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osgiapache-karafapache-felixblueprint-osgi

Create A Service And Allow Only One Bundle To Hold That Service At any Time

I'm trying to create a service such that once it is created it only allows itself to be held by a single consumer/bundle at any one time. (If this is against the philosophy/specification of OSGi then that obviously provides a quick answer but reference to the OSGi specs. stating this would be appreciated.)

To implement such a requirement I implemented the ServiceFactory interface thinking that whenever there was a requirement for the service the getService(Bundle bundle, ServiceRegistration<S> registration) method would be called and it would be where I could determine if the Bundle was a new consumer or not and act accordingly.

It appears that this is not the case in the scenario I have tested this in.

Using a Apache Karaf and instantiating a consumer of the Service via Blueprint it would seem that the getService method is never called. Instead the consumer's binding method for the service is called directly but injecting a proxy service object.

While I understand that Blueprint uses proxies surely there is still the obligation of the ServiceFactory contract to fulfil even if it's a proxy object consuming the service?

Why do I want to do this? I am attempting to wrap JavaFX and the Stage class and because JavaFX isn't OSGi friendly I am attempting to co-ordinate access to the Stage object. I'm aware that there are frameworks such as Drombler but a brief look at them made me think that it doesn't suit my use case. They appear too restrictive for my needs e.g. I don't necessarily wish to layout an application in the manner Drombler uses.

Solution

  • It depends what you mean by a consumer. ServiceFactory does give you the chance to create a separate instance of a service per bundle that calls getService on your service. It's not clear from your question but I suspect you weren't seeing the getService invoked multiple times because you were fetching the service from the same consumer bundle. In this case, ServiceFactory simply returns the same object repeatedly.

    As for your general question about restricting access to a single consumer, no that really goes against the OSGi philosophy. I'm sorry I don't have a spec reference for you but the clue is in the name: it's a service that is available to all.