feat(traffic-controller): network traffic controller in frontend

gnes/service/frontend.py

@@ -138,22 +138,25 @@ def Search(self, request, context):
         def StreamCall(self, request_iterator, context):
             with self.zmq_context as zmq_client:
                 num_request = 0
+                # network traffic control
+                max_outstanding = 1000
                 for request in request_iterator:
-                    zmq_client.send_message(self.add_envelope(request, zmq_client), -1)
-                    num_request += 1
+                    timeout = 25
+                    if self.args.timeout > 0:
+                        timeout = min(0.5 * self.args.timeout, 50)
 
                     while num_request > 10:
                         try:
-                            # fetch response in real time to reduce network overload
-                            timeout = 50
-                            if self.args.timeout > 0:
-                                timeout = min(0.5 * self.args.timeout, 100)
-
                             msg = zmq_client.recv_message(timeout)
                             yield self.remove_envelope(msg)
                             num_request -= 1
                         except TimeoutError:
+                            if num_request > max_outstanding:
+                                self.logger.warning("the network traffic exceed max outstanding (%d > %d)" % (num_request, max_outstanding))
+                                continue
                             break
+                    zmq_client.send_message(self.add_envelope(request, zmq_client), -1)
+                    num_request += 1
 
                 for _ in range(num_request):
                     msg = zmq_client.recv_message(self.args.timeout)