[issue40907] cpython/lib/queue.py: put() does not acquire not_empty before notifying on it

[r n]

r n  added the comment:

Sorry, please ignore my previous comment, I can see that the issue is not in 
the queue, but probably be somewhere in my setup. 
I'll close this bug therefore. Thanks again for the clarification.

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resolution:  -> not a bug
stage:  -> resolved
status: open -> closed

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[issue40907] cpython/lib/queue.py: put() does not acquire not_empty before notifying on it

[r n]

r n  added the comment:

Thanks for the response.
However, if you see, every condition object has their own queue of waiters in 
self._waiters, that get notified during notify(), which are different for 
not_empty and not_full.
I see a hang very very rarely, like 1/25 times, in my program, which keeps, 
reading from and writing to a queue from multiple threads.

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nosy: +r n2

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[issue40907] cpython/lib/queue.py: put() does not acquire not_empty before notifying on it

[Raymond Hettinger]

Raymond Hettinger  added the comment:

Also note that threading.Condition.notify() would raise a RuntimeError if the 
underlying lock had not been acquired.

Have you observed any behavior to the contrary?

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[issue40907] cpython/lib/queue.py: put() does not acquire not_empty before notifying on it

[Raymond Hettinger]

New submission from Raymond Hettinger :

This code looks correct to me.  For condition variables, the requirement is 
that the underlying lock be held when notify() is called.  The not_full and 
not_empty condition variables share the same underlying lock, so it is 
sufficient that not_empty.notify() is called inside the body of "with 
self.not_full".

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nosy: +tim.peters

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[issue40907] cpython/lib/queue.py: put() does not acquire not_empty before notifying on it

[r n]

Change by r n :


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versions: +Python 3.10, Python 3.9

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[issue40907] cpython/lib/queue.py: put() does not acquire not_empty before notifying on it

[r n]

Change by r n :


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nosy: +rhettinger -r n2
title: cpython/queue.py: put() does not acquire not_empty before notifying on 
it -> cpython/lib/queue.py: put() does not acquire not_empty before notifying 
on it

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