chore: fix streaming pull close unit test flakiness (#361)

* chore: fix streaming pull close test flakiness

* Store shutdown thread on the manager instance

google/cloud/pubsub_v1/subscriber/_protocol/streaming_pull_manager.py

@@ -148,6 +148,7 @@ def __init__(
         self._closing = threading.Lock()
         self._closed = False
         self._close_callbacks = []
+        self._regular_shutdown_thread = None  # Created on intentional shutdown.
 
         # Generate a random client id tied to this object. All streaming pull
         # connections (initial and re-connects) will then use the same client
@@ -539,13 +540,13 @@ def close(self, reason=None):
                 an "intentional" shutdown. This is passed to the callbacks
                 specified via :meth:`add_close_callback`.
         """
-        thread = threading.Thread(
+        self._regular_shutdown_thread = threading.Thread(
             name=_REGULAR_SHUTDOWN_THREAD_NAME,
             daemon=True,
             target=self._shutdown,
             kwargs={"reason": reason},
         )
-        thread.start()
+        self._regular_shutdown_thread.start()
 
     def _shutdown(self, reason=None):
         """Run the actual shutdown sequence (stop the stream and all helper threads).

tests/unit/pubsub_v1/subscriber/test_streaming_pull_manager.py

@@ -550,6 +550,19 @@ def make_running_manager(**kwargs):
     )
 
 
+def await_manager_shutdown(manager, timeout=None):
+    # NOTE: This method should be called after manager.close(), i.e. after the shutdown
+    # thread has been created and started.
+    shutdown_thread = manager._regular_shutdown_thread
+
+    if shutdown_thread is None:  # pragma: NO COVER
+        raise Exception("Shutdown thread does not exist on the manager instance.")
+
+    shutdown_thread.join(timeout=timeout)
+    if shutdown_thread.is_alive():  # pragma: NO COVER
+        pytest.fail("Shutdown not completed in time.")
+
+
 def test_close():
     (
         manager,
@@ -561,6 +574,7 @@ def test_close():
     ) = make_running_manager()
 
     manager.close()
+    await_manager_shutdown(manager, timeout=3)
 
     consumer.stop.assert_called_once()
     leaser.stop.assert_called_once()
@@ -583,6 +597,7 @@ def test_close_inactive_consumer():
     consumer.is_active = False
 
     manager.close()
+    await_manager_shutdown(manager, timeout=3)
 
     consumer.stop.assert_not_called()
     leaser.stop.assert_called_once()
@@ -596,6 +611,7 @@ def test_close_idempotent():
 
     manager.close()
     manager.close()
+    await_manager_shutdown(manager, timeout=3)
 
     assert scheduler.shutdown.call_count == 1
 
@@ -640,6 +656,7 @@ def test_close_no_dispatcher_error():
     dispatcher.start()
 
     manager.close()
+    await_manager_shutdown(manager, timeout=3)
 
     error_callback.assert_not_called()
 
@@ -651,6 +668,7 @@ def test_close_callbacks():
 
     manager.add_close_callback(callback)
     manager.close(reason="meep")
+    await_manager_shutdown(manager, timeout=3)
 
     callback.assert_called_once_with(manager, "meep")
 
@@ -660,6 +678,7 @@ def test_close_blocking_scheduler_shutdown():
     scheduler = manager._scheduler
 
     manager.close()
+    await_manager_shutdown(manager, timeout=3)
 
     scheduler.shutdown.assert_called_once_with(await_msg_callbacks=True)
 
@@ -669,6 +688,7 @@ def test_close_nonblocking_scheduler_shutdown():
     scheduler = manager._scheduler
 
     manager.close()
+    await_manager_shutdown(manager, timeout=3)
 
     scheduler.shutdown.assert_called_once_with(await_msg_callbacks=False)
 
@@ -690,6 +710,7 @@ def fake_nack(self):
     manager._messages_on_hold._messages_on_hold.append(messages[2])
 
     manager.close()
+    await_manager_shutdown(manager, timeout=3)
 
     assert sorted(nacked_messages) == [b"msg1", b"msg2", b"msg3"]