Send :name_conflict message to losing process when registries merge

[arjan]

When 2 clustered registries register the same name at exactly the same time, it will seem like name registration succeeds for both registries. The function returns {:ok, pid} for both of these calls.

However, due to the eventual consistent nature of the CRDT, a conflict resolution will take place, and the CRDT will pick one of the two processes as the "winner" of the name. The losing process will then receive a message to indicate that it has lost the name registration. The message looks like this:

{:name_conflict, {name, value}, registry_name, winning_pid}

[derekkraan]

Thanks, this looks great!

I was thinking about this last night, maybe it would be better to send an exit signal with the reason. Then it's still a message that processes can respond to, but the default behaviour (exiting vs ignoring) is perhaps better.

What do you think?

[derekkraan]

Consider: Elixir.Registry (and Horde.Registry) links your process to itself, so if the registry goes down, you get an exit signal. Also, it's common to write {:ok, pid} = Horde.Registry.register(...) in the init/1 callback of your process, and also just let it crash if that fails. (At least, this is what I do).

[arjan]

Yes so to catch this signal you then need to be trapping exits. I think that's fine. I'll fix this, hold on

[derekkraan]

Yes, this is looking great. Thanks!