PYTHON-644#686
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This does not eliminate, but it shrinks, the window for the race condition that caused PYTHON-644. In this race, _set_result could be called from the event loop before send_request calls _start_timer. The goal of the _CANCELLED sentinel is to allow permanent cancelling of all future timers for a given ResponseFuture. Unfortunately, there's still a race -- if _timer is cancelled during _start_timer.
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Closing this PR for now, while I investigate a lockless solution that Adam suggested. |
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This change adds a sentinel to indicate when a
ResponseFuture's timer has been cancelled. This is similar to #685, but also uses a lock to eliminate race conditions. For instance, the lock prevents this series of events:_on_speculative_executeon thread 1_set_final_resultcancels the timer on thread 2_on_speculative_executestarts a new timer on thread 1With these changes, I have not produced memory leaks with the script provided in PYTHON-644 when running it locally many times.
@aholmberg and I both suspect that there's a better solution than explicit locking, but I haven't figured it out yet.