Bugs item #1746071, was opened at 2007-07-01 10:49
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Category: Python Library
Group: Python 2.5
Status: Open
Resolution: None
Priority: 5
Private: No
Submitted By: David Benbennick (dbenbenn)
Assigned to: Nobody/Anonymous (nobody)
Summary: class mutex doesn't do anything atomically
Initial Comment:
>>> import mutex
>>> print mutex.mutex.testandset.__doc__
Atomic test-and-set -- grab the lock if it is not set,
return True if it succeeded.
The above docstring is wrong: the method is not atomic. This is easy to see by
inspecting the method's code:
def testandset(self):
"""Atomic test-and-set -- grab the lock if it is not set,
return True if it succeeded."""
if not self.locked:
self.locked = 1
return True
else:
return False
Therefore, it is possible for two threads to lock the same mutex
simultaneously. So the mutex module cannot be used for mutual exclusion.
The documentation for mutex says "The mutex module defines a class that allows
mutual-exclusion via acquiring and releasing locks."
[http://docs.python.org/lib/module-mutex.html]. Perhaps it would be a good
idea to make the module actually do what the documentation says.
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