[Python-Dev] Const access to CPython objects outside of GIL? (original) (raw)

Tim Peters tim.peters at gmail.com
Tue Jul 17 11:59:02 EDT 2018

[Tim]> There is no intention to support GIL-free access to any Python objects. So

> that's the contract: "All warranties are null & void if you do just about > anything while not holding the GIL".

[Antoine]

Actually, accessing a Pybuffer that's been obtained in the regular way

(e.g. with PyObject_GetBuffer) is safe even without the GIL.

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.

If someone wants to muck with the obj member of a Py_buffer struct, then they're back in "Python object" territory (obj is a PyObject*) and so are on their own if they don't obtain the GIL. Likewise all bets are off if they don't hold the GIL when calling PyObject_GetBuffer() to begin with, or PyBuffer_Release() when they're done.

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.

So your "safe" comes with footnotes too, even though Py_buffer isn't itself a PyObject*. -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://mail.python.org/pipermail/python-dev/attachments/20180717/40791e1a/attachment.html>

More information about the Python-Dev mailing list