Comment #96 on issue 62 by [email protected]: Lifecycle support http://code.google.com/p/google-guice/issues/detail?id=62
I think closing/destroying objects when they go out of scope is a red herring.
It sounds like people really want the ability to start and stop per injector services in the right order. While the lifecycle of the service is the same as the injector's, the object isn't necessarily in singleton scope– maybe the service isn't eligible for injection into other objects (see Binder.requestInjection()).
@PostConstruct and @PreDestroy seem like a bad fit here. First, they don't speak to starting and stopping services. Second, and less important than the naming and semantics, using annotations will be slower and more error prone than using a marker interface.
How do we decide which objects are eligible to be started? Strawman: any object that's created or injected during injector creation. This includes eager singletons, objects passed to requestInjection(), and any transitive dependencies. Note: This could get a little weird if you use DEVELOPMENT vs. PRODUCTION stages.
One could use an InjectionListener named ServiceManager to collect any object that implements Guava's Service interface. After injector creation, you call ServiceManager.start(). ServiceManager stops collecting objects (by ignoring any further callbacks), and then it iterates over the objects in the order in which they were created–so you can use dependencies to control the order services are started in–and it starts each service.
When you're ready to stop, call ServiceManager.stop(). It'll stop the services in the reverse order.
Once Guice supports concurrent singleton injection (by inspecting the dependency graphs), ServiceManager could keep track of which threads the callbacks come in on. Then it could make sure that objects instantiated in the same thread are also started in the same thread.
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