Threading may be overkill. Perl implements a nice fork() even in windows.

for (@ARGV) {
  if( -f $_ ) {
      unless( fork ) {
          system($cmdname, $_) == 0 or die;
      }
  }
}
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I suspect you mean something other than the above, but it's hard to tell. Perhaps look at DB_File? Elaborate on the problem and my answer is likely to change significantly.