Rather than starting/stopping threads to feed input, it would be preferable to feed them work to do. Here is a snipped of the code I use (In production on Windows/perl 58/ Activestate):

use threads;
use Thread::Queue;

our $KIDS   = $count > 20? 10 : int ($count / 4) || 1; # Some way to c
+ontrol max # of threads


my $work_Q   = new Thread::Queue;
## Start the kids
my @kids = map{ threads->create( \&kid, $_) } 1 .. $KIDS;
$work_Q->enqueue( keys %ServerInfo ); # Feed the QUEUE with work to do
+ ....
## Tell them to stop
$work_Q->enqueue( (undef) x $KIDS ); # THis tells each thread to QUIT

## And wait for Kids to finish..
my %results = map {$_->join} @kids;

#----------------------------------------------------
sub kid {
    my $kidnumber = shift;
    my @results=();
    my $tid = threads->tid;
    my $count=0;
    my $pinger = Net::Ping->new("icmp",$TimeOut);
    #printf "Kid: %02d started<br>\n", $tid;

    while( my $work = $work_Q->dequeue ) {
        $count ++;
        push @results, $work,  Ping_it($pinger, $work) ;
    }
    push @results,"KID$kidnumber",$count;
    #print "kid: $tid ending after processing $count items.<br>\n";
    return @results;
}
[download]