Hello,
I had a similar problem recently. The suggestions made here were not fitting for me since I live under Win32.

I solved it roughly that way:
1. The "Cancel"-Button sets $abort=1;.
2. The LongRun-Routine behind my "Run"-button:

sub runlong
{ # <== Maybe set local grab here for cancel-button
  my $t=time()+30;
  while(time()<$t) # loop a loong time   =8]
  { # Insert what ever need here

    #
    $mw->update(idletask); # Refresh Window
    DoOneEvent(0);  # Simulate Mainloop.
    last if $abort != 0; # Bail out on User interaction
  }
  # <== Maybe remove grab here, if set above
  $abort=0;
}
[download]

- Steppl