STINNER Victor added the comment:
The problem is the weakref callback of _module_locks. It seems like the
callback is called after a second thread replaced _module_locks[name]
* Thread 1: _get_module_lock('random') sets _module_locks['random'] and
registers a weakref callback on the newly created lock
* Thread 1: the lock is destroyed, the weakref callback will be called as soon
as possible
* Thread 2: _get_module_lock('random') sees that the weakref is dead and so
replaces _module_locks['random'] with a new lock, and registers a new weakref
callback on the second lock
* Thread 1: Call the weakref callback removing _module_locks['random'] -- BUG:
the callback is called too late, after Thread 2 already sets a new lock
* Thread 2: The lock is destroyed, the second weakref callback will be called
as soon as possible
* Thread 2: The second callback is called and fails with KeyError since
_module_locks['random'] was already called in the Thread 1 in the meanwhile
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Python tracker <[email protected]>
<http://bugs.python.org/issue31070>
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