Merge pull request #53 from stephenc-pace/fix/prevent-streaming-lockup

Cooperate with eventlet

nameko_grpc/streams.py

@@ -2,6 +2,8 @@
 import struct
 from queue import Empty, Queue
 
+from eventlet import greenthread
+
 from nameko_grpc.compression import compress, decompress
 from nameko_grpc.errors import GrpcError
 from nameko_grpc.headers import HeaderManager
@@ -201,6 +203,14 @@ def flush_queue_to_buffer(self):
                 )
                 self.buffer.write(data)
 
+            # This while loop can lockup the main thread for a long time if we have a
+            # large queue of large messages to process. We need to yield to cooperate
+            # with eventlet greenthreads and this is the canonical way of doing so.
+            # Calling :func:`~greenthread.sleep` with *seconds* of 0 is the
+            #     canonical way of expressing a cooperative yield
+            # TODO: Consider alternative solutions, ie breaking the flush into chunks
+            greenthread.sleep(0)
+
     def serialize_message(self, message):
         return message.SerializeToString()