From: Marcelo <marcelo.magallon@...>
Date: 2008-03-27T11:55:10+09:00
Subject: Re: "loop do IO.select([io], nil, nil)" eats 95% of CPU, any other way?

On Wed, Mar 26, 2008 at 10:34 AM, Iñaki Baz Castillo <ibc@aliax.net> wrote:

>  --------------
>  class MyServer < GServer
>     def serve(io)
>         loop do
>               if IO.select([io], nil, nil)
>                   ....
>  --------------
>
>  A "top" says to me that Ruby is eating more than 90% of CPU and there
>  is no connections yet... :(
>  Any other suggestion?

 I don't know what GServer is, but I guess that serve is called when
 there's a connection.  As John points out, if io.eof? is true, select
 will return immediately.  For example:

#!/usr/bin/env ruby

loop do
    open("fifo") do |f|
        puts "Opened fifo"
        loop do
            ready, = select([f], nil, nil, nil).first
            break if ready.nil?
            p ready.read(1000)
            break if ready.eof?
        end
    end
    puts "Closed fifo"
end

 You'll see that it opens the fifo, blocks on it, once you write to it
 select returns, and once you reach EOF the inner loop breaks and the
 fifo is closed.  You can do something like:

 $ ruby -e 'puts "x"*2000' > fifo

 and you'll see the inner loop consuming all the input.

 If you remove:

            break if ready.eof?

 you'll see the behaviour you describe.

 Short answer: are you sure serve is called only if there's a connection?

 Marcelo