php Pthread 多线程 (三) Mutex 互斥量

当我们用多线程操作同一个资源时，在同一时间内只能有一个线程能够对资源进行操作，这时就需要用到互斥量了。比如我们对同一个文件进行读写操作时。

<?php
class Add extends Thread {
    private $name = '';
    private $res = null;
    private $mutex = null;
   
    public function __construct($name,$res,$mutex = null) {
        $this->name = $name;
        $this->res = $res;
        $this->mutex = $mutex;
    }

    public function run() {
        if($this->mutex) {
            //给互斥量加锁
            Mutex::lock($this->mutex);
        }
        //从文件中获取数据
        $data = trim(fgets($this->res));
        $data = intval($data);
        ++$data;
        //重置文件指针到开始处
        fseek($this->res,0);
        //写入数据
        fwrite($this->res,$data);
        //重置文件指针
        fseek($this->res,0);
        echo "Thread {$this->name} add {$data} rn";
        if($this->mutex) {
            //给互斥量解锁
            Mutex::unlock($this->mutex);
        }
    }
}

$fp = fopen('./add.txt','r+');

//创建互斥量，立即加锁
$mutex = Mutex::create(true);

$threads = array();
for($ix = 0; $ix < 20; ++$ix) {
    $thread = new Add($ix,$fp,$mutex);
    $thread->start();
    $threads[] = $thread;
}

Mutex::unlock($mutex);

foreach($threads as $thread) {
    $thread->join();
}

//销毁互斥量
Mutex::destroy($mutex);

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