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Michael Sparks  
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 More options Oct 20 2008, 3:09 pm
From: Michael Sparks <spark...@gmail.com>
Date: Mon, 20 Oct 2008 20:09:22 +0100
Local: Mon, Oct 20 2008 3:09 pm
Subject: Re: [kamaelia-list] Re: propogating shutdowns
On Monday 20 October 2008 19:27:27 Jason Baker wrote:

> The graphline will shut down if and only if all of its children have
> shut down.  If wiring those up is too tedious, you can also use a
> backplane and PublishTo/SubscribeTo components to send out all the
> shutdown messages.

That's a novel approach, and kinda goes in reverse regarding historical
development of the backplane. In the beginning the Fanout component was
created as a splitter, specifically for passing on shutdown to a collection
of components.

Then later on, the graphline component was created. Later still, the splitter
was created, and then Matt's Plug Splitter. I then attached services (in and
out) to the PlugSplitter to create the backplane, publishto and subscribeto
components.

[1]http://kamaelia.googlecode.com/svn/trunk/Sketches/MPS/Experiments/Opt...

As a result your suggestion here kinda goes full circle. :-)

However it strikes me as a little heavy handed - it'd just be nice for the
graphline to just pass on the

(mentioning this because sometimes a little history is useful to understand
just how the frog got boiled)

> Example (just off the top of my head, not tested):

> bp = Backplane('shutdown')

It's an interesting example/usecase though because it allows you to pass
shutdown message through to graphlines nested inside graphlines. (since
Backplane services currently have a global shared namespace)

> A final option would be to work something out with splitters,

This makes me smile for obvious reasons :)

> So to answer your question more directly, there isn't an easy way to
> do this.  :(

But there should be, without boiling frogs :)

> If there is a way that you would LIKE to do this as opposed to this,
> let us know.  I'm sure something could be added that would suit your
> needs in the next version of Kamaelia.

Interestingly, I jumped straight to this point. My feeling is that a shutdown
message to the graphline's control inbox is that unless the subcomponent's
control inboxes have been wired to (by the linkages argument) that we should
pass on the shutdown message to those subcomponents. (The reason for
not sending to all of them would be that it's possible there's an ordering
dependency on shutdown and the graphline's linkages may already do
this)

Michael.
--
http://www.kamaelia.org/Home


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