Solution to 8.11 Problem 2 in _Programming Erlang: Software for a Concurrent World_

ring.erl

% Write a ring benchmark. Create N processes in a ring. Send a mes- sage 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.

-module(ring).
-author(hugo).
-export([create_ring/2, benchmark/2]).

benchmark(N, M) ->
    statistics(runtime),
    statistics(wall_clock),

    Entry = self(),
    E = spawn(fun() -> create_ring(N, M, Entry) end),
    E ! "Start",
    receive
        stop -> ok
    end,

    {_, T1} = statistics(runtime),
    {_, T2} = statistics(wall_clock),
    io:format("Ring benchmark for ~p processes and ~p messages 
              = ~p (~p) millisecends.~n", [N, M, T1, T2]).

create_ring(N, M) ->
    io:format("Spawn Node#[~p]~n", [N]),
    Ch = create_node(N - 1, self()),
    loop(N, Ch, M).

create_ring(N, M, Entry) ->
    create_ring(N, M),
    Entry ! stop.

create_node(0, Root) -> Root;
create_node(N, Root) ->
    io:format("Spawn Node#[~p]~n", [N]),
    Ch = create_node(N - 1, Root),
    spawn(fun() -> loop(N, Ch) end).

loop(Seq, Ch, M) ->
    receive
        stop ->
            io:format("[Node#~p] Stop~n", [Seq]),
            Ch ! stop,
            ok;
        Message when M > 0 ->
            io:format("------ Loop ~p~n", [M]),
            io:format("[Node~p] Get message: [~p].~n", [Seq, Message]),
            Ch ! Message,
            loop(Seq, Ch, M - 1);
        _ ->
            Ch ! stop,
            loop(Seq, Ch)
    end.

loop(Seq, Ch) ->
    receive
        stop ->
            io:format("[Node~p] Stop~n", [Seq]),
            Ch ! stop,
            ok;
        Message ->
            io:format("[Node~p] Get message: [~p].~n", [Seq, Message]),
            Ch ! Message,
            loop(Seq, Ch)
    end.