Nservicebus Singleton pattern - hook into currently existing objects

I am working through the first steps of figuring out Nservicebus and planning a reasonably large scale (at least for me) app.

I want the app to be able to scale out onto X machines. It will have a number of services, such as:

LogonService UserManagementService GameService RoomService etc...

The clients would talk to the server through WCF. The services themselves would talk to each other via NServiceBus and MSMQ. Sacha Barber has written an excellent article on getting started with NServiceBus and has come up against the same situation I am going to hit. There is a further chat between Udi and Sacha about thi开发者_如何学Pythons here.

My Question is, when a service is handling a message how does it know about the rest of the app in that service? As Sacha puts it, "a handler will automagically" appear when a message needs dealing with. So when this is created how does it know about the other objects that are already up and running. For example in the GameService, it would have a list of all games currently running. How would it access this?

I guess the two options that I can think of, (as Sacha pointed out), are:

Mediator pattern Singleton

Out of the two I think I would rather register a singleton with Castle Windsor and use it that way.

Is this an appropriate use of the Singleton pattern, (as you often see people referring to the Singleton as the "Devil", I don't want to miss use it if possible).

Is there a better solution to this problem?

Thanks

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For state that need to be kept in memory I would also use the Singleton pattern. Otherwise state is usually maintained in the datastore and read by the handler for each message proceed.

public Handle(SomeMessage msg)
{
   var aggregateRoot = writeStore.Get(msg.SomeId);

   aggregate.DoSomeAction(msg.SomeOtherData);

   //if write store does not support dirty tracking
   writeStore.Save(aggregateRoot);
}

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Singletons are pretty awful if you want to do unit tests among other things. NServiceBus uses Spring (by default) as a dependency injection framework when initialising the message handlers. Ideally, you'd plug into Spring yourself and register your objects so they can be injected via. spring.

Having said that, Singletons are an easy way to achieve what you want. However if the only reason you'd be making an object a singleton is for NServiceBus to access it, I'd suggest finding a better way to do it.