Additional: I was wrong - using sleep instead of pause does not work. there is no difference whatsoever between:

while (1) {

my $url = "http://kronometrix.org/";
$http->setopt(CURLOPT_URL, $url);
my $retcode = $http->perform();

## Get the results
my $response =  $http->getinfo(CURLINFO_HTTP_CODE);

if ($retcode == 0) { 
    print "Ok, Status: $response\n"; 
} else { print "Error, Status: $response\n"; }

    ### Check for end
    last if ++$loop == $loop_max;

    ### Interval
    pause;
}
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and

while (1) {

my $url = "http://kronometrix.org/";
$http->setopt(CURLOPT_URL, $url);
my $retcode = $http->perform();

## Get the results
my $response =  $http->getinfo(CURLINFO_HTTP_CODE);

if ($retcode == 0) { 
    print "Ok, Status: $response\n"; 
} else { print "Error, Status: $response\n"; }

    ### Check for end
    last if ++$loop == $loop_max;

    ### Interval
    sleep;
}
[download]

The code gets stuck after 2 run samples. Always 2 . not sure why. It seems to me something between WWW::Culr (libcurl) and perl regarding alarms and timers.