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Title: gh-112202: Ensure that condition.notify() succeeds even when racing with Task.cancel() by kristjanvalur · Pull Request #112201 · python/cpython · GitHub

Open Graph Title: gh-112202: Ensure that condition.notify() succeeds even when racing with Task.cancel() by kristjanvalur · Pull Request #112201 · python/cpython

X Title: gh-112202: Ensure that condition.notify() succeeds even when racing with Task.cancel() by kristjanvalur · Pull Request #112201 · python/cpython

Description: If Condition.notify() raises an exception that could have occurred after the task was selected to be woken up, wake up another task instead, if available. This ensures that the typical case, of waking up one task to handle something, will succeed even if the candidate task is cancelled at the same time or otherwise wakes up with an error. This may result in a spurious wakeup of a waiting task, which is what the Condition Variable protocol specifies, precisely because waking up tasks conservatively (rather wake up too many than too few) is the safest and simplest to implement, and missing wakeups are serious (and cause deadlocks), while extra wakeups are easily handled by application code. IMHO trying to guarantee that we never perform any extra wakeups would complicate the code too much and be too hard to verify, particularly since that is not a guarantee that Condition Variables are supposed to provide. The PR includes Tests Fix to asyncio.Condition where raising an exception out of condition.wait after having released the lock will result in a second task being awoken, if available Documentation changes explaining the Condition Variable protocol and how if favors too many wakeups over to few wakeups (i.e. how "spurious wakeups" may occur) 📚 Documentation preview 📚: https://cpython-previews--112201.org.readthedocs.build/ Issue: gh-112202

Open Graph Description: If Condition.notify() raises an exception that could have occurred after the task was selected to be woken up, wake up another task instead, if available. This ensures that the typical case, of wa...

X Description: If Condition.notify() raises an exception that could have occurred after the task was selected to be woken up, wake up another task instead, if available. This ensures that the typical case, of wa...

Opengraph URL: https://github.com/python/cpython/pull/112201

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fa8d5e4 Handle race between task.cancel() and contidion.notify() kristjanvalur Nov 17, 2023 https://github.com/python/cpython/pull/112201/commits/fa8d5e40877ce17a4bc23c979dd96abc9aa60ff6
df113e5 Improve test, add another test case kristjanvalur Nov 18, 2023 https://github.com/python/cpython/pull/112201/commits/df113e5765356953e0554cacf32706299a72b69e
13827d1 📜🤖 Added by blurb_it. blurb-it[bot] Jan 12, 2024 https://github.com/python/cpython/pull/112201/commits/13827d15d1c5bb6ab16e426fb5f1202b9b939ba7
c8e6b13 Update Doc/library/asyncio-sync.rst kristjanvalur Jan 12, 2024 https://github.com/python/cpython/pull/112201/commits/c8e6b13f490e3efa9c1a1e21b7f878a9032c3f6f
db3f83a Apply suggestions from code review kristjanvalur Jan 16, 2024 https://github.com/python/cpython/pull/112201/commits/db3f83ae5d29f666d9da14b5de4f84a87a363afe
0dad880 Change mention of "coroutines" to "tasks" where appopriate in in-line… kristjanvalur Jan 16, 2024 https://github.com/python/cpython/pull/112201/commits/0dad8803b4d43e6a85ece682351afb59ecb56b17
12bb758 awoken/awakened kristjanvalur Jan 16, 2024 https://github.com/python/cpython/pull/112201/commits/12bb7585483917191fe32ab130adf32b0bca8066
92566a1 Apply suggestions from code review kristjanvalur Feb 3, 2024 https://github.com/python/cpython/pull/112201/commits/92566a139137b651b93b13aefacd29bd9c81c43a
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