Catching signals under Linux

[weismat]

I am having trouble that my script should change a shared variable based on a signal. The signal is caught and the shared variable is changed, but the program does automatically stop. See below some a small piece of code as an example. I am using Perl 5.10.0 and CentOS 4.

use threads;
use threads::shared;
$SIG{'HUP'}='switchFlag';
$flag::shared;
my $thr=threads->new(\&printer);
$thr->detach();
sleep 10000;
print "I am here\n";
exit;

sub printer{
  while(1) {
     sleep 1;
     print "Shared: $flag\n";
  }
}


sub switchFlag{
  $flag=!$flag;
  print "signal caught";
  $SIG{'HUP'}='switchFlag';
}

Update: Same behaviour with Perl 5.8 under Solaris 10...