my $thread300 = async {
    while( sleep 300 ) {
        ...
    }
};

##</code><code>##

my $timeToExit : shared = 0;
sub shutdown{
   print logTime." INT|ABRT|QUIT|TERM received....shutting down service.\n";

   $timeToExit = 1; ## Tell the threads to quit
   sleep 1;  ## give them time to react

   close(LOOK_FOR_LEASE) if fileno(LOOK_FOR_LEASE);
   close(OUTPUT) if fileno(OUTPUT);
   close(ERROR)  if fileno(ERROR);
   threads->exit();

}

...

my $thread300 = async {
    my $sleepTime = 300;
    while( !$timeToExit ) {
        sleep 1 and next while --$sleepTime;
        $sleepTime = 300;
        ...
    }
};

##</code><code>##

c:\test> \perl32\bin\perl -Mthreads -e"print $]; async{ sleep 1000 }->detach; sleep 5"
5.008009

c:\test>