Hi again,

One may want to have the manager-process receive and loop through @sample and @good. That will incur an additional CPU core for the manager-process itself.

use strict;
use warnings;

use MCE;

open my $sample_fh, ">", "sample.txt" or die "open error: $!";
open my $good_fh,   ">", "good.txt"   or die "open error: $!";

# worker function

sub task {
    my ( $mce, $slurp_ref, $chunk_id ) = @_;
    my ( @sample, @good );

    # open file handle to scalar ref
    open my $input_fh, "<", $slurp_ref;

    # append to scalars inside the loop
    while (<$input_fh>) {
        if (/^sample\s+(\S+)/) {
            push @sample, $1;
        }
        elsif (/^good\s+(\S+)/) {
            push @good, $1;
        }
    }

    close $input_fh;

    # send arrays to the manager-process
    MCE->gather(\@sample, \@good);
}

# manager function

sub gather {
    my ( $sample, $good ) = @_;

    # process sample
    for ( @{ $sample } ) {
        ;
    }

    # process good
    for ( @{ $good } ) {
        ;
    }
}

# spawn workers early, optionally
my $mce = MCE->new(
    chunk_size  => '1m', # 1 megabyte
    max_workers => 4,
    use_slurpio => 1,
    user_func   => \&task,
    gather      => \&gather,
)->spawn;

# process input file(s)
$mce->process({ input_data => "test.txt" });

# shutdown workers
$mce->shutdown;

# close output handles
close $sample_fh;
close $good_fh;
[download]

The extra time comes from workers appending to local arrays. Likewise, the manager-process receiving and looping through the arrays. There are 4 workers and the manager process running simultaneously on a machine with 4 real cores.

$ time perl test_demo.pl

real    0m9.932s
user    0m43.956s
sys     0m0.452s
[download]

Update:

$ time /opt/perl-5.20.3/bin/perl test_demo.pl

real    0m20.858s
user    1m20.164s
sys     0m8.488s
[download]