From: "Mauricio Fernández" <batsman.geo@...>
Date: 2003-05-19T01:14:21+09:00
Subject: Re: select strange behavier

On Sun, May 18, 2003 at 09:09:22PM +0900, Simon Strandgaard wrote:
> On Sun, 18 May 2003 21:41:36 +0900, Marcin 'Qrczak' Kowalczyk wrote:
> 
> > block not longer than a specific timeout. In ancient times without select the 
> > only option was busy waiting.
>                   ^^^^^^^^^^^^
> 
> Busy waiting is what everyone wants to avoid.. 
> The same in my 'select' case, because of EOF notify then the thread
> behaves exactly as if I were *busy waiting*.
> 
> I don't want polling, I want blocking!
> 
> Any suggestions to how I should get rid of this *busy waiting* ???

Essentially removing the IO object that got to EOF from the array of
objects to be examined:

(slight modification of the code you posted)

batsman@tux-chan:/tmp$ expand -t2 aj.rb
def system(command)
  r1, w1 = IO.pipe # stdout
  r2, w2 = IO.pipe # stderr
  fdes = [r1,r2]
  thread = Thread.new do
    loop do
      res = select(fdes, nil, nil, 0.1)[0]
      p res
      if res.include?(r1)
        unless r1.eof
          Redir.instance.write_out r1.read
        else
          fdes.delete r1
          thread.kill if fdes == []
        end
      end
      if res.include?(r2)
        unless r2.eof
          Redir.instance.write_error r2.read
        else
          fdes.delete r2
          thread.kill if fdes == []
        end
      end
    end
  end
  #sleep 0.3    # if we sleep then no output is captured, why ???
  pid = fork do
    r1.close; r2.close
    $defout.reopen(w1); $stdout.reopen(w1); $stderr.reopen(w2)
    exec(command)
    # todo: should I care closing w1+w2 correctly?
  end
  w1.close; w2.close
  Process.waitpid(pid)
  # todo: Wait until the pipes r1+r2 is flushed completly
  sleep 0.5
  r1.close; r2.close
  thread.kill
end


 
> 
> --
> Simon Strandgaard

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