iOS 多线程访问同一个属性,加锁防止出现意外修改的问题：

//上锁 和 解锁 宏定义 (使用信号量实现)

define Lock() dispatch_semaphore_wait(self->_semaphore, DISPATCH_TIME_FOREVER)

define Unlock() dispatch_semaphore_signal(self->_semaphore)

//成员变量 信号
dispatch_semaphore_t _semaphore;
Manager *manager;

• (BOOL)connected {
  Lock();
  BOOL isConnect = manager.connectEnabled;
  Unlock();
  return isConnect;
  }

• (void)setConnected:(BOOL) isConnect {
  Lock();
  manager.connectEnabled = isConnect;
  Unlock();
  }