[New-bugs-announce] [issue38744] python 3.8 hang in multiprocessing.Pool() locking on FreeBSD

[Dmitry Marakasov]

New submission from Dmitry Marakasov <amdmi3 at amdmi3.ru>:

System: FreeBSD 12.0-RELEASE, amd64.

This simple program

    from multiprocessing import Pool
    from time import sleep

    Pool().map(sleep, [0.01] * 10)

works fine with python 3.7, but is likely (about 20-50% probability on my 4 core box) to hang with python 3.8. Example backtraces after interruption:

% python3.8 1.py
^CException ignored in: <Finalize object, dead>
Traceback (most recent call last):
  File "/usr/local/lib/python3.8/multiprocessing/util.py", line 201, in __call__
Process ForkPoolWorker-2:
Process ForkPoolWorker-4:
    res = self._callback(*self._args, **self._kwargs)
  File "/usr/local/lib/python3.8/multiprocessing/pool.py", line 689, in _terminate_pool
    cls._help_stuff_finish(inqueue, task_handler, len(pool))
  File "/usr/local/lib/python3.8/multiprocessing/pool.py", line 674, in _help_stuff_finish
    inqueue._rlock.acquire()
KeyboardInterrupt: 
Process ForkPoolWorker-3:
Process ForkPoolWorker-1:

% python3.8 1.py
^CException ignored in: <Finalize object, dead>
Traceback (most recent call last):
  File "/usr/local/lib/python3.8/multiprocessing/util.py", line 201, in __call__
Process ForkPoolWorker-3:
Process ForkPoolWorker-4:
Process ForkPoolWorker-1:
    res = self._callback(*self._args, **self._kwargs)
  File "/usr/local/lib/python3.8/multiprocessing/pool.py", line 689, in _terminate_pool
    cls._help_stuff_finish(inqueue, task_handler, len(pool))
  File "/usr/local/lib/python3.8/multiprocessing/pool.py", line 674, in _help_stuff_finish
    inqueue._rlock.acquire()
KeyboardInterrupt: 
Process ForkPoolWorker-2:

% python3.8 1.py
^CException ignored in: <Finalize object, dead>
Process ForkPoolWorker-2:
Process ForkPoolWorker-3:
Traceback (most recent call last):
  File "/usr/local/lib/python3.8/multiprocessing/util.py", line 201, in __call__
Process ForkPoolWorker-1:
    res = self._callback(*self._args, **self._kwargs)
  File "/usr/local/lib/python3.8/multiprocessing/pool.py", line 689, in _terminate_pool
    cls._help_stuff_finish(inqueue, task_handler, len(pool))
  File "/usr/local/lib/python3.8/multiprocessing/pool.py", line 674, in _help_stuff_finish
Traceback (most recent call last):
Traceback (most recent call last):
  File "/usr/local/lib/python3.8/multiprocessing/process.py", line 313, in _bootstrap
    self.run()
  File "/usr/local/lib/python3.8/multiprocessing/process.py", line 313, in _bootstrap
    self.run()
  File "/usr/local/lib/python3.8/multiprocessing/process.py", line 108, in run
    self._target(*self._args, **self._kwargs)
  File "/usr/local/lib/python3.8/multiprocessing/process.py", line 108, in run
    self._target(*self._args, **self._kwargs)
  File "/usr/local/lib/python3.8/multiprocessing/pool.py", line 114, in worker
    task = get()
  File "/usr/local/lib/python3.8/multiprocessing/pool.py", line 114, in worker
    task = get()
  File "/usr/local/lib/python3.8/multiprocessing/queues.py", line 355, in get
    with self._rlock:
  File "/usr/local/lib/python3.8/multiprocessing/queues.py", line 355, in get
    with self._rlock:
  File "/usr/local/lib/python3.8/multiprocessing/synchronize.py", line 95, in __enter__
    return self._semlock.__enter__()
  File "/usr/local/lib/python3.8/multiprocessing/synchronize.py", line 95, in __enter__
    return self._semlock.__enter__()
KeyboardInterrupt
KeyboardInterrupt
    inqueue._rlock.acquire()
KeyboardInterrupt: 
Traceback (most recent call last):
  File "/usr/local/lib/python3.8/multiprocessing/process.py", line 313, in _bootstrap
    self.run()
  File "/usr/local/lib/python3.8/multiprocessing/process.py", line 108, in run
    self._target(*self._args, **self._kwargs)
  File "/usr/local/lib/python3.8/multiprocessing/pool.py", line 114, in worker
    task = get()
  File "/usr/local/lib/python3.8/multiprocessing/queues.py", line 356, in get
    res = self._reader.recv_bytes()
  File "/usr/local/lib/python3.8/multiprocessing/connection.py", line 216, in recv_bytes
    buf = self._recv_bytes(maxlength)
  File "/usr/local/lib/python3.8/multiprocessing/connection.py", line 414, in _recv_bytes
    buf = self._recv(4)
  File "/usr/local/lib/python3.8/multiprocessing/connection.py", line 379, in _recv
    chunk = read(handle, remaining)
KeyboardInterrupt
Process ForkPoolWorker-4:

Related issue in FreeBSD bugzilla: https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=241801

----------
components: Library (Lib)
messages: 356243
nosy: AMDmi3
priority: normal
severity: normal
status: open
title: python 3.8 hang in multiprocessing.Pool() locking on FreeBSD
versions: Python 3.8

_______________________________________
Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue38744>
_______________________________________