.. which occurs when a user adds a listener from different threads after the promise is done and the notifications for the listeners, that were added before the promise is done, is in progress. For instance:
Thread-1: p.addListener(listenerA);
Thread-1: p.setSuccess(null);
Thread-2: p.addListener(listenerB);
Thread-2: p.executor.execute(taskNotifyListenerB);
Thread-1: p.executor.execute(taskNotifyListenerA);
taskNotifyListenerB should not really notify listenerB until taskNotifyListenerA is finished.
To fix this issue:
- Change the semantic of (listeners == null) to determine if the early
listeners [1] were notified
- If a late listener is added before the early listeners are notified,
the notification of the late listener is deferred until the early
listeners are notified (i.e. until listeners == null)
- The late listeners with deferred notifications are stored in a lazily
instantiated queue to preserve ordering, and then are notified once
the early listeners are notified.
[1] the listeners that were added before the promise is done
[2] the listeners that were added after the promise is done
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