[New-bugs-announce] [issue14881] multiprocessing.dummy craches when self._parent._children does not exist

Itay Brandes report at bugs.python.org
Tue May 22 10:51:10 CEST 2012

New submission from Itay Brandes <akari.il at gmail.com>:

multiprocessing.dummy crashes when attempting to create a ThreadPool from a Thread.

The following code will crush on 2.7.3:

    import multiprocessing.dummy
    import threading
    class Worker(threading.Thread):
        def __init__(self):
        def run(self):
            poll = multiprocessing.dummy.Pool(5)
            print str(poll)
    w = Worker()

will crush with the following traceback:

    poll = multiprocessing.dummy.Pool(5)
  File "C:\Python27\lib\multiprocessing\dummy\__init__.py", line 150, in Pool
    return ThreadPool(processes, initializer, initargs)
  File "C:\Python27\lib\multiprocessing\pool.py", line 685, in __init__
    Pool.__init__(self, processes, initializer, initargs)
  File "C:\Python27\lib\multiprocessing\pool.py", line 136, in __init__
  File "C:\Python27\lib\multiprocessing\pool.py", line 199, in _repopulate_pool
  File "C:\Python27\lib\multiprocessing\dummy\__init__.py", line 73, in start
    self._parent._children[self] = None
AttributeError: 'Worker' object has no attribute '_children'

If you have access to the thread itself, you can set the _children attribute youself (w._children = weakref.WeakKeyDictionary()), but it is not possible with threads different from threading.thread (Such as PyQt4's QThread thread, which is essential for GUI programming).

The fix that I found is to edit the Python27\Lib\multiprocessing\dummy\__init__.py file. The crashing code is line number 73.
This line should be nested in an if block:

        if hasattr(self._parent, '_children'):
            self._parent._children[self] = None

That way the code is fixed.

components: None
messages: 161339
nosy: Itay.Brandes
priority: normal
severity: normal
status: open
title: multiprocessing.dummy craches when self._parent._children does not exist
type: crash
versions: Python 2.7

Python tracker <report at bugs.python.org>

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