What is the best way to wait for ThreadPoolExecutor to finish threading in java?


I an using ThreadPoolExecutor in java to excute multi threads, and I have to do something after threads finish, and have to wait.

So I want to ask what is the best way to do that?

Is that right I do in the way?


boolean loop = true;
Integer x = threadPool.getPoolSize();
while (threadPool.getPoolSize() != 0) {

Shutdown will initiate an orderly shutdown in which previously submitted tasks are executed, but no new tasks will be accepted.

    System.out.println("All tasks submitted...No new tasks will be admitted");

However, I would strongly recommend using awaitTermination as this will allow current thread to block until all tasks have completed execution after a shutdown request, or the timeout occurs, or the current thread is interrupted, whichever happens first.

    try {
        executor.awaitTermination(3, TimeUnit.SECONDS);
    } catch (InterruptedException e) {


 The runState provides the main lifecyle control, taking on values:

 *   RUNNING:  Accept new tasks and process queued tasks
 *   SHUTDOWN: Don't accept new tasks, but process queued tasks
 *   STOP:     Don't accept new tasks, don't process queued tasks,
 *             and interrupt in-progress tasks
 *   TIDYING:  All tasks have terminated, workerCount is zero,
 *             the thread transitioning to state TIDYING
 *             will run the terminated() hook method
 *   TERMINATED: terminated() has completed

The numerical order among these values matters, to allow ordered comparisons. The runState monotonically increases over time, but need not hit each state. The transitions are:

On invocation of shutdown(), perhaps implicitly in finalize()

On invocation of shutdownNow()

When both queue and pool are empty

When pool is empty

When the terminated() hook method has completed. Threads waiting in awaitTermination() will return when the state reaches TERMINATED.

Detecting the transition from SHUTDOWN to TIDYING is less straightforward than you'd like because the queue may become empty after non-empty and vice versa during SHUTDOWN state, but we can only terminate if, after seeing that it is empty, we see that workerCount is 0.

Going back to your question, when you call getPoolSize() it checks the state of the threadpool when it is in TIDYING state. Hence, I think the correct check should be against TERMINATED state. Although, the results are the same if you have not implemented terminated() method.