[3.15] gh-161353: Fix handle leak in test_tcl (GH-161368) (#161650)

Fix handle leaks in test_tcl when the test is run with -R 3:3. Call
explicitly Tcl_FinalizeThread() in test_returning_deeply_nested() to
clean up explicitly per-thread state. The test is run in a thread
because of the @run_with_limited_c_stack() decorator.

On Windows, Tcl_CreateInterp() creates an event in the Tcl notifier
implementation. The event is stored in per-thread state which is only
cleaned up at exit.

Add the private _tkinter._finalize_thread() function.
(cherry picked from commit 2781ffe)

Co-authored-by: Victor Stinner <vstinner@python.org>

Author: gpshead

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_setvar_evil(self):
         # gh-161388

Modules/_tkinter.c

@@ -3399,6 +3399,20 @@ _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[] =
@@ -3490,6 +3504,7 @@ static PyMethodDef moduleMethods[] =
     _TKINTER_CREATE_METHODDEF
     _TKINTER_SETBUSYWAITINTERVAL_METHODDEF
     _TKINTER_GETBUSYWAITINTERVAL_METHODDEF
+    _TKINTER__FINALIZE_THREAD_METHODDEF
     {NULL,                 NULL}
 };