Safest way to add servers using pecl-memcached and persistent connections.

pecl_memcached_safe.php

<?php

// Let's assume this is coming from a config file somewhere
// that maybe we can't trust, or could allow for someone to
// accidently add the same host/port twice.
$servers = array(
    array("host" => 'localhost', "port" => 11211, "weight" => 10),
    array("host" => 'localhost', "port" => 11212, "weight" => 20)
);

$mc = new Memcached("test");

$current_servers = $mc->getServerList();

/**
 * The pecl/memcached docs tell us:
 *
 * http://php.net/manual/en/memcached.addservers.php
 *
 * The same server may appear multiple times in the server pool, because no
 * duplication checks are made. This is not advisable; instead, use the weight
 * option to increase the selection weighting of this server.
 *
 * So, we will make a unique list based on host and port. Why don't we include
 * weight? Well, first, if you are using weight, why would you add the same
 * server more once? Second, getServerList() does not return weight, so two
 * entries with the same host and port can not be differentiated.
 *
 */
$unique_servers = array();
foreach($servers as $server_info) {
    $key = $server_info["host"].":".$server_info["port"];
    if(!empty($unique_servers[$key])){
        trigger_error("Skipping duplicate memcached server $key. It is not advised to add the same server to the server list more than once. Use weight instead.", E_USER_NOTICE);
    } else {
        $unique_servers[$key] = $server_info;
    }
}

// copy our unique values back into the server list
$servers = array_values($unique_servers);

// If there are no current servers, simply reset add the servers
if(empty($current_servers)){

    $mc->addServers($servers);

} else {

    // assume we don't need to reset the list
    $reset = false;

    if(count($servers) == count($current_servers)){

        // if the lists are the same size, loop through the current
        // list and remove ones that are in the unique list
        foreach($current_servers as $cur_key => $cur_server_info) {
            $key = $cur_server_info["host"].":".$cur_server_info["port"];
            if(isset($unique_servers[$key])){
                unset($current_servers[$cur_key]);
            }
        }

        // if all the servers matched, we are good, if not, reset
        if(count($current_servers) > 0){
            $reset = true;
        }

    } else {

        // reset if the count does not match
        $reset = true;
    }

    if($reset){
        // reset the list and add the proper list
        $mc->resetServerList();
        $mc->addServers($servers);
    }

}