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vstinner merged 1 commit into from
Feb 6, 2020
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bpo-39542: Document limited C API changes #18378

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49 changes: 42 additions & 7 deletions Doc/whatsnew/3.9.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -319,13 +319,6 @@ Optimizations
Build and C API Changes
=======================

* Provide :c:func:`Py_EnterRecursiveCall` and :c:func:`Py_LeaveRecursiveCall`
as regular functions for the limited API. Previously, there were defined as
macros, but these macros didn't work with the limited API which cannot access
``PyThreadState.recursion_depth`` field. Remove ``_Py_CheckRecursionLimit``
from the stable ABI.
(Contributed by Victor Stinner in :issue:`38644`.)

* Add a new public :c:func:`PyObject_CallNoArgs` function to the C API, which
calls a callable Python object without any arguments. It is the most efficient
way to call a callable Python object without any argument.
Expand Down Expand Up @@ -359,6 +352,48 @@ Build and C API Changes
* The ``COUNT_ALLOCS`` special build macro has been removed.
(Contributed by Victor Stinner in :issue:`39489`.)

* Changes in the limited C API (if ``Py_LIMITED_API`` macro is defined):

* Provide :c:func:`Py_EnterRecursiveCall` and :c:func:`Py_LeaveRecursiveCall`
as regular functions for the limited API. Previously, there were defined as
macros, but these macros didn't work with the limited API which cannot
access ``PyThreadState.recursion_depth`` field.

* Exclude the following functions from the limited C API:

* ``_Py_CheckRecursionLimit``
* ``_Py_NewReference()``
* ``_Py_ForgetReference()``
* ``_PyTraceMalloc_NewReference()``
* ``_Py_GetRefTotal()``
* The trashcan mechanism which never worked in the limited C API.
* ``PyTrash_UNWIND_LEVEL``
* ``Py_TRASHCAN_BEGIN_CONDITION``
* ``Py_TRASHCAN_BEGIN``
* ``Py_TRASHCAN_END``
* ``Py_TRASHCAN_SAFE_BEGIN``
* ``Py_TRASHCAN_SAFE_END``

* The following static inline functions or macros become regular "opaque"
function to hide implementation details:

* ``_Py_NewReference()``
* ``PyObject_INIT()`` and ``PyObject_INIT_VAR()`` become aliases to
:c:func:`PyObject_Init` and :c:func:`PyObject_InitVar` in the limited C
API, but are overriden with static inline function otherwise. Thanks to
that, it was possible to exclude ``_Py_NewReference()`` from the limited
C API.

* Move following functions and definitions to the internal C API:

* ``_PyDebug_PrintTotalRefs()``
* ``_Py_PrintReferences()``
* ``_Py_PrintReferenceAddresses()``
* ``_Py_tracemalloc_config``
* ``_Py_AddToAllObjects()`` (specific to ``Py_TRACE_REFS`` build)

(Contributed by Victor Stinner in :issue:`38644` and :issue:`39542`.)


Deprecated
==========
Expand Down