FIx CPU time consuming in green_poller poll()

The current implementation of GreenPoller.poll() calls
eventlet.sleep() in `while True:` loop. It causes high CPU load,
so should be refactored to use queue.get() with timeout.

Change-Id: I48f1d8db39c4d7df8bd7f0bc9898ebefcd8df9e8

oslo_messaging/_drivers/zmq_driver/poller/green_poller.py

@@ -16,9 +16,7 @@ import logging
 import threading
 
 import eventlet
-import six
 
-from oslo_messaging._drivers import common as rpc_common
 from oslo_messaging._drivers.zmq_driver import zmq_poller
 
 LOG = logging.getLogger(__name__)
@@ -27,7 +25,7 @@ LOG = logging.getLogger(__name__)
 class GreenPoller(zmq_poller.ZmqPoller):
 
     def __init__(self):
-        self.incoming_queue = six.moves.queue.Queue()
+        self.incoming_queue = eventlet.queue.LightQueue()
         self.green_pool = eventlet.GreenPool()
         self.thread_by_socket = {}
 
@@ -46,17 +44,10 @@ class GreenPoller(zmq_poller.ZmqPoller):
             eventlet.sleep()
 
     def poll(self, timeout=None):
-        incoming = None
         try:
-            with eventlet.Timeout(timeout, exception=rpc_common.Timeout):
-                while incoming is None:
-                    try:
-                        incoming = self.incoming_queue.get_nowait()
-                    except six.moves.queue.Empty:
-                        eventlet.sleep()
-        except rpc_common.Timeout:
-            return None, None
-        return incoming[0], incoming[1]
+            return self.incoming_queue.get(timeout=timeout)
+        except eventlet.queue.Empty:
+            return (None, None)
 
     def close(self):
         for thread in self.thread_by_socket.values():