You need to wait for all of your threads to join up with the parent:

use threads;

# Create 5 threads:
threads->create(sub { print "Hello from # $_[0]\n" }, $_ )
  for 1...5;

# Then when you want to just let your threads work:
$_->join foreach threads->list;

# Now the threads are done:
print "threads are all done!";
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