A simple, working solution:

#! perl -slw
use strict;
use threads;
use Thread::Queue;

$|++;

sub worker {
    my( $Q ) = @_;
    while( my $workitem = $Q->dequeue ) {
        print "Processing $workitem";
        sleep rand 10;
    }
}

our $THREADS //= 2;

my $Q = new Thread::Queue;

$SIG{'INT'} = sub{
    print "Sigint seen";
    $Q->dequeue while $Q->pending;
    $Q->enqueue( (undef) x $THREADS );
};

$Q->enqueue( <DATA> );

my @threads = map threads->new( \&worker, $Q ), 1 .. $THREADS;
$Q->enqueue( (undef) x $THREADS );
sleep 1 while $Q->pending;
$_->join for @threads;

__DATA__
WorkItem 1
WorkItem 2
WorkItem 3
WorkItem 4
WorkItem 5
WorkItem 6
WorkItem 7
WorkItem 8
WorkItem 9
WorkItem 10
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