[issue44614] Broken Pipe in Server of Manager in multiprocessing when finalizing, sometimes

[Mark Shannon]

Change by Mark Shannon :


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pull_requests:  -25654

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[issue44614] Broken Pipe in Server of Manager in multiprocessing when finalizing, sometimes

[Mark Shannon]

Change by Mark Shannon :


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keywords: +patch
nosy: +Mark.Shannon
nosy_count: 1.0 -> 2.0
pull_requests: +25654
stage:  -> patch review
pull_request: https://github.com/python/cpython/pull/27109

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[issue44614] Broken Pipe in Server of Manager in multiprocessing when finalizing, sometimes

[Florian Streibelt]

New submission from Florian Streibelt :

It seems that the shutdown() method of the Server in in managers.py is already 
sending the result of its execution directly into the connection, and then the 
handle_request() method is trying to send ('#RETURN', None) yet again after 
returning from the call to shutdown() which sometimes yields a Broken Pipe 
Exception.

with the following line in handle_request():
result = func(c, *args, **kwds)
a call to shutown() is made, and in shutdown() I see:
c.send(('#RETURN', None))

and back in handle_request():
msg = ('#RETURN', result)
…
c.send(msg)

attached you find a minimal example that shows this behaviour sometimes, if 
logging is set to not more than DEBUG. I am guessing that the Broken Pipe 
depends on a race with the other side being closed.

Although the race condition does not look like having an impact, it is highly 
confusing when debugging. 


log:
  INFO   MainProcess util.py:54  sending shutdown message 
to manager
 DEBUGBaseManager-12 util.py:50  manager received shutdown 
message
  INFOBaseManager-12 util.py:54  Failure to send message: 
('#RETURN', None)
  INFOBaseManager-12 util.py:54  process shutting down
  INFOBaseManager-12 util.py:54   ... request was (None, 
'shutdown', (), {})
 DEBUGBaseManager-12 util.py:50  running all "atexit" 
finalizers with priority >= 0
  INFOBaseManager-12 util.py:54   ... exception was 
BrokenPipeError(32, 'Broken pipe')
 DEBUGBaseManager-12 util.py:50  running the remaining 
"atexit" finalizers
  INFOBaseManager-12 util.py:54  process exiting with 
exitcode 0

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components: Library (Lib)
files: race2.py
messages: 397358
nosy: mutax
priority: normal
severity: normal
status: open
title: Broken Pipe in Server of Manager in multiprocessing when finalizing, 
sometimes
type: behavior
versions: Python 3.9
Added file: https://bugs.python.org/file50145/race2.py

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