Question

我的问题：如何在ThreadPoolExecutor上执行一堆线程对象并等待它们全部完成后再继续？

我是ThreadPoolExecutor的新手。因此，此代码是一项测试，以了解它是如何工作的。现在我甚至没有用BlockingQueue填充对象，因为我不知道如何在没有用另一个execute()调用RunnableObject的情况下启动队列。无论如何，现在我只是打电话给awaitTermination()，但我想我仍然缺少一些东西。任何提示都会很棒！感谢。

public void testThreadPoolExecutor() throws InterruptedException {
  int limit = 20;
  BlockingQueue q = new ArrayBlockingQueue(limit);
  ThreadPoolExecutor ex = new ThreadPoolExecutor(limit, limit, 20, TimeUnit.SECONDS, q);
  for (int i = 0; i < limit; i++) {
    ex.execute(new RunnableObject(i + 1));
  }
  ex.awaitTermination(2, TimeUnit.SECONDS);
  System.out.println("finished");
}

RunnableObject类：

package playground;

public class RunnableObject implements Runnable {

  private final int id;

  public RunnableObject(int id) {
    this.id = id;
  }

  @Override
  public void run() {
    System.out.println("ID: " + id + " started");
    try {
      Thread.sleep(2354);
    } catch (InterruptedException ignore) {
    }
    System.out.println("ID: " + id + " ended");
  }
}

Answer 1

你应该循环awaitTermination

ExecutorService threads;
// ...
// Tell threads to finish off.
threads.shutdown();
// Wait for everything to finish.
while (!threads.awaitTermination(10, TimeUnit.SECONDS)) {
  log.info("Awaiting completion of threads.");
}

Answer 2

您的问题似乎是在将所有作业提交到池后，您没有致电shutdown。如果没有shutdown()，您的awaitTermination将始终返回false。

ThreadPoolExecutor ex =
    new ThreadPoolExecutor(limit, limit, 20, TimeUnit.SECONDS, q);
for (int i = 0; i < limit; i++) {
  ex.execute(new RunnableObject(i + 1));
}
// you are missing this line!!
ex.shutdown();
ex.awaitTermination(2, TimeUnit.SECONDS);

您还可以执行以下操作，等待所有工作完成：

List<Future<Object>> futures = new ArrayList<Future<Object>>();
for (int i = 0; i < limit; i++) {
  futures.add(ex.submit(new RunnableObject(i + 1), (Object)null));
}
for (Future<Object> future : futures) {
   // this joins with the submitted job
   future.get();
}
...
// still need to shutdown at the end
ex.shutdown();

此外，由于您正在等待2354毫秒，但仅等待2 SECONDS的所有作业终止，awaitTermination将始终返回{{1} }}

最后，听起来你担心创建一个新的false而你又想重用第一个ThreadPoolExecutor。不要。与您编写的用于检测作业是否完成的任何代码相比，GC开销将极低。

引用javadocs ThreadPoolExecutor.shutdown()：

启动有序关闭，其中先前提交的任务已执行，但不会接受任何新任务。如果已经关闭，调用没有额外的效果。

在ThreadPoolExecutor.awaitTermination(...)方法中，它正在等待执行程序的状态转到TERMINATED。但首先，如果调用SHUTDOWN，则州必须转到shutdown();如果调用STOP，则必须转到shutdownNow()。

Answer 3

这与执行者本身无关。只需使用界面java.util.concurrent.ExecutorService.invokeAll(Collection<? extends Callable<T>>)即可。它将一直阻塞，直到所有Callable完成。

执行者意味着长寿;超出一组任务的生命周期。 shutdown适用于应用程序完成和清理的时间。

Answer 4

如果/当抛出InterruptedException时，这是一个处理重试的接受答案的变体：

executor.shutdown();

boolean isWait = true;

while (isWait)
{
    try
    {             
        isWait = !executor.awaitTermination(10, TimeUnit.SECONDS);
        if (isWait)
        {
            log.info("Awaiting completion of bulk callback threads.");
        }
    } catch (InterruptedException e) {
        log.debug("Interruped while awaiting completion of callback threads - trying again...");
    }
}

Answer 5

另一种方法是使用CompletionService，如果你必须尝试任何任务结果非常有用：

//run 3 task at time
final int numParallelThreads = 3;

//I used newFixedThreadPool for convenience but if you need you can use ThreadPoolExecutor
ExecutorService executor = Executors.newFixedThreadPool(numParallelThreads);
CompletionService<String> completionService = new ExecutorCompletionService<String>(executor);

int numTaskToStart = 15;

for(int i=0; i<numTaskToStart ; i++){
    //task class that implements Callable<String> (or something you need)
    MyTask mt = new MyTask();

    completionService.submit(mt);
}

executor.shutdown(); //it cannot be queued more task

try {
    for (int t = 0; t < numTaskToStart ; t++) {
        Future<String> f = completionService.take();
        String result = f.get();
        // ... something to do ...
    }
} catch (InterruptedException e) {
    //termination of all started tasks (it returns all not started tasks in queue)
    executor.shutdownNow();
} catch (ExecutionException e) {
    // ... something to catch ...
}

Answer 6

试试这个，

ThreadPoolExecutor ex =
    new ThreadPoolExecutor(limit, limit, 20, TimeUnit.SECONDS, q);
for (int i = 0; i < limit; i++) {
  ex.execute(new RunnableObject(i + 1));
}

要添加的行

ex.shutdown();
ex.awaitTermination(timeout, unit)

如何等待ThreadPoolExecutor完成

6 个答案: