From 9578288a3e5a7f42d1f3bec139c0c85b87775c90 Mon Sep 17 00:00:00 2001
From: Steve Dower <steve.dower@python.org>
Date: Wed, 28 Feb 2024 13:58:25 +0000
Subject: [PATCH] gh-116012: Preserve GetLastError() across calls to
 TlsGetValue on Windows (GH-116014)

---
 .../2024-02-27-23-21-55.gh-issue-116012.B9_IwM.rst       | 1 +
 Python/pystate.c                                         | 9 ---------
 Python/thread_nt.h                                       | 7 ++++++-
 3 files changed, 7 insertions(+), 10 deletions(-)
 create mode 100644 Misc/NEWS.d/next/Windows/2024-02-27-23-21-55.gh-issue-116012.B9_IwM.rst

diff --git a/Misc/NEWS.d/next/Windows/2024-02-27-23-21-55.gh-issue-116012.B9_IwM.rst b/Misc/NEWS.d/next/Windows/2024-02-27-23-21-55.gh-issue-116012.B9_IwM.rst
new file mode 100644
index 00000000000..a55e5b1c7b5
--- /dev/null
+++ b/Misc/NEWS.d/next/Windows/2024-02-27-23-21-55.gh-issue-116012.B9_IwM.rst
@@ -0,0 +1 @@
+Ensure the value of ``GetLastError()`` is preserved across GIL operations.
diff --git a/Python/pystate.c b/Python/pystate.c
index a80c1b7fb9c..a370fff857a 100644
--- a/Python/pystate.c
+++ b/Python/pystate.c
@@ -2528,16 +2528,7 @@ PyGILState_Check(void)
         return 0;
     }
 
-#ifdef MS_WINDOWS
-    int err = GetLastError();
-#endif
-
     PyThreadState *tcur = gilstate_tss_get(runtime);
-
-#ifdef MS_WINDOWS
-    SetLastError(err);
-#endif
-
     return (tstate == tcur);
 }
 
diff --git a/Python/thread_nt.h b/Python/thread_nt.h
index 7922b2d7e84..9dca833ff20 100644
--- a/Python/thread_nt.h
+++ b/Python/thread_nt.h
@@ -513,5 +513,10 @@ void *
 PyThread_tss_get(Py_tss_t *key)
 {
     assert(key != NULL);
-    return TlsGetValue(key->_key);
+    int err = GetLastError();
+    void *r = TlsGetValue(key->_key);
+    if (r || !GetLastError()) {
+        SetLastError(err);
+    }
+    return r;
 }