[3.12] pythongh-130730: Fix multiprocessing test_active_children() (pythonGH-130837) (python#130846)

pythongh-130730: Fix multiprocessing test_active_children() (pythonGH-130837)

Replace a sleep with an event: sleep is not a reliable
synchronization primitive.
(cherry picked from commit 3dd3675)

Co-authored-by: Victor Stinner <[email protected]>

Author: miss-islington

Lib/test/_test_multiprocessing.py

@@ -588,12 +588,16 @@ def test_cpu_count(self):
     def test_active_children(self):
         self.assertEqual(type(self.active_children()), list)
 
-        p = self.Process(target=time.sleep, args=(DELTA,))
+        event = self.Event()
+        p = self.Process(target=event.wait, args=())
         self.assertNotIn(p, self.active_children())
 
-        p.daemon = True
-        p.start()
-        self.assertIn(p, self.active_children())
+        try:
+            p.daemon = True
+            p.start()
+            self.assertIn(p, self.active_children())
+        finally:
+            event.set()
 
         p.join()
         self.assertNotIn(p, self.active_children())