From: Bill Kelly <billk@...>
Date: 2006-01-09T02:48:45+09:00
Subject: Re: Newbie question about threads and gets

From: "Jacek Olszak" <jacekolszak@o2.pl>
> 
> I've a simple question - how can I write an application with two 
> threads, where first thread reads the user input. I want both threads to 
> run SIMULTANEOUSLY.
> So .. here is my code:
> 
> a=Thread.new do
>    $stdin.gets
> end
> 
> b=Thread.new do
>  5.times do
>    print "b"
>    $stdout.flush
>    Thread.pass
>  end
> end
> 
> a.join
> b.join
> 
> Unfortunelty "gets" block my whole application - the "b" thread waits 
> until user writes something to the stdin. But I want the b thread not 
> wait and run at the same time.

This tends to be a problem with Windows ruby.  It seems unlikely to be
resolved until Ruby gets native threads (on the horizon with YARV.)

Here's how I've worked around it.  If anyone knows a better way, please
share:

if RUBY_PLATFORM =~ /win32/
  require 'Win32API'
  $win32_console_kbhit = Win32API.new("msvcrt", "_kbhit", [], 'I')
  def console_input_ready?
    $win32_console_kbhit.call != 0
  end
  def nonblocking_stdin_gets
    sleep(0.1) until console_input_ready?
    $stdin.gets  # don't bother to use getc, it also blocks until user hits <return>
  end
else
  def nonblocking_stdin_gets
    $stdin.gets   # it just works, on unix
  end
end

So you can use nonblocking_stdin_gets in place of $stdin.gets.  It's an
imperfect solution, though.  It will be nonblocking _until_ the user starts
typing.  Then it will block until they hit <return>.  (Note, I've tried doing 
it character-by-character, with $stdin.getc or $stdin.sysread(1), but it
still blocks until the user hits <return>.)  There's probably a way to put
the windows console into unbuffered mode, which would improve this
hack (so we could use $stdin.getc in conjunction with console_input_ready?.)

Anyway, hope this helps . . .

Regards,

Bill