面试题：读写锁实现
代码中存在bug，暂时无法修复
1 #include <condition_variable> 2 #include <mutex> 3 4 class rw_lock { 5 private: 6 std::mutex mtx; 7 std::condition_variable cv1; //block by a writer 8 std::condition_variable cv2; //block by a reader 9 int waiteForWrite; 10 int waiteForRead; 11 int reading; 12 enum { 13 RLOCK, WLOCK, NOLOCK 14 }; 15 int state; 16 public: 17 //first write. 18 void r_lock() { 19 std::unique_lock<std::mutex> lck(mtx); 20 while (state == WLOCK || waiteForWrite != 0) { 21 waiteForRead++; 22 cv1.wait(lck); 23 } 24 reading++; 25 state = RLOCK; 26 } 27 28 void r_unlock() { 29 std::unique_lock<std::mutex> lck(mtx); 30 reading--; 31 if (reading == 0) { 32 state = NOLOCK; 33 cv2.notify_all(); 34 } 35 } 36 37 //request write lock 