From: "Iñaki Baz Castillo" <ibc@...>
Date: 2008-03-27T07:49:14+09:00
Subject: Re: "loop do IO.select([io], nil, nil)" eats 95% of CPU, any other  way?

El Miércoles, 26 de Marzo de 2008, John Carter escribió:

> Hmm.From the "man select" page...
>
>        timeout is an upper bound on the amount of time elapsed before
>         select() returns.  It may be zero, causing select() to return
>         immediately.  (This is useful for polling.)  If timeout is NULL
>         (no timeout), select() can block indefinitely.
>
> My guess is you have one too few nil's in there and the default timeout is
> 0 not nil.

Yes, true, with "strace" I see:

...
sigprocmask(SIG_BLOCK, NULL, [])        = 0
sigprocmask(SIG_BLOCK, NULL, [])        = 0
sigprocmask(SIG_BLOCK, NULL, [])        = 0
sigprocmask(SIG_BLOCK, NULL, [])        = 0
sigprocmask(SIG_BLOCK, NULL, [])        = 0
select(4, [3], [], [], {0, 0})          = 0 (Timeout)  <---
sigprocmask(SIG_BLOCK, NULL, [])        = 0
sigprocmask(SIG_BLOCK, NULL, [])        = 0
sigprocmask(SIG_BLOCK, NULL, [])        = 0
sigprocmask(SIG_BLOCK, NULL, [])        = 0
sigprocmask(SIG_BLOCK, NULL, [])        = 0
...


but I've tryed with all the values in the 4º parameter of "IO.select":
  IO.select([io], nil, nil, 0)
  IO.select([io], nil, nil, nil)
  IO.select([io], nil, nil, X)

and nothing changes, in all cases I see the same with "strace". ¿?¿



> to discover why linux is such a great place to develop on.... you can
> _always_ find out what is really going on with any program.

Sure I use Linux... what else? XD


> As a little side comment...  You can _always_ take a program written
> around a select & state machine and make it multi-threaded doing
> blocking I/O or conversely refactor a multi-threaded app into a select
> based state machine.

Of course I need to read a lot about IO methods :)


Thanks a lot.


-- 
Iñaki Baz Castillo