Re: xAP / xPL Gateway

[mark_harrison_uk2]

--- In <a
href="/group/xAP_developer/post?postID=hQXA7VArBicnCT8iPRS26kRWbi7oXavG1A62JK7Ddaeokexf7z1k2k9P052sxNXVXYSIaccjIze3pSE_wej8wTQu1D-ChvJZ">xAP_developer@xxxxxxx</a>,
"Ian Lowe" <ian@w...> wrote:
> ----- Original Message -----
> From: "mark_harrison_uk2" <mph@a...>
> >
> > --- In <a
href="/group/xAP_developer/post?postID=hQXA7VArBicnCT8iPRS26kRWbi7oXavG1A62JK7Ddaeokexf7z1k2k9P052sxNXVXYSIaccjIze3pSE_wej8wTQu1D-ChvJZ">xAP_developer@xxxxxxx</a>,
"Ian Lowe" <ian@w...> wrote:
> > > ----- Original Message -----
> > > From: "Stuart Booth" <lists@x>
> >
> > > From an end user p.o.v. mucking about with "this app
can be a
hub",
> > > or "this is a hub app" etc, is (imo) just too much
hassle.
> >
> > Nooo.. It's all auto-detecting in Stuart's framework.
> >
> > The end user simply runs the apps (s)he wants.
> >
> > The first one to start sets itself up as a hub. The rest detect
it
> > (whether they're Stuart's or not) and use it.
> >
> > Zero configuration for user. The user doesn't even realise this
is
> > going on.
>
> Ah, I got the impression that we had a few different hubs?

We do. There's a non-.NET ones for slower Windows PCs, a Linux one.

However, the comment to which I was replying was about the difficulty
of configuring applications that could also be hubs. It's only
Stuart's that have this capability, as far as I know? The other hubs
are simply standalone things that aren't also applications in their
own right.

> As long as all of the applications behave in this well-formed way,
it should
> work fine. As xPLHal starts as a windows service, it will be
running long
> before anyone gets to the running applications stage
> , so each of the xAPps
> launched by the end user will just detect the hub and go..

That assumes that no other xAP applications to run on the same PC are
themselves services. Things like xAPWatcher (James Traynor's system
monitoring app) would make very useful services.

Is it possible to control service startup order? I know that service
dependancy trees are there, but are they under installer control (as
opposed to developer control.) Ie - can an installer set up something
within Windows which says "don't start service B until service A is
running"?

The problem with putting them under developer control is that if
service B (xAPWatcher, say) ABSOLUTELY DEPENDED on service A
(xPLHal), then it wouldn't work on machines on which xPLHal was not
installed.

Likewise, it's not reasonable to MANDATE that xAP developers check
for the presence of xPLHal at install time, and set dependancies if
it exists.

> Remember, this is for the server running xPLHal only: it doesn't
apply to
> any other machine running xAP on your network. As far as I can see,
this
> won't change anyone's behaviour or experience.

The question of "if I run xPLHal, then I can't run any other
Hub"...
well, if that's the price of xAPL (sic) then I can live with that.

I don't really see any pragmatic objection to your going ahead as you
describe.

Maybe the answer is simply to put a note in the xPLHal documentation
that highlights that it MUST be the hub and has to be run before any
other xAPplications on the same PC ???

As you say, anyone with a network sophisticated enough to use both is
going to have multiple PCs and applications can run elsewhere. The
main reason for distributing my xAP network is that Homevision lives
upstairs in node zero where the hard-wired PIRs terminate... The main
application server lives in my study... and the Meteor server lives
in Mary's study where the phone line is :-) It wouldn't be a problem
for me to run xPLHal on the Meteor server, and xAPMeteor DOES run in
a user context rather than as a service.

PS - I agree that this group is exactly the right place to have these
discussions. xAP-automation is really for announcements and support,
rather than developer issues.

Regards,

Mark