my $notifyObj = Win32::ChangeNotify( ... );
my $found = 0;
my $abandoned = 0;

sub checkNotify(
    my $rv = $notifyObj->wait( 0 );
    $found = 1 if $rv = 1;
    $abandoned = 1 if $fv = -1;
    die 'Notify error' unless defined $rv;
}

$mainWindow->after( 100, \&checkNotify );