An Elixir Noob Stumbles into Concurrency-oriented Programming

Like many Rubyists today, I too am learning Elixir. So far, it’s been an exciting endeavor. I started out by reading Elixir in Action and was totally blown away by the first chapter in which the author, Saša Jurić, teaches the reader about Erlang concurrency. Indeed, the Erlang VM (aka BEAM), is an amazing thing: it supports it’s own processes (rather than OS processes) that execute code concurrently accross CPU cores. Whats more, the BEAM processes are super cheap; they don’t share memory; and, if long-running, schedulers will prevent them from halting the entire system by giving processes limited execution windows. When I finished that first chapter, I was hooked.

Since then, I’ve been spending time learning Elixir as basically a weekend project. I read a couple more chapters of Elixir in Action and familiarized myself with the basic concepts of functional programming in Elixir. I learned about the power of pattern matching, recurision and how to work with immutable data. While all of these concepts are great, what about the concurrent awesomeness of the BEAM?

On March 2-3, 2017, I attended Elixir Daze where I heard Jesse Anderson’s The ABCs of OTP. His fantastic talk pointed me in the right direction. Per his recommendation, I picked up a copy of The Little Elixir & OTP Guidebook and got to work. Now, I’m on the good stuff: OTP.

Concurrent Processes and Blasting Off Rockets

If you have just started learning Elixir but want a quick and tiny taste of concurrent programming, here is something you can do in quickly in IEx. It super high level, absurdly trivial, tip-of-the-iceberg stuff using primitives, but it’s a just an introduction. Down below, I’ve provided some links to some real resources to learn more.

  1. What’s cooler than blasting off a rocket? Blasting off two rockets at the same time. Create a file called blast_off.ex and add the following code.

     defmodule BlastOff do
   def get_ready do
     receive do
       :countdown ->
         Enum.each(10..0, fn(i) ->
           IO.puts i
           :timer.sleep(1000)
         end)
         IO.puts "Blast Off!"
     end
   end
 end

    Here we define a module BlastOff with one function called get_ready. The interesting thing here is the receive/1 function. The processes running the receive/1 function will wait for a message that matches the pattern defined within the do block. In our receive/1 function we’re expecting a message that is the symbol, :countdown. Upon receipt of the :countdown message we start a countdown from 10 to 0 printing each number and sleeping for 1 second.

  2. Now lets start up IEx session with our BlastOff module loaded.

    iex blast_off.ex

  3. Use spawn/3 to start up a process that runs our BlastOff.get_ready/0 function. It’s going to wait for the :countdown message. We bind the result of this function to pid1.

    iex> pid1 = spawn(BlastOff, :get_ready, [])
#PID<0.92.0>

    The spawn/3 function creates a process out of the given module, function and arguments. In our case the augment list is empty since our get_ready function doesn’t take any arguments.

  4. Lets spawn another process and bind the result to pid2.

    iex> pid2 = spawn(BlastOff, :get_ready, [])
#PID<0.94.0>

  5. Fire up the Erlang Observer iex> :observer.start. We should see our processes.

    observer

    Notice now little memory these processes are consuming (those numbers are in bytes).

  6. Now, let’s launch a couple rockets. Send the :countdown message to our processes and observe the results. In the example below, we’re iterating over the list of pids we created earlier then using send/2 to send each pid the :countdown message.

    iex> Enum.each([pid1, pid2], fn(pid) -> send(pid, :countdown) end)

    You should now see the results of both processes counting down at the same time.

This example is painfully trivial, but it serves as a very simple introduction into concurrent processes in Elixir. Going beyond this, means diving into GenServer and OTP: the really good stuff that makes Elixir truly awesome and powerful. Here are some great resources to learn more.

Resources for Further Learning