本文主要介紹了PHP信號量基本用法，較為詳細的分析了PHP信號量的基本概念、使用技巧與相關注意事項，需要的朋友可以參考下。希望對大家有幫助。
具體如下：
一些理論基礎：
#信號量：又稱為信號燈、旗語用來解決進程（線程同步的問題），類似於一把鎖，訪問前獲取鎖（獲取不到則等待），訪問後釋放鎖。
臨界資源：每次僅允許一個行程存取的資源。
臨界區：每個行程中存取臨界資源的那段程式碼叫臨界區
程式互斥：兩個或以上的行程不能同時進入關於同一群組共享變數的臨界區域，即一個進程正在存取臨界資源，另一個進程要想存取必須等待。
進程同步主要研究如何確定數個進程之間的執行順序和避免數據競爭的問題即，如何讓多個進程能一塊很好的協作運行
舉例：（來自百度百科）
以一個停車場的運作為例。簡單起見，假設停車場只有三個車位，一開始有三個車位都是空的。這時如果同時來了五輛車，看門人允許其中三輛直接進入，然後放下車攔，剩下的車則必須在入口等待，此後來的車也都不得不在入口處等待。這時，有一輛車離開停車場，看門人得知後，打開車攔，放入外面的一輛進去，如果又離開兩輛，則又可以放入兩輛，如此往復。
在這個停車場系統中，車位是公共資源，每輛車好比一個線程，看門人起的就是信號量的作用。
$key=ftok(__FILE__,'t'); /** * 获取一个信号量资源 int $key [, int $max_acquire = 1 [, int $perm = 0666 [, int $auto_release = 1 ]]] $max_acquire:最多可以多少个进程同时获取信号 $perm:权限 默认 0666 $auto_release：是否自动释放信号量 */ $sem_id=sem_get($key); #获取信号 sem_acquire($seg_id); //do something 这里是一个原子性操作 //释放信号量 sem_release($seg_id); //把次信号从系统中移除 sem_remove($sem_id); //可能出现的问题 $fp = sem_get(fileinode(__DIR__), 100); sem_acquire($fp); $fp2 = sem_get(fileinode(__DIR__), 1)); sem_acquire($fp2);
Implementation of a read-write semaphore in PHP:
##
class rw_semaphore {
const READ_ACCESS = 0;
const WRITE_ACCESS = 1;
/**
* @access private
* @var resource - mutex semaphore
*/
private $mutex;
/**
* @access private
* @var resource - read/write semaphore
*/
private $resource;
/**
* @access private
* @var int
*/
private $writers = 0;
/**
* @access private
* @var int
*/
private $readers = 0;
/**
* Default constructor
*
* Initialize the read/write semaphore
*/
public function __construct() {
$mutex_key = ftok('/home/cyrus/development/php/sysvipc/rw_semaphore.php', 'm');
$resource_key = ftok('/home/cyrus/development/php/sysvipc/rw_semaphore.php', 'r');
$this->mutex = sem_get($mutex_key, 1);
$this->resource = sem_get($resource_key, 1);
}
/**
* Destructor
*
* Remove the read/write semaphore
*/
public function __destruct() {
sem_remove($this->mutex);
sem_remove($this->resource);
}
/**
* Request acess to the resource
*
* @param int $mode
* @return void
*/
private function request_access($access_type = self::READ_ACCESS) {
if ($access_type == self::WRITE_ACCESS) {
sem_acquire($this->mutex);
/* update the writers counter */
$this->writers++;
sem_release($this->mutex);
sem_acquire($this->resource);
} else {
sem_acquire($this->mutex);
if ($this->writers > 0 || $this->readers == 0) {
sem_release($this->mutex);
sem_acquire($this->resource);
sem_acquire($this->mutex);
}
/* update the readers counter */
$this->readers++;
sem_release($this->mutex);
}
}
private function request_release($access_type = self::READ_ACCESS) {
if ($access_type == self::WRITE_ACCESS) {
sem_acquire($this->mutex);
/* update the writers counter */
$this->writers--;
sem_release($this->mutex);
sem_release($this->resource);
} else {
sem_acquire($this->mutex);
/* update the readers counter */
$this->readers--;
if ($this->readers == 0)
sem_release($this->resource);
sem_release($this->mutex);
}
}
/**
* Request read access to the resource
*
* @return void
*/
public function read_access() { $this->request_access(self::READ_ACCESS); }
/**
* Release read access to the resource
*
* @return void
*/
public function read_release() { $this->request_release(self::READ_ACCESS); }
/**
* Request write access to the resource
*
* @return void
*/
public function write_access() { $this->request_access(self::WRITE_ACCESS); }
/**
* Release write access to the resource
*
* @return void
*/
public function write_release() { $this->request_release(self::WRITE_ACCESS); }
}$SHM_KEY = ftok("/home/joeldg/homeymail/shmtest.php", 'R');
$shmid = sem_get($SHM_KEY, 1024, 0644 | IPC_CREAT);
$data = shm_attach($shmid, 1024);
// we now have our shm segment
// lets place a variable in there
shm_put_var ($data, $inmem, "test");
// now lets get it back. we could be in a forked process and still have
// access to this variable.
printf("shared contents: %s\n", shm_get_var($data, $inmem));
shm_detach($data);相關推薦：
#php之Constructor Prototype Pattern 原型模式詳解#
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