How can a threadpool be reused after shutdown

As stated in the documentation, you cannot reuse an ExecutorService that has been shut down. I'd recommend against any workarounds, since (a) they may not work as expected in all situations; and (b) you can achieve what you want using standard classes.

You must either

1. instantiate a new ExecutorService; or

2. not terminate the ExecutorService.

The first solution is easily implemented, so I won't detail it.

For the second, since you want to execute an action once all the submitted tasks have finished, you might take a look at ExecutorCompletionService and use it instead. It wraps an ExecutorService which will do the thread management, but the runnables will get wrapped into something that will tell the ExecutorCompletionService when they have finished, so it can report back to you:

ExecutorService executor = ...; ExecutorCompletionService ecs = new ExecutorCompletionService(executor); for (int i = 0; i < totalTasks; i++) { ... ecs.submit(...); ... } for (int i = 0; i < totalTasks; i++) { ecs.take(); }

The method take() on the ExecutorCompletionService class will block until a task has finished (either normally or abruptly). It will return a Future, so you can check the results if you wish.

I hope this can help you, since I didn't completely understand your problem.