Question

Is there a join()-like method for threads that have been executed through the ThreadPoolExecutor?

If I submit a few Callables to the executor instead and use the get() method on the Futures that they return, will I get similar behavior to a Thread.join()?

Answer 1

They are similar in the sense they both Thread#join() and Future#get() will block until the thread/cllable is finished. In the Thread#join() case, the call returns when the thread dies. No result is returned. In the Future#get() case, it will return when the callable is finished executing its task, but the executing thread will not die (it’s usually part of a thread pool, so it will make itself available back to the pool).

If these tasks that you submit to the ExecuterService are mission-critical, it is good practice to add a shutdown hook to your application that calls threadPool.shutdown() to allow for a graceful completion of all running threads, and waits for threadPool.isTerminated() to become true, or waits for threadPool.awaitTermination(max time before force shutdown) to return.