TrampolineScheduler NullPointerException

[DylanSale]

There is an issue in TrampolineScheduler on 0.20.4 where it can throw a NullPointerException in InnerCurrentThreadScheduler enqueue(Action0 action, long execTime)

        private Subscription enqueue(Action0 action, long execTime) {
            if (innerSubscription.isUnsubscribed()) {
                return Subscriptions.empty();
            }
            PriorityQueue<TimedAction> queue = QUEUE.get();
            final TimedAction timedAction = new TimedAction(action, execTime, COUNTER_UPDATER.incrementAndGet(TrampolineScheduler.this));
            queue.add(timedAction);

            if (wip.getAndIncrement() == 0) {
                do {
                    queue.poll().action.call();
                } while (wip.decrementAndGet() > 0);
                return Subscriptions.empty();
            } else {
                // queue wasn't empty, a parent is already processing so we just add to the end of the queue
                return Subscriptions.create(new Action0() {

                    @Override
                    public void call() {
                        PriorityQueue<TimedAction> _q = QUEUE.get();
                        if (_q != null) {
                            _q.remove(timedAction);
                        }
                    }

                });
            }
        }

The Exception happens on queue.poll().action.call();.
From what I can tell, the queue is empty, and poll is returning null.

This is happening inside a nested observable.redo().timeout().redo() chain (the redo().timeout() happens earlier in the application, it isn't just one after the other like that), if that helps. I'm not in a position to create a simple replication example however.

My current theory is: One of the redos could be unsubscribing, calling _q.remove, while the wip loop is running (perhaps unsubscribe is happening on another thread?), causing the queue to become empty, and the next loop of the wip loop returns null. I think the queue.poll() call should check for null.

[benjchristensen]

Thanks for the report. I'll take a look.

[benjchristensen]

Fixed (I hope) in #1736

[akarnokd]

Hi. Fixed in 1.x branch via #2471. Can you verify the fix works for your case?