Example OSGi services that use OSGi R7 Async Remote Services. When used with ECF's Remote Services Implementation and a supporting distribution provider, the method call will be invoked asynchronously by the service consumer. As described here, return value given in the service interface has one of the Java types: CompletableFuture, Future, CompletionStage, or Promise, then the service method will be invoked without blocking and with an (optional) timeout.

For example, here is a 'hello' service interface:

public interface IHello {

    String sayHello(String from, String message);
	
    CompletableFuture sayHelloAsync(String from, String message);
	
    Promise sayHelloPromise(String from, String message);
	
}

Since the sayHelloAsync and sayHelloPromise methods can be used over a network by remote service consumers with a guarantee of asynchronous invocation and optionally with a given timeout. Here is an implementation that uses the OSGi R7 specified intents to do so:

@Component(immediate=true,property = { "service.intents=osgi.async",  // R7 osgi.async remote service property
                                       "service.exported.interfaces=*",  // RSA-required remote service property
				       "osgi.basic.timeout:Long=50000"  // timeout of 50000ms=50 seconds
									                   }
public class HelloImpl implements IHello {

...implementation of IHello...

When the HelloImpl service instance is exported, the osgi.async property will require the distribution provider to create a proxy that returns a CompletableFuture instance immediately, and require the remote service invocation timeout after 50 seconds. Here is an example consumer for this service:

void bindHello(IHello hello) {
	
    hello.sayHelloAsync("JavaAsync","Howdy Python").whenComplete((resp,except) -> {
                                                        if (except != null)
                                                            except.printStackTrace();
                                                        else
                                                            System.out.println("sayHelloAsync received result="+resp);
                                                    });
}

When invoked, the sayHelloAsync call will immediately return a CompletableFuture instance that will timeout after 50s, or call whenComplete before that timeout with either a valid resp instance or an exception. This runtime behavior is provided via a R7-compliant distribution provider.

This repostiory contains this example, as well as other examples of both synchronous and asynchronous remote services.