[erlang-questions] Ring Benchmark Problem

[Robert Virding]

A much better way than sending the path around is for every process to keep
track for itself the next process in the ring so you just need to send the
message between the processes. At least if you are after speed. If you do
do need to be able to dynamically restructure the ring it would be easy to
add an extra message where you tell a process its new next process.

Robert


On 11 January 2015 at 20:48, Harit Himanshu <harit.subscriptions@REDACTED>
wrote:

> Hello there,
>
> I need help with code review on my attempt to following problem
>
>  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 have not timed this yet, and guidance on recommended ways to time is
> very much appreciated.
>
> For now, following is the code for ring that I wrote. Please let me know
> if there are any shortcomings or code could be written in an much idiomatic
> way.
>
> Thanks a lot
> + Harit
>
> *Code*
>
> -module(ring).
> -author("harith").
>
> %% API
> -export([message/2]).
>
> % create ring of N processes and
> % send M messages between them
> message(N, M) when is_integer(N), is_integer(M), N > 0, M > 0 ->
>   Ring = create_ring(N),
>   [Start | T] = Ring,
>   Start ! {T, Ring, 1, M}.
>
> create_ring(N) ->
>   Processes = [spawn(fun() -> loop() end) || _ <- lists:seq(1, N)],
>   [H | _] = Processes,
>   lists:append(Processes, [H]).
>
> loop() ->
>   receive
>     {[H | T], _L, CurrentMessage, M} ->
>       io:format("~p received ~p~n", [self(), CurrentMessage]),
>       H ! {T, _L, CurrentMessage, M},
>       loop();
>     {[], Ring, CurrentMessage, M} ->
>       io:format("~p received ~p with empty list~n", [self(),
> CurrentMessage]),
>       case CurrentMessage < M of
>         true ->
>           [_ | [Next | T]] = Ring,
>           NewMessage = CurrentMessage + 1,
>           io:format("sending message ~p to ~p~n", [NewMessage, Next]),
>           Next ! {T, Ring, NewMessage, M};
>         false -> io:format("done sending ~p messages in ~p ring, taking
> rest now.~n",[M, Ring])
>       end,
>       loop()
>   end.
>
> *Output*
> 1> ring:message(4, 3).
> <0.33.0> received 1
> {[<0.34.0>,<0.35.0>,<0.36.0>,<0.33.0>],
>  [<0.33.0>,<0.34.0>,<0.35.0>,<0.36.0>,<0.33.0>],
>  1,3}
> <0.34.0> received 1
> <0.35.0> received 1
> 2> <0.36.0> received 1
> 2> <0.33.0> received 1 with empty list
> 2> sending message 2 to <0.34.0>
> 2> <0.34.0> received 2
> 2> <0.35.0> received 2
> 2> <0.36.0> received 2
> 2> <0.33.0> received 2 with empty list
> 2> sending message 3 to <0.34.0>
> 2> <0.34.0> received 3
> 2> <0.35.0> received 3
> 2> <0.36.0> received 3
> 2> <0.33.0> received 3 with empty list
> 2> done sending 3 messages in
> [<0.33.0>,<0.34.0>,<0.35.0>,<0.36.0>,<0.33.0>] ring, taking rest now.
> 2>
>
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