From dac62e27cdc309d769faa7520c3e8c5f2fb94c9b Mon Sep 17 00:00:00 2001
From: Victor Stinner <vstinner@python.org>
Date: Mon, 28 Aug 2023 19:03:03 +0200
Subject: [PATCH] gh-85283: Add PyInterpreterState_IsMain() function

This function can be used to convert the syslog extension to the
limited C API. The PyInterpreterState_Main() is not available in the
limited C API.
---
 Doc/c-api/init.rst                                       | 9 +++++++++
 Doc/data/stable_abi.dat                                  | 1 +
 Doc/whatsnew/3.13.rst                                    | 4 ++++
 Include/pystate.h                                        | 5 +++++
 Lib/test/test_stable_abi_ctypes.py                       | 1 +
 .../C API/2023-08-28-19-07-42.gh-issue-85283.BFzfPr.rst  | 2 ++
 Misc/stable_abi.toml                                     | 2 ++
 Modules/syslogmodule.c                                   | 3 ++-
 PC/python3dll.c                                          | 1 +
 Python/pystate.c                                         | 6 ++++++
 10 files changed, 33 insertions(+), 1 deletion(-)
 create mode 100644 Misc/NEWS.d/next/C API/2023-08-28-19-07-42.gh-issue-85283.BFzfPr.rst

diff --git a/Doc/c-api/init.rst b/Doc/c-api/init.rst
index 60f5c81cff572c..68b2f529a74b2c 100644
--- a/Doc/c-api/init.rst
+++ b/Doc/c-api/init.rst
@@ -1126,6 +1126,15 @@ All of the following functions must be called after :c:func:`Py_Initialize`.
 
    .. versionadded:: 3.8
 
+.. c:function:: int PyInterpreterState_IsMain(PyInterpreterState *interp)
+
+   Return true (non-zero) if the interpreter is the main interpreter.
+   Return false (zero) otherwise.
+
+   See also :c:func:`PyInterpreterState_Main`.
+
+   .. versionadded:: 3.13
+
 .. c:type:: PyObject* (*_PyFrameEvalFunction)(PyThreadState *tstate, _PyInterpreterFrame *frame, int throwflag)
 
    Type of a frame evaluation function.
diff --git a/Doc/data/stable_abi.dat b/Doc/data/stable_abi.dat
index cc6349a0330e8c..a3585024ccaa39 100644
--- a/Doc/data/stable_abi.dat
+++ b/Doc/data/stable_abi.dat
@@ -326,6 +326,7 @@ function,PyInterpreterState_Delete,3.2,,
 function,PyInterpreterState_Get,3.9,,
 function,PyInterpreterState_GetDict,3.8,,
 function,PyInterpreterState_GetID,3.7,,
+function,PyInterpreterState_IsMain,3.13,,
 function,PyInterpreterState_New,3.2,,
 function,PyIter_Check,3.8,,
 function,PyIter_Next,3.2,,
diff --git a/Doc/whatsnew/3.13.rst b/Doc/whatsnew/3.13.rst
index a17b549aec5d8f..40d60a22bb0d62 100644
--- a/Doc/whatsnew/3.13.rst
+++ b/Doc/whatsnew/3.13.rst
@@ -886,6 +886,10 @@ New Features
   (with an underscore prefix).
   (Contributed by Victor Stinner in :gh:`108014`.)
 
+* Add :c:func:`PyInterpreterState_IsMain` function to test if an interpreter
+  is the main interpreter.
+  (Contributed by Victor Stinner in :gh:`85283`.)
+
 Porting to Python 3.13
 ----------------------
 
diff --git a/Include/pystate.h b/Include/pystate.h
index e6b4de979c87b8..46d4aea91ca61d 100644
--- a/Include/pystate.h
+++ b/Include/pystate.h
@@ -37,6 +37,11 @@ PyAPI_FUNC(int64_t) PyInterpreterState_GetID(PyInterpreterState *);
 #endif
 #if !defined(Py_LIMITED_API) || Py_LIMITED_API+0 >= 0x03030000
 
