python - multiprocessing.Manager().dict() で ConnectionRefusedError [Errno 61] を取得する

Question

簡単に言えば、メインスレッドで a の内容を印刷しようとしmultiprocessing.Manager().dict()たのですが、奇妙なエラーが発生しました。

20このエラーが発生したのは、プールの数が(はい、正確に)より大きく、20でのみmacOS(完全に動作するLinux) の場合のみです。

仕様:

  CPU: Intel(R) Core(TM) i9-9880H CPU @ 2.30GHz
macOS: 11.2.3

最小のエラー コードが添付されています。

#!/usr/bin/env python3

from contextlib import suppress
import multiprocessing as mp
import time


def run():
    D[mp.current_process().name] = 'some val'
    time.sleep(0.5)


if __name__ == '__main__':
    mp.set_start_method('fork')
    D, rets = mp.Manager().dict(), []
    with mp.Pool(25) as p:
        for _ in range(33):
            rets.append(p.apply_async(run))
        while rets:
            for ret in rets[:]:
                with suppress(mp.TimeoutError):
                    ret.get(timeout=0)
                    rets.remove(ret)
                    print(len(D))

エラー：

multiprocessing.pool.RemoteTraceback:
"""
Traceback (most recent call last):
  File "/usr/local/Cellar/python@3.9/3.9.2_4/Frameworks/Python.framework/Versions/3.9/lib/python3.9/multiprocessing/managers.py", line 801, in _callmethod
    conn = self._tls.connection
AttributeError: 'ForkAwareLocal' object has no attribute 'connection'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/usr/local/Cellar/python@3.9/3.9.2_4/Frameworks/Python.framework/Versions/3.9/lib/python3.9/multiprocessing/pool.py", line 125, in worker
    result = (True, func(*args, **kwds))
  File "/Users/???", line 9, in run
    D[mp.current_process().name] = 'some val'
  File "<string>", line 2, in __setitem__
  File "/usr/local/Cellar/python@3.9/3.9.2_4/Frameworks/Python.framework/Versions/3.9/lib/python3.9/multiprocessing/managers.py", line 805, in _callmethod
    self._connect()
  File "/usr/local/Cellar/python@3.9/3.9.2_4/Frameworks/Python.framework/Versions/3.9/lib/python3.9/multiprocessing/managers.py", line 792, in _connect
    conn = self._Client(self._token.address, authkey=self._authkey)
  File "/usr/local/Cellar/python@3.9/3.9.2_4/Frameworks/Python.framework/Versions/3.9/lib/python3.9/multiprocessing/connection.py", line 507, in Client
    c = SocketClient(address)
  File "/usr/local/Cellar/python@3.9/3.9.2_4/Frameworks/Python.framework/Versions/3.9/lib/python3.9/multiprocessing/connection.py", line 635, in SocketClient
    s.connect(address)
ConnectionRefusedError: [Errno 61] Connection refused
"""

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "/Users/???", line 22, in <module>
    ret.get(timeout=0)
  File "/usr/local/Cellar/python@3.9/3.9.2_4/Frameworks/Python.framework/Versions/3.9/lib/python3.9/multiprocessing/pool.py", line 771, in get
    raise self._value
ConnectionRefusedError: [Errno 61] Connection refused