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Created on 2017-07-20 11:29 by mickp, last changed 2022-04-11 14:58 by admin.
| Files | ||||
|---|---|---|---|---|
| File name | Uploaded | Description | Edit | |
| WaitersSleepers.py | mickp, 2017-07-20 11:29 | A script to demonstrate to the issue. | ||
| WaitersSleepers.py | pitrou, 2017-07-20 14:05 | |||
| Messages (4) | |||
|---|---|---|---|
| msg298713 - (view) | Author: Mick Phillips (mickp) | Date: 2017-07-20 11:29 | |
If a process was waiting on an Event but dies for some reason, nothing else can set the Event. I think the Event._cond lock can not be acquired. See attached for a demonstration. I see the same behaviour in Python 2.7.5 and Python 3.5.2. Is this expected behaviour? |
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| msg298719 - (view) | Author: Antoine Pitrou (pitrou) *  |
Date: 2017-07-20 13:33 | |
Hi Mick, thanks for reporting this issue. You're right that the behaviour isn't expected. |
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| msg298720 - (view) | Author: Mick Phillips (mickp) | Date: 2017-07-20 13:42 | |
Thanks for confirming. If anyone finds this and is looking for a workaround, here's what I'm using:
while not event.is_set()
try:
time.sleep(timeout)
except (KeyboardInterrupt, IOError):
pass
|
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| msg298722 - (view) | Author: Antoine Pitrou (pitrou) * |
Date: 2017-07-20 14:05 | |
As a matter of fact, the bug is in Condition (which is used by Event.wait() but not by Event.is_set(), hence your workaround). Here is a reproducer script. This looks like a hard issue to solve. There is no way to know whether a process that used to be waiting for a Condition was killed. |
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| History | |||
|---|---|---|---|
| Date | User | Action | Args |
| 2022-04-11 14:58:49 | admin | set | github: 75158 |
| 2017-07-20 14:20:00 | pitrou | set | nosy:
+ sbt |
| 2017-07-20 14:05:30 | pitrou | set | files:
+ WaitersSleepers.py messages: + msg298722 title: Multiprocessing: Event.set() blocks indefinitely if a process waiting on it has died. -> multiprocessing.Condition.notify_all() blocks indefinitely if a process waiting on it has died |
| 2017-07-20 13:42:03 | mickp | set | messages: + msg298720 |
| 2017-07-20 13:33:16 | pitrou | set | versions:
+ Python 3.6, Python 3.7 nosy: + pitrou messages: + msg298719 stage: needs patch |
| 2017-07-20 11:29:48 | mickp | create | |