refactor: remove vllm prefill worker background loop check (#3529)

Signed-off-by: PeaBrane <yanrpei@gmail.com>

components/src/dynamo/vllm/handlers.py

@@ -129,43 +129,6 @@ class DecodeWorkerHandler(BaseWorkerHandler):
         super().__init__(runtime, component, engine, default_sampling_params)
         self.prefill_worker_client = prefill_worker_client
         self.prefill_router_client = prefill_router_client
-        self.can_prefill = 0
-        self._prefill_check_task = None
-
-        if self.prefill_worker_client or self.prefill_router_client:
-            self._prefill_check_task = asyncio.create_task(self._prefill_check_loop())
-
-    async def _prefill_check_loop(self):
-        """Background task that checks prefill router/worker availability every 5 seconds."""
-        while True:
-            try:
-                router_count = (
-                    len(self.prefill_router_client.instance_ids())
-                    if self.prefill_router_client is not None
-                    else 0
-                )
-                worker_count = (
-                    len(self.prefill_worker_client.instance_ids())
-                    if self.prefill_worker_client is not None
-                    else 0
-                )
-                self.can_prefill = max(router_count, worker_count)
-                logger.debug(
-                    f"Prefill availability - Routers: {router_count}, Workers: {worker_count}"
-                )
-            except asyncio.CancelledError:
-                logger.warning("Prefill check loop cancelled.")
-                raise
-            except Exception as e:
-                logger.error(f"Error in prefill check loop: {e}")
-
-            await asyncio.sleep(5)
-
-    def cleanup(self):
-        """Cancel background tasks."""
-        if self._prefill_check_task is not None:
-            self._prefill_check_task.cancel()
-        super().cleanup()
 
     async def generate(self, request, context):
         request_id = str(uuid.uuid4().hex)
@@ -185,7 +148,11 @@ class DecodeWorkerHandler(BaseWorkerHandler):
                 setattr(sampling_params, key, value)
 
         # Use prefill router or worker if available
-        if self.can_prefill:
+        can_prefill = (
+            self.prefill_worker_client is not None
+        ) and self.prefill_worker_client.instance_ids()
+
+        if can_prefill:
             # Create prefill sampling params with modifications
             prefill_sampling_params = deepcopy(sampling_params)
             if prefill_sampling_params.extra_args is None:
@@ -217,15 +184,13 @@ class DecodeWorkerHandler(BaseWorkerHandler):
                             prefill_request, context=context
                         )
                     )
-                elif self.prefill_worker_client is not None:
+                else:
                     # Fallback to direct worker with same format
                     prefill_response = await anext(
                         await self.prefill_worker_client.round_robin(
                             prefill_request, context=context
                         )
                     )
-                else:
-                    raise ValueError("No prefill router or worker available")
 
                 prefill_output = prefill_response.data()