Amaury Forgeot d'Arc <[EMAIL PROTECTED]> added the comment: After 4 hours spent with the debugger I think I have an explanation and a correction of one of the problems. Note that this only affects the "Manager" tests.
- The threading.local type overrides getattr and setattr: on every call, it fetches a dictionary stored in the current ThreadState, and installs it in its self->dict member, allowing the regular PyObject_Generic[Get|Set]Attr functions to actually work on thread-local data. - Of course, for this to work the GIL must not be released in any way between the moment self->dict is set, until object's dictionary is retrieved inside PyObject_Generic[Get|Set]Attr. This condition makes the code a bit fragile. With current 2.6b1, there is no path in PyObject_Generic[Get|Set]Attr that releases the GIL before the dict is retrieved - no decref, no jump into python code (at least when the attribute name is a string). It's almost a miracle, indeed. - The problem is in threadmodule.c, the paragraph starting at line 285: the first time the local object is accessed, it calls the __init__ method of the threading.local derived class. And this calls python code, and can release the GIL. - The consequences are dramatic: this let the possibility for another thread to start, use the same local object, install its thread-local dict in self->dict, and stop here; the first thread will wake up with the wrong dict... - in the multiprocessing case, a remote call to a synchronization function grabs the wrong channel, and get bogus results... hence the "cannot wait on un-aquired (sic) lock" message. The actual correction is very short: only one "else" to remove... Here is a patch with a test. Added file: http://bugs.python.org/file10766/threadlocal.patch _______________________________________ Python tracker <[EMAIL PROTECTED]> <http://bugs.python.org/issue3088> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
