From: Robert Klemme <bob.news@...>
Date: 2004-02-25T21:39:52+09:00
Subject: Re: io/nonblock - blocks w/threads?


"Ara.T.Howard" <Ara.T.Howard@noaa.gov> schrieb im Newsbeitrag
news:Pine.LNX.4.44.0402242241480.28543-100000@fattire.ngdc.noaa.gov...
>
> this program does not work as expected w/o inserting the
'Thread.critical'
> bits - i must say i do not understand why, can someone help me
understand?
>
>   require 'tk'
>   require 'open3'
>   require 'io/nonblock'
>   $VERBOSE=nil
>
>   r=TkRoot.new
>   l=TkLabel.new r, :text=>`ruby -e "p Time.now"`
>   l.pack
>
>   command='ruby -e "loop{p Time.now; sleep 1}"'
>   i,o,e = Open3::popen3 command
>   i.close
>   text = nil
>
>   Thread.new do
>     loop do
>       rios, = select [o,e], nil, nil
>       rios.map do |rio|

Why do you use map here?  Apparently you don't access the result of
mapping so each would be more appropriate.

>         next if rio.eof?
>         Thread.critical = true             # blocks w/o this
>         rio.nonblock{ text = rio.read }
>         Thread.critical = false            # blocks w/o this
>         l.configure :text=>text
>       end
>     end
>   end
>
>   Tk.mainloop
>
>
> is this an o.k. technique to prevent a non-blocking read not to hand a
> multi-threaded ap?

I'm not really sure I understand correctly what you're after.  Could you
elaborate that?

Generally speaking there's one piece of advice:

When using Thread.critical= it is always best to do reset the flag in an
ensure clause to make sure that the reset occurs under all conditions:

Thread.critical = true
begin
  # do stuff
ensure
  Thread.critical = false
end

>  i'm think of adding an asychronous processing option to my
> session library using this feature... actually i suppose it'd always be
o.k.
> for this to be there...

Regards

    robert