Allow to remove second _send_reply() call

Added a new configuration option `send_single_reply` which allows to
send a single AMQP reply instead of two. This will reduce amount of RPC
calls and increase transport productivity.

The new behaviour is not compatible with the old logic, so isn't
backward compatible and disabled by default.

DocImpact
A new configuration option added.

Blueprint: remove-double-reply

Change-Id: Idab118b22163e734aca010f325cddfaec26bfa0f

oslo_messaging/_drivers/amqp.py

@@ -49,6 +49,18 @@ amqp_opts = [
                 default=False,
                 deprecated_group='DEFAULT',
                 help='Auto-delete queues in AMQP.'),
+    cfg.BoolOpt('send_single_reply',
+                default=False,
+                help='Send a single AMQP reply to call message. The current '
+                     'behaviour since oslo-incubator is to send two AMQP '
+                     'replies - first one with the payload, a second one to '
+                     'ensure the other have finish to send the payload. We '
+                     'are going to remove it in the N release, but we must '
+                     'keep backward compatible at the same time. This option '
+                     'provides such compatibility - it defaults to False in '
+                     'Liberty and can be turned on for early adopters with a '
+                     'new installations or for testing. Please note, that '
+                     'this option will be removed in M release.')
 ]
 
 UNIQUE_ID = '_unique_id'

oslo_messaging/_drivers/amqpdriver.py

@@ -71,8 +71,12 @@ class AMQPIncomingMessage(base.IncomingMessage):
             return
         with self.listener.driver._get_connection(
                 rpc_amqp.PURPOSE_SEND) as conn:
-            self._send_reply(conn, reply, failure, log_failure=log_failure)
-            self._send_reply(conn, ending=True)
+            if self.listener.driver.send_single_reply:
+                self._send_reply(conn, reply, failure, log_failure=log_failure,
+                                 ending=True)
+            else:
+                self._send_reply(conn, reply, failure, log_failure=log_failure)
+                self._send_reply(conn, ending=True)
 
     def acknowledge(self):
         self.listener.msg_id_cache.add(self.unique_id)
@@ -257,7 +261,8 @@ class ReplyWaiter(object):
 class AMQPDriverBase(base.BaseDriver):
 
     def __init__(self, conf, url, connection_pool,
-                 default_exchange=None, allowed_remote_exmods=None):
+                 default_exchange=None, allowed_remote_exmods=None,
+                 send_single_reply=False):
         super(AMQPDriverBase, self).__init__(conf, url, default_exchange,
                                              allowed_remote_exmods)
 
@@ -270,6 +275,8 @@ class AMQPDriverBase(base.BaseDriver):
         self._reply_q_conn = None
         self._waiter = None
 
+        self.send_single_reply = send_single_reply
+
     def _get_exchange(self, target):
         return target.exchange or self._default_exchange
 

oslo_messaging/_drivers/impl_qpid.py

@@ -778,7 +778,10 @@ class QpidDriver(amqpdriver.AMQPDriverBase):
             conf, conf.oslo_messaging_qpid.rpc_conn_pool_size,
             url, Connection)
 
-        super(QpidDriver, self).__init__(conf, url,
-                                         connection_pool,
-                                         default_exchange,
-                                         allowed_remote_exmods)
+        super(QpidDriver, self).__init__(
+            conf, url,
+            connection_pool,
+            default_exchange,
+            allowed_remote_exmods,
+            conf.oslo_messaging_qpid.send_single_reply,
+        )

oslo_messaging/_drivers/impl_rabbit.py

@@ -1085,10 +1085,13 @@ class RabbitDriver(amqpdriver.AMQPDriverBase):
             conf, conf.oslo_messaging_rabbit.rpc_conn_pool_size,
             url, Connection)
 
-        super(RabbitDriver, self).__init__(conf, url,
-                                           connection_pool,
-                                           default_exchange,
-                                           allowed_remote_exmods)
+        super(RabbitDriver, self).__init__(
+            conf, url,
+            connection_pool,
+            default_exchange,
+            allowed_remote_exmods,
+            conf.oslo_messaging_rabbit.send_single_reply,
+        )
 
     def require_features(self, requeue=True):
         pass