php 初始化静态变量

class Counter {
    public static $count = 0;

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

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

Counter::increment();
Counter::increment();
echo Counter::getCount(); // 输出 2

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

    public static function increment() {
        if (self::$lock === null) {
            self::$lock = new SplLock();
        }
        self::$lock->lock();
        self::$count++;
        self::$lock->unlock();
    }

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

class Counter {
    public static $count = 0;

    public static function increment() {
        $count = self::$count;
        while (!atomic_compare_exchange_weak(&$count, $count + 1, self::$count)) {
            // 循环直到成功
        }
        self::$count = $count + 1;
    }

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