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

how about this?

Object lock = new Object();
CountDownLatch cdl = new CountDownLatch(threadNum);
for (int i = 0; i < threadNum; i++) {
    executorService.execute(() -> {

        synchronized (lock) {
            cdl.countDown();
            try {
                lock.wait();
            } catch (InterruptedException e) {
                Thread.currentThread().interrupt();
            }
        }
    });
}
cdl.await();
synchronized (lock) {
    lock.notifyAll();
}

if you do not add new tasks to ExecutorService , this may wait for all current tasks completed