I tried this:

use Proc::Queue size=>2, qw(run_back);
Proc::Queue::trace(1);

my @ARGV = ("file1.fasta","file2.fasta");

for ( @ARGV  )
{  run_back
   {
      eval{  run_code($_) };
      print STDERR $0."[$$]: $@\n" if $@;
   }

}
1 while wait != -1;

run_code {
  my $file = shift;
  #do the rest
}
[download]

It gives this:

Proc::Queue::run_back(CODE(0x824a9d0)) called at mycode_itr.pl line 37
Proc::Queue::fork called at mycode_itr.pl line 37
Proc::Queue::run_back(CODE(0x824a9d0)) called at mycode_itr.pl line 37
Proc::Queue::fork called at mycode_itr.pl line 37
Proc::Queue::wait called at mycode_itr.pl line 38
[download]

Is it correct or is it an error message? If correct, what does it mean? However, now it does show 2 instances under "top".