hierarchical_mutex high_level_mutex(10000);
hierarchical_mutex  low_level_mutex(5000);int do_low_level_stuff();int low_level_func()
{lock_guard<hierarchical_mutex> lk(low_level_mutex);return do_low_level_stuff();
}void high_level_stuff(int some_param);void high_level_func()
{lock_guard<hierarchical_mutex> lk(high_level_mutex);high_level_stuff(low_level_func);
}void thread_a()
{high_level_func();
}hierarchical_mutex other_mutex(100);
void do_other_stuff();void other_stuff()
{high_levek_func();do_other_stuff();
}void thread_b()
{lock_guard<hierarchical_mutex> lk(other_mutex);other_stuff();
}

class hierarchical_mutex
{mutex                                   internal_mutex;unsigned long const                     hierarchy_value;unsigned                                previous_hierarchy_value;static  thread_local unsigned long 　　 this_thread_hierarchy_value;// second mutex must now be less than //that of the mutex already held 　　//in order for the check to passvoid check_for_hierarcy_violation(){if(this_thread_hierarchy_value <= hierarchy_value){throw std::logic_error("mutex hierarchical violated");}}void update_hierarchy_value(){previous_hierarchy_value     = this_thread_hierarchy_value;this_thread_hierarchy_value = hierarchy_value;}
public:explicit hierarchical_mutex(unsigned long value): hierarchy_value(value),previous_hierarchy_value(0){}void lock(){check_for_hierarcy_violation();internal_mutex.lock();update_hierarchy_value();}void unlock(){this_thread_hierarchy_value = previous_hierarchy_value;internal_mutex.unlock();}bool try_lock(){check_for_hierarcy_violation();if(!internal_mutex.try_lock()){return false;}update_hierarchy_value();return true;}
};// initialized to the maximum value,
// so initially any mutex can be locked
thread_local unsigned longhierarchical_mutex::this_thread_hierarchy_value(ULONG_MAX);