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PHP信號(hào)量基本用法實(shí)例詳解

 更新時(shí)間:2016年02月12日 13:32:34   作者:思齊_  
這篇文章主要介紹了PHP信號(hào)量基本用法,較為詳細(xì)的分析了PHP信號(hào)量的基本概念、使用技巧與相關(guān)注意事項(xiàng),需要的朋友可以參考下

本文實(shí)例講述了PHP信號(hào)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(chǔ):

信號(hào)量:又稱為信號(hào)燈、旗語 用來解決進(jìn)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(gè)進(jìn)程訪問的資源。
臨界區(qū):每個(gè)進(jìn)程中訪問臨界資源的那段代碼叫臨界區(qū)
進(jìn)程互斥:兩個(gè)或以上的進(jìn)程不能同時(shí)進(jìn)入關(guān)于同一組共享變量的臨界區(qū)域,即一個(gè)進(jìn)程正在訪問臨界資源,另一個(gè)進(jìn)程要想訪問必須等待。
進(jìn)程同步主要研究如何確定數(shù)個(gè)進(jìn)程之間的執(zhí)行順序和避免數(shù)據(jù)競(jìng)爭(zhēng)的問題 即,如何讓多個(gè)進(jìn)程能一塊很好的協(xié)作運(yùn)行

舉例子:(來自百度百科)

以一個(gè)停車場(chǎng)的運(yùn)作為例。簡(jiǎn)單起見,假設(shè)停車場(chǎng)只有三個(gè)車位,一開始三個(gè)車位都是空的。這時(shí)如果同時(shí)來了五輛車,看門人允許其中三輛直接進(jìn)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(shí),有一輛車離開停車場(chǎng),看門人得知后,打開車攔,放入外面的一輛進(jìn)去,如果又離開兩輛,則又可以放入兩輛,如此往復(fù)。

在這個(gè)停車場(chǎng)系統(tǒng)中,車位是公共資源,每輛車好比一個(gè)線程,看門人起的就是信號(hào)量的作用。

$key=ftok(__FILE__,'t');
/**
 * 獲取一個(gè)信號(hào)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(gè)進(jìn)程同時(shí)獲取信號(hào)
 $perm:權(quán)限 默認(rèn) 0666
 $auto_release:是否自動(dòng)釋放信號(hào)量
 */
$sem_id=sem_get($key);
#獲取信號(hào)
sem_acquire($seg_id);
//do something 這里是一個(gè)原子性操作
//釋放信號(hào)量
sem_release($seg_id);
//把次信號(hào)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(nèi)存+信號(hào) 實(shí)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 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); 

以上列子來源php手冊(cè)  sem_get 函數(shù)comment

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