FluffySkyCat opened a new issue, #1290:
URL: https://github.com/apache/curator/issues/1290
# DistributedDoubleBarrier - Barrier bypass due to spurious wakeups or
SyncConnected events
Present since Curator 4.1.0 (CURATOR-495).
DistributedDoubleBarrier.enter() can return true before the required number
of participants have arrived. A single participant can pass through the barrier
with no other participants. We discovered this by tracing test flakiness in an
internal software test suite.
The bug has two parts:
1. internalEnter() uses do { ... } while (false), which executes exactly
once. After wait() returns, the method exits without re-checking the
participant count despite Object.wait() being subject to spurious wakeups.
2. The watcher fires on any ZooKeeper event, including SyncConnected session
events. Since CURATOR-495 (4.1.0), the notification is async via runSafe(), so
hasBeenNotified can be set to true by a session event during wait(). Since the
actual member count isn't checked, this results in a barrier participant
proceeding erroneously.
The untimed enter() is not affected — it always takes an unconditional
wait() path that doesn't rely on hasBeenNotified.
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