PHP訊號量的用法及執行個體

本篇文章主要介紹PHP訊號量的用法及執行個體，感興趣的朋友參考下，希望對大家有所協助。

理論基礎：

訊號量：又稱為號誌、旗語 用來解決進程（線程同步的問題），類似於一把鎖，訪問前擷取鎖（擷取不到則等待），訪問後釋放鎖。
臨界資源：每次僅允許一個進程訪問的資源。
臨界區：每個進程中訪問臨界資源的那段代碼叫臨界區
進程互斥：兩個或以上的進程不能同時進入關於同一組共用變數的臨界地區，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個進程之間的執行順序和避免資料競爭的問題 即，如何讓多個進程能一塊很好的協作運行

執行個體如下：

$key=ftok(__FILE__,'t');/** * 擷取一個訊號量資源 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擷取訊號 $perm:許可權 預設 0666 $auto_release：是否自動釋放訊號量 */$sem_id=sem_get($key);#擷取訊號sem_acquire($seg_id);//do something 這裡是一個原子性操作//釋放訊號量sem_release($seg_id);//把次訊號從系統中移除sem_remove($sem_id);//可能出現的問題$fp = sem_get(fileinode(__DIR__), 100);sem_acquire($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); }}

共用記憶體+訊號 實現原子性操作

$SHM_KEY = ftok("/home/joeldg/homeymail/shmtest.php", 'R');$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);

總結：以上就是本篇文的全部內容，希望能對大家的學習有所協助。

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