use 5.010;
use strict;
use warnings;

use Parallel::ForkManager;
use Data::Printer;

my $pm = Parallel::ForkManager->new(2);

$pm->run_on_finish(
    sub {
        # result from the child will be passed as 6th arg to callback
        my $res = $_[5];
        p $res;
    }
);

for (1..3) {
    $pm->start and next;
    # from here and till $pm->finish child process running
    # do something useful and store result in $res
    my $res = { aaa => $_ };
    # this will terminate child and pass $res to parent process
    $pm->finish(0, $res);
}

$pm->wait_all_children;
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