I have code where a forked process is generating a list in $data and passing that to the callback like in this simplified version: 
use strict;
use feature ':5.10';
use Parallel::ForkManager;

our $pm = Parallel::ForkManager->new(8);

$pm -> run_on_finish ( # called BEFORE the first call to start()
    sub {
        my ($pid, $exit_code, $ident, $exit_signal, $core_dump, $data_
+structure_reference) = @_;

        # retrieve data structure from child
        if (defined($data_structure_reference)) {  # children are not 
+forced to send anything
             my $string = ${$data_structure_reference};  # child passe
+d a string reference
             if ($string) { 
                  #how to process $string? 
             };
        }
        else {  # problems occurring during storage or retrieval will 
+throw a warning
            say qq|No message received from child process $pid!|;
        }
    }
);

LOOP:
foreach my $instance (0..100) {
    $pm->start and next LOOP; # do the fork
    my $data;
    foreach my $i (0..50) {
        push(@$data,int(rand(10));
    }
    $pm->finish(0,\$data); # exit the child process
}

$pm->wait_all_children;

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The docs say you can use this method to return a data structure, but they refer to the thing returned as a string. Is $string really a string or is it an object?

In reply to Parallel:ForkManager how to pass back a list by cormanaz

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