use strict;
use warnings;
use threads;
use threads::shared;

# enable autoflush on the handle
STDERR->autoflush;

my $sem_stderr :shared;
sub print_err { lock $sem_stderr; print STDERR @_; }

sub task {
    my $id = shift;
    my $str = "ab " x 3000;
    for (1..10000) {
        print_err($str, "\n");
    }
}

threads->create('task', $_) for 1..40;
$_->join for threads->list;

##</code><code>##

use strict;
use warnings;
use threads;
use MCE::Shared;

mce_open my $err_fh, '>>', \*STDERR;

sub task {
    my $id = shift;
    my $str = "ab " x 3000;
    for (1..10000) {
        print $err_fh $str, "\n";
    }
}

threads->create('task', $_) for 1..40;
$_->join for threads->list;

##</code><code>##

use strict;
use warnings;
use MCE::Hobo;
use MCE::Shared;

mce_open my $err_fh, '>>', \*STDERR;

sub task {
    my $id = shift;
    my $str = "ab " x 3000;
    for (1..10000) {
        print $err_fh $str, "\n";
    }
}

MCE::Hobo->create('task', $_) for 1..40;
$_->join for MCE::Hobo->list;

##</code><code>##

MD5 (output.txt) = b5bf2b49acd0926a9fa156def91579a0
400000 1200000000 3600400000 output.txt