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PEP 651: Revise C-API (#1772) 

*Removes Py_CheckStackDepthWithHeadRoom and makes Py_EnterRecursiveCall call Py_CheckStackDepth.
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Mark Shannon 2021-01-20 16:23:53 +00:00 committed by GitHub
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@ -116,8 +116,7 @@ then a ``StackOverflow`` exception should be raised.
C-API
-----
There will be no C-API for modifying Python recursion depth.
It will be managed internally by the interpreter.
A new function, ``Py_CheckStackDepth()`` will be added, and the behavior of ``Py_EnterRecursiveCall()`` will be modified slightly.
Py_CheckStackDepth()
''''''''''''''''''''
@ -126,32 +125,15 @@ Py_CheckStackDepth()
will return 0 if there is no immediate danger of C stack overflow.
It will return -1 and set an exception, if the C stack is near to overflowing.
Py_CheckStackDepthWithHeadRoom()
''''''''''''''''''''''''''''''''
``int Py_CheckStackDepthWithHeadroom(const char *where, int headroom)``
Behaves like ``Py_CheckStackDepth(where)`` but reduces the effective stack size
by ``headroom`` bytes when determining the risk of C stack overflow.
This function should be used when additional C stack will be
needed for cleanup.
``Py_CheckStackDepth(where)`` is equivalent to ``Py_CheckStackDepthWithHeadRoom(where, 0)``.
Unless absolutely necessary to perform complex cleanup,
authors of extension modules are advised to use ``Py_CheckStackDepth()``
and return immediately on failure.
Py_EnterRecursiveCall()
'''''''''''''''''''''''
This will become a synonym for Py_CheckStackDepth().
``Py_EnterRecursiveCall()`` will be modified to call ``Py_CheckStackDepth()`` before performing its current function.
PyLeaveRecursiveCall()
''''''''''''''''''''''
This will have no effect.
``Py_LeaveRecursiveCall()`` will remain unchanged.
Backwards Compatibility
=======================
@ -162,9 +144,15 @@ For example, the gdb scripts for Python will need to be aware that there may be
per C frame.
C code that uses the ``Py_EnterRecursiveCall()``, ``PyLeaveRecursiveCall()`` pair of
functions will continue to work correctly.
functions will continue to work correctly. In addition, ``Py_EnterRecursiveCall()``
may raise a ``StackOverflow`` exception.
New code should use the ``Py_CheckStackDepth()`` function, unless the code wants to
count as a Python function call with regard to the recursion limit.
We recommend that "python-like" code, such as Cython-generated functions,
use ``Py_EnterRecursiveCall()``, but other code use ``Py_CheckStackDepth()``.
New code should use the ``Py_CheckStackDepth()`` function.
Security Implications
=====================