1. Passing data. This contains the $ctr suggestion by Corion.

use v5.32;
use Parallel::ForkManager;
use Data::Dumper;

my $pm = Parallel::ForkManager->new(8);
$pm->set_waitpid_blocking_sleep(0);

our @results;

$pm->run_on_finish( sub {
    my ($pid, $exit_code, $ident, $exit_signal, $core_dump, $data_ref)
+ = @_;
    push @results, ${$data_ref};
});

our @duplicated = (10..20);
our $ctr = 0;

say "processing duplicates...";
LOOP:
foreach my $pid (@duplicated) {
    unless ($ctr % 1000) {say $ctr;}
    $ctr++;
    $pm->start and next LOOP; # do the fork
    #do stuff
    my $ans = $pid;
    $pm->finish(0, \$ans); # exit the child process
}

$pm->wait_all_children;

say scalar(@results);
# print Dumper(\@results);
[download]

2. Using MCE::Child with Parallel::ForkManager similarities.

use v5.32;
use MCE::Child;
use Data::Dumper;

our @results;

MCE::Child->init(
    max_workers => 8,
    posix_exit  => 1,
    on_finish   => sub {
        my ($pid, $exit_code, $ident, $exit_signal, $core_dump, $data_
+ref) = @_;
        push @results, ${$data_ref};
    }
);

our @duplicated = (10..20);
our $ctr = 0;

say "processing duplicates...";
foreach my $pid (@duplicated) {
    unless ($ctr % 1000) {say $ctr;}
    $ctr++;
    MCE::Child->create(sub {
        #do stuff
        my $ans = $pid;
        return \$ans;
    });
}

MCE::Child->wait_all;

say scalar(@results);
# print Dumper(\@results);
[download]

3. Using MCE::Shared to construct a shared array.

use v5.32;
use MCE::Shared;
use Parallel::ForkManager;
use Data::Dumper;

my $pm = Parallel::ForkManager->new(8);
$pm->set_waitpid_blocking_sleep(0);

# create a shared array object
# this starts the shared-manager process
our $results = MCE::Shared->array();

our @duplicated = (10..20);
our $ctr = 0;

say "processing duplicates...";
LOOP:
foreach my $pid (@duplicated) {
    unless ($ctr % 1000) {say $ctr;}
    $ctr++;
    $pm->start and next LOOP; # do the fork
    #do stuff
    my $ans = $pid;
    $results->push($ans);
    $pm->finish; # exit the child process
}

$pm->wait_all_children;

# destroy the shared object and retrieve the array
# unblesses MCE::Shared::Array, becoming plain array ref
$results = $results->destroy({ unbless => 1 });

# stop the shared-manager process
MCE::Shared->stop;

say scalar(@{$results});
# print Dumper($results);
[download]

4. Using MCE and a shared counter variable.

use v5.32;
use MCE;
use MCE::Shared;
use Data::Dumper;

our @results;
our $shared_ctr = MCE::Shared->scalar(0);

my $mce = MCE->new(
    gather      => \@results,
    chunk_size  => 1,
    max_workers => 8,
    posix_exit  => 1,
    user_func   => sub {
        my ($mce, $chunk_ref, $chunk_id) = @_;
        my $ctr = $shared_ctr->getincr;
        unless ($ctr % 1000) {MCE->say($ctr);}
        #do stuff
        my $ans = $chunk_ref->[0];  # or $_
        MCE->gather($ans);
    }
)->spawn;

our @duplicated = (10..20);

$mce->process({ input_data => \@duplicated });
$mce->shutdown;

# stop the shared-manager process
MCE::Shared->stop;

say scalar(@results);
# print Dumper(\@results);
[download]

5. Using MCE without MCE::Shared.

use v5.32;
use MCE;
use Data::Dumper;

our @results;
our $global_ctr = 0;

sub getincr {
    my $ctr = $global_ctr++;
    return $ctr;
}

my $mce = MCE->new(
    gather      => \@results,
    chunk_size  => 1,
    max_workers => 8,
    posix_exit  => 1,
    user_func   => sub {
        my ($mce, $chunk_ref, $chunk_id) = @_;
        my $ctr = MCE->do('getincr');
        unless ($ctr % 1000) {MCE->say($ctr);}
        #do stuff
        my $ans = $chunk_ref->[0];  # or $_
        MCE->gather($ans);
    }
)->spawn;

our @duplicated = (10..20);

$mce->process({ input_data => \@duplicated });
$mce->shutdown;

say scalar(@results);
# print Dumper(\@results);
[download]

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