gh-161353: Fix handle leak in test_tcl

Lib/test/test_tcl.py

@@ -595,6 +595,11 @@ def test_returning_deeply_nested(self):
         interp.eval('set x a; for {set i 0} {$i < %d} {incr i} {set x [list $x]}'
                     % support.exceeds_recursion_limit())
         self.assertRaises(RecursionError, interp.getvar, 'x')
+        interp = None
+
+        # gh-161353: Clean up explicitly per-thread state to avoid leaking an
+        # event handle on Windows when test_tcl is run with -R 3:3 option.
+        _tkinter._finalize_thread()
 
     def test_user_command(self):
         result = None

Modules/_tkinter.c

@@ -3584,6 +3584,20 @@ _tkinter_getbusywaitinterval_impl(PyObject *module)
     return Tkinter_busywaitinterval;
 }
 
+/*[clinic input]
+_tkinter._finalize_thread
+
+Clean up per-thread state.
+[clinic start generated code]*/
+
+static PyObject *
+_tkinter__finalize_thread_impl(PyObject *module)
+/*[clinic end generated code: output=4ed0d3be4d1f8de8 input=ea68096ee9b83d23]*/
+{
+    Tcl_FinalizeThread();
+    Py_RETURN_NONE;
+}
+
 #include "clinic/_tkinter.c.h"
 
 static PyMethodDef Tktt_methods[] =
@@ -3681,6 +3695,7 @@ static PyMethodDef moduleMethods[] =
     _TKINTER_CREATE_METHODDEF
     _TKINTER_SETBUSYWAITINTERVAL_METHODDEF
     _TKINTER_GETBUSYWAITINTERVAL_METHODDEF
+    _TKINTER__FINALIZE_THREAD_METHODDEF
     {NULL,                 NULL}
 };