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gh-153020: Fix race condition on event_tstate in _tkinter #153640

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gh-153020: Fix race condition on event_tstate in _tkinter #153640

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4c998f3
gh-153020: Fix race condition on event_tstate in _tkinter
tangyuan0821 Jul 13, 2026
00a72c2
gh-153020: Add NEWS entry for _tkinter data race fix
tangyuan0821 Jul 13, 2026
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2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Library/2026-07-13-10-37-32.gh-issue-153020.eventTs.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,2 @@
Fix a data race in :mod:`!_tkinter` input event handling in free-threaded
builds.
8 changes: 5 additions & 3 deletions Modules/_tkinter.c
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Original file line number Diff line number Diff line change
Expand Up @@ -31,6 +31,7 @@ Copyright (C) 1994 Steen Lumholt.
#endif

#include "pycore_long.h" // _PyLong_IsNegative()
#include "pycore_pyatomic_ft_wrappers.h" // FT_ATOMIC_LOAD_PTR, FT_ATOMIC_STORE_PTR
#include "pycore_unicodeobject.h" // _PyUnicode_AsUTF8String

#ifdef MS_WINDOWS
Expand Down Expand Up @@ -3655,7 +3656,7 @@ EventHook(void)
int tfile;
stdin_ready = 0;
#endif
PyEval_RestoreThread(event_tstate);
PyEval_RestoreThread(FT_ATOMIC_LOAD_PTR(event_tstate));
errorInCmd = 0;
#ifdef MS_WINDOWS
hStdin = GetStdHandle(STD_INPUT_HANDLE);
Expand Down Expand Up @@ -3687,7 +3688,7 @@ EventHook(void)
#endif
Py_BEGIN_ALLOW_THREADS
if(tcl_lock)PyThread_acquire_lock(tcl_lock, 1);
tcl_tstate = event_tstate;
tcl_tstate = FT_ATOMIC_LOAD_PTR(event_tstate);

result = Tcl_DoOneEvent(TCL_DONT_WAIT);

Expand Down Expand Up @@ -3725,7 +3726,7 @@ EnableEventHook(void)
{
#ifdef WAIT_FOR_STDIN
if (PyOS_InputHook == NULL) {
event_tstate = PyThreadState_Get();
FT_ATOMIC_STORE_PTR(event_tstate, PyThreadState_Get());
PyOS_InputHook = EventHook;
}
#endif
Expand All @@ -3737,6 +3738,7 @@ DisableEventHook(void)
#ifdef WAIT_FOR_STDIN
if (Tk_GetNumMainWindows() == 0 && PyOS_InputHook == EventHook) {
PyOS_InputHook = NULL;
FT_ATOMIC_STORE_PTR(event_tstate, NULL);
}
#endif
}
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