[rabbitmq-discuss] 2.0: The Future of Pika

[Jason J. W. Williams]

I like the cleanness of the new style, and think the blocking adapter is the
core of what Pika brings to the party. Whether you're using Eventlet,
Tornado or Twisted, all of the async frameworks have their
own idiosyncrasies that it seems to me make it difficult to have one unified
adapter for async.

Also, the 0.9 series already broke backwards compatibility once. Doing it
again with 2.0 I think would make folks already dependent on it circumspect
about doing development with the 0.9 series. If the API is going to change
again I would recommend that the old API be turned into a wrapper around the
new approach, that way anyone developing with the 0.9 series has a clear
upgrade path without their projects breaking. It'll allow folks to develop
new projects on Pika today knowing they'll still work tomorrow, and that
they can ease into the new style as it's available.

Just my thoughts. :)

-J

On Sat, Mar 12, 2011 at 4:12 PM, Gavin M. Roy <gmr at myyearbook.com> wrote:

>  I've been listening to a lot of the conversations at PyCon about
> asynchronous development. The basic sentiment I've picked up on is that
> Callback Passing Style (CPS) is not currently in favor in the Python
> community.  This in addition to the popular use of the BlockingConnection in
> Pika has lead me to think about how to plan Pika's future enhancements.
> After some conversation with Tony, I believe I have an outline that should
> appeal to Python developers while keeping Pika asynchronous at its core and
> retaining CPS. I think that CPS is very powerful and believe it's still very
> important to Pika's future.
>
> After I release 0.9.5, I will start development on Pika 2.0 which will be
> an effort to create a more pythonic approach to using Pika while retaining
> the ability to use CSP and keeping it asynchronous at its core.
>
> The roadmap for changes to Pika 2.0:
>
> - Backwards incompatible change that drops Python 2.4, 2.5 support
> - Adding Python 3 support
> - Remove existing connection adapter system
> - Implement new pattern for use, behavior based use focused on
> both Asynchronous callback passing style and "Pythonic" development.
>   - Both behaviors available from the same API calling same classes and
> methods
>   - Async:
>     - Merge existing connections into one connection system with IOLoop
> override
>       - Supporting internal IOLoop, tornado, twisted
>   - Pythonic:
>     - high-level blocking on synchronous AMQP commands
>     - Generator for receiving messages from Basic.Publish
> - API notation closer to AMQP spec for implementation.
> - *.*Ok frames will only be passed back in CPS use.
>   - Calling methods like queue.declare will return a success indicator and
> attributes returned in the Ok frame will be assigned to attributes of the
> class.
> - basic.consume and basic.get will return a single object with a
> materialized view of the Method, Header and Body frames.
> - Build in support for specific broker types and pure AMQP 0-9-1.
>
> Here's an example of what I expect Pika 2.0 to look like for non-CSP use.
> Note this is more of an idea of how it will work for someone using Pika than
> a spec or actual code.
>
>     from pika.rabbitmq import Connection
>     from pika import Basic
>     from pika import Channel
>     from pika import Exchange
>     from pika import Queue
>
>     from sys import exit
>
>     # All the attributes can be passed in via constructor or assigned
>     connection = Connection()
>     connection.host = 'localhost'
>     connection.port = 5762
>     connection.user = 'guest'
>     connection.pass = 'guest'
>     connection.vhost = '/'
>
>     # Not much new here
>     try:
>         connection.open()
>     except pika.ConnectException as e:
>         print "Could not connect: %s" % e
>         sys.exit(0)
>
>     # Channel construction outside of connection context, instead pass
>     # the Connection in
>     channel = Channel()
>     try:
>         channel.open(connection)
>     except pika.TimeoutException as e:
>         print "Could not open a channel: %s" % e
>     except pika.ConnectionClosedException as e:
>         print "Could not open a channel, the connection is closed"
>
>     # All the attributes can be passed in via constructor or assigned
>     exchange = Exchange(channel)
>     exchange.name = 'test'
>     exchange.type = 'fanout'
>     exchange.durable = True
>     exchange.declare()
>
>     # All the attributes can be passed in via constructor or assigned
>     queue = Queue(channel)
>     queue.name = 'my_queue'
>     queue.auto_delete = False
>     queue.durable = True
>     queue.passive = False
>
>     # Declare the queue and expect a bool
>     if not queue.declare():
>         raise Exception("Could not declare my queue")
>
>     # Print info about the queue that was mapped automatically when
>     # Queue.DeclareOk was received
>     print 'Queue "%s"' % queue.name
>     print ' Depth     : ' % queue.message_count
>     print ' Consumers : %i' % queue.consumer_count
>
>     # Bind the queue
>     queue.bind(exchange=exchange, routing_key='test.my_queue')
>
>     # A generator returns one object for a message
>     for message in Basic.consume(my_channel, routing_key="test.my_queue"):
>         print 'Delivery Tag   : %s' % message.delivery_tag
>         print 'Channel        : %i' % message.channel
>         print 'Body Size      : %i' % len(message.body)
>         print 'Properties'
>         print '  Content-Type : %s' % message.properties.content_type
>         print '  Timestamp    : %s' % message.properties.timestamp
>         print '  User Id      : %s' % message.properties.user_id
>         print '  App Id       : %s' % message.properties.app_id
>         print 'Body           : %s' % message.body
>
> I am looking for feedback on this direction. Do these changes and the
> example make sense to existing Pika and RabbitMQ uses?  Would you change
> anything about this direction? What would you improve?
>
> Regards,
>
> Gavin
>
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