Re: Using lookupService()

Hello, Daniel.

Some simple (read naive) observations below...

On Tue, Dec 19, 2006 at 06:04:21PM +0100, Daniel Evers wrote:
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> Hello!
> 
> I'm trying to find a service that I advertised on another peer, using
> PeerGroup.lookupService(). Since that doesn't work, I have some questions:

My experience is limited to searching for service instances on the local peer,
whereby I use lookupService() effectively.  I have not read the platform
source code in this regard, but I always assumed the result came out of an internal
hashtable that gets populated when you "set" the various services via "params"
on the new app peergroup.

iow, the lookup does not do any sort of network discovery.  And if it
did, you'd sort of be looking at some sort of RMI scheme whereby you
either pulled bytecodes from the network for purposes of executing them
locally, or you actually do some sort of RMI on them.  This is way off
in the weeds, sorry.  But that's what it sounds like you're thinking.
I could be wrong.

> 1. I like to publish the advertisements inside a new group. All examples
> I found (mostly in the book by Brendon J. Wilson) use the net peer
> group's discovery service to publish the advertisements, not the group
> they create. Shouldn't they/I use newgroup.getDiscoveryService()?

Any advertisement published with newgroup.publish/remotepublish should be
discoverable via newgroup.getRemoteAdvertisements/getLocalAdvertisements.
One cannot acquire advertisements published via newgroup.DiscoveryService
with the discovery service of some other group.  I don't think.

> 2. I can't find the service implementation. I create the class adv, spec
> adv and impl adv for the service and according to the examples I've
> seen, only the class and spec advs are published. The implementation adv
> is added to the group's parameters (using StdPeerGroupParamAdv etc.).
> Since I cannot find this advertisement, shouldn't it be published along
> with the others?

Other readers:  help.

> 3. Something strange: I have 2 example services doing nothing, just
> printing log statements on startApp(), init() and so on. I create and
> treat both the same, but one service is always started (without using
> it), i.e. I get log messages from init() and startApp(), but the other
> one isn't. When are init() and startApp() called?

I advise turning your debug level up and look for indications that
the platform cannot find the impl class whose log messages you believe
are missing.

> 4. [Maybe related to 3.] Do I have to call newgroup.startApp() after
> creating a new group to start the services? And must/should I join this
> group, or am I joining it automatically?

To the best of my knowledge and recollection, calling
netpeergroup.newGroup() creates and starts the group.  i.e., you should
not have to explicitly call startApp().  

In your log output, even at level INFO (I think), grep for and find all
services in the net and app peergroup as they are configured, loaded
and started:

Consider this example for the PeerInfo Service.  Grep for 

Configuring PeerInfo Service
Loaded privileged module
Module started

Every formal service will output this to the log file, including the
worldgroup (I think??), the netpeergroup, and your app group via the
services you "set" on the service map for your app group.

> Sorry to bother with so many questions, but I'm "punishing" google for

No need to apologize.  We've all passed this way.

Mark


-- 
Mark S. Petrovic
Pasadena, CA 
http://www.petrovic.org