IHandlerActivator

IHandlerActivator is the handler activator, and it should be able to instantiate handlers.

When a message comes in and needs to be handled, Rebus will pass the message down through the pipeline for incoming messages.

Unless you have changed the default behavior, the message will at some point reach the ActivateHandlersStep which will use the IHandlerActivator and call GetHandlers<TMessage>() on it, expecting in return a sequence of objects that implements IHandleMessages<TMessage>.

The resulting handler instances will be stored in the incoming step context, allowing the DispatchIncomingMessageStep to dispatch the message to them.