asynchronus memcache on php

Question

I am trying to write a method which will do asynchronus memcache queries.

This is my simple get/set memcache client class.

Class MemcacheClient
{
    private $socket;

    private $reply;

    private $replies = array(
        'OK' => true,
        'EXISTS' => false,
        'DELETED' => true,
        'STORED' => true,
        'NOT_STORED' => false,
        'NOT_FOUND' => false,
        'ERROR' => null,
        'CLIENT_ERROR' => null, 
        'SERVER_ERROR' => null
    );

    public function __construct($host, $port)
    {
        $this->socket = stream_socket_client("$host:$port", $errno, $errstr);

        if(!$this->socket) {
            throw new Exception("$errst ($errno)");
        }
    }

    public function get($key)
    {
        $reply = $this->query("get $key");

        return $reply;
    }

    public function set($key, $value, $exptime = 0, $flags = 0)
    {
        return $this->query(array("set $key $flags $exptime ".strlen($value), $value));
    }

    public function aget($key, $function)
    {

    }

    public function process()
    {

    }

    public function hasTasks()
    {

    }

    private function query($query)
    {
        $query = is_array($query) ? implode("\r\n", $query) : $query;

        fwrite($this->socket, $query."\r\n");

        return $this->parseLine();
    }

    private function parseLine()
    {
        $line = fgets($this->socket);
        $this->reply = substr($line, 0, strlen($line) - 2);

        $words = explode(' ', $this->reply);

        $result = isset($this->replies[$words[0]]) ? $this->replies[$words[0]] : $words;

        if (is_null($result)) {
            throw new Exception($this->reply);
        }

        if ($result[0] == 'VALUE') {
            $value = fread($this->socket, $result[3] + 2);

            return $value;
        }

        return $result;
    }
}

I'm looking for something like

$memClient->aget('key', function($data) {echo $data;});

Any ideas how it could be implemented? Will appreciate any help.

Thanks!