使用linux共享内存的实现的php内存队列

<?php
/**
* 使用共享内存的PHP循环内存队列实现
* 支持多进程, 支持各种数据类型的存储
* 注: 完成入队或出队操作,尽快使用unset(), 以释放临界区
*
* @author wangbinandi@gmail.com
* @created 2009-12-23
*/
class SHMQueue
{
private $maxQSize = 0; // 队列最大长度

private $front = 0; // 队头指针
private $rear = 0; // 队尾指针

private $blockSize = 256; // 块的大小(byte)
private $memSize = 25600; // 最大共享内存(byte)
private $shmId = 0;

private $filePtr = './shmq.ptr';

private $semId = 0;
public function __construct()
{
$shmkey = ftok(__FILE__, 't');

$this->shmId = shmop_open($shmkey, "c", 0644, $this->memSize );
$this->maxQSize = $this->memSize / $this->blockSize;

// 申請一个信号量
$this->semId = sem_get($shmkey, 1);
sem_acquire($this->semId); // 申请进入临界区

$this->init();
}

private function init()
{
if ( file_exists($this->filePtr) ){
$contents = file_get_contents($this->filePtr);
$data = explode( '|', $contents );
if ( isset($data[0]) && isset($data[1])){
$this->front = (int)$data[0];
$this->rear = (int)$data[1];
}
}
}

public function getLength()
{
return (($this->rear - $this->front + $this->memSize) % ($this->memSize) )/$this->blockSize;
}

public function enQueue( $value )
{
if ( $this->ptrInc($this->rear) == $this->front ){ // 队满
return false;
}

$data = $this->encode($value);
shmop_write($this->shmId, $data, $this->rear );
$this->rear = $this->ptrInc($this->rear);
return true;
}

public function deQueue()
{
if ( $this->front == $this->rear ){ // 队空
return false;
}
$value = shmop_read($this->shmId, $this->front, $this->blockSize-1);
$this->front = $this->ptrInc($this->front);
return $this->decode($value);
}

private function pt