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[C API] PyOS_ReadlineFunctionPointer API rely on private _PyOS_ReadlineTState variable removed in Python 3.13 #112446
Description
Hi,
I removed the _PyOS_ReadlineTState variable from the public C API (it was moved to the internal C API). The gdb project sets its readline callback and uses the _PyOS_ReadlineTState variable and so fails to build on Python 3.13.0 alpha2: https://bugzilla.redhat.com/show_bug.cgi?id=2250652
gdb: PyOS_ReadlineFunctionPointer = gdbpy_readline_wrapper;
The gdb function uses _PyOS_ReadlineTState to use the Python C API:
PyEval_RestoreThread (_PyOS_ReadlineTState);
gdbpy_convert_exception (except);
PyEval_SaveThread ();source: py-gdb-readline.c
The _PyOS_ReadlineTState variable was added in 2004 by commit 30ea2f2.
The callback is called with the GIL released. The _PyOS_ReadlineTState variable is used to acquire again the GIL.
In 2020, I made fixes related to GIL but not directly to this issue:
Activity
vstinner commentedon Dec 8, 2023
The documentation https://docs.python.org/dev/c-api/veryhigh.html#c.PyOS_ReadlineFunctionPointer should also mention the internal lock, at least explain that the callback cannot be called twice at the same time in two threads.
vstinner commentedon Dec 12, 2023
Well, if a readline callback needs to use the Python C API,
PyGILState_Ensure()andPyGILState_Release()to be used to temporarily acquire/release the GIL. I'm not sure of the advantage of usingPyEval_RestoreThread (_PyOS_ReadlineTState)andPyEval_SaveThread()instead.