OSGi: Is it valid to register services within a declarative service component activation method?

This is a duplicate of another question, but copying from the other one:

I've run into an issue with Felix SCR where I get the message:

ServiceFactory.getService() resulted in a cycle

The reason this appers to be occuring is because within an activation method, call it ServiceAImpl (which provides ServiceA), the service registers another service, call it ServiceB.

I have another service component, call it ServiceCImpl, which depends on both ServiceA and ServiceB. By ServiceAImpl registering ServiceB, ServiceCImpl has become satisfied and within the same call to activate ServiceAImpl, the ServiceCImpl binding methods are called. When the binding method for ServiceA is called, the cycle is detected and the component fails to initialize.

Maybe there is a way to allow the SCR to wait to bind the ServiceCImpl or maybe I need to be regis开发者_运维知识库tering ServiceB differently?

I guess what doesn't make sense is why the Felix SCR will activate ServiceCImpl within the activation method of ServiceAImpl. I wouldn't think that ServiceCImpl would be considered satisfied until after the activation method has exited. Perhaps this is an issue of using declarative services while still registering services directly with the framework?

Haven't tried other SCR implementations, like Equinox's version, but I might try that to see if there is a difference, but maybe somebody knows if this is a OSGi thing or a Felix thing?

Additional Info: As to why ServiceB is not a service component...ServiceA actually has a service reference of 0..n for another service, call it ServiceD. Everytime a ServiceD interface is provided by a component, a ServiceB is registered using the same service object. Normally the same provider of ServiceD could provide ServiceB, but the idea is to make the overall interface for developers more simplistic so they don't have to provide multiple service interfaces (also, ServiceB has some properties that are set automatically that would have to be done manually and possibly could be done incorrectly).

The reason this appears to be happening is that ServiceAImpl is a delayed component that has already been loaded so ServiceA is in fact already resgistered before the component is activated. However, when another component comes along that needs ServiceA, this causes ServiceAImpl to be activated. Part of the activation process of ServiceAImpl is to register ServiceB which immediately causes ServiceCImpl to be activated. A change was made in FELIX-2368 to immediately activate a component by making most SCR operations synchronous.

A workaround is to make ServiceAImpl an immediate component which isn't desired as it shouldn't be activated if nothing needs the service. In this case, the activation method is completed when the component is loaded and by the time it is needed and bound to another component there is no problem.

I've tried to recreate this scenario with a small set of test bundles and the ProSyst OSGi FW. However, if I register a service with DS, I am not able to register an other service from within the activate() method. If I just use DS to obtain services, I can register services as usual. So there is probably really a problem with DS/SCR...

Example:

public class ServiceAImpl implements ServiceA, ServiceB, ManagedService {

public void activate(ComponentContext _context) {
    _context.getBundleContext().registerService(
            ManagedService.class.getName(),
            this,
            null);
    _context.getBundleContext().registerService(
            ServiceB.class.getName(),
            this,
            null);
}


@Override
public void doA() {
    System.out.println("Doing A Stuff");

}


@Override
public void doB() {
    System.out.println("Doing B Stuff");
}


@Override
public void updated(Dictionary arg0) throws ConfigurationException {

}

} This class will register 2 Services (ServiceB, ManagedService) with this bnd. file:

Private-Package: org.test.impl
Service-Component: org.test.impl.ServiceAImpl
Bundle-Category: test

but only 1 service (ServiceA) with this sample:#

Private-Package: org.test.impl
Service-Component: org.test.impl.ServiceAImpl;provide:=org.test.ServiceA
Bundle-Category: test

So probably you should/have to try to register the services either via DS/SCR or the "classic way" via bundle context.