Description

vindex10

opened on Aug 7, 2024

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Bug report

Bug description:

I'm receiving a warning when using the multiprocessing.Pool in spawn mode.

/opt/pyenv/versions/3.12.4/lib/python3.12/multiprocessing/resource_tracker.py:254: UserWarning: resource_tracker: There appear to be 1 leaked semaphore objects to clean up at shutdown
  warnings.warn('resource_tracker: There appear to be %d '

A similar issue was brought up and fixed before, when multiprocessing.Process was used:
#30617

The test case introduced by the PR above: https://github.com/python/cpython/blob/3.12/Lib/test/_test_multiprocessing.py#L6040C7-L6040C24

To trigger the warning, I just replaced the Process with Pool as follows:

import multiprocessing as mp
ctx = mp.get_context('spawn')
global_resource = ctx.Semaphore()
def submain(): pass
if __name__ == '__main__':
    p = ctx.Pool(processes=3).starmap(submain, [tuple() for i in range(5)])

CPython versions tested on:

3.11, 3.12, CPython main branch

Operating systems tested on:

Linux

Reacted by Rinat Nazarov and Joshua

Activity

1. vindex10

   added

   type-bugAn unexpected behavior, bug, or errorAn unexpected behavior, bug, or error

   on Aug 7, 2024
2. hanke-it-nrw commented on Dec 17, 2024

   

   hanke-it-nrw

   on Dec 17, 2024

   More actions

   I have the same issue with context forkserver:

   import multiprocessing as mp
   from multiprocessing import Queue
   ctx = mp.get_context('forkserver')
   global_resource = ctx.Semaphore()
   def submain(): pass
   if __name__ == '__main__':
       p = ctx.Pool(processes=3).starmap(submain, [tuple() for i in range(5)])
   

   Only the number of leaked objects differ

   /usr/lib64/python3.11/multiprocessing/resource_tracker.py:254: UserWarning: resource_tracker: There appear to be 3 leaked semaphore objects to clean up at shutdown
     warnings.warn('resource_tracker: There appear to be %d '
   

   CPython versions tested on:

   3.11, 3.12, CPython main branch

   Operating systems tested on:

   Linux
3. picnixz

   added

   stdlibStandard Library Python modules in the Lib/ directoryStandard Library Python modules in the Lib/ directory

   topic-multiprocessing

   on Dec 17, 2024

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