cam macrae - blog

Following my post Which language to learn next I picked up the pdf book Programming Erlang and have devoted and hour or two a day for the last week to learning Erlang.

One of the early concurrent programming exercises goes like this:

Write a ring benchmark. Create N processes in a ring. Send a message round the ring M times so that a total of N * M messages get sent. Time how long this takes for different values of N and M.

I won't post a solution because that kinda defeats the purpose of the exercise, but here is my start function with the timing code. For clarity, the call to initproc/4 causes initproc/4 to recurse N-1 times.

start(N, M) when N > 0 ->
    MasterPid = spawn(fun() -> initproc(master) end),
    FirstChildPid = spawn(fun() -> initproc(2, N, M, MasterPid) end),
    register(ctl, self()),
    statistics(runtime),
    statistics(wall_clock),
    MasterPid ! {start, M, FirstChildPid, hola},
    receive
    _Any -> 
        {_, Time1} = statistics(runtime),
        {_, Time2} = statistics(wall_clock),
        io:format("Run time: ~p (~p) ms~n", [Time1, Time2]),  
        unregister(ctl)
    end.

Here are some results from my Macbook 2GHz, 2Gb ram:

   10 Procs, 100 messages -> Run time: 0 (1) ms
   10 Procs, 1000 messages -> Run time: 0 (5) ms
   

Messaging is obviously very fast in Erlang!

   10 Procs, 10000 messages -> Run time: 30 (32) ms
   100 Procs, 10000 messages -> Run time: 300 (308) ms
   

Can it be that linear?

   1000 Procs, 10000 messages -> Run time: 2920 (3043) ms
   1000 Procs, 100000 messages -> Run time: 28840 (29974) ms
   

Crikey!

   10000 Procs, 100 messages -> Run time: 580 (614) ms
   10000 Procs, 1000 messages -> Run time: 6060 (6279) ms
   10000 Procs, 10000 messages -> Run time: 61420 (64036) ms
   

It took me a good half hour to become bored by playing with different values of M and N! (Should this be embarrassing or a badge of honour?)

Of course this is a toy application, but it's pretty obvious Erlang is a serious bit of kit.

Programming Erlang is a well written book from which I've already learned so much, and not just about Erlang, but programming in general. All up I'm excited to continue the journey.