On 5/1/07, Tim Peters <[EMAIL PROTECTED]> wrote:
[Neal Norwitz] >> In rev 54982 (the first time this crash was seen), I see something >> which might create a problem. In python/trunk/Modules/posixmodule.c >> (near line 6300): >> >> + PyMem_FREE(mode); >> Py_END_ALLOW_THREADS Shouldn't do that. [Brett Cannon] > The PyMem_MALLOC call that creates 'mode' is also called without explicitly > holding the GIL. Or that ;-)
Luckily I misread the code so it doesn't do that boo-boo.
Can you call PyMem_FREE() without the GIL held? I couldn't find it>> documented either way. > I believe the GIL does not need to be held, but obviously Tim or someone > with more memory experience should step in to say definitively. The GIL should be held. The relevant docs are in the Python/C API manual, section "8.1 Thread State and the Global Interpreter Lock": Therefore, the rule exists that only the thread that has acquired the global interpreter lock may operate on Python objects or call Python/C API functions. PyMem_XYZ is certainly a "Python/C API function". There are functions you can call without holding the GIL, and section 8.1 intends to give an exhaustive list of those. These are functions that can't rely on the GIL, like PyEval_InitThreads() (which /creates/ the GIL), and various functions that create and destroy thread and interpreter state. > If you look at Include/pymem.h, PyMem_FREE gets defined as PyObject_FREE in > a debug build. PyObject_Free is defined at _PyObject_DebugFree. That > function checks that the memory has not been written with the debug bit > pattern and then calls PyObject_Free. That call just sticks the memory back > into pymalloc's memory pool which is implemented without using any Python > objects. But pymalloc's pools have a complex internal structure of their own, and cannot be mucked with safely by multiple threads simultaneously.
Ah, OK. That makes sense. Glad I pointed out my ignorance then. =) -Brett
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