You should have told us what line the error occurred on. I'm guessing

  $pids[$_] = { child_fh  => 0,
                parent_fh => 0,
                pid       => 0
              };
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should be

  $pids[$_] = { child_fh  => undef,
                parent_fh => undef,
                pid       => undef
              };
[download]