+#if !defined(Py_LIMITED_API) || Py_LIMITED_API+0 >= 0x030d0000
+PyAPI_FUNC(int) PyInterpreterState_IsMain(PyInterpreterState *interp);
+#endif
+
+
 /* State unique per thread */
 
 /* New in 3.3 */
diff --git a/Lib/test/test_stable_abi_ctypes.py b/Lib/test/test_stable_abi_ctypes.py
index 1f3cf612c18f6d..b422f8afdf684d 100644
--- a/Lib/test/test_stable_abi_ctypes.py
+++ b/Lib/test/test_stable_abi_ctypes.py
@@ -355,6 +355,7 @@ def test_windows_feature_macros(self):
     "PyInterpreterState_Get",
     "PyInterpreterState_GetDict",
     "PyInterpreterState_GetID",
+    "PyInterpreterState_IsMain",
     "PyInterpreterState_New",
     "PyIter_Check",
     "PyIter_Next",
diff --git a/Misc/NEWS.d/next/C API/2023-08-28-19-07-42.gh-issue-85283.BFzfPr.rst b/Misc/NEWS.d/next/C API/2023-08-28-19-07-42.gh-issue-85283.BFzfPr.rst
new file mode 100644
index 00000000000000..0f8d06216178f1
--- /dev/null
+++ b/Misc/NEWS.d/next/C API/2023-08-28-19-07-42.gh-issue-85283.BFzfPr.rst	
@@ -0,0 +1,2 @@
+Add :c:func:`PyInterpreterState_IsMain` function to test if an interpreter
+is the main interpreter. Patch by Victor Stinner.
diff --git a/Misc/stable_abi.toml b/Misc/stable_abi.toml
index 2030a085abf27c..e6502d7af02e8f 100644
--- a/Misc/stable_abi.toml
+++ b/Misc/stable_abi.toml
@@ -2452,3 +2452,5 @@
     added = '3.13'
 [function.PyLong_AsInt]
     added = '3.13'
+[function.PyInterpreterState_IsMain]
+    added = '3.13'
diff --git a/Modules/syslogmodule.c b/Modules/syslogmodule.c
index 6db8de9c491dd9..674ddde3ad05db 100644
--- a/Modules/syslogmodule.c
+++ b/Modules/syslogmodule.c
@@ -69,7 +69,8 @@ static char S_log_open = 0;
 static inline int
 is_main_interpreter(void)
 {
-    return (PyInterpreterState_Get() == PyInterpreterState_Main());
+    PyInterpreterState *interp = PyInterpreterState_Get();
+    return PyInterpreterState_IsMain(interp);
 }
 
 static PyObject *
diff --git a/PC/python3dll.c b/PC/python3dll.c
index ee3a7d7b4e5be1..98d42a19bb52b2 100755
--- a/PC/python3dll.c
+++ b/PC/python3dll.c
@@ -315,6 +315,7 @@ EXPORT_FUNC(PyInterpreterState_Delete)
 EXPORT_FUNC(PyInterpreterState_Get)
 EXPORT_FUNC(PyInterpreterState_GetDict)
 EXPORT_FUNC(PyInterpreterState_GetID)
+EXPORT_FUNC(PyInterpreterState_IsMain)
 EXPORT_FUNC(PyInterpreterState_New)
 EXPORT_FUNC(PyIter_Check)
 EXPORT_FUNC(PyIter_Next)
diff --git a/Python/pystate.c b/Python/pystate.c
index 01651d79f9acc0..0d8a4179c6c6a1 100644
--- a/Python/pystate.c
+++ b/Python/pystate.c
@@ -583,6 +583,12 @@ _PyRuntimeState_ReInitThreads(_PyRuntimeState *runtime)
 // lifecycle
 //----------
 
+int
+PyInterpreterState_IsMain(PyInterpreterState *interp)
+{
+    return _Py_IsMainInterpreter(interp);
+}
+
 /* Calling this indicates that the runtime is ready to create interpreters. */
 
 PyStatus