From: Romulo Ceccon <redmine@...>
Date: 2009-05-12T03:14:53+09:00
Subject: [ruby-core:23431] [Bug #1460] IO#select returns wrong fd list after Kernel#sleep (Windows)

Bug #1460: IO#select returns wrong fd list after Kernel#sleep (Windows)
http://redmine.ruby-lang.org/issues/show/1460

Author: Romulo Ceccon
Status: Open, Priority: Normal
Category: core, Target version: Ruby 1.8.6
ruby -v: ruby 1.8.6 (2008-08-11 patchlevel 287) [i386-mswin32]

The following script never ends on Windows XP/Vista:

  require 'thread'
  
  a = IO.pipe
  puts "pipe: #{a.inspect}"
  
  th = Thread.new do
    if res = IO.select([a[0]], [], [], 1)
      puts "select ok: #{res.inspect}"
      c = a[0].read(1)
      puts "read ok: #{c}"
    else
      puts "timeout"
    end
  end
  
  puts "sleep"
  sleep(1)
  puts "done"

The main thread stops at "sleep(1)" and the secondary thread at "c = a[0].read(1)". This is the output I get:

  pipe: [#<IO:0x2b616f4>, #<IO:0x2b616cc>]
  sleep
  select ok: [[#<IO:0x2b616f4>], [], []]
  (ruby freezes here)

The Kernel#sleep call makes IO#select return with the pipe handle, even though it hasn't signaled. Then the call to IO#read blocks because no data is available. I couldn't come up with a workaround because IO#read_nonblock does not work with pipes in Windows (raises "Bad file descriptor" (calling IO#fcntl with O_NONBLOCK is also not possible)).


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