncrementalRunable(3, aHolder)));

List<Future<Object>> futures = executor.invokeAll(calls);

注意： invokeAll() 在所有任务完成之前不会返回（通过失败或完成成功执行）。

Answer 4

如果你想等待任务完成，你不应该像这样使用执行器。 如果你不想/不能关闭你的线程池执行器怎么办？ 这是更推荐的方式：

    ExecutorService exec = Executors.newFixedThreadPool(3);
    Collection<Future<?>> tasks = new LinkedList<Future<?>>();

    Future<T> future = exec.submit(A);
    tasks.add(future);
    future = exec.submit(B);
    tasks.add(future);
    future = exec.submit(C);
    tasks.add(future);

    // wait for tasks completion
    for (Future<?> currTask : tasks) {
            try {
                currTask.get();
            } catch (Throwable thrown) {
                Logger.error(thrown, "Error while waiting for thread completion");
            }
        }

Answer 5

 exec.shutdown();
    // Wait until all threads are finish
    exec.awaitTermination();