If you can install the forks module, your code could be very simple:

use forks;
my $max_threads = 30;
for( 1...$max_threads )
{
  threads->create( \&munge_files, shift(@files_to_munge) );
}# end for()

# Wait for our threads to finish:
$_->join foreach threads->list;

# All done!
print "Job was completed.\n";

sub munge_files {
  my ($file) = @_;
  # Do stuff with $file...
}
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