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From "Brian Bouterse (JIRA)" <j...@apache.org>
Subject [jira] [Created] (QPID-5799) Allow qpid.messaging.endpoints.session to have all associated receivers mointored via epoll mechanism
Date Wed, 04 Jun 2014 13:43:01 GMT
Brian Bouterse created QPID-5799:

             Summary: Allow qpid.messaging.endpoints.session to have all associated receivers
mointored via epoll mechanism
                 Key: QPID-5799
                 URL: https://issues.apache.org/jira/browse/QPID-5799
             Project: Qpid
          Issue Type: Improvement
          Components: Python Client
            Reporter: Brian Bouterse

Kombu [0] is a python producer/consumer software that I've written a qpid transport[1] for.
This qpid transport for Kombu, uses qpid.messaging, and has all consuming receivers associated
with a single session endpoint.

Celery[2] uses Kombu, and has an asynchronous I/O event loop, and would like to monitor a
single file descriptor for reading to know when there is any message available on any receiver
associated with the session endpoint.

Currently as a workaround, I create a pipe with one read and one write file descriptors. I
register the read file descriptor with Celery to monitor. I then start a separate thread (Thread1)
that calls next_receiver() on the session in an infinite loop. Each time next_receiver() returns
instead of fetching the message, Thread1 writes a symbol to the file descriptor Celery is
monitoring. Celery then calls the on_readable() callback from the MainThread, which removes
a symbol from the pipe Celery is monitoring (clearing the epoll readable attribute), and then
calls next_receiver() again only this time from MainThread, to acquire the receiver, and fetch()
the message and process it.

This architecture is not ideal in two ways.
1. There is a redundant call to next_receiver() that happens with every read.

2. A separate thread to "monitor" qpid messaging should not be required, when Celery is already
capable of monitoring a single file descriptor, and can call the read method which would use
next_receiver() to drain from all receivers associated with the session.

[0]:  https://github.com/celery/kombu
[1]:  https://github.com/pulp/kombu/blob/pulp-dep-3.0.15-with-qpid/kombu/transport/qpid.py
[2]:  https://github.com/celery/celery

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