java - How to wait for a ThreadPoolExecutor to finish

Question

My Question: How to execute a bunch of threaded objects on a ThreadPoolExecutor and wait for them all to finish before moving on?

I'm new to ThreadPoolExecutor. So this code is a test to learn how it works. Right now I don't even fill the BlockingQueue with the objects because I don't understand how to start the queue without calling execute() with another RunnableObject. Anyway, right now I just call awaitTermination() but I think I'm still missing something. Any tips would be great! Thanks.

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");
}

The RunnableObject class:

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

You should loop on 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.");
}