[reSIProcate-users] why is asyncProvideContacts() called twice for a registration

[Michael Trank <mtrank@xxxxxxxxxxxxx>]

For a registration using an external infosystem as a place to 
authenticate requests and store registered contacts, I see that the 
ServerRegistration class has  a state machine that requires that the  
list of current contacts for a  subscriber be provided *twice* by 
calling asyncProvideContacts().

I understand the first time, when the current list from the back-end 
system is brought into ServerRegistration, and ServerRegistraion goes 
through this provided list, adds or updates the contact for the request 
that has just been received, and then pushes this back to the back-end 
system with asyncUpdateContacts() from my implementation of the  
ServerRegistrationHandler.

But then ServerRegistration gets put into 
asyncStateAcceptedWaitingForFinalContactList state.

What is the need to wait again for another list from the back-end? Is it 
expected that the back-end will or might do something besides update 
it's own list?

Does this have something to do with the "transaction log"?