RE: [equinox-dev] When is DS done loading services?

[Thomas Watson <tjwatson@xxxxxxxxxx>]

Otto, you make a good observation on any thread apps. They will be started as soon as the application container is ready to start them, only main threaded apps currently wait until after the start-level has reached the final start-level. The timing issues are still the same but the window is smaller for main threaded apps because they give the DS thread a little more time to finish registering services.

Tom



"Cortez, Otto" ---09/03/2008 05:21:04 PM---Is that true of all extension of the org.eclipse.core.runtime.applications extension point, that they don’t start until the pl

From:	"Cortez, Otto" <OttoCortez@xxxxxxxxxxxxx>
To:	"Equinox development mailing list" <equinox-dev@xxxxxxxxxxx>
Date:	09/03/2008 05:21 PM
Subject:	RE: [equinox-dev] When is DS done loading services?

---

Is that true of all extension of the org.eclipse.core.runtime.applications extension point, that they don’t start until the platform has been initialized?  Even when they run in any thread and not just the main?
 
I would be happy enough to be able to say: if you declare your services in this way, we will wait for those to be initialized before we start, otherwise we won’t guarantee your service will be available.  I was hopping to be able to do that through DS, so waiting for the DS thread to stop seems fine, although it would be nice to have a more formal way to do this, through public API.
 
In our application, we don’t expect bundles to be started and stopped dynamically (at least not too often), so we are really only worried about knowing what services there are at the initial startup.
 
I was trying to figure out a good way to safeguard against the dynamism of the services.  I don’t think there is an issue with the services which require 0..1 or 1..1 instances of another service, but I don’t know what to do about the services which require 0..n and 1..n because you don’t really know how many more services there might be without doing what DS seems to already do, look through the manifests and find the declared services.  I suppose you could also wait for the platform to stop starting bundles, but then DS could still be running so I’d still need a way to know when it was done.
 
Thanks,
Otto

---

From: equinox-dev-bounces@xxxxxxxxxxx [mailto:equinox-dev-bounces@xxxxxxxxxxx] On Behalf Of Thomas Watson
Sent: Wednesday, September 03, 2008 1:30 PM
To: Equinox development mailing list
Subject: RE: [equinox-dev] When is DS done loading services?

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



BJ Hargrave---09/03/2008 02:04:43 PM---But even DS only knows about started bundles. If a bundle is started after DS has processed some bundle, then new services can

From:	BJ Hargrave/Austin/IBM@IBMUS
To:	Equinox development mailing list <equinox-dev@xxxxxxxxxxx>
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 Member, IBM OSGi Fellow and CTO of the OSGi Alliance hargrave@xxxxxxxxxx

office: +1 386 848 1781 mobile: +1 386 848 3788

From:	"Cortez, Otto" <OttoCortez@xxxxxxxxxxxxx>
To:	"Equinox development mailing list" <equinox-dev@xxxxxxxxxxx>
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: equinox-dev-bounces@xxxxxxxxxxx [mailto:equinox-dev-bounces@xxxxxxxxxxx] 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 Member, IBM OSGi Fellow and CTO of the OSGi Alliance hargrave@xxxxxxxxxx

office: +1 386 848 1781 mobile: +1 386 848 3788

From:	Stoyan Boshev <s.boshev@xxxxxxxxxxx>
To:	Equinox development mailing list <equinox-dev@xxxxxxxxxxx>
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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