From: Eric Wong <normalperson@...>
Date: 2009-11-22T07:43:19+09:00
Subject: Re: issues with Kernel#select

Tim Pease <tim.pease@gmail.com> wrote:
> Waking up a thread that is waiting in Kernel#select does not appear to work in ruby 1.9  Can someone please confirm that this is the case. Is this the intended behavior, or is this a bug?
> 
> 
> > cat a.rb
> require 'socket'
> 
> pair = Socket.pair(Socket::AF_UNIX, Socket::SOCK_STREAM, 0)
> t = Thread.new {
>   Kernel.select pair, nil, nil, nil
>   puts "Thread is about to exit ..."
> }
> t.wakeup
> t.join
> 
> > ruby --version
> ruby 1.8.7 (2009-06-12 patchlevel 174) [i686-darwin10]
> 
> > ruby a.rb
> Thread is about to exit ...
> 
> > ruby1.9 --version
> ruby 1.9.1p243 (2009-07-16 revision 24175) [i386-darwin10]
> 
> > ruby1.9 a.rb   #=> hangs forever!!!!
> 
> 
> 
> Any thoughts out there ???

Hi Tim,

1.9 is actually doing what I expect it to do, that is waiting
indefinitely because the timeout argument for select is nil.  I might
consider the 1.8.7 behavior a bug, but then again the underlying
select(2) syscall is allowed to have spurious wakeups.  So even without
a timeout argument, select may always return even when nothing is
readable.

-- 
Eric Wong