Suicidal Snail in PHP

<?php
/* Suicidal Snail
*
* @author Ian Barber <ian(dot)barber(at)gmail(dot)com>
*/

/* ---------------------------------------------------------------------
* This is our subscriber
* It connects to the publisher and subscribes to everything. It
* sleeps for a short time between messages to simulate doing too
* much work. If a message is more than 1 second late, it croaks.
*/

define("MAX_ALLOWED_DELAY", 100); // msecs

function subscriber()
{
$context = new ZMQContext();

// Subscribe to everything
$subscriber = new ZMQSocket($context, ZMQ::SOCKET_SUB);
$subscriber->connect("tcp://localhost:5556");
$subscriber->setSockOpt(ZMQ::SOCKOPT_SUBSCRIBE, "");

// Get and process messages
while (true) {
$clock = $subscriber->recv();
// Suicide snail logic
if (microtime(true)*100 - $clock*100 > MAX_ALLOWED_DELAY) {
echo "E: subscriber cannot keep up, aborting", PHP_EOL;
break;
}

// Work for 1 msec plus some random additional time
usleep(1000 + rand(0, 1000));
}
}

/* ---------------------------------------------------------------------
* This is our server task
* It publishes a time-stamped message to its pub socket every 1ms.
*/

function publisher()
{
$context = new ZMQContext();

// Prepare publisher
$publisher = new ZMQSocket($context, ZMQ::SOCKET_PUB);
$publisher->bind("tcp://*:5556");

while (true) {
// Send current clock (msecs) to subscribers
$publisher->send(microtime(true));
usleep(1000); // 1msec wait
}
}

/*
* This main thread simply starts a client, and a server, and then
* waits for the client to croak.
*/

$pid = pcntl_fork();
if ($pid == 0) {
publisher();
exit();
}

$pid = pcntl_fork();
if ($pid == 0) {
subscriber();
exit();
}