If I use the original code (above) and simply remove the $MW->destroy() call from abort_routine, the segmentation fault disappears. Each time I click the button, the abort_routine gets called again, but of course without the $MW->destroy, the box never closes and the programme never exits.

When I modify the abort_routine code to include the counter you suggested and test for non-zero at the outset, the segmentation fault still happens as soon as I try and destroy the box. Also, if I replace abort_routine with a do_close which contains only the $MW->destroy, I also get the segmentation fault.

I've also tried using an alternate handle for the second box ($MW2), but I still get the segfault.

It seems that its the second call to $MW->destroy that's doing the damage. Is there something I need to do to clean-up after the first call???

Thanks,
Stefan

I've sort of run out of ideas, especially as I've not actually seen the problem! However $mw->OnDestroy and Dialog Box may be of some help.

---

DWIM is Perl's answer to Gödel

After all of that, I have 'solved' the problem - but in truth, this is not a solution. The behaviour is bizarre. I'd not have found this without the feedback above - so thankyou - but I'm still at a loss to understand whats going on. Let me describe.

In playing around, I found that I can provoke segmentation faults on my stock-standard Fedora-7 system by simply adding or removing a comment. See below.

#!/usr/bin/perl -w
use Tk;
use strict;

my $MW;
my $Array_Index="";
my @Widget_List;
my $Abort_Has_Run;

MAIN:
{
  debug("+MAIN");
  my $my_ref;
  my @file_references ;
  my $i;

  $MW = MainWindow->new;
  $Abort_Has_Run = 0 ;

  push @Widget_List, $MW->title("test box 1");
  push @Widget_List, $MW->Label(-text=>"Choose one option",
            -font=>"courierfont") -> pack;

  @file_references = ("Ref1", "Ref2", "Ref3", "Ref4");
  $i=1;

  foreach $my_ref (@file_references)
  {
    push @Widget_List, $MW->Button(-text => "$my_ref",
         -command => [ \&do_button, "$my_ref,$i"]) -> pack;
    $i++;
  }

  MainLoop();
  debug ("-MAIN");
}

sub do_button
{
  my $params;
  my $widget;

  debug("+do_button");
  $params = shift;
  (my $ref, $Array_Index) = split (/,/,$params);
  debug("do_button Array_Index: $Array_Index");

  # DO SOMETHING USEFUL HERE TO START A PROCESS

#  $MW->Label(-text=>"This line will cause a segfault") -> pack;

  foreach $widget (@Widget_List)
  {
    $widget->destroy();
  }

  $MW->Button(-text => "Shutdown and close",
      -command => [ \&abort_routine]) -> pack;

  $MW->OnDestroy([\&abort_routine]);
  debug("-do_button");
}

sub abort_routine
{
  return if $Abort_Has_Run == 1 ;
  $Abort_Has_Run = 1 ;

  debug("+abort_routine");

  # DO SOMETHING USEFUL HERE TO CLEAN UP THE PROCESS

  $MW->destroy();
  debug("-abort_routine");
}

sub debug
{
  my @msg = shift;
  print @msg, "\n";
}
[download]

If I run the code as above, I repeatedly provoke a segmentation fault. Notice that there is a line which is commented out as such.

#  $MW->Label(-text=>"This line will cause a segfault") -> pack;
[download]

If I REMOVE the comment on this line, the code DOES NOT segfault. However if I comment the line out, I get a segfault EVERY TIME.

Que? What gives??
Stefan