[Python-Dev] GIL required for all Python calls? (original) (raw)

Guido van Rossum guido at python.org
Thu Jan 7 05:29:03 CET 2010

On Wed, Jan 6, 2010 at 7:32 PM, Benjamin Peterson <benjamin at python.org> wrote:

2010/1/6 John Arbash Meinel <john.arbash.meinel at gmail.com>: > AFAIK, the only things that don't require the GIL are macro functions, > like PyStringASSTRING or PyTupleSETITEM. PyErrSetString, for > example, will be increfing and setting the exception state, so certainly > needs the GIL to be held.

As a general rule, I would say, no Py* macros are safe without the gil either (the exception being PyENDALLOWTHREADS), since they mutate Python objects which must be protected.

That's keeping it on the safe side, since there are some macros like PyString_AS_STRING() that are also safe, if you are owning at least one reference to the string object.

At the same time, "no Py* macros" is not quite strong enough, since if you called PyString_AS_STRING() before releasing the GIL but you don't own a reference to the string object, the string might be deallocated behind your back by another thread.

A better rule would be "you may access the memory buffer in a PyString or PyUnicode object with the GIL released as long as you own a reference to the string object." Everything else is out of bounds (or not worth the bother).

-- --Guido van Rossum (python.org/~guido)

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