ExecutorService, how to wait for all tasks to finish

Question

What is the simplest way to to wait for all tasks of ExecutorService to finish? My task is primarily computational, so I just want to run a large number of jobs

Answer 1

Sounds like you need ForkJoinPool and use the global pool to execute tasks.

public static void main(String[] args) {
    // the default `commonPool` should be sufficient for many cases.
    ForkJoinPool pool = ForkJoinPool.commonPool(); 
    // The root of your task that may spawn other tasks. 
    // Make sure it submits the additional tasks to the same executor that it is in.
    Runnable rootTask = new YourTask(pool); 
    pool.execute(rootTask);
    pool.awaitQuiescence(...);
    // that's it.
}

The beauty is in pool.awaitQuiescence where the method will block utilize the caller's thread to execute its tasks and then return when it is really empty.