Hi Neil,
you have exactly pointed out my problem with OSGi in RCP applications!
I believe the solution is to use Declarative Services. In DS, services
can be registered in the service registry before the actual
implementation object for the service is instantiated -- in fact, this
is the default behaviour. A bundle offering services via DS still need
to be activated, but now the activation is "free" because a
classloader does not need to be created for the bundle until the
service is actually used.
Is DS really the only way? I have downloaded Eclipse M6 and tested the
DS-Editor. Well, how do I say it polite? If I have 2, 3 or even more
components in one bundle that require OSGi services I have to create
(if I got it right) 2, 3 or even more XML files with service-component-
descriptions. This sounds like XML-hell.
To make this work in an Eclipse RCP environment, there are two
possible approaches. First, explicitly name the bundles offering
services in config.ini, and add the @start modifier. If you do not
know in advance the names of the bundles then you could have an
extender bundle which automatically starts any bundle with a
Service-Component header.
I can't use the config.ini as I really don't know the names of the
bundles in advance. That's why we start each serviceimpl bundle in the
corresponding service bundle. But in case I do not want to use DS our
second solution was to start all bundles whose names end with
xxxx.serviceimpl in a dedicated startUp-bundle.
Kind regards,
Eugen
Am Apr 30, 2009 um 16:23 schrieb Neil Bartlett:
While I agree with Peter and Hal, I think the heart of your problem is
the mismatch between the preferred lifecycles of bundles in Eclipse
environment vs the services-based approach.
In Eclipse (both the SDK and RCP apps), activation of bundles is done
as late as possible. Lazy activation helps to ensure that Eclipse
starts quickly, and code implementing things like views and buttons is
only loaded when the user actually shows an interest in those things,
e.g. by clicking the button. The whole Eclipse extension registry is
set up to enable this by examining bundles when they are in the
RESOLVED state.
Services traditionally have a different lifecycle: they are offered up
by a bundle before it knows whether any other component (or the user)
actually wants them! So the bundle needs to be "eagerly" activated...
but Eclipse strongly discourages this practice because bundle
activation has an up-front cost.
I believe the solution is to use Declarative Services. In DS, services
can be registered in the service registry before the actual
implementation object for the service is instantiated -- in fact, this
is the default behaviour. A bundle offering services via DS still need
to be activated, but now the activation is "free" because a
classloader does not need to be created for the bundle until the
service is actually used.
To make this work in an Eclipse RCP environment, there are two
possible approaches. First, explicitly name the bundles offering
services in config.ini, and add the @start modifier. If you do not
know in advance the names of the bundles then you could have an
extender bundle which automatically starts any bundle with a
Service-Component header.
Regards,
Neil
On Thu, Apr 30, 2009 at 8:46 AM, Eugen Reiswich
<[email protected]> wrote:
Hi OSGi-devs,
I have the following problem with osgi services. We develop basically
applications where dynamic is not an issue. So what I would like to
make
sure in my application is that all services are registred properly
at start
up - if not, the application will be shut down. In addition to that
I want
to reuse my bundles in RCP applications so any concept must also be
applicable for RCP applications.
Say I have two bundles:
1. org.mycompany.service (contains a service interface)
2. org.mycompany.serviceimpl (contains the service implementation and
registers withing his activator an osgi-service)
What we do within the service bundle is this:
public void start(BundleContext context) throws Exception {
Bundle[] bundles = context.getBundles();
// find the implementation for the service bundle
for (Bundle bundle : bundles) {
if ("org.mycompany.serviceimpl".equals(bundle.getSymbolicName())) {
// service impl found
if (bundle.getState() != Bundle.ACTIVE) {
bundle.start();
}
}
}
// check if servicimpl has registred service properly
ServiceReference serviceReference = context
.getServiceReference(IMyService.class.getName());
if (serviceReference == null) {
// shut down application
}
...
From my point of view this is pretty error prone and difficult to
maintain.
Is there a best practice approach how I can make sure that all
services are
registered properly at start up of my application? How can I start my
serviceimpl bundles in RCP application as no one depends on this
bundle
which is why the are never started?
We have spend now a lot of time to find solutions for this problem
but they
all seem to be improvable.
Regards,
Eugen
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