使用层次锁来避免死锁

列表3.8 简单的层级互斥量实现

点击查看代码

class hierarchical_mutex
{
  std::mutex internal_mutex;

  unsigned long const hierarchy_value;
  unsigned long previous_hierarchy_value;

  static thread_local unsigned long this_thread_hierarchy_value;  // 1

  void check_for_hierarchy_violation()
  {
    if(this_thread_hierarchy_value <= hierarchy_value)  // 2
    {
      throw std::logic_error(“mutex hierarchy violated”);
    }
  }

  void update_hierarchy_value()
  {
    previous_hierarchy_value=this_thread_hierarchy_value;  // 3
    this_thread_hierarchy_value=hierarchy_value;
  }

public:
  explicit hierarchical_mutex(unsigned long value):
      hierarchy_value(value),
      previous_hierarchy_value(0)
  {}

  void lock()
  {
    check_for_hierarchy_violation();
    internal_mutex.lock();  // 4
    update_hierarchy_value();  // 5
  }

  void unlock()
  {
    this_thread_hierarchy_value=previous_hierarchy_value;  // 6
    internal_mutex.unlock();
  }

  bool try_lock()
  {
    check_for_hierarchy_violation();
    if(!internal_mutex.try_lock())  // 7
      return false;
    update_hierarchy_value();
    return true;
  }
};
thread_local unsigned long
     hierarchical_mutex::this_thread_hierarchy_value(ULONG_MAX);  // 8