use strict;
use warnings;
$| = 1;
use threads;
use threads::shared;
use Data::Dumper; $Data::Dumper::Indent = 0;

my $root = shared_clone [ threads-> tid ];
my $depth: shared = -1;

sub worker {
    my $i = threads-> tid;
    while ( 1 ) {
        my $ary = $root;
        for ( 0 .. $depth ) {
            $ary-> [0] .= $i;
            $ary = $ary-> [1] 
        }
        $ary-> [0] .= $i;
        $ary-> [1] = shared_clone [ $i ];
        $depth ++;
        print '*'; sleep 3;
    }
}

for ( 1 .. 3 ) {
    threads-> create( \&worker )-> detach;
    sleep 1
}

sleep 2;
print "\n", Dumper( $root ), "\n";

__END__

******
$VAR1 = ['0123123',['123123',['23123',['3123',['123',['23',[3]]]]]]];