From: Hidetoshi NAGAI <nagai@...>
Date: 2009-04-07T06:50:57+09:00
Subject: Re: Ruby/Tk refresh problem

From: Diego Virasoro <Diego.Virasoro@gmail.com>
Subject: Ruby/Tk refresh problem
Date: Mon, 6 Apr 2009 19:39:15 +0900
Message-ID: <14fd4ffc-9fc4-4a36-bf2e-a0bb7b278d5f@f19g2000yqo.googlegroups.com>
> I am using Ruby 1.8.7 with Tk. The code runs fine. However, a few
> instructions that I set while the program is busy (basically before
> starting heavy computation it sets a TkLabel to display "Busy"... and
> once it's done it sets it back to "") do not seem to have much of an
> effect.

Maybe, you call the heavy computation *IN* a callback. 
If so, that is a very bad way on event-driven programing. 

The heavy part blocks the eventloop. 
And then, the GUI cannot receive any events. 
That is, the GUI seems to freeze. 

A callback procedure should return as soon as possible. 
One of the simple way to do that is to make a thread executing the
heavy computation. 
Of course, you never join the thread in a callback.
Instead of joining, you should generate an event (TkVariable#wait may 
be useful) to tell the finishing of the thread. 

For example, the following is a bad sample. 
------------------------------------------------------------------
require 'tk'
l = TkLabel.new(:text=>'MESSAGE').pack
TkTimer.new(500, -1,
            proc{l.foreground 'black'},
            proc{l.foreground 'red'}).start
TkButton.new(:text=>'start heavy work',
             :command=>proc{10.times{|n| sleep 1; p n}}).pack
Tk.mainloop
------------------------------------------------------------------
When clicking the button, this GUI seems to freeze.

Please compare with the following.
------------------------------------------------------------------
require 'tk'
l = TkLabel.new(:text=>'MESSAGE').pack
TkTimer.new(500, -1,
            proc{l.foreground 'black'},
            proc{l.foreground 'red'}).start
TkButton.new(:text=>'start heavy work',
             :command=>proc{Thread.new{10.times{|n| sleep 1; p n}}}).pack
Tk.mainloop
------------------------------------------------------------------

The following is another sample.
------------------------------------------------------------------
require 'tk'
l = TkLabel.new(:text=>'MESSAGE').pack
TkTimer.new(500, -1,
            proc{l.foreground 'black'},
            proc{l.foreground 'red'}).start
b = TkButton.new(:text=>'start heavy work',
             :command=>proc{
                   b.state :disable
                   Thread.new{
                     10.times{|n| sleep 1; p n}
                     b.state :normal
                   }
                 }).pack
Tk.mainloop
------------------------------------------------------------------
This example shows one of the way to catch the finishing of a heavy
operation. 
-- 
Hidetoshi NAGAI (nagai@ai.kyutech.ac.jp)