block until ExecutorService is done

Question

Possible Duplicates:
ExecutorService, how to wait for all tasks to finish
Java ExecutorService: awaitTermination of all recursively created tasks

Is there a way to block the current thread until an ExecutorService has finished all its tasks?

executor.execute(task1);
executor.execute(task2);
executor.execute(task3);
executor.execute(task4);
executor.execute(task5);
// ...now I want to block until all tasks have finished executing...
System.out.println("done!")

Answer 1

You can use a ThreadPoolExecutor with a pool size set to System.getRuntime().availableProcessors()^{Java 6} or Runtime.getRuntime().availableProcessors()^{Java 8} and .execute() it all the tasks you want to execute, then call tpe.shutdown() and then wait in a while(!tpe.terminated()) { /* waiting for all tasks to complete */} which blocks for all the submitted tasks to complete. where tpe is a reference to your ThreadPoolExecutor instance.

Or if it is more appropriate use an ExecutorCompletionService A CompletionService that uses a supplied Executor to execute tasks. This class arranges that submitted tasks are, upon completion, placed on a queue accessible using take. The class is lightweight enough to be suitable for transient use when processing groups of tasks.