# Ruby/Tk refresh problem

**URL:** <https://www.ruby-forum.com/t/ruby-tk-refresh-problem/164829>\
**Category:** Ruby\
**Created:** [April 6, 2009, 12:40pm UTC](https://www.ruby-forum.com/t/ruby-tk-refresh-problem/164829 "2009-04-06T12:40:32Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![diego\_v](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/eb8c5e/32.png) [@diego\_v](https://www.ruby-forum.com/u/diego_v)\
**Post date:** [April 6, 2009, 12:40pm UTC](https://www.ruby-forum.com/t/ruby-tk-refresh-problem/164829/1 "2009-04-06T12:40:32Z")

</div>

Hello,  
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.

My fear is that it might be a problem like refreshing, whereby Tk  
doesn’t receive the instruction until it’s too late. Is there a way to  
flush all the instructions to Tk and let it do its magic before  
continuing running my code?

Thanks.

Diego

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<div class="post-metadata">

**Author:** ![diego\_v](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/eb8c5e/32.png) [@diego\_v](https://www.ruby-forum.com/u/diego_v)\
**Post date:** [April 6, 2009, 11:52pm UTC](https://www.ruby-forum.com/t/ruby-tk-refresh-problem/164829/2 "2009-04-06T23:52:12Z")

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From: Diego V. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)  
Subject: Ruby/Tk refresh problem  
Date: Mon, 6 Apr 2009 19:39:15 +0900  
Message-ID:  
[removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)

> 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

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<div class="post-metadata">

**Author:** ![diego\_v](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/eb8c5e/32.png) [@diego\_v](https://www.ruby-forum.com/u/diego_v)\
**Post date:** [April 6, 2009, 11:53pm UTC](https://www.ruby-forum.com/t/ruby-tk-refresh-problem/164829/3 "2009-04-06T23:53:23Z")

</div>

Have you tried “Tk.update” call ?

Antonio

Diego V. wrote:

> Hello,  
> 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.
> 
> My fear is that it might be a problem like refreshing, whereby Tk  
> doesn’t receive the instruction until it’s too late. Is there a way to  
> flush all the instructions to Tk and let it do its magic before  
> continuing running my code?
> 
> Thanks.
> 
> Diego