Memcache 一般用于缓存服务。但是很多时候，比如一个消息广播系统，需要一个消息队列。直接从数据库取消息，负载往往不行。如果将整个消息队列用一个key缓存到memcache里面.

对于一个很大的消息队列，频繁进行进行大数据库的序列化 和 反序列化，有太耗费。下面是我用PHP 实现的一个消息队列，只需要在尾部插入一个数据，就操作尾部，不用操作整个消息队列进行读取，与操作。但是，这个消息队列不是线程安全的，我只是尽量的避免了冲突的可能性。如果消息不是非常的密集，比如几秒钟才一个，还是可以考虑这样使用的。
如果你要实现线程安全的，一个建议是通过文件进行锁定，然后进行操作。下面是代码：

 
class Memcache_Queue 
{ 
private $memcache; 
private $name; 
private $prefix; 
function __construct($maxSize, $name, $memcache, $prefix = "__memcache_queue__") 
{ 
if ($memcache == null) { 
throw new Exception("memcache object is null, new the object first."); 
} 
$this->memcache = $memcache; 
$this->name = $name; 
$this->prefix = $prefix; 
$this->maxSize = $maxSize; 
$this->front = 0; 
$this->real = 0; 
$this->size = 0; 
} 
function __get($name) 
{ 
return $this->get($name); 
} 
function __set($name, $value) 
{ 
$this->add($name, $value); 
return $this; 
} 
function isEmpty() 
{ 
return $this->size == 0; 
} 
function isFull() 
{ 
return $this->size == $this->maxSize; 
} 
function enQueue($data) 
{ 
if ($this->isFull()) { 
throw new Exception("Queue is Full"); 
} 
$this->increment("size"); 
$this->set($this->real, $data); 
$this->set("real", ($this->real + 1) % $this->maxSize); 
return $this; 
} 
function deQueue() 
{ 
if ($this->isEmpty()) { 
throw new Exception("Queue is Empty"); 
} 
$this->decrement("size"); 
$this->delete($this->front); 
$this->set("front", ($this->front + 1) % $this->maxSize); 
return $this; 
} 
function getTop() 
{ 
return $this->get($this->front); 
} 
function getAll() 
{ 
return $this->getPage(); 
} 
function getPage($offset = 0, $limit = 0) 
{ 
if ($this->isEmpty() || $this->size < $offset) { 
return null; 
} 
$keys[] = $this->getKeyByPos(($this->front + $offset) % $this->maxSize); 
$num = 1; 
for ($pos = ($this->front + $offset + 1) % $this->maxSize; $pos != $this->real; $pos = ($pos + 1) % $this->maxSize) 
{ 
$keys[] = $this->getKeyByPos($pos); 
$num++; 
if ($limit > 0 && $limit == $num) { 
break; 
} 
} 
return array_values($this->memcache->get($keys)); 
} 
function makeEmpty() 
{ 
$keys = $this->getAllKeys(); 
foreach ($keys as $value) { 
$this->delete($value); 
} 
$this->delete("real"); 
$this->delete("front"); 
$this->delete("size"); 
$this->delete("maxSize"); 
} 
private function getAllKeys() 
{ 
if ($this->isEmpty()) 
{ 
return array(); 
} 
$keys[] = $this->getKeyByPos($this->front); 
for ($pos = ($this->front + 1) % $this->maxSize; $pos != $this->real; $pos = ($pos + 1) % $this->maxSize) 
{ 
$keys[] = $this->getKeyByPos($pos); 
} 
return $keys; 
} 
private function add($pos, $data) 
{ 
$this->memcache->add($this->getKeyByPos($pos), $data); 
return $this; 
} 
private function increment($pos) 
{ 
return $this->memcache->increment($this->getKeyByPos($pos)); 
} 
private function decrement($pos) 
{ 
$this->memcache->decrement($this->getKeyByPos($pos)); 
} 
private function set($pos, $data) 
{ 
$this->memcache->set($this->getKeyByPos($pos), $data); 
return $this; 
} 
private function get($pos) 
{ 
return $this->memcache->get($this->getKeyByPos($pos)); 
} 
private function delete($pos) 
{ 
return $this->memcache->delete($this->getKeyByPos($pos)); 
} 
private function getKeyByPos($pos) 
{ 
return $this->prefix . $this->name . $pos; 
} 
}