Geoff:
Good to see you in these parts again.
Gotta confess, I've never understood that one myself. At the same
time, I've never attempted to use activatable services, which is
probably why I haven't come across this problem.
Having said that, reading through the LDS Spec, it seems that it's
designed to deal with discovery in the case of activatable services.
<quote from docs/spec/html/lds-spec.html>
The facilities of the lookup discovery service are of particular value
in a scenario in which a new lookup service is added to a long-lived
djinn containing multiple inactive services. Without the use of a lookup
discovery service, the time frame over which the new lookup service is
fully populated can be both unpredictable and unbounded.
To understand why this time frame can be unpredictable, consider the
fact that an inactive service has no way of discovering a new lookup
service. This means that each inactive service in the djinn that wishes
to discover and join a new lookup service must first activate. Since
activation of a service occurs when some client attempts to use the
service, the amount of time that passes between the arrival of the new
lookup service and the activation of the service can vary greatly over
the range of services in the djinn. Thus, the time frame over which the
lookup service becomes fully populated cannot be predicted because it
could take arbitrarily long before all of the services activate and then
discover and join the new lookup service.
In addition to being unpredictable, the time it takes for the lookup
service to fully populate can also be unbounded. This is because there
is no guarantee that the lookup service will send multicast
announcements between the time the service activates and the time it
deactivates. If the timing is right, it is possible that one or more of
the services in the djinn may never discover and join the new lookup
service. Thus, without the use of the lookup discovery service, the new
lookup service may never fully populate.
</quote>
Greg.
On Fri, 2013-09-13 at 18:04, Geoffrey Arnold wrote:
> Hello again, old friends :)
>
> I was recently singing the praises of Jini which inspired a few of our devs
> to go check it out. One particularly precocious engineer came back with a
> question about the LookupDiscoveryService, and after considering a number
> of common Jini-related tasks I still couldn't come up with a valid use
> case. Any thoughts would be greatly appreciated.
>
> Thanks,
> Geoff.
