Below, using the MCE::Flow model for ease of passing MCE options and code block. This will increase performance for $input1 by 2.5x or more.
use MCE::Flow;
my $input1 = shift @ARGV;
my @lengths;
mce_flow_f {
chunk_size => '2m', max_workers => 'auto',
use_slurpio => 1, gather => \@lengths
},
sub {
my ($mce, $slurp_ref, $chunk_id) = @_;
my (@chunk_lengths);
open my $IN1, '<', $slurp_ref;
while (<$IN1>) {
chomp;
push @chunk_lengths, length $_ unless />/;
}
close $IN1;
MCE->gather(@chunk_lengths);
}, $input1;
MCE::Flow::finish;
print scalar @lengths, "\n";