x/gantt
Code Issues Proposed changes

Merge "Help clarify rpc API with docs and a bit of code."

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This commit is contained in:
Jenkins
2011-12-23 10:19:53 +00:00
committed by Gerrit Code Review
parent 285cb959c7 f529b3c9b7
commit 2d24184868
4 changed files with 182 additions and 24 deletions
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118
nova/rpc/__init__.py
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@@ -3,6 +3,7 @@
# Copyright 2010 United States Government as represented by the
# Administrator of the National Aeronautics and Space Administration.
# All Rights Reserved.
# Copyright 2011 Red Hat, Inc.
#
# Licensed under the Apache License, Version 2.0 (the "License"); you may
# not use this file except in compliance with the License. You may obtain
@@ -26,32 +27,107 @@ flags.DEFINE_string('rpc_backend',
'nova.rpc.impl_kombu',
"The messaging module to use, defaults to kombu.")
def create_connection(new=True):
"""Create a connection to the message bus used for rpc.
For some example usage of creating a connection and some consumers on that
connection, see nova.service.
:param new: Whether or not to create a new connection. A new connection
will be created by default. If new is False, the
implementation is free to return an existing connection from a
pool.
:returns: An instance of nova.rpc.common.Connection
"""
return _get_impl().create_connection(new=new)
def call(context, topic, msg):
"""Invoke a remote method that returns something.
:param context: Information that identifies the user that has made this
request.
:param topic: The topic to send the rpc message to. This correlates to the
topic argument of
nova.rpc.common.Connection.create_consumer() and only applies
when the consumer was created with fanout=False.
:param msg: This is a dict in the form { "method" : "method_to_invoke",
"args" : dict_of_kwargs }
:returns: A dict from the remote method.
"""
return _get_impl().call(context, topic, msg)
def cast(context, topic, msg):
"""Invoke a remote method that does not return anything.
:param context: Information that identifies the user that has made this
request.
:param topic: The topic to send the rpc message to. This correlates to the
topic argument of
nova.rpc.common.Connection.create_consumer() and only applies
when the consumer was created with fanout=False.
:param msg: This is a dict in the form { "method" : "method_to_invoke",
"args" : dict_of_kwargs }
:returns: None
"""
return _get_impl().cast(context, topic, msg)
def fanout_cast(context, topic, msg):
"""Broadcast a remote method invocation with no return.
This method will get invoked on all consumers that were set up with this
topic name and fanout=True.
:param context: Information that identifies the user that has made this
request.
:param topic: The topic to send the rpc message to. This correlates to the
topic argument of
nova.rpc.common.Connection.create_consumer() and only applies
when the consumer was created with fanout=True.
:param msg: This is a dict in the form { "method" : "method_to_invoke",
"args" : dict_of_kwargs }
:returns: None
"""
return _get_impl().fanout_cast(context, topic, msg)
def multicall(context, topic, msg):
"""Invoke a remote method and get back an iterator.
In this case, the remote method will be returning multiple values in
separate messages, so the return values can be processed as the come in via
an iterator.
:param context: Information that identifies the user that has made this
request.
:param topic: The topic to send the rpc message to. This correlates to the
topic argument of
nova.rpc.common.Connection.create_consumer() and only applies
when the consumer was created with fanout=False.
:param msg: This is a dict in the form { "method" : "method_to_invoke",
"args" : dict_of_kwargs }
:returns: An iterator. The iterator will yield a tuple (N, X) where N is
an index that starts at 0 and increases by one for each value
returned and X is the Nth value that was returned by the remote
method.
"""
return _get_impl().multicall(context, topic, msg)
_RPCIMPL = None
def get_impl():
def _get_impl():
"""Delay import of rpc_backend until FLAGS are loaded."""
global _RPCIMPL
if _RPCIMPL is None:
_RPCIMPL = import_object(FLAGS.rpc_backend)
return _RPCIMPL
def create_connection(new=True):
return get_impl().create_connection(new=new)
def call(context, topic, msg):
return get_impl().call(context, topic, msg)
def cast(context, topic, msg):
return get_impl().cast(context, topic, msg)
def fanout_cast(context, topic, msg):
return get_impl().fanout_cast(context, topic, msg)
def multicall(context, topic, msg):
return get_impl().multicall(context, topic, msg)

