bpo-35081: Add _PyThreadState_GET() internal macro (GH-10266)

If Py_BUILD_CORE is defined, the PyThreadState_GET() macro access
_PyRuntime which comes from the internal pycore_state.h header.
Public headers must not require internal headers.

Move PyThreadState_GET() and _PyInterpreterState_GET_UNSAFE() from
Include/pystate.h to Include/internal/pycore_state.h, and rename
PyThreadState_GET() to _PyThreadState_GET() there.

The PyThreadState_GET() macro of pystate.h is now redefined when
pycore_state.h is included, to use the fast _PyThreadState_GET().

Changes:

* Add _PyThreadState_GET() macro
* Replace "PyThreadState_GET()->interp" with
  _PyInterpreterState_GET_UNSAFE()
* Replace PyThreadState_GET() with _PyThreadState_GET() in internal C
  files (compiled with Py_BUILD_CORE defined), but keep
  PyThreadState_GET() in the public header files.
* _testcapimodule.c: replace PyThreadState_GET() with
  PyThreadState_Get(); the module is not compiled with Py_BUILD_CORE
  defined.
* pycore_state.h now requires Py_BUILD_CORE to be defined.

1 files changed, 34 insertions, 0 deletions

diff --git a/Include/internal/pycore_state.h b/Include/internal/pycore_state.h
index ff25d2e..9a084f7 100644
--- a/Include/internal/pycore_state.h
+++ b/Include/internal/pycore_state.h
@@ -4,6 +4,10 @@
 extern "C" {
 #endif
 
+#ifndef Py_BUILD_CORE
+#  error "Py_BUILD_CORE must be defined to include this header"
+#endif
+
 #include "pystate.h"
 #include "pythread.h"
 
@@ -214,6 +218,36 @@ PyAPI_FUNC(_PyInitError) _PyRuntime_Initialize(void);
     (_PyRuntime.finalizing == tstate)
 
 
+/* Variable and macro for in-line access to current thread
+   and interpreter state */
+
+/* Get the current Python thread state.
+
+   Efficient macro reading directly the 'gilstate.tstate_current' atomic
+   variable. The macro is unsafe: it does not check for error and it can
+   return NULL.
+
+   The caller must hold the GIL.
+
+   See also PyThreadState_Get() and PyThreadState_GET(). */
+#define _PyThreadState_GET() \
+    ((PyThreadState*)_Py_atomic_load_relaxed(&_PyRuntime.gilstate.tstate_current))
+
+/* Redefine PyThreadState_GET() as an alias to _PyThreadState_GET() */
+#undef PyThreadState_GET
+#define PyThreadState_GET() _PyThreadState_GET()
+
+/* Get the current interpreter state.
+
+   The macro is unsafe: it does not check for error and it can return NULL.
+
+   The caller must hold the GIL.
+
+   See also _PyInterpreterState_Get()
+   and _PyGILState_GetInterpreterStateUnsafe(). */
+#define _PyInterpreterState_GET_UNSAFE() (_PyThreadState_GET()->interp)
+
+
 /* Other */
 
 PyAPI_FUNC(_PyInitError) _PyInterpreterState_Enable(_PyRuntimeState *);