my $RUNNING = 0;
$mw->repeat( 50 => sub { $taxis->taxis(\$RUNNING) unless $RUNNING} ];
MainLoop;

package taxis;
sub taxis
{
   my ($self, $r_running, @whatever, ) = @_;
   $mw->update;   
   $$r_running = 1;
   # do other stuff that takes a while
   $$r_running = 0;
   return;
}

##</code><code>##

sub taxis
{
   my ($self, $r_running, @whatever, ) = @_;
   $mw->update;   
   $$r_running = 1;
   # other stuff
   my $null = 0;
   $self->taxis(\$null, $whatever); 
   $$r_running = 0;
   return;
}