Question

我的同事要求我帮助解决他正在研究的守护程序脚本所遇到的问题。他遇到了一个涉及multiprocessing.Manager的奇怪错误，我设法用以下五行重现：

import multiprocessing, os, sys
mgr = multiprocessing.Manager()
pid = os.fork()
if pid > 0:
    sys.exit(0)

在CentOS 6 Linux和Python 2.6上运行时，出现以下错误：

Traceback (most recent call last):
  File "/usr/lib64/python2.6/multiprocessing/util.py", line 235, in _run_finalizers
    finalizer()
  File "/usr/lib64/python2.6/multiprocessing/util.py", line 174, in __call__
    res = self._callback(*self._args, **self._kwargs)
  File "/usr/lib64/python2.6/multiprocessing/managers.py", line 576, in _finalize_manager
    if process.is_alive():
  File "/usr/lib64/python2.6/multiprocessing/process.py", line 129, in is_alive
    assert self._parent_pid == os.getpid(), 'can only test a child process'
AssertionError: can only test a child process
Error in atexit._run_exitfuncs:
Traceback (most recent call last):
  File "/usr/lib64/python2.6/atexit.py", line 24, in _run_exitfuncs
    func(*targs, **kargs)
  File "/usr/lib64/python2.6/multiprocessing/util.py", line 269, in _exit_function
    p.join()
  File "/usr/lib64/python2.6/multiprocessing/process.py", line 117, in join
    assert self._parent_pid == os.getpid(), 'can only join a child process'
AssertionError: can only join a child process
Error in sys.exitfunc:
Traceback (most recent call last):
  File "/usr/lib64/python2.6/atexit.py", line 24, in _run_exitfuncs
    func(*targs, **kargs)
  File "/usr/lib64/python2.6/multiprocessing/util.py", line 269, in _exit_function
    p.join()
  File "/usr/lib64/python2.6/multiprocessing/process.py", line 117, in join
    assert self._parent_pid == os.getpid(), 'can only join a child process'
AssertionError: can only join a child process

我怀疑错误是由于os.fork和multiprocessing.Manager之间的某些交互，并且他应该使用多处理模块来创建新进程而不是os.fork。谁能证实这一点和/或解释发生了什么？如果我的预感是正确的，为什么这是使用os.fork的错误地方？

Answer 1

问题在于Manager创建了一个流程并尝试在sys.exit停止它。由于在fork期间（懒惰）复制进程的内存，父进程和子进程都会尝试停止进程并等待它停止。但是，作为例外，只提到父进程可以做到这一点。如果不使用os.fork，则使用multiprocessing.Process，这将生成一个新进程，该进程不会尝试在Manager处关闭sys.exit。

Python multiprocessing.Manager和os.fork产生奇怪的行为

1 个答案: