[issue30931] Race condition in asyncore wrongly closes channel

[Jaume]

New submission from Jaume:

If a socket is closed and polled here 
https://github.com/python/cpython/blob/0d0a32fb91cdfea1626e6c6b77a9bc44e15a2b8a/Lib/asyncore.py#L183
 the flag returned will be select.POLLNVAL (note that this can happen despite 
dispatcher.close() being called).

This wouldn't be a problem but before here 
https://github.com/python/cpython/blob/0d0a32fb91cdfea1626e6c6b77a9bc44e15a2b8a/Lib/asyncore.py#L185
 a new socket may be created with the same fd (which wouldn't be strange since 
that fd is now available), so the retrieved socket will be the newly created 
one instead of the old one and the new one will be close.

This is regularly happening to us, I could try to explain better, but that's 
really it.

--
messages: 298359
nosy: walkhour
priority: normal
severity: normal
status: open
title: Race condition in asyncore wrongly closes channel
versions: Python 2.7

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[issue30931] Race condition in asyncore wrongly closes channel

[Jaume]

Changes by Jaume :


--
type:  -> resource usage
versions: +Python 3.3, Python 3.4, Python 3.5, Python 3.6, Python 3.7

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[issue30931] Race condition in asyncore wrongly closes channel

[Jaume]

Changes by Jaume :


--
pull_requests: +2771

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[issue30931] Race condition in asyncore wrongly closes channel

[Jaume]

Changes by Jaume :


--
pull_requests: +2823

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[issue30985] Set closing variable in asyncore at close

[Jaume]

Changes by Jaume :


--
nosy: walkhour
priority: normal
severity: normal
status: open
title: Set closing variable in asyncore at close

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[issue30985] Set closing variable in asyncore at close

[Jaume]

Changes by Jaume :


--
pull_requests: +2854

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[issue30931] Race condition in asyncore may access the wrong dispatcher

[Jaume]

Jaume added the comment:

There's an alternative fix which follows a similar approach to the one you 
mention: https://github.com/python/cpython/pull/2707/.

I personally don't like too much to reuse again again an old variable as it's 
true that we don't know how people are using it (although I take they use it as 
a boolean since it's assigned to False).

On the other side this approach copies the map when it's not strictly necessary 
to do use just because we can't do it the proper way by using closing, as shown 
in the PR using it: https://github.com/python/cpython/pull/2764/files

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