Bundle and components lifecycles.

[Luc Dewavrin <lu...@gmail.com>]

Hi,

I have a newbie question regarding bundle lifecycle and declarative services
lifecycle : are they linked together ?
I would like the services of my bundle to be singletons and my bundle should
be activated only when services are instantiated. Is it possible to do that
by configuration ?

Can a service by declaration become a singleton in my bundle ( a la Spring
container) ? i mean all the services dependent on that service should be
bound with the same implementation (for a given bundle).

Considering that my service is a singleton. If i instantiate it in the
bundle activator, can i force my bundle to be activated only when the
service is loaded ?

Thanks for your help,
Luc

Re: Bundle and components lifecycles.

[Clement Escoffier <cl...@gmail.com>]

On 28.04.2009, at 22:39, Luc Dewavrin wrote:

> Hi,
>
> I have a newbie question regarding bundle lifecycle and declarative  
> services
> lifecycle : are they linked together ?

Your DS components are created and activated only if the bundle  
containing them is ACTIVE (i.e. started). As soon as this bundle is  
stopped, your components are disposed.

>
> I would like the services of my bundle to be singletons and my  
> bundle should
> be activated only when services are instantiated. Is it possible to  
> do that
> by configuration ?


>
>
> Can a service by declaration become a singleton in my bundle ( a la  
> Spring
> container) ? i mean all the services dependent on that service  
> should be
> bound with the same implementation (for a given bundle).

Not sure about DS because it uses the global service registry. But it  
should use the "better" available service provider. So, if you use the  
"service.ranking" property you can achieve this (every consumer will  
se the best provider). However for sure iPOJO supports that thanks to  
its composite. A composite is a kind of isolated service registry, so  
every component instance living in the composite use only services  
from this service registry.


>
>
> Considering that my service is a singleton. If i instantiate it in the
> bundle activator, can i force my bundle to be activated only when the
> service is loaded ?

Maybe it is possible to to that with the lazzy activation. So, the  
bundle is activated only when the first class of the bundle is loaded.



Clement


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Re: Bundle and components lifecycles.

[Christopher Armstrong <ca...@fastmail.com.au>]

Hi

Unfortunately everything is the other way around. The services in OSGi  
are not really "instantiated", but "registered". Your bundle needs to  
be activated, and then it registers the services in the framework.  
When another bundle requests the services, they need to be published  
into the framework first.

It should be impossible for the scenario where a bundle to requests a  
service, and as a result, causes a bundle to be activated. This is  
because the services model doesn't tie bundles to services - any  
bundle can have code implements and publishes the same service  
interface, so it is impossible for the framework to know which bundle  
it should activate (especially if there is more than one).

Declarative services is an OSGi spec that covers an extension which  
allows your bundle's "components" to be published as services when it  
is activated. You can register "delayed" components which are  
registered in the framework, but not "configured" (see DS  
specification) until they are requested, however your bundle must be  
activated of course.

Cheers
Chris

On 29/04/2009, at 6:39 AM, Luc Dewavrin wrote:

> Hi,
>
> I have a newbie question regarding bundle lifecycle and declarative  
> services
> lifecycle : are they linked together ?
> I would like the services of my bundle to be singletons and my  
> bundle should
> be activated only when services are instantiated. Is it possible to  
> do that
> by configuration ?
>
>
> Can a service by declaration become a singleton in my bundle ( a la  
> Spring
> container) ? i mean all the services dependent on that service  
> should be
> bound with the same implementation (for a given bundle).
>
> Considering that my service is a singleton. If i instantiate it in the
> bundle activator, can i force my bundle to be activated only when the
> service is loaded ?
>
> Thanks for your help,
> Luc

--------
Christopher Armstrong
carmstrong@fastmail.com.au






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