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fix: Address potential race condition in FeatureStore update_availability #391

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fix: Address potential race condition in FeatureStore update_availability #391

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49 changes: 25 additions & 24 deletions ldclient/impl/datasystem/fdv2.py
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Original file line number Diff line number Diff line change
Expand Up @@ -170,38 +170,39 @@ def __wrapper(self, fn: Callable):
raise

def __update_availability(self, available: bool):
try:
self.__lock.lock()
if available == self.__last_available:
return
self.__last_available = available
finally:
state_changed = False
poller_to_stop = None
task_to_start = None

self.__lock.lock()
if available == self.__last_available:
self.__lock.unlock()
return

state_changed = True
self.__last_available = available

if available:
poller_to_stop = self.__poller
self.__poller = None
elif self.__poller is None:
task_to_start = RepeatingTask("ldclient.check-availability", 0.5, 0, self.__check_availability)
self.__poller = task_to_start
self.__lock.unlock()
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@cursor cursor bot Dec 24, 2025

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Missing try/finally causes deadlock if exception occurs

The refactored __update_availability method removes the try/finally pattern that previously ensured the lock was always released. If any exception occurs between self.__lock.lock() and self.__lock.unlock() (for example, during RepeatingTask construction on line 189), the lock will remain held indefinitely, causing a deadlock for all subsequent operations trying to acquire the same lock. The original code and the equivalent method in ldclient/client.py properly use try/finally to guarantee lock release.

Fix in Cursor Fix in Web


if available:
log.warning("Persistent store is available again")
else:
log.warning("Detected persistent store unavailability; updates will be cached until it recovers")

status = DataStoreStatus(available, True)
self.__store_update_sink.update_status(status)

if available:
try:
self.__lock.lock()
if self.__poller is not None:
self.__poller.stop()
self.__poller = None
finally:
self.__lock.unlock()
if poller_to_stop is not None:
poller_to_stop.stop()

return

log.warning("Detected persistent store unavailability; updates will be cached until it recovers")
task = RepeatingTask("ldclient.check-availability", 0.5, 0, self.__check_availability)

self.__lock.lock()
self.__poller = task
self.__poller.start()
self.__lock.unlock()
if task_to_start is not None:
task_to_start.start()

def __check_availability(self):
try:
Expand Down Expand Up @@ -487,7 +488,7 @@ def synchronizer_loop(self: 'FDv2'):

log.info("Recovery condition met, returning to primary synchronizer")
except Exception as e:
log.error("Failed to build primary synchronizer: %s", e)
log.error("Failed to build synchronizer: %s", e)
break

except Exception as e:
Expand Down