I tested now example from documentation. Looks all correct. 
  use Parallel::ForkManager;

  $pm = new Parallel::ForkManager(100);
  my @all_data = qw/1/;
  foreach $data (@all_data) {
    # Forks and returns the pid for the child:
    my $pid = $pm->start; 
    print "PID $pid\n";
    $pid and next;
    print "$data", "\n";
    while(){}; # 100% CPU
    $pm->finish; # Terminates the child process
  }
 $pm->wait_all_children;

[download]
Perhaps you code differs from this. Can you simplify it to proof-of-concept and post here?

In reply to Re: forkManager PID 1 less than top by vsespb
in thread forkManager PID 1 less than top by MAR99

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