#!/usr/bin/perl
use strict;
use warnings;
use IO::Socket::UNIX;

use constant SOCKET => 'test_socket.sock';

my $mode = shift or die "Specify a mode\n";

if ($mode eq 'server') {
    my $server = IO::Socket::UNIX->new(
        Type   => SOCK_STREAM,
        Local  => SOCKET,
        Listen => 1,
    ) or die $!;
    while (my $conn = $server->accept()) {
        sleep 5;

        my $name = <$conn>;
        print {$conn} "Hello $name";
        close $conn;
    }
}
elsif ($mode eq 'client') {
    my $client = IO::Socket::UNIX->new(
        Type    => SOCK_STREAM,
        Peer    => SOCKET,
        Timeout => 2,
    ) or die $!;
    print {$client} 'John', "\n";
    print "Got reponse: ", scalar <$client>;
    close $client;
}
else {
    die "Unsupported mode: $mode\n";
}

##</code><code>##

my $ALARM_EXCEPTION = "alarm clock restart";
eval {
    local $SIG{ALRM} = sub { die $ALARM_EXCEPTION };
    alarm 10;
    flock(FH, 2)    # blocking write lock
                    || die "cannot flock: $!";
    alarm 0;
};
if ($@ && $@ !~ quotemeta($ALARM_EXCEPTION)) { die }

##</code><code>##

use POSIX qw[ ETIMEDOUT EWOULDBLOCK ];
use Socket qw[ SOL_SOCKET SO_RCVTIMEO ];

my $client = IO::Socket::UNIX->new(
    Type => SOCK_STREAM,
    Peer => SOCKET,
) or die $!;
my $timeval = pack 'l!l!,
    2,  # seconds
    0;  # microseconds
$socket->setsockopt(SOL_SOCKET, SO_RCVTIMEO, $timeval) or die $!;

print {$client} "John", "\n";
my $response = <$client>;
die 'Timeout' if !$response and $! == ETIMEDOUT || $! == EWOULDBLOCK;
...