event vs. non-event approach for writing to a child

event.pl

#!/usr/bin/env perl

use strict;
use warnings;
use feature ':5.10';

use AnyEvent;
use AnyEvent::Handle;

open my $fd, '|-', 'perl -ne "sleep 1; print"' or die $!;

my $done = AnyEvent->condvar;
my $h = AnyEvent::Handle->new( fh => $fd );

for(1..100){
    warn $_;
    $h->push_write("$_"x100000);
    $h->push_write("\n");
    sleep 1 if $_ % 10 == 0; # lets you observe that some writes take place before the end of the loop
}
warn "wait for writes";
$h->on_drain(sub { $done->send });
$done->wait;
warn "bye";

# the slow child never blocks the parent's main loop; all blocking happens right before exit

nonevent.pl

#!/usr/bin/env perl

use strict;
use warnings;
use feature ':5.10';


open my $fd, '|-', 'perl -ne "sleep 1; print"' or die $!;

for(1..100){
    warn $_;
    print $fd "$_"x100000;
    print $fd "\n";
}

warn "bye";

# slow child blocks the parent's for loop