74
nova/rpc/common.py
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@@ -1,3 +1,23 @@
# vim: tabstop=4 shiftwidth=4 softtabstop=4
# Copyright 2010 United States Government as represented by the
# Administrator of the National Aeronautics and Space Administration.
# All Rights Reserved.
# Copyright 2011 Red Hat, Inc.
#
# Licensed under the Apache License, Version 2.0 (the "License"); you may
# not use this file except in compliance with the License. You may obtain
# a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
# License for the specific language governing permissions and limitations
# under the License.
from nova import exception
from nova import flags
from nova import log as logging
@@ -26,3 +46,57 @@ class RemoteError(exception.NovaException):
self.value = value
self.traceback = traceback
super(RemoteError, self).__init__(**self.__dict__)
class Connection(object):
"""A connection, returned by rpc.create_connection().
This class represents a connection to the message bus used for rpc.
An instance of this class should never be created by users of the rpc API.
Use rpc.create_connection() instead.
"""
def close(self):
"""Close the connection.
This method must be called when the connection will no longer be used.
It will ensure that any resources associated with the connection, such
as a network connection, and cleaned up.
"""
raise NotImplementedError()
def create_consumer(self, topic, proxy, fanout=False):
"""Create a consumer on this connection.
A consumer is associated with a message queue on the backend message
bus. The consumer will read messages from the queue, unpack them, and
dispatch them to the proxy object. The contents of the message pulled
off of the queue will determine which method gets called on the proxy
object.
:param topic: This is a name associated with what to consume from.
Multiple instances of a service may consume from the same
topic. For example, all instances of nova-compute consume
from a queue called "compute". In that case, the
messages will get distributed amongst the consumers in a
round-robin fashion if fanout=False. If fanout=True,
every consumer associated with this topic will get a
copy of every message.
:param proxy: The object that will handle all incoming messages.
:param fanout: Whether or not this is a fanout topic. See the
documentation for the topic parameter for some
additional comments on this.
"""
raise NotImplementedError()
def consume_in_thread(self):
"""Spawn a thread to handle incoming messages.
Spawn a thread that will be responsible for handling all incoming
messages for consumers that were set up on this connection.
Message dispatching inside of this is expected to be implemented in a
non-blocking manner. An example implementation would be having this
thread pull messages in for all of the consumers, but utilize a thread
pool for dispatching the messages to the proxy objects.
"""
raise NotImplementedError()

5
nova/rpc/impl_carrot.py
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@@ -42,6 +42,7 @@ import greenlet
from nova import context
from nova import exception
from nova import flags
from nova.rpc import common as rpc_common
from nova.rpc.common import RemoteError, LOG
from nova.testing import fake
@@ -51,7 +52,7 @@ eventlet.monkey_patch()
FLAGS = flags.FLAGS
class Connection(carrot_connection.BrokerConnection):
class Connection(carrot_connection.BrokerConnection, rpc_common.Connection):
"""Connection instance object."""
def __init__(self, *args, **kwargs):
@@ -105,7 +106,7 @@ class Connection(carrot_connection.BrokerConnection):
# ignore all errors
pass
self._rpc_consumers = []
super(Connection, self).close()
carrot_connection.BrokerConnection.close(self)
def consume_in_thread(self):
"""Consumer from all queues/consumers in a greenthread"""

9
nova/rpc/impl_kombu.py
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@@ -33,6 +33,7 @@ import greenlet
from nova import context
from nova import exception
from nova import flags
from nova.rpc import common as rpc_common
from nova.rpc.common import RemoteError, LOG
# Needed for tests
@@ -512,7 +513,7 @@ ConnectionPool = Pool(
order_as_stack=True)
class ConnectionContext(object):
class ConnectionContext(rpc_common.Connection):
"""The class that is actually returned to the caller of
create_connection(). This is a essentially a wrapper around
Connection that supports 'with' and can return a new Connection or
@@ -569,6 +570,12 @@ class ConnectionContext(object):
"""Caller is done with this connection."""
self._done()
def create_consumer(self, topic, proxy, fanout=False):
self.connection.create_consumer(topic, proxy, fanout)
def consume_in_thread(self):
self.connection.consume_in_thread()
def __getattr__(self, key):
"""Proxy all other calls to the Connection instance"""
if self.connection: