Relax test timing (bpo-29861) to avoid sporadic failures (python#1120)

(cherry picked from commit 685cdb9)

Lib/test/_test_multiprocessing.py

@@ -2000,6 +2000,20 @@ def test_map_no_failfast(self):
         # check that we indeed waited for all jobs
         self.assertGreater(time.time() - t_start, 0.9)
 
+    def test_release_task_refs(self):
+        # Issue #29861: task arguments and results should not be kept
+        # alive after we are done with them.
+        objs = [CountedObject() for i in range(10)]
+        refs = [weakref.ref(o) for o in objs]
+        self.pool.map(identity, objs)
+
+        del objs
+        time.sleep(DELTA)  # let threaded cleanup code run
+        self.assertEqual(set(wr() for wr in refs), {None})
+        # With a process pool, copies of the objects are returned, check
+        # they were released too.
+        self.assertEqual(CountedObject.n_instances, 0)
+
 
 def raising():
     raise KeyError("key")