[Tim] > > Same as the docs, I use "Python object" to mean a pointer to PyObject. > In
> that sense, a Py_buffer is no more a "Python object" than, e.g,, is a > > Py_ssize_t. > [Antoine > Yes, and the payload of an int object is not a "Python object". > The OP mentioned PyInt_AS_LONG as an example, so clearly the question > was broader than you're painting it to be. > Ah, but I don't know that. The docs carve out no exception for the PyInt_AS_LONG API function, and since that doesn't appear to exist in Python 3 anymore (the only Python source I have on my box right now) I couldn't stare at the implementation to guess. Staring at implementations is the _only_ way to guess. > If they want to muck with the `buf` member without the GIL, then if they > > care about races among multiple threads mucking with `buf`, they'll have > to > > supply their own mutual exclusion mechanism. > > Define "muck with". Precisely my point: _your_ unqualified "safe" is missing all the qualifications needed to spell out when it's actually safe. "safe" is a subtler question than you're painting it to be ;-) As long as you're reading the memory area(s) pointed to by the Py_buffer object, you're fine. If you plan to write > to that memory, obviously you'll need to make sure the various threads > don't overwrite each other, i.e. distribute the work carefully. > > But that's a normal provision for multi-threaded algorithms, not a > Python-specific restriction. I'm assuming someone asking a question > about multi-threaded access to CPython objects already knows all > this :-) While I don't assume that. Looking it up, if they stared at #define PyInt_AS_LONG <https://help.autodesk.com/cloudhelp/2018/ENU/MotionBuilder-SDK/cpp_ref/intobject_8h.html#a225d34d2e970c9942b56910a20c29277> (op) (((PyIntObject <https://help.autodesk.com/cloudhelp/2018/ENU/MotionBuilder-SDK/cpp_ref/struct_py_int_object.html> *)(op))->ob_ival) in Python 2 and had to _ask_ whether it was safe to invoke without the GIL, then a more plausible assumption is they're going more by poke-&-hope than by reasoning.
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