You can do better in the server. Let $loop->listen() set up the socket rather than doing it yourself. Also, don't use $newclient->send() as that may block; $self->write() will put data into the Stream's outbound queue to be delivered as normal. 
#####################3 server.pl
use strict;
use warnings;
use diagnostics;
use Time::HiRes qw(time);
use IO::Async::Stream;
use IO::Async::Loop;
use Socket qw( SOCK_STREAM );

my $loop = IO::Async::Loop->new();

$loop->listen(
    service   => 8888,
    socktype  => SOCK_STREAM,
    queuesize => 5,
    reuseaddr => 1,

    on_accept => sub {
        my ( $newclient ) = @_;

        $loop->add(
            IO::Async::Stream->new(
                handle => $newclient,

                on_read => sub {
                    my ( $self, $buffref, $closed ) = @_;
                    warn 'READ: ', $$buffref;
                    my $send_start = time;
                    $self->write( 'ECHO: ' . $$buffref );
                    warn 'TIME TO SEND TO CLIENT: ', time - $send_start;
                    $$buffref = '';
                    return 0;
                },
            ),
        );
    },

    on_resolve_error => sub { print STDERR "Cannot resolve - $_[0]\n"; },
    on_listen_error  => sub { print STDERR "Cannot listen\n"; },
);

$loop->loop_forever();

In reply to Re^2: Event based handling of multiple connections with AnyEvent by PEVANS
in thread Event based handling of multiple connections with AnyEvent by bennymack

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.