From cd8c6333df4d302d91f760d4f5b524acc69ce36f Mon Sep 17 00:00:00 2001
From: tangyuan0821 <tangyuan0821@email.cn>
Date: Mon, 13 Jul 2026 10:34:12 +0800
Subject: [PATCH 1/2] gh-153020: Fix race condition on event_tstate in _tkinter

---
 Modules/_tkinter.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/Modules/_tkinter.c b/Modules/_tkinter.c
index f5fb1841f0d5940..2fbafba27435c1f 100644
--- a/Modules/_tkinter.c
+++ b/Modules/_tkinter.c
@@ -3655,7 +3655,7 @@ EventHook(void)
     int tfile;
     stdin_ready = 0;
 #endif
-    PyEval_RestoreThread(event_tstate);
+    PyEval_RestoreThread(_Py_atomic_load_ptr(&event_tstate));
     errorInCmd = 0;
 #ifdef MS_WINDOWS
     hStdin = GetStdHandle(STD_INPUT_HANDLE);
@@ -3687,7 +3687,7 @@ EventHook(void)
 #endif
         Py_BEGIN_ALLOW_THREADS
         if(tcl_lock)PyThread_acquire_lock(tcl_lock, 1);
-        tcl_tstate = event_tstate;
+        tcl_tstate = _Py_atomic_load_ptr(&event_tstate);
 
         result = Tcl_DoOneEvent(TCL_DONT_WAIT);
 
@@ -3725,7 +3725,7 @@ EnableEventHook(void)
 {
 #ifdef WAIT_FOR_STDIN
     if (PyOS_InputHook == NULL) {
-        event_tstate = PyThreadState_Get();
+        _Py_atomic_store_ptr(&event_tstate, PyThreadState_Get());
         PyOS_InputHook = EventHook;
     }
 #endif
@@ -3737,6 +3737,7 @@ DisableEventHook(void)
 #ifdef WAIT_FOR_STDIN
     if (Tk_GetNumMainWindows() == 0 && PyOS_InputHook == EventHook) {
         PyOS_InputHook = NULL;
+        _Py_atomic_store_ptr(&event_tstate, NULL);
     }
 #endif
 }

From 6e7c0ef270ef269d88063b176072ef312b4bfea8 Mon Sep 17 00:00:00 2001
From: tangyuan0821 <tangyuan0821@email.cn>
Date: Mon, 13 Jul 2026 10:38:54 +0800
Subject: [PATCH 2/2] gh-153020: Add NEWS entry for _tkinter data race fix

---
 .../Library/2026-07-13-10-37-32.gh-issue-153020.eventTs.rst     | 2 ++
 1 file changed, 2 insertions(+)
 create mode 100644 Misc/NEWS.d/next/Library/2026-07-13-10-37-32.gh-issue-153020.eventTs.rst

diff --git a/Misc/NEWS.d/next/Library/2026-07-13-10-37-32.gh-issue-153020.eventTs.rst b/Misc/NEWS.d/next/Library/2026-07-13-10-37-32.gh-issue-153020.eventTs.rst
new file mode 100644
index 000000000000000..1dd8485ade46201
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2026-07-13-10-37-32.gh-issue-153020.eventTs.rst
@@ -0,0 +1,2 @@
+Fix a data race in :mod:`!_tkinter` input event handling in free-threaded
+builds.