Message of set_members documented

[F2011B]

I tried to implement a DeltaCrdt handoff using the Tanx example from 2018, I was not able to understand where the message :set_members originated. Maybe it is already documented in hex, however I have not found it on the first glance.

[F2011B]

I have tried to use the Tanx example , to understand how a handoff can be used to persist state over changing cluster layout. I cut out the handoff part and included it into a small example project. The :set_members message is handled by the handoff implementation to set the neighbours of its DeltaCRDTs.

code snippet from Tanx.Handoff.Impl (file handoff/impl.ex)

    def handle_call({:set_members, members}, _from, state) do
    Logger.info("In Set Members!!! #{inspect(members)}")

    existing_members = MapSet.new(Map.keys(DeltaCrdt.read(members_crdt_name(state.name))))
    new_members = MapSet.new(member_names(members))

    Enum.each(MapSet.difference(existing_members, new_members), fn removed_member ->
      DeltaCrdt.mutate_async(members_crdt_name(state.name), :remove, [removed_member])
    end)

I am not sure about the source of this message. It seems that this message is sent by Horde.Cluster.set_members to its members.

Maybe there is a better example for implementing state handoff. Maybe you can clarify that with a really small example. @derekkraan I have to note I am a total noob to elixir, therefore thank you for your kind response.

[derekkraan]

I see where the confusion is coming from. In the Tanx example app, Daniel is taking advantage of the existing Horde.Cluster.set_members/2 function. Buuuuut, while this function is public, I would classify the {:set_members, members} message as private. So I don't think it would make sense to document this here.

The Tanx example depends on delta_crdt, and I think that's really something that should be grokked before using it for state handoff like this (imho). There is a guide on state handoff, https://hexdocs.pm/horde/state_handoff.html#content, if you can suggest improvements to that then that would be much appreciated, although I would like to keep it storage-agnostic (and not go into details of how to wire up delta_crdt into a cluster, for example).

[derekkraan]

Closing this issue but still happy to answer your questions here (or in the #horde channel on Slack)