message_ring.erl

message_ring.erl

-module(message_ring).

-compile(export_all).

-export([]).

%% Problem Statement: 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.

-record(state, {index,
                next=undefined,
                total_procs,
                total_msgs,
                num_msgs=0}).


start(N, M) ->
    State = #state{index=0, total_procs=N, total_msgs=M},
    Pid = spawn_link(?MODULE, init, [State]),
    register(ringhead, Pid),
    Pid.


init(#state{index=Index, total_procs=N}=S) ->
    case Index < N of
        true ->
            % spawn new process
            % io:format("spawning next process~n"),
            Pid = spawn_link(?MODULE, init, [S#state{index=Index+1, total_procs=N}]),
            loop(S#state{next=Pid});
        false ->
            io:format("linking last element to first to form a ring~n"),
            loop(S#state{next=whereis(ringhead)})
    end.


loop(#state{next=Next, total_msgs=M, num_msgs=X}=S) ->
    receive
        {forward, Msg} ->
            case X == M of
                true ->
                    io:format("message reached end of the ring~n"),
                    loop(S);
                false ->
                    %% io:format("~w received message \"~w\", forwarding to ~w~n",
                    %%           [self(), Msg, Next]),
                    Next ! {forward, Msg},
                    loop(S#state{num_msgs=X+1})
            end
    end.