From: Kristof Bastiaensen <kristof@...>
Date: 2004-08-30T04:50:39+09:00
Subject: Re: Blocking Problem

On Sun, 29 Aug 2004 07:28:59 +0900, Zachary P. Landau wrote:

Hi,

Since you are using Gtk, maybe the Gdk::Input.add method
could help you.  You can invoke it like this:

  Gdk::Input.add(my_io.to_i, Gdk::Input::Condition::READ) do
    #block to execute when data is ready in the io
  end

This is the version for gtk2, the gtk (1.2) version is a
little different.
You must have a Gtk.main loop for this to work.
I hope this is helpful.

Regards,
KB

> 
> Hello,
> 
> I'm having trouble with IO blocking when reading from a device.  It may be
> hard for people to help since most people won't be able to test this
> themselves, but I'll give it a shot.
> 
> I'm trying to read from the CueCat Linux driver, which sits in
> /dev/scanner/cuecat.  It is sort of like a pipe, you can use File.read and
> it outputs a line with a barcode (and some other information).
> 
> The problem is, I can't avoid blocking.  There is a GTK application, and
> then a separate thread that tries to read barcodes and whenever it finds
> one, it tells the GTK app.
> 
> So my code looks like this:
> 
> Thread.new do
>     File.open(CUECAT_DEV, File::RDONLY | File::NONBLOCK) do |cuecat|
> 	loop do
> 	    id, barcode_type, barcode = cuecat.gets.split(/,/) # do stuff with
> 	    the barcode
> 	end
>     end
> end
> 
> When I use a named pipe instead of CUECAT_DEV, it doesn't block.  But when
> I use the actual /dev/scanner/cuecat, it blocks.  Unfortunately, blocking
> locks up the entire application.
> 
> I tried getting around the issue by using Gtk.timeout_add instead, but
> that didn't help.
> 
> The mailing list has some posts about blocking problems, but they are
> related to sockets and pipes.  As I mentioned earlier, the above code
> works when CUECAT_DEV is a pipe.