php 静态类变量

class Counter {
    public static $count = 0;

    public function __construct() {
        self::$count++;
    }

    public static function getCount() {
        return self::$count;
    }
}

$obj1 = new Counter();
$obj2 = new Counter();

echo Counter::getCount(); // 输出 2

class Counter {
    public static $count = 0;
    private static $lock;

    public function __construct() {
        self::$lock = fopen("lock.txt", "w");
        flock(self::$lock, LOCK_EX);
        self::$count++;
        flock(self::$lock, LOCK_UN);
        fclose(self::$lock);
    }

    public static function getCount() {
        self::$lock = fopen("lock.txt", "w");
        flock(self::$lock, LOCK_SH);
        $count = self::$count;
        flock(self::$lock, LOCK_UN);
        fclose(self::$lock);
        return $count;
    }
}

class Counter {
    public static $count = 0;

    public function __construct() {
        self::$count = self::atomicIncrement(self::$count);
    }

    public static function getCount() {
        return self::$count;
    }

    private static function atomicIncrement($value) {
        return $value + 1;
    }
}