Issue #25150: Hide the private _Py_atomic_xxx symbols from the public

Python.h header to fix a compilation error with OpenMP. PyThreadState_GET()
becomes an alias to PyThreadState_Get() to avoid ABI incompatibilies.

It is important that the _PyThreadState_Current variable is always accessed
with the same implementation of pyatomic.h. Use the PyThreadState_Get()
function so extension modules will all reuse the same implementation.

Include/pyatomic.h

-/* Issue #23644: <stdatomic.h> is incompatible with C++, see:
-   https://gcc.gnu.org/bugzilla/show_bug.cgi?id=60932 */
-#if !defined(Py_LIMITED_API) && !defined(__cplusplus)
 #ifndef Py_ATOMIC_H
 #define Py_ATOMIC_H
+#ifdef Py_BUILD_CORE
 
 #include "dynamic_annotations.h"
 
@@ -248,5 +246,5 @@ _Py_ANNOTATE_MEMORY_ORDER(const volatile void *address, _Py_memory_order order)
 #define _Py_atomic_load_relaxed(ATOMIC_VAL) \
     _Py_atomic_load_explicit(ATOMIC_VAL, _Py_memory_order_relaxed)
 
+#endif  /* Py_BUILD_CORE */
 #endif  /* Py_ATOMIC_H */
-#endif  /* Py_LIMITED_API */

Include/pystate.h

@@ -177,20 +177,13 @@ PyAPI_FUNC(int) PyThreadState_SetAsyncExc(long, PyObject *);
 /* Variable and macro for in-line access to current thread state */
 
 /* Assuming the current thread holds the GIL, this is the
-   PyThreadState for the current thread.
-
-   Issue #23644: pyatomic.h is incompatible with C++ (yet). Disable
-   PyThreadState_GET() optimization: declare it as an alias to
-   PyThreadState_Get(), as done for limited API. */
-#if !defined(Py_LIMITED_API) && !defined(__cplusplus)
+   PyThreadState for the current thread. */
+#ifdef Py_BUILD_CORE
 PyAPI_DATA(_Py_atomic_address) _PyThreadState_Current;
-#endif
-
-#if defined(Py_DEBUG) || defined(Py_LIMITED_API) || defined(__cplusplus)
-#define PyThreadState_GET() PyThreadState_Get()
+#  define PyThreadState_GET() \
+             ((PyThreadState*)_Py_atomic_load_relaxed(&_PyThreadState_Current))
 #else
-#define PyThreadState_GET() \
-    ((PyThreadState*)_Py_atomic_load_relaxed(&_PyThreadState_Current))
+#  define PyThreadState_GET() PyThreadState_Get()
 #endif
 
 typedef

Misc/NEWS

@@ -11,6 +11,10 @@ Release date: TBA
 Core and Builtins
 -----------------
 
+- Issue #25150: Hide the private _Py_atomic_xxx symbols from the public
+  Python.h header to fix a compilation error with OpenMP. PyThreadState_GET()
+  becomes an alias to PyThreadState_Get() to avoid ABI incompatibilies.
+
 Library
 -------