[erlang-questions] Erlang vs IO

Bengt Kleberg <>
Wed Sep 3 17:09:08 CEST 2008


Greetings,

If you are reading a file (as opposed to stdin) you can use
file:read_file/2 (if you have enough RAM) or file:read/2 (after using
the flag 'raw' when doing file:open/2).


bengt

On Wed, 2008-09-03 at 17:27 +0300, Imre Palik wrote:
> Hi,
> 
> It is me messing up something, or the IO in erlang is quite slow?  I run the following program on a largish file:
> 
> -module(intest).
> -export([run/0]).
> 
> problem_loop(0, _, Acc) ->
>     io:fwrite("~w~n", [Acc]),
>     void;
> problem_loop(I, D, A) ->
>     {ok, [V]} = io:fread([], "~d"),
>     if
>         0 == V rem D ->
>             problem_loop(I - 1, D, A + 1);
>         true ->
>             problem_loop(I - 1, D, A)
>     end.
> 
> 
> run() ->
>     {ok, [Iter, Div]} = io:fread([], "~d ~d"),
>     problem_loop(Iter, Div, 0).
> 
> Then both of my cores started to run at 100%, which I find weird in itself with an IO bound problem.  Also, I compared the runtime with the following program written in scheme
> 
> #!/usr/bin/guile -s
> !#
> 
> (define (intest iter div acc)
>   (if (= iter 0)
>       (display acc)
>       (if (= 0 (remainder (read) div))
>           (intest (- iter 1) div (+ acc 1))
>           (intest (- iter 1) div acc))))
> 
> (intest (read) (read) 0)
> 
> 
> The scheme implementation was 10 times as fast as the erlang, and it only used one of the cores.
> 
> How can I get a decent IO performance out of erlang?  Am I making some mistakes in my erlang code? Should I upgrade my erlang system? (I am running R12B on windows)
> 
> Thx.
> 
> ImRe
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