Interface for Coordinators

[tanneberger]

Channel or Connection based Coordinators

What is the purpose of a coordinator?
I would say: Figure out until which logical time there are no incoming messages.

Hence every NetworkChannel needs an associated ChannelCoordinator which keeps track of incoming messages and talks with the other federate to figure out until which timestamp there are no incoming messages from that other federate.

Derived Interface

struct ChannelCoordinater {
  // until which tag the federate has advanced
  Tag (*last_known_tag)(ChannelCoordinator* channel_coord);
  
  // function called by the network channel 
  void (*handle_incoming_message)(
      ChannelCoordinator* channel_coord, 
      const FederatedMessage* msg);
      
  void (*tag_complete)(ChannelCoordinator* channel_coord, Tag tag);
}

[edwardalee]

Be careful with phrases like "tag smaller then the given tag", which does not mean the same thing as "tag smaller than or equal to the given tag." This distinction is important.

[erlingrj]

A question we should answer up front is this:
"Does it make any sense to coordinate different connections (they can go both ways) between two federates with different techniques?"

I don't think there is any use-case for coordinating different connections with the same direction. But there might be a use-case for doing different coordination in each direction.