perf: Check for cancellation on response thread (#54)

Co-authored-by: Iman Tabrizian <[email protected]>

Author: kthui

src/model.py

@@ -287,9 +287,13 @@ def response_loop(self):
             # To signal shutdown a None item will be added to the queue.
             if item is None:
                 break
-            response_sender, response, response_flag = item
+            response_state, response, response_flag = item
+            response_sender = response_state["response_sender"]
             try:
                 response_sender.send(response, response_flag)
+                # Stop checking for cancellation if the last response is generated.
+                if not response_state["last_response_generated"]:
+                    response_state["is_cancelled"] = response_sender.is_cancelled()
             except Exception as e:
                 self.logger.log_error(
                     f"An error occurred while sending a response: {e}"
@@ -338,6 +342,11 @@ async def generate(self, request):
         Forwards single request to LLM engine and returns responses.
         """
         response_sender = request.get_response_sender()
+        response_state = {
+            "response_sender": response_sender,
+            "is_cancelled": False,
+            "last_response_generated": False,  # last response ready but not yet sent
+        }
         self.ongoing_request_count += 1
         decrement_ongoing_request_count = True
         try:
@@ -399,10 +408,26 @@ async def generate(self, request):
             )
 
             async for output in response_iterator:
-                if response_sender.is_cancelled():
+                is_cancelled = response_state["is_cancelled"]
+                if not stream:
+                    is_cancelled = response_sender.is_cancelled()
+                if is_cancelled:
                     self.logger.log_info("[vllm] Cancelling the request")
                     await self.llm_engine.abort(request_id)
                     self.logger.log_info("[vllm] Successfully cancelled the request")
+                    if stream:
+                        response_state["last_response_generated"] = True
+                        response = pb_utils.InferenceResponse(
+                            error=pb_utils.TritonError(
+                                message="Request was cancelled",
+                                code=pb_utils.TritonError.CANCELLED,
+                            )
+                        )
+                        flags = pb_utils.TRITONSERVER_RESPONSE_COMPLETE_FINAL
+                        decrement_ongoing_request_count = False
+                        self._response_queue.put_nowait(
+                            (response_state, response, flags)
+                        )
                     break
                 if stream:
                     prev_outputs_lengths = None
@@ -414,9 +439,10 @@ async def generate(self, request):
                     response = self.create_stream_response(output, prev_outputs_lengths)
                     flags = 0
                     if output.finished:
+                        response_state["last_response_generated"] = True
                         flags = pb_utils.TRITONSERVER_RESPONSE_COMPLETE_FINAL
                         decrement_ongoing_request_count = False
-                    self._response_queue.put_nowait((response_sender, response, flags))
+                    self._response_queue.put_nowait((response_state, response, flags))
                 prev_outputs = output
 
             last_output = output