I want to make the progress update asynchronous, but don't know where to start. I suspect the answer involves threads, but I have relatively limited experience using them. On the other hand I feel that using separate threads might be overkill and that there is probably a better way to handle this (though I have yet to find it).

See Re: my within a loop and Tk::after

Thanks for the tip. I tried Tk::After, but that doesn't seem to work. Perhaps I misunderstood the cpan page. The modified code is below.

my $button=$mw->Button(-text=>'Update');
$button->after(0, [\&update, \$prog ]);
$button->pack;
$mw->ProgressBar(-variable=>\$prog)->pack;
[download]

For some reason the callback function is now executed immediately after the script is run (and still not asynchronously), rather than after the button event. Any help would be much appreciated.

Thanks

For some reason the callback function is now executed immediately... $button->after(0, [\&update, \$prog ]);

What do you think that 0 (zero) that you have as the first argument to ->after() means?

---

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In the absence of evidence, opinion is indistinguishable from prejudice.

G'day hermes1908,

Welcome to the monastery.

I don't think your users would be too happy having to manually update the download progress by pressing a button. This is really something you'd want to display dynamically. Consider how it's done in a simple text-based scenario (e.g. wget) or in a graphical context such as your browser: you don't need to hit keys or press buttons to see what progress has been made.

When designing a GUI, think about how it's been done previously and how your users would expect it to work. Unless you are intending to present something that is fundamentally different from the norm, stick with the status quo.

Here's a working (albeit barebones) script that simulates 3 files being downloaded simultaneously and shows progress dynamically.

#!/usr/bin/env perl

use strict;
use warnings;

use Tk;
use Tk::ProgressBar;

my @file_data = (
    { name => 'File1', size => 1000 },
    { name => 'File2', size => 5000 },
    { name => 'File3', size => 2500 },
);

my $mw = MainWindow->new();
$mw->geometry('400x200+50+50');

my $control_F = $mw->Frame()->pack(-side => 'bottom');
$control_F->Button(-text => 'Exit', -command => sub { exit }
    )->pack(-padx => 5, -pady => 5);

my $progress_F = $mw->Frame(
)->pack(-padx => 10, -pady => 10, -fill => 'both', -expand => 1);

for my $file_datum (@file_data) {
    my $download_amount = 0;
    my $download_percent;
    my $download_F = $progress_F->Frame(
        )->pack(-padx => 10, -pady => 10, -side => 'top', -fill => 'x'
+);
    $download_F->Label(-text => $file_datum->{name}
        )->pack(-padx => 5, -side => 'left'); 
    $download_F->ProgressBar(-variable => \$download_percent
        )->pack(-padx => 5, -side => 'left', -fill => 'x', -expand => 
+1);
    $download_F->repeat(25 => sub {
        $download_amount += int rand 10;
        if ($download_amount > $file_datum->{size}) {
            $download_amount = $file_datum->{size};
        }
        $download_percent = $download_amount / $file_datum->{size} * 1
+00;
    });
}

MainLoop;
[download]

Thanks for the example, but the idea was that I would prompt the user for input (using an entry widget) and then initiate the download. The updates are supposed to be asynchronous so a button doesn't need to pushed to see the progress. The idea is that once a download has been initiated the update function should run in the background so as not to hang up the application (the download link is retrieved via an entry widget). Your sample code has the same issue that mine did, namely that the download routine runs before the gui is even displayed. Do you have the same issue when you run your code? Perhaps something is wrong with my version of Tk ( though I've had this problem on two different machines running different linux distributions, so that's unlikely).

I think that you may be missing the focus of kcott's post. It is the repeat function.

Obviously, you start the progress bar when you are ready.

Example

use Tk;
use Tk::ProgressBar;
my $mw = MainWindow->new();
my $per = 0;
$mw->ProgressBar(-variable=>\$per)->pack;
$mw->Button(-text=>"Go",-command=>\&GoForIt)->pack;
MainLoop;

######### This is the important bit ###########
sub GoForIt {
    $mw->repeat(25=>sub{$per+=10;return if $per>100;;$mw->update;sleep
+(1)})
}
[download]

What you're describing doesn't make any sense to me: I can't see how the (simulated) downloads in my code could have possibly run before the GUI is displayed.

When you ran my code, did you really see all progress bars showing completion? I see them starting at the far left and moving towards the right.

Did you change my code before running it? I can't think of any reason why the code I posted would not run, as is, under Linux; however, if you did change it, please show the actual code you are running.

-- Ken

Re: [HELP] Chat, two routines, Tk says

Welcome, see The Perl Monks Guide to the Monastery and PerlMonks FAQ

 [tk chat] -> tk chat -> Tk encrypted echoing-chat client and server

 [tk thread] -> tk thread -> Need help in using threads in Tk, uses mechanize and links to -> PerlTk on a thread...

#!/usr/bin/perl

use strict;
use warnings;
use Tk;
use Tk::ProgressBar;

my $mw = MainWindow->new(-title => 'ProgressBar example');
my $percent_done = '';

my $progress = $mw->ProgressBar(
    -width => 30,
    -from => 0,
    -to => 100,
    -blocks => 50,
    -colors => [0, 'red', 50, 'white' , 80, 'blue'],
    -variable => \$percent_done
)->pack(-fill => 'x');

$mw->Button(-text => 'Go!', -command=> sub {
    foreach (my $i = 0; $i < 1000; ++$i) { 
        $percent_done = $i/10;
        print "$i\n";
        $mw->update; 
    }
})->pack(-side => 'bottom');

MainLoop;
[download]

Thanks, but my problem is not in using the progressbar widget (I can do this successfully), but in making the callback which updates it execute asynchronously. My update function is more complicated than a simple for loop (as in your example) and takes a while to run (so I need the application to be responsive in the mean time).

The example that I gave you can be used with threads ideally, eg., using the button in each of your threads. It shouldn't detract from your application's responsiveness. Yes, you'll need to understand threads:-).