[3.6] bpo-31234: Join threads in tests (#3589)

* bpo-31234: Join threads in tests (#3572)

Call thread.join() on threads to prevent the "dangling threads"
warning.

(cherry picked from commit 18e95b4176)

* bpo-31234: Join threads in test_hashlib (#3573)

* bpo-31234: Join threads in test_hashlib

Use thread.join() to wait until the parallel hash tasks complete
rather than using events. Calling thread.join() prevent "dangling
thread" warnings.

* test_hashlib: minor PEP 8 coding style fixes

(cherry picked from commit 8dcf22f442)

* bpo-31234: Join threads in test_threading (#3579)

Call thread.join() to prevent the "dangling thread" warning.

(cherry picked from commit b8c7be2c52)

* bpo-31234: Join threads in test_queue (#3586)

Call thread.join() to prevent the "dangling thread" warning.

(cherry picked from commit 167cbde50a)

* bpo-31234: Join timers in test_threading (#3598)

Call the .join() method of threading.Timer timers to prevent the
"threading_cleanup() failed to cleanup 1 threads" warning.

(cherry picked from commit da3e5cf961)

Lib/test/test_threading.py

@@ -575,6 +575,7 @@ class ThreadTests(BaseTestCase):
         self.assertFalse(t.is_alive())
         # And verify the thread disposed of _tstate_lock.
         self.assertIsNone(t._tstate_lock)
+        t.join()
 
     def test_repr_stopped(self):
         # Verify that "stopped" shows up in repr(Thread) appropriately.
@@ -601,6 +602,7 @@ class ThreadTests(BaseTestCase):
                 break
             time.sleep(0.01)
         self.assertIn(LOOKING_FOR, repr(t)) # we waited at least 5 seconds
+        t.join()
 
     def test_BoundedSemaphore_limit(self):
         # BoundedSemaphore should raise ValueError if released too often.
@@ -915,6 +917,7 @@ class ThreadingExceptionTests(BaseTestCase):
         thread = threading.Thread()
         thread.start()
         self.assertRaises(RuntimeError, thread.start)
+        thread.join()
 
     def test_joining_current_thread(self):
         current_thread = threading.current_thread()
@@ -928,6 +931,7 @@ class ThreadingExceptionTests(BaseTestCase):
         thread = threading.Thread()
         thread.start()
         self.assertRaises(RuntimeError, setattr, thread, "daemon", True)
+        thread.join()
 
     def test_releasing_unacquired_lock(self):
         lock = threading.Lock()
@@ -1090,6 +1094,8 @@ class TimerTests(BaseTestCase):
         self.callback_event.wait()
         self.assertEqual(len(self.callback_args), 2)
         self.assertEqual(self.callback_args, [((), {}), ((), {})])
+        timer1.join()
+        timer2.join()
 
     def _callback_spy(self, *args, **kwargs):
         self.callback_args.append((args[:], kwargs.copy()))