I think part of the problem here is the term "application". In this case we are talking about an RCP application which is defined as an Eclipse extension to the org.eclipse.core.runtime.applications extension point. When launching Eclipse the default application is started after the platform has been initialized and the start-level has reached the final state.
RCP applications have historically depended on the platform to be "fully
booted" and ready before their application is started. This mentality does
not mix well with the dynamic nature of OSGi services. When DS is added to
the mix the boot sequence become less predictable because services are not
registered synchronously as bundles get started during the bootup process
(incrementing the start-level). Currently the Eclipse application
container just assumes the application is ready to launch after the the
platform has been initialized and the final start-level has been reached.
To work around the issue you will need to do something like BJ says and
make the application handle dynamic service registrations. The problem you
will run into is that the Eclipse application container has no idea that
your Eclipse application depends on services before it is ready to launch.
So in addition to making your application handle dynamic services, you will
also need to handle waiting for your "required" services to be available in
your application start method before allowing your application start method
to continue to bring up your application. Or you can simply allow your
application to start and put safeguards in to handle when a service is not
available yet.
It would be great if we could figure out a better way to mix the use of
extensions and services together in an Eclipse application.
Tom
From: BJ Hargrave/Austin/[EMAIL PROTECTED]
To: Equinox development mailing list <[email protected]>
Date:: 09/03/2008 02:04 PM
Subject: RE: [equinox-dev] When is DS done loading services?
But even DS only knows about started bundles. If a bundle is started after
DS has processed some bundle, then new services can be registered. There is
no way for DS to know about all possible services being ready since some
may come from bundles yet to be started. The best DS could tell you is that
it is done processing services from bundles that are currently started.
It is far better in the long run for the application to handle dynamism.
Anything you do today to try and enforce some ordering will likely fail in
the future when some thing changes about the set of installed bundles.
--
BJ Hargrave
Senior Technical Staff office: +1 386
Member, IBM 848 1781
OSGi Fellow and CTO of mobile: +1 386
the OSGi Alliance 848 3788
[EMAIL PROTECTED]
From: "Cortez, Otto" <[EMAIL PROTECTED]>
To: "Equinox development mailing list" <[email protected]>
Date: 2008/09/03 02:48 PM
Subject: RE: [equinox-dev] When is DS done loading services?
It is more important for us to know what functionality is installed and
available before parts of the application execute then it is for us to
support dynamism. I would like to keep the dynamism if we can, but to do
that and provide reliable execution I think the application would need to
guarantee that all services known through the bundle manifests will be
initialized before we start processing. I guess using extensions might be
a better fit.
I’m not sure if we need DS to synchronously register services as much as
some way to listen to DS events or know its state, like is it just sitting
around waiting for more bundles to be activated or deactivated. I was
focused on services being managed by DS since I thought DS would know
weather it was done initializing all services listed in the active bundles’
manifest files and then we would be able to say to users which may supply
functionality, well if you use DS then we could guarantee that we wouldn’t
start until DS had initialized your services.
Thanks,
Otto
From: [EMAIL PROTECTED] [
mailto:[EMAIL PROTECTED] On Behalf Of BJ Hargrave
Sent: Wednesday, September 03, 2008 7:22 AM.
To: Equinox development mailing list
Subject: Re: [equinox-dev] When is DS done loading services?
The whole point of services is that the are dynamic. The fact the DS is
"processing" them on behalf of some bundle does not mean that another
bundle should know or observe that.
Bundles which depend upon a service need to deal with that service's
dynamism. You can't assume a bundle's activator or starting a bundle will
synchronously register some services. I would not support an option for DS
to synchronously register services during bundle start as this means people
will improperly use that.
You may also be seeing an impedance mismatch between the lifecycle of
extensions and services. Extensions become active when the bundle is
resolved while services become active only when the bundle is started.
Switching to use extensions will not allow for dynamism (unless you want to
write all the code to use the extension registry API to do so.)
You may be able to use startlevels to mitigate the issue (make sure all
bundles providing service B are started before bundles using B), but this
is also a hack. It would be better if service A dealt with the dynamics of
service B such that service A has a dynamic dependency on service B and is
able to accept B's being registered and unregistered at any time.
--
BJ Hargrave
Senior Technical Staff office: +1 386
Member, IBM 848 1781
OSGi Fellow and CTO of mobile: +1 386
the OSGi Alliance 848 3788
[EMAIL PROTECTED]
From: Stoyan Boshev <[EMAIL PROTECTED]>
To: Equinox development mailing list <[email protected]>
Date: 2008/09/03 07:51 AM
Subject: Re: [equinox-dev] When is DS done loading services?
Hi Otto,
I guess your problem is connected to the asynchronous processing of the
DS services.
As far as I understand the situation is: your application bundles are
started, then your application is started but at this moment not all of
the DS services are inited yet because they are being asynchronously
processed.
Unfortunately currently there is no way to find out when DS completes
the DS services processing.
I think if there was an option that DS bundle process the DS services in
the started bundles synchronously, it would solve your problem. So I
will open bug(enhancement) about that and hopefully this will be
implemented soon.
As a possible workaround you could observe the running threads and when
the thread with name "Component Resolve Thread" disappears this would
mean that DS bundle has no more work to do and eventually all of your DS
services are processed. I realize this is not a clean solution (that's
why I call it workaround) but at this moment I cannot find out a more
appropriate working solution without modifications in the DS bundle.
Stoyan
Cortez, Otto wrote:
> I made a post to the Eclipse newcomers group a few weeks ago, but did
> not get a response. I don’t know if this is the appropriate place for
> this question, but hopefully someone can point me in the right direction.
>
>
>
> We are building a headless RCP application and we would like to use DS
> to make functionality available. The problem we are running into is
> that not all of the services we declared through DS get loaded and are
> visible before our application executes.
>
>
>
> For example, I have a service A which needs 0..n instances of another
> service B. The issue I'm running into is that if the implementations of
> service B are spread across several bundles, then the service A will not
> have seen all instances of service B when it is called since the
> application starts (and sometimes ends) running before DS is done
> looking through all the bundles and registering all the services in the
> active bundles.
>
> Is there a way to know when declarative services is done looking through
> the active bundles and loading the services found in them? Am I missing
> something?
>
>
>
> It seems that using the plug-in registry may solve this issue. Is that
> perhaps a better way to go?
>
>
>
> Thanks,
> Otto
>
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--
---------------------------------------------------------
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ProSyst Labs EOOD
1606 Sofia, Bulgaria . 48 Vladajska Str.
Tel. +359 2 953 05 88; Fax +359 2 953 26 17
Mobile: +359 88 898 29 17
http://www.prosyst.com. . [EMAIL PROTECTED]
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