CODEWITHSUNDEEP
erlang
hellomatey27
hellomatey27

Reputation: 115

Getting to grips with Erlang messages

I'm still trying to come to grips with Erlang messages, and while playing around with it, I came up with this case. It seems like it should work, but it just hangs indefinitely.

Can someone who is more used to Erlang please explain what I am doing wrong? And yes, I am aware that I don't even look at what is returned. This is the result of trying to reduce the code to isolate the problem.

-module(test).
-export([caller/2]).

callee(V1, V2, From) ->
  From ! {V1, V2}.

caller(V1, V2) ->
  spawn(fun() ->
    callee(V1, V2, self()) end),
  receive
    _ ->
      {V1, V2}
  end.

Upvotes: 2

Views: 43

Answers (2)

Hynek -Pichi- Vychodil
Hynek -Pichi- Vychodil

Reputation: 26121

This bit will help you understand where is the problem.

1> Self = self(), spawn(fun() -> io:format("Self: ~p, self():~p ~n", [Self, self()]) end).
Self: <0.83.0>, self():<0.85.0> 
<0.85.0>

Upvotes: 1

pdexter
pdexter

Reputation: 811

If you assign the result of self() to a variable outside the function in the call to spawn and then pass in that variable instead of the literal self() then the message sent in callee will correctly be sent to the process running caller (the process waiting on receive).

Upvotes: 1

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