Mixture of shutdown() and shutdownNow()

Question

ScheduledExecutorService inherits two methods from the ExecutorService, shutdown() and shutdownNow(). The difference between them:

shutdown initiates an orderly shutdown in which previously submitted tasks are executed, but no new tasks will be accepted. Invocation has no additional effect if already shut down.

shutdownNow attempts to stop all actively executing tasks, halts the processing of waiting tasks, and returns a list of the tasks that were awaiting execution.

Now I want to halt processing of waiting tasks while I don't want to interrupt currently executing tasks. I can't interrupt the threads because third party libraries are involved and they don't deal well with interrupts :-( But I need to cancel scheduled tasks, that are not currently executing since most of them are scheduled in an hour or so.

What's the best way to deal with this? What options Do I have?

Answer 1

Sounds like calling setExecuteExistingDelayedTasksAfterShutdownPolicy(false) on your executor should do the trick:

Sets the policy on whether to execute existing delayed tasks even when this executor has been shutdown. In this case, these tasks will only terminate upon shutdownNow, or after setting the policy to false when already shutdown. This value is by default true.

Since it's true by default, these tasks are executed. If you set it to false, they shouldn't be executed any more. This shouldn't be confused with submitted tasks which the docs you quote refer to. They are just waiting in the queue to be executed right away, when there is a free worker.