注意看test_hierarchy_lock函數
如果thread t2的不注釋，就會報錯。
這是因為層級鎖強調的單個線程內上鎖的順序。
線程t2若已經獲取了hmtx2，再試圖獲取hmtx1就會因為違反層級順序而拋出異常。

#include <mutex>
#include <thread>
//層級鎖
class hierarchical_mutex {
public:explicit hierarchical_mutex(unsigned long value) :_hierarchy_value(value),_previous_hierarchy_value(0) {}hierarchical_mutex(const hierarchical_mutex&) = delete;hierarchical_mutex& operator=(const hierarchical_mutex&) = delete;void lock() {check_for_hierarchy_violation(); // 必須_this_thread_hierarchy_value >= 待獲取鎖的層級值 當前層級值，才繼續_internal_mutex.lock();update_hierarchy_value(); // _this_thread_hierarchy_value 變成 待獲取鎖的層級值}void unlock() {if (_this_thread_hierarchy_value != _hierarchy_value) {throw std::logic_error("mutex hierarchy violated");}_this_thread_hierarchy_value = _previous_hierarchy_value;_internal_mutex.unlock();}bool try_lock() {check_for_hierarchy_violation();if (!_internal_mutex.try_lock()) {return false;}update_hierarchy_value();return true;}
private:std::mutex  _internal_mutex;//當前層級值unsigned long const _hierarchy_value;//上一次層級值unsigned long _previous_hierarchy_value;//本線程記錄的層級值static thread_local  unsigned long  _this_thread_hierarchy_value;void check_for_hierarchy_violation() {if (_this_thread_hierarchy_value <= _hierarchy_value) {throw  std::logic_error("mutex  hierarchy violated");}}void  update_hierarchy_value() {_previous_hierarchy_value = _this_thread_hierarchy_value;_this_thread_hierarchy_value = _hierarchy_value;}
};
thread_local unsigned long hierarchical_mutex::_this_thread_hierarchy_value(ULONG_MAX);
void test_hierarchy_lock() {hierarchical_mutex  hmtx1(1000);hierarchical_mutex  hmtx2(500);std::thread t1([&hmtx1, &hmtx2]() {std::this_thread::sleep_for(std::chrono::milliseconds(500));hmtx1.lock();hmtx2.lock();hmtx2.unlock();hmtx1.unlock();});std::thread t2([&hmtx1, &hmtx2]() {hmtx2.lock();
//		hmtx1.lock();
//		hmtx1.unlock();hmtx2.unlock();});t1.join();t2.join();
}int main(){test_hierarchy_lock();return 0;
}