Question

下面是我的python脚本。

import multiprocessing
# We must import this explicitly, it is not imported by the top-level
# multiprocessing module.
import multiprocessing.pool
import time

from random import randint


class NoDaemonProcess(multiprocessing.Process):
    # make 'daemon' attribute always return False
    def _get_daemon(self):
        return False
    def _set_daemon(self, value):
        pass
    daemon = property(_get_daemon, _set_daemon)

# We sub-class multiprocessing.pool.Pool instead of multiprocessing.Pool
# because the latter is only a wrapper function, not a proper class.
class MyPool(multiprocessing.pool.Pool):
    Process = NoDaemonProcess

def sleepawhile(t):
    print("Sleeping %i seconds..." % t)
    time.sleep(t)
    return t

def work(num_procs):
    print("Creating %i (daemon) workers and jobs in child." % num_procs)
    pool = multiprocessing.Pool(num_procs)

    result = pool.map(sleepawhile,
        [randint(1, 5) for x in range(num_procs)])

    # The following is not really needed, since the (daemon) workers of the
    # child's pool are killed when the child is terminated, but it's good
    # practice to cleanup after ourselves anyway.
    pool.close()
    pool.join()
    return result

def test():
    print("Creating 5 (non-daemon) workers and jobs in main process.")
    pool = MyPool(20)

    result = pool.map(work, [randint(1, 5) for x in range(5)])

    pool.close()
    pool.join()
    print(result)

if __name__ == '__main__':
    test()

这正在ubuntu服务器中运行，我正在使用python 3.6.7

在apt-get升级后我可以正常工作

group argument must be None for now

我可能遇到的错误是什么。我应该更改python版本。升级后是否应该回滚更改。

编辑1

Stacktrace异常：-

Traceback (most recent call last):
  File "/src/mainapp.py", line 104, in bulkfun
    p = MyPool(20)
  File "/usr/lib/python3.6/multiprocessing/pool.py", line 175, in __init__
    self._repopulate_pool()
  File "/usr/lib/python3.6/multiprocessing/pool.py", line 236, in _repopulate_pool
    self._wrap_exception)
  File "/usr/lib/python3.6/multiprocessing/pool.py", line 250, in _repopulate_pool_static
    wrap_exception)
  File "/usr/lib/python3.6/multiprocessing/process.py", line 73, in __init__
    assert group is None, 'group argument must be None for now'
AssertionError: group argument must be None for now

编辑2

该代码适用于python2.7，python3.5 但是，如果我使用python 3.6.7运行，则会收到如下错误。

Creating 5 (non-daemon) workers and jobs in main process.
Traceback (most recent call last):
  File "multi.py", line 52, in <module>
    test()
  File "multi.py", line 43, in test
    pool = MyPool(5)
  File "/usr/lib/python3.6/multiprocessing/pool.py", line 175, in __init__
    self._repopulate_pool()
  File "/usr/lib/python3.6/multiprocessing/pool.py", line 236, in _repopulate_pool
    self._wrap_exception)
  File "/usr/lib/python3.6/multiprocessing/pool.py", line 250, in _repopulate_pool_static
    wrap_exception)
  File "/usr/lib/python3.6/multiprocessing/process.py", line 73, in __init__
    assert group is None, 'group argument must be None for now'
AssertionError: group argument must be None for now

Answer 1

这里也一样。
在我的情况下，此代码有效（python 3.6.7）。（https://stackoverflow.com/a/53180921/10742388）

class NoDaemonProcess(multiprocessing.Process):
    @property
    def daemon(self):
        return False

    @daemon.setter
    def daemon(self, value):
        pass


class NoDaemonContext(type(multiprocessing.get_context())):
    Process = NoDaemonProcess

# We sub-class multiprocessing.pool.Pool instead of multiprocessing.Pool
# because the latter is only a wrapper function, not a proper class.
class MyPool(multiprocessing.pool.Pool):
    def __init__(self, *args, **kwargs):
        kwargs['context'] = NoDaemonContext()
        super(MyPool, self).__init__(*args, **kwargs)

我认为此问题来自process.py（https://github.com/python/cpython/blob/8ca0fa9d2f4de6e69f0902790432e0ab2f37ba68/Lib/multiprocessing/process.py#L189）

的更改

Answer 2

我在将Travis发行版从14.04升级到16.04时遇到了这个问题，而python 3.6开始失败。我已经找到了解决此问题的方法，因为它是对另一个软件包的修复-FIX: Python 2.7-3.7.1 compatible NonDaemonPool

class NonDaemonPool(multiprocessing.pool.Pool):
    def Process(self, *args, **kwds):
        proc = super(NonDaemonPool, self).Process(*args, **kwds)

        class NonDaemonProcess(proc.__class__):
            """Monkey-patch process to ensure it is never daemonized"""
            @property
            def daemon(self):
                return False

            @daemon.setter
            def daemon(self, val):
                pass

        proc.__class__ = NonDaemonProcess
        return proc

目前在multiprocessing.pool中，错误组参数必须为None。

2 个答案: