Order of messages sent via a Phoenix Channel

Phoenix Forum Questions / Help
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1

First of all, sorry for the super noob question.

I’m currently studying Elixir/Phoenix while using it for a hobby project.
I have a mobile messaging app that connects to a single node Phoenix server.
Upon making a connection to the server, the server will send a list of messages to the client app.
Can we expect messages to be received in the same order as the server sent them?

Thanks in advance!

2

I’m not totally sure, but I think: yes.

Pubsub is very easy, it just keeps a list of subscribers an dispatches events to them:

def dispatch(entries, from, message) do
  for {pid, _} <- entries, pid != from do
    send(pid, message)
  end

  :ok
end

So the question is, does erlang guarantee ordered messages:

10.8 Is the order of message reception guaranteed?

Yes, but only within one process.

If there is a live process and you send it message A and then message B, it’s guaranteed that if message B arrived, message A arrived before it.

On the other hand, imagine processes P, Q and R. P sends message A to Q, and then message B to R. There is no guarantee that A arrives before B. (Distributed Erlang would have a pretty tough time if this was required!)

[Erlang -- Academic and Historical Questions]

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