Re: Refreshing stuff in the background ( continued )

[muppet <scott asofyet org>]

On Jun 5, 2006, at 8:59 PM, Daniel Kasak wrote:

> Hi all.
>
> Following on from my previous email, I've broken up all the code that
> refreshes various notebook pages into separate subs. I've made an  
> array
> of hashes describing each page, and with a coderef to the sub that  
> does
> the requerying for that page.
>
> The main bit of code that triggers everything is:
>
> sub refresh_pages {
>
>     my $self = shift;
>
>     # Refresh the active page immediately
>     my $active_page =
> $self->{form}->get_widget("TabForm_main_notebook")->get_current_page;
>
>     print "Refreshing page: $self->{refreshers}[$active_page]-> 
> {name}\n";
>
>     $self->{refreshers}[$active_page]->{refresh}();
>
>     my $counter = 0;
>
>     foreach my $refresher ( @{$self->{refreshers}} ) {
>     if ( $counter ne $active_page ) {
>         print "Refreshing page: $refresher->{name}\n";
>         $refresher->{refresh}();
>     }
>     $counter ++;
>     }
>
>     Glib::Source->remove( $self->{refresh_timeout} );
>
> }
>
>  ... and I trigger this code with the line:
>
> $self->{refresh_timeout} = Glib::Idle->add ( sub { $self- 
> >refresh_pages } );
>
> This code runs fine - ie it refreshes all the pages. However, even
> though the window is 'responsive' ( ie redraws ), nothing actually
> updates until ALL the pages are refreshed. So when I run the app  
> from an
> Eterm, I see the lines:
>
> Refreshing page: xxx
> Refreshing page: yyy
>
> etc
>
> and when the *final* one prints, *then* the window is actually updated
> with the new data.
>
> What am I doing wrong?

Screen updates don't happen immediately; they are queued in idles.

So, instead of

        install idle
    Main loop
        idle handler
            foreach @items
                refresh $_

break the list up into a chain of idle handlers:

        install idle
    Main loop
        idle handler
            refresh shift @items
            install idle if @items
    Main loop
        idle handler
            refresh shift @items
            install idle if @items
    ...

Yes, this can make you code rather more indirect and disconnected,  
but it gets the job done.  If you structure things as a worker queue,  
it begins to fall together more naturally.

--
Meg: Brian!  Chris picked his nose and keeps trying to touch me with  
his finger!
Chris: What good is mining nose gold if I can't share it with the  
townspeople?
   -- Family Guy