Activity worker: refactoring part 2 (#899)

Author: dandavison

temporalio/worker/_activity.py

@@ -138,24 +138,21 @@ def __init__(
                 self._dynamic_activity = defn
 
     async def run(self) -> None:
-        # Create a task that fails when we get a failure on the queue
-        async def raise_from_queue() -> NoReturn:
+        """Continually poll for activity tasks and dispatch to handlers."""
+
+        async def raise_from_exception_queue() -> NoReturn:
             raise await self._fail_worker_exception_queue.get()
 
-        exception_task = asyncio.create_task(raise_from_queue())
+        exception_task = asyncio.create_task(raise_from_exception_queue())
 
-        # Continually poll for activity work
         while True:
             try:
-                # Poll for a task
                 poll_task = asyncio.create_task(
                     self._bridge_worker().poll_activity_task()
                 )
                 await asyncio.wait(
                     [poll_task, exception_task], return_when=asyncio.FIRST_COMPLETED
-                )  # type: ignore
-                # If exception for failing the worker happened, raise it.
-                # Otherwise, the poll succeeded.
+                )
                 if exception_task.done():
                     poll_task.cancel()
                     await exception_task
@@ -169,11 +166,14 @@ async def raise_from_queue() -> NoReturn:
                     # size of 1000 should be plenty for the heartbeat queue.
                     activity = _RunningActivity(pending_heartbeats=asyncio.Queue(1000))
                     activity.task = asyncio.create_task(
-                        self._run_activity(task.task_token, task.start, activity)
+                        self._handle_start_activity_task(
+                            task.task_token, task.start, activity
+                        )
                     )
                     self._running_activities[task.task_token] = activity
                 elif task.HasField("cancel"):
-                    self._cancel(task.task_token, task.cancel)
+                    # TODO(nexus-prerelease): does the task get removed from running_activities?
+                    self._handle_cancel_activity_task(task.task_token, task.cancel)
                 else:
                     raise RuntimeError(f"Unrecognized activity task: {task}")
             except temporalio.bridge.worker.PollShutdownError:
@@ -210,9 +210,10 @@ async def wait_all_completed(self) -> None:
         if running_tasks:
             await asyncio.gather(*running_tasks, return_exceptions=False)
 
-    def _cancel(
+    def _handle_cancel_activity_task(
         self, task_token: bytes, cancel: temporalio.bridge.proto.activity_task.Cancel
     ) -> None:
+        """Request cancellation of a running activity task."""
         activity = self._running_activities.get(task_token)
         if not activity:
             warnings.warn(f"Cannot find activity to cancel for token {task_token!r}")
@@ -277,12 +278,17 @@ async def _heartbeat_async(
                 )
                 activity.cancel(cancelled_due_to_heartbeat_error=err)
 
-    async def _run_activity(
+    async def _handle_start_activity_task(
         self,
         task_token: bytes,
         start: temporalio.bridge.proto.activity_task.Start,
         running_activity: _RunningActivity,
     ) -> None:
+        """Handle a start activity task.
+
+        Attempt to execute the user activity function and invoke the data converter on
+        the result. Handle errors and send the task completion.
+        """
         logger.debug("Running activity %s (token %s)", start.activity_type, task_token)
         # We choose to surround interceptor creation and activity invocation in
         # a try block so we can mark the workflow as failed on any error instead
@@ -291,7 +297,9 @@ async def _run_activity(
             task_token=task_token
         )
         try:
-            await self._execute_activity(start, running_activity, completion)
+            result = await self._execute_activity(start, running_activity, task_token)
+            [payload] = await self._data_converter.encode([result])
+            completion.result.completed.result.CopyFrom(payload)
         except BaseException as err:
             try:
                 if isinstance(err, temporalio.activity._CompleteAsyncError):
@@ -320,7 +328,7 @@ async def _run_activity(
                     and running_activity.cancellation_details.details.paused
                 ):
                     temporalio.activity.logger.warning(
-                        f"Completing as failure due to unhandled cancel error produced by activity pause",
+                        "Completing as failure due to unhandled cancel error produced by activity pause",
                     )
                     await self._data_converter.encode_failure(
                         temporalio.exceptions.ApplicationError(
@@ -404,8 +412,12 @@ async def _execute_activity(
         self,
         start: temporalio.bridge.proto.activity_task.Start,
         running_activity: _RunningActivity,
-        completion: temporalio.bridge.proto.ActivityTaskCompletion,
-    ):
+        task_token: bytes,
+    ) -> Any:
+        """Invoke the user's activity function.
+
+        Exceptions are handled by a caller of this function.
+        """
         # Find activity or fail
         activity_def = self._activities.get(start.activity_type, self._dynamic_activity)
         if not activity_def:
@@ -525,7 +537,7 @@ async def _execute_activity(
             else None,
             started_time=_proto_to_datetime(start.started_time),
             task_queue=self._task_queue,
-            task_token=completion.task_token,
+            task_token=task_token,
             workflow_id=start.workflow_execution.workflow_id,
             workflow_namespace=start.workflow_namespace,
             workflow_run_id=start.workflow_execution.run_id,
@@ -564,16 +576,9 @@ async def _execute_activity(
         impl: ActivityInboundInterceptor = _ActivityInboundImpl(self, running_activity)
         for interceptor in reversed(list(self._interceptors)):
             impl = interceptor.intercept_activity(impl)
-        # Init
+
         impl.init(_ActivityOutboundImpl(self, running_activity.info))
-        # Exec
-        result = await impl.execute_activity(input)
-        # Convert result even if none. Since Python essentially only
-        # supports single result types (even if they are tuples), we will do
-        # the same.
-        completion.result.completed.result.CopyFrom(
-            (await self._data_converter.encode([result]))[0]
-        )
+        return await impl.execute_activity(input)
 
     def assert_activity_valid(self, activity) -> None:
         if self._dynamic_activity: