Passing objects between clients

[Chris Muller]

Hi Nick, have a look at MagmaTestCase>>#testSequenceNumberGenerator,
in the MagmaTester package.  This demonstrates how to use MagmaCounter
to synchronize a counter object between all clients.

By using a couple of Counters that index into a MagmaArray, you may
implement a "MagmaQueue", that would be synchronized between all
clients.

If you don't want the clients to have to poll the database for a piece
of work, please also note the "Ma Client Server" framework is easy to
use independently of Magma, and is pretty robust.  Whoever is pushing
the work onto the queue could simply send the work directly to another
MagmaClient or send just a reference-id to the work-request in the
database (have a look at #requiredProgress for making the latter
work).

The MagmaTester uses "Ma Client Server", on its own, without Magma, to
run its test-suite.  By having a "conductor" image which simply sends
out remotePerform:withArguments: to three other images (two clients
and a server) to tell them to do various things for the test.  See the
swiki for more information on "Ma Client Server".

 - Chris


> I'm interested in using it to allow pieces of work (which I'll call 'jobs')
> to be handed out to one or more Squeak images ('workers').
>
> On startup, each worker opens a connection to the Magma server, checks to
> see whether there are any jobs waiting to be done. If there are, the worker
> will take the first job off the queue, run it, and ultimately commit the
> result of the job back into Magma.
>
> Other Magma clients are periodically going to push new jobs onto the end of
> the queue.
>
> My first attempt just used an OrderedCollection to represent the queue, with
> one Magma client adding Arrays of numbers to it with #add: to simulate jobs
> being added; and another client removing them with #removeFirst; to simulate
> jobs being accepted by a worker.
>
> This approach is prone to conflicts, presumably because each #add: or
> #removeFirst: is attempting to rewrite the entire internal state of the
> OrderedCollection.
>
> So my question is, is there a better way of doing this? Use Magma to pass
> semaphores between clients? Or just live with the conflicts?
>
> Thanks for any insight.
>
> -Nick
>
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