Elixir

Sending and Receiving

Apr 2, 2016

Use send and receive to communicate between processes.

defmodule Person do
  def tell(receiver, message) do
    IO.puts "[#{inspect self}] Sending #{message} to #{inspect receiver}"
    send receiver, {:ok, self, message}
  end
  
  def listen do
    IO.puts "[#{inspect self}] is listening"
    receive do
      {:ok, sender, message} ->
        IO.puts "[#{inspect self}] Received #{message} from #{inspect sender}"
    end
    listen
  end
end

In the above module, we have two functions:

  • tell sends a message to a receiver using send. send takes a pid and a message - usually a tuple
  • listen recursively calls receive, which is a blocking operation that waits for a message to the current process’ pid and executes some code in response

On iex:

iex> jeff = spawn(Person, :listen, [])
[#PID<0.78.0>] is listening
#PID<0.78.0>
iex(3)> Person.tell(jeff, "Sup jeff")
[#PID<0.57.0>] Sending Sup jeff to #PID<0.78.0>
[#PID<0.78.0>] Received Sup jeff from #PID<0.57.0>
[#PID<0.78.0>] is listening
{:ok, #PID<0.57.0>, "Sup jeff"}

In the above, #PID<0.57.0> refers to our current process, and #PID<0.78.0> refers to the jeff process.