check for worker registration

rpc/service.py

@@ -321,8 +321,8 @@ async def DeregisterDriver(self, request, context):
     async def RegisterTaskGraph(self, request, context):
         stime = self.__stime()
 
-        if not self.__framework_registered():
-            msg = f"[{stime}] Trying to register a task graph (id={request.id}, name={request.name}) but no framework has been registered yet."
+        if not self.__worker_registered():
+            msg = f"[{stime}] Failed to register task graph (id={request.id}, name={request.name}) because no worker has been registered yet."
             self._logger.error(msg)
             return erdos_scheduler_pb2.RegisterTaskGraphResponse(
                 success=False, message=msg, num_executors=0
@@ -672,6 +672,11 @@ def __stime(self) -> EventTime:
     def __framework_registered(self):
         return self._simulator is not None
 
+    def __worker_registered(self):
+        return (
+            self.__framework_registered() and len(self.__get_worker_pool().workers) > 0
+        )
+
     def __get_worker_pool(self):
         # Simulator maintains only one worker pool, so this should be fine
         return next(iter(self._simulator._worker_pools.worker_pools))