New submission from Mario Juric <mju...@ias.edu>:
The implementation of OrderedDict.__reduce__() in Python 2.7.1 is not thread
safe because of the following four lines:
tmp = self.__map, self.__root
del self.__map, self.__root
inst_dict = vars(self).copy()
self.__map, self.__root = tmp
If one thread is pickling an OrderedDict, while another accesses it, a race
condition occurs if the accessing thread accesses the dict after self.__map and
self.__root have been delated, and before they've been set again (above).
This leads to an extremely difficult bug to diagnose when using
multiprocessing.Queue to exchange OrderedDicts between multiple processes
(because Queue uses a separate feeder thread to do the pickling).
The fix seems relatively easy -- use:
inst_dict = vars(self).copy()
del inst_dict['_OrderedDict__map'], inst_dict['_OrderedDict__root']
instead of the above four lines.
PS: This issue+fix may also apply to Python 3.x, although I haven't tested it
there.
----------
components: Library (Lib)
messages: 134023
nosy: mjuric
priority: normal
severity: normal
status: open
title: OrderedDict.__reduce__ not threadsafe
type: behavior
versions: Python 2.7
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Python tracker <rep...@bugs.python.org>
<http://bugs.python.org/issue11875>
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