Message 148782 - Python tracker

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Author	rhettinger
Recipients	rhettinger
Date	2011年12月03日.00:30:27
SpamBayes Score	5.694156e-06
Marked as misclassified	No
Message-id	<1322872228.97.0.525171057572.issue13521@psf.upfronthosting.co.za>

Content
A dialog on python-dev suggests that dict.setdefault() was intended to be atomic and that a number of experienced developers have deployed code relying on its atomicity: http://mail.python.org/pipermail/python-3000/2007-July/008693.html The actual implementation shows a second call to PyDict_Setitem() which can call PyObject_Hash() which can call arbitrary Python code. http://hg.python.org/cpython/file/2.7/Objects/dictobject.c#l1937 This fix is straight-forward, use the results of the initial lookup to insert the default object. This will make the operation atomic and it will make it faster.

Content

A dialog on python-dev suggests that dict.setdefault() was intended to be atomic and that a number of experienced developers have deployed code relying on its atomicity: http://mail.python.org/pipermail/python-3000/2007-July/008693.html
The actual implementation shows a second call to PyDict_Setitem() which can call PyObject_Hash() which can call arbitrary Python code. http://hg.python.org/cpython/file/2.7/Objects/dictobject.c#l1937
This fix is straight-forward, use the results of the initial lookup to insert the default object. This will make the operation atomic and it will make it faster.

History
Date	User	Action	Args
2011年12月03日 00:30:29	rhettinger	set	recipients: + rhettinger
2011年12月03日 00:30:28	rhettinger	set	messageid: <1322872228.97.0.525171057572.issue13521@psf.upfronthosting.co.za>
2011年12月03日 00:30:28	rhettinger	link	issue13521 messages
2011年12月03日 00:30:27	rhettinger	create

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