本文實例講述了PHP信號量基本用法。分享給大家供大家參考，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），類似于一把鎖，訪問前獲取鎖（獲取不到則等待），訪問后釋放鎖。
臨界資源：每次僅允許一個進程訪問的資源。
臨界區(qū)：每個進程中訪問臨界資源的那段代碼叫臨界區(qū)
進程互斥：兩個或以上的進程不能同時進入關于同一組共享變量的臨界區(qū)域，即一個進程正在訪問臨界資源，另一個進程要想訪問必須等待。
進程同步主要研究如何確定數(shù)個進程之間的執(zhí)行順序和避免數(shù)據(jù)競爭的問題 即，如何讓多個進程能一塊很好的協(xié)作運行
舉例子：（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，然后放下車攔，剩下的車則必須在入口等待，此后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，看門人得知后，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(tǒng)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');/** * 獲取一個信號量資源 int $key [, int $max_acquire = 1 [, int $perm = 0666 [, int $auto_release = 1 ]]] $max_acquire:最多可以多少個進程同時獲取信號 $perm:權限 默認 0666 $auto_release：是否自動釋放信號量 */$sem_id=sem_get($key);#獲取信號sem_acquire($seg_id);//do something 這里是一個原子性操作//釋放信號量sem_release($seg_id);//把次信號從系統(tǒng)中移除sem_remove($sem_id);//可能出現(xiàn)的問題$fp = sem_get(fileinode(__DIR__), 100);sem_acquire($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); }} 共享內存+信號 實現(xiàn)原子性操作
$SHM_KEY = ftok("/home/joeldg/homeymail/shmtest.php", 'R');$shmid = sem_get($SHM_KEY, 1024, 0644 | IPC_CREAT);$data = shm_attach($shmid, 1024);// we now have our shm segment// lets place a variable in thereshm_put_var ($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); 以上列子來源php手冊 sem_get 函數(shù)comment
