As others have said, don't call find within find - it's not reentrant.

Your first internal use of find can definitely be eliminated (since you're just calling find on a file) and replaced with the following simpler code:

  if (-f $_) {
    if (-s _ == 0) {
      print $File::Find::name, "\n";
    }
  }
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For directories it appears you want to visit the directory twice - once when it is encountered and later when File::Find is done with all of its entries. To do this, look up the documentation on the postprocess option. It specifically says it is useful for summarizing a directory, such as calculating its disk usage.

Not tested, but should illustrate the idea:

my %usage;

sub wanted {
  if (-f $_) {
    my $size = -s _;
    $usage{$File::Find::dir} += $size;
    if ($size == 0) {
      print $File::Find::name, "\n";
    }
  }
}

sub postprocess {
  print "Usage of $File::Find::dir is $usage{$File::Find::dir}\n";
}

find({wanted => \&wanted, postprocess => \&postprocess}, ...);
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