How to cancel pending items from a ScheduledThreadPoolExecutor?

Question

I have a task which requires me to schedule tasks and remove them when a certain event occurs. I'm using a ScheduledThreadPoolExecutor to schedule the tasks, that's pretty straightforward. But, I found two ways to cancel the pending items, both of them look a bit odd.

I'm curious if any of them is at production quality. If neither of them, then what do you suggest?

Here is a skeleton of what I do:

private final ScheduledThreadPoolExecutor scheduler = new ScheduledThreadPoolExecutor(1);

public void doStuff() {
    //...
    scheduler.schedule(new Runnable() {/*...*/}, 10, TimeUnit.MILISECONDS)
}

public void actOnEvent() {
    cancelPendingItems();
    doMoreStuff();
}

public void cancelPendnigItems() {
    // TODO implement me
}

This is candidate 1:

public void cancelPendingItems() {
    scheduler.getQueue().clear();
}

This is candidate 2:

public void cancelPendingItems() {
    for (Runnable task : scheduler.getQueue()) {
        scheduler.remove(task);
    }
}

Both look like a hack to me because they depend on the ScheduledThreadPoolExecutor.queue property which isn't specified in the ScheduledExecutor interface. I'm a bit worried that I might violate an invariant of ScheduledThreadPoolExecutor and I will detect it too late.

So, are these snippets going to do what I want them to do? Are there any better/cleaner ways to do it?

Answer 1

Note that ScheduledExecutorService.schedule returns a ScheduledFuture. Just store these and when your cancel method is called, use the cancel method on the stored futures to cancel their future iterations.