add support to rpc for multicall

nova/rpc.py

@@ -32,8 +32,11 @@ import uuid
 
 from carrot import connection as carrot_connection
 from carrot import messaging
+import eventlet
 from eventlet import greenpool
 from eventlet import greenthread
+from eventlet import queue
+
 
 from nova import context
 from nova import exception
@@ -131,7 +134,8 @@ class Consumer(messaging.Consumer):
                 self.connection = Connection.recreate()
                 self.backend = self.connection.create_backend()
                 self.declare()
-            super(Consumer, self).fetch(no_ack, auto_ack, enable_callbacks)
+            return super(Consumer, self).fetch(
+                    no_ack, auto_ack, enable_callbacks)
             if self.failed_connection:
                 LOG.error(_('Reconnected to queue'))
                 self.failed_connection = False
@@ -347,8 +351,9 @@ def _unpack_context(msg):
         if key.startswith('_context_'):
             value = msg.pop(key)
             context_dict[key[9:]] = value
+    context_dict['msg_id'] = msg.pop('_msg_id', None)
     LOG.debug(_('unpacked context: %s'), context_dict)
-    return context.RequestContext.from_dict(context_dict)
+    return RpcContext.from_dict(context_dict)
 
 
 def _pack_context(msg, context):
@@ -365,26 +370,27 @@ def _pack_context(msg, context):
     msg.update(context)
 
 
-def call(context, topic, msg):
-    """Sends a message on a topic and wait for a response."""
+class RpcContext(context.RequestContext):
+    def __init__(self, *args, **kwargs):
+        msg_id = kwargs.pop('msg_id', None)
+        self.msg_id = msg_id
+        super(RpcContext, self).__init__(*args, **kwargs)
+
+    def reply(self, *args, **kwargs):
+        msg_reply(self.msg_id, *args, **kwargs)
+
+
+def multicall(context, topic, msg):
+    """Make a call that returns multiple times."""
     LOG.debug(_('Making asynchronous call on %s ...'), topic)
     msg_id = uuid.uuid4().hex
     msg.update({'_msg_id': msg_id})
     LOG.debug(_('MSG_ID is %s') % (msg_id))
     _pack_context(msg, context)
 
-    class WaitMessage(object):
-        def __call__(self, data, message):
-            """Acks message and sets result."""
-            message.ack()
-            if data['failure']:
-                self.result = RemoteError(*data['failure'])
-            else:
-                self.result = data['result']
-
-    wait_msg = WaitMessage()
     conn = Connection.instance()
     consumer = DirectConsumer(connection=conn, msg_id=msg_id)
+    wait_msg = MulticallWaiter(consumer)
     consumer.register_callback(wait_msg)
 
     conn = Connection.instance()
@@ -392,18 +398,59 @@ def call(context, topic, msg):
     publisher.send(msg)
     publisher.close()
 
+    return wait_msg
+
+
+class MulticallWaiter(object):
+    def __init__(self, consumer):
+        self._consumer = consumer
+        self._results = queue.Queue()
+        self._closed = False
+
+    def close(self):
+        self._closed = True
+        self._consumer.close()
+
+    def __call__(self, data, message):
+        """Acks message and sets result."""
+        message.ack()
+        if data['failure']:
+            self._results.put(RemoteError(*data['failure']))
+        else:
+            self._results.put(data['result'])
+
+    def __iter__(self):
+        return self.wait()
+
+    def wait(self):
+        # TODO(termie): This is probably really a much simpler issue but am
+        #               trying to solve the problem quickly. This works but
+        #               I'd prefer to dig in and do it the best way later on.
+
+        def _waiter():
+            while not self._closed:
                 try:
-        consumer.wait(limit=1)
+                    self._consumer.wait(limit=1)
                 except StopIteration:
                     pass
-    consumer.close()
-    # NOTE(termie): this is a little bit of a change from the original
-    #               non-eventlet code where returning a Failure
-    #               instance from a deferred call is very similar to
-    #               raising an exception
-    if isinstance(wait_msg.result, Exception):
-        raise wait_msg.result
-    return wait_msg.result
+        eventlet.spawn(_waiter)
+
+        while True:
+            result = self._results.get()
+            if isinstance(result, Exception):
+                raise result
+            if result == None:
+                self.close()
+                raise StopIteration
+            yield result
+
+
+def call(context, topic, msg):
+    """Sends a message on a topic and wait for a response."""
+    rv = multicall(context, topic, msg)
+    for x in rv:
+        rv.close()
+        return x
 
 
 def cast(context, topic, msg):

nova/tests/test_rpc.py

@@ -49,6 +49,17 @@ class RpcTestCase(test.TestCase):
                                                  "args": {"value": value}})
         self.assertEqual(value, result)
 
+    def test_multicall_succeed_three_times(self):
+        """Get a value through rpc call"""
+        value = 42
+        result = rpc.multicall(self.context,
+                              'test',
+                              {"method": "echo_three_times",
+                               "args": {"value": value}})
+
+        for x in result:
+            self.assertEqual(value, x)
+
     def test_context_passed(self):
         """Makes sure a context is passed through rpc call"""
         value = 42
@@ -126,6 +137,12 @@ class TestReceiver(object):
         LOG.debug(_("Received %s"), context)
         return context.to_dict()
 
+    @staticmethod
+    def echo_three_times(context, value):
+        context.reply(value)
+        context.reply(value)
+        context.reply(value)
+
     @staticmethod
     def fail(context, value):
         """Raises an exception with the value sent in"""