From: Tim Pease <tim.pease@...>
Date: 2009-11-23T08:04:06+09:00
Subject: Re: issues with Kernel#select


On Nov 21, 2009, at 3:43 PM, Eric Wong wrote:

> 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.

Thanks for the answer. My suspicion is that the Ruby 1.8 green threads can be woken up, but the Ruby 1.9 system threads "do the right thing"; hence, the discrepancy in observed behavior. Good to know that it's not a bug in 1.9.

/me goes off to rework code

Blessings,
TwP