Advanced concurrancy

[Michael Sparks]

Peter Tillotson wrote:

> Hi,
> 
> I'm looking for an advanced concurrency module for python and don't seem
> to be able to find anything suitable. Does anyone know where I might
> find one? I know that there is CSP like functionality built into
> Stackless but i'd like students to be able to use a standard python build.

Please take a look at Kamaelia* - it /probably/ has what you're after by the
sounds of things. Currently the unit for sequential process can be either
generators or threads, and is single CPU, single process, however we do
expect to make the system multi-process and multi-system.
   * http://kamaelia.sourceforge.net/

Currently it runs on Linux, Mac OS X, Windows and a subset works nicely on
Series 60 mobiles. (That has separate packaging) It works with standard
Python versions 2.2 and upwards.

The basic idea in Kamaelia is you have a class that represents a concurrent
unit that communicates with local interfaces only which are essentially
queues. The specific metaphor we use is that of an office worker with
inboxes and outboxes with deliveries made between outboxes to inboxes.
There also exists a simple environmental/service lookup facility which acts
like an assistant in the above metaphor, and has natural similarities to a
Linda type system.

(The actual rationale for the assistant facility though is based on
biological systems. We have communicating linked concurrent components -
which is much like many biological systems. However in addition to that
most biological systems also have a hormonal system - which is part of the
thinking behind the assistant system)

Generators (when embedded in a class) lend themselves very nicely to this
sort of model in our experience /because/ they are limited to a single
level (with regard to yield).

It's probably suitable for your students because we've tested the system on
pre-university trainees, and vacation trainees, and found they're able to
pick up the system, learn the basic ideas within a week or so (I have some
exercises on how to build a mini- version if that helps), and build
interesting systems. 

For example we had a pre-university trainee start with us at the beginning
of the year, learn python, Kamaelia, and build a simple streaming system
taking a video file, taking snapshots and sending those to mobile phones
and PC's - this was over a period of 3 months. He'd only done a little bit
of access in the past, and a little bit of VB. Well that as well as a
simple learning system simulating a digital TV decode chain, but taking a
script instead of a transport stream.

We recently made a 0.2.0 release of the system (not announced on c.l.p yet)
that includes (basic) support for a wide range of multimedia/networked apps
which might help people getting started. Some interesting new additions in
the release are an IPython integration - allowing you to build Kamaelia
systems on the fly using a shell, much like you can build unix pipelines,
as well as a visual introspection tool (and network graph visualiser) which
allows you to see inside systems as they are running. (This has turned out
to be extremely useful - as you can expect with any CSP-type system)

The specific use cases you mention are also very closed aligned with our
aims for the project. 

We're essentially working on making concurrency easy and natural to use,
(starting from the domain of networked multimedia). You can do incremental
development and transformation in exactly the way it sounds like you want,
and build interesting systems. We're also working on the assumption that if
you do that you can get performance later by specific optimisations (eg
more CPUs).
   * Example of incremental component development here:
         http://tinyurl.com/dp8n7

By the time we reach a 1.0 release (of Kamaelia) we're also aiming to be
able to integrate cleanly with Twisted (on Twisted's grounds), but it is
highly usable already - especially in your area. (In CVS we have tools for
building game type systems easily & Tk integration as well. Tk based CSP
systems are particularly fun to work with (as in fun, not "fun" :). One
project we are seriously looking at is a visual editor for these CSP-type
systems, since that appears now to be low hanging fruit.

We've got a white paper about Kamaelia here:
   * http://www.bbc.co.uk/rd/pubs/whp/whp113.shtml

This is "textualisation" of a presentation I gave at ACCU earlier in the
year and is an overview of the core areas of the system - hopefully enough
to let you know whether to look further!

I also gave an updated talk at Europython - the presentation for which can
be downloaded from here:
   * http://www.python-in-business.org/ep2005/talk.chtml?talk=2589&track=692

Last week I also gave a more pragmatic, shorter talk at Open Tech which is
an introduction to Kamaelia, it's goals, and several examples of CSP type
systems ranging from simple audio clients/servers through to presentation
tools. That presentation can be downloaded from here:
   * http://kamaelia.sourceforge.net/Kamaelia_OT2005.tgz

Both the Europython & Open tech bundles actually include the core
concurrency systems (called Axon), and the component modules (Kamaelia) in
the bundle, in addition to the slides and install docs. The presentation
tools included in the bundles are written in python using Kamaelia.

The project website is here: http://kamaelia.sourceforge.net/

> I'm trying to develop distributed / Grid computing modules based on
> python. The aim is to be able to use barriers for synchronisation and
> channels for communication between processes running on a single box.
> Then the jump to multiple processes on multiple boxes and eventually to
> MPI implementations. Hopefully, each jump should not be that big a leap.
> 
> Of course it would be nice if there was a robust way of managing
> concurrency in python aswell ;-)

It's getting there - the recent PEP regarding the ability to cause a
generator to have an exception thrown inside it provides very similar to
Unix signals as provided via "kill", which will be nice when 2.5 is
released.

Hopefully you find the system useful,

Best Regards,


Michael.
--
Michael Sparks, Senior R&D Engineer, Digital Media Group
Michael.Sparks at rd.bbc.co.uk, http://kamaelia.sourceforge.net/
British Broadcasting Corporation, Research and Development
Kingswood Warren, Surrey KT20 6NP

This e-mail may contain personal views which are not the views of the BBC.