You don't need 2 join subs. As you can see, all threads are in main's thread->list. You probably should 'use warnings' and 'use strict' too, it will help you keep from confusing variables.

my @list = threads->list;  
      print scalar(@list),"\n";                 
   foreach my $thr ( threads->list ) { 
    $thr->join;  
  }
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