MainLoop waits for something to happen but in your example nothing will ever happen. If you add a button, you can see that the script is still responsive. 

use strict;
use warnings;
use Tk;

my $mw = new MainWindow(-background=>'Gray');
my $btn = $mw->Button(
        -text    => "Exit",
        -command => sub {  print "Button pressed\n"; } )->pack(); 
MainLoop;

[download]

UPDATE: In other words, you need to completely set up your application, GUI and response functions and then call MainLoop. MainLoop will watch the GUI and react to any user interaction by executing the provided callback functions.

If you knew this all already, then there must be a bug in your program elsewhere.

In reply to Re: perl tk MainLoop hangs by hdb
in thread perl tk MainLoop hangs by zemplen

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.