Wait for activity completions on worker shutdown (#370)

Fixes #368

temporalio/worker/_activity.py

@@ -195,6 +195,13 @@ async def drain_poll_queue(self) -> None:
             except temporalio.bridge.worker.PollShutdownError:
                 return
 
+    # Only call this after run()/drain_poll_queue() have returned. This will not
+    # raise an exception.
+    async def wait_all_completed(self) -> None:
+        running_tasks = [v.task for v in self._running_activities.values() if v.task]
+        if running_tasks:
+            await asyncio.gather(*running_tasks, return_exceptions=False)
+
     def _cancel(
         self, task_token: bytes, cancel: temporalio.bridge.proto.activity_task.Cancel
     ) -> None:

temporalio/worker/_worker.py

@@ -467,6 +467,13 @@ async def raise_on_shutdown():
         for task in tasks:
             task.cancel()
 
+        # If there's an activity worker, we have to let all activity completions
+        # finish. We cannot guarantee that because poll shutdown completed
+        # (which means activities completed) that they got flushed to the
+        # server.
+        if self._activity_worker:
+            await self._activity_worker.wait_all_completed()
+
         # Do final shutdown
         try:
             await self._bridge_worker.finalize_shutdown()