执行者中的Thread.join()等价物

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程序中的所有线程完成,即所有线程完成工作后应打印"所有线程完成..."？

Answer 1

如果要等待任务完成,则不应使用此类执行程序.如果您不希望/无法关闭线程池执行程序,该怎么办？这是一种更推荐的方式:

    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 2

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:

根据@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()在完成所有任务之前(通过失败或完成成功执行),将不会返回.