A little confused about spawning new processes

Eyup, don’t name your process, hold the pid instead.

And yes, every process’s state/stack is distinct.

Alright, that problem is solved then, after holding the pid in a variable I need to access it from other blocks in the same module, the commands are in a case, since the >>start command starts the link with the Agent I can’t access the variable outside of that block, which can be the most efficient way of getting that pid? Thanks for the help.

Well I certainly would not use an Agent, but to pass it out of a block you just return it from that block, what issue were you having with that?

Ah, sorry, not a block, it was a clause, as far as I know you can’t return values from case clauses, right?

I have something like this:

case msg.content do
  @prefix <> "start" ->
    # Main server
    {:ok, pid} = Cass.Server.start_link(
      %{name: msg.author.username, id: msg.author.id}
    )

  @prefix <> "queue" ->
    # here I need to get the pid to know it's state
end

Or what would you recommend me to do in this situation?

Also, the result of the last expression in a case clause gets returned:

value =
  case true do
    true -> 1
    false -> 0
  end

value # 0

*Everything* returns something, and your @prefix <> "start" -> is returning {:ok, pid}, just assign the output of the case msg.content do to a variable and pass it around in whatever you are holding state in. ^.^

This would work for a single node, but not multi-node, so it depends on your use case.

Ah, I didn’t know that, thanks both for your input!

Argh, sorry but I think that I should explain my issue a little better and give more context, I’m using a library for Discord and the way that you listen for events is through a handle_event function and then you match the contents of the message with, well, what you’re expecting, this is part of my code:

def handle_event({:MESSAGE_CREATE, {msg}, _ws_state}, state) do
    case msg.content do
      @prefix <> "start" ->
        {:ok, pid} = Cass.Server.start_link(
          %{name: msg.author.username, id: msg.author.id}
        )
        pid # at first glance what I understood was this and that'd be it if I wanted to just return something out of this whole "case", right?
      @prefix <> "queue" ->
        Setup.get_agent(pid) # use the pid returned above as a parameter here?
    end
end

I’m getting errors saying that the pid variable doesn’t exist because of the scope, right? I mean, even if the process is running I can’t use that pid. I tried using the content of the variable as the return statement of the case, something like:

pid =
  case msg.content do
    @prefix <> "start" ->
      Cass.Server.start_link(
        %{name: msg.author.username, id: msg.author.id}
      )
    _ ->
      :ignore
  end

But, uh, I can’t use two case statements, so… I really don’t know how to initialize the process and pass the variable to get the state later on

I need to explicitly initialize the process when the >>start command is specified because then how can I spawn the process? I tried moving the start_link function above the case but that’d match every time a message is sent and that’s a total mess, if I just wanted to use the bot on a single server it would be done already. I thought I had it but I’m still confused… well, not confused because I understand the process, I just don’t know how to implement it…

Yeah you are not storing the pid anywhere here at all. ^.^

Assuming your state is a map, then you can do this:

def handle_event({:MESSAGE_CREATE, {msg}, _ws_state}, state) do
    case msg.content do
      @prefix <> "start" ->
        {:ok, pid} = Cass.Server.start_link(
          %{name: msg.author.username, id: msg.author.id}
        )
        %{state | pid: pid} # You return your updated state from this function, so you do that here
      @prefix <> "queue" ->
        Setup.get_agent(state.pid)
        state # Not changing the state so just passing it right back out
    end
end

So yeah, you were not actually storing the pid anywhere. ^.^