php 信号量 关闭,PHP信号量基本用法实例详解
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(chēng)為信號(hào)燈、旗語(yǔ) 用來(lái)解決進(jìn)程(線程同步的問(wèn)題)，類(lèi)似于一把鎖，訪問(wèn)前獲取鎖(獲取不到則等待)，訪問(wèn)后釋放鎖。
臨界資源：每次僅允許一個(gè)進(jìn)程訪問(wèn)的資源。
臨界區(qū)：每個(gè)進(jìn)程中訪問(wèn)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(wèn)臨界資源，另一個(gè)進(jìn)程要想訪問(wèn)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(wèn)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(lái)自百度百科)
以一個(gè)停車(chē)場(chǎng)的運(yùn)作為例。簡(jiǎn)單起見(jiàn)，假設(shè)停車(chē)場(chǎng)只有三個(gè)車(chē)位，一開(kāi)始三個(gè)車(chē)位都是空的。這時(shí)如果同時(shí)來(lái)了五輛車(chē)，看門(mén)人允許其中三輛直接進(jìn)入，然后放下車(chē)攔，剩下的車(chē)則必須在入口等待，此后來(lái)的車(chē)也都不得不在入口處等待。這時(shí)，有一輛車(chē)離開(kāi)停車(chē)場(chǎng)，看門(mén)人得知后，打開(kāi)車(chē)攔，放入外面的一輛進(jìn)去，如果又離開(kāi)兩輛，則又可以放入兩輛，如此往復(fù)。
在這個(gè)停車(chē)場(chǎng)系統(tǒng)中，車(chē)位是公共資源，每輛車(chē)好比一個(gè)線程，看門(mén)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(wèn)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(lái)源php手冊(cè)? sem_get 函數(shù)comment
希望本文所述對(duì)大家PHP程序設(shè)計(jì)有所幫助。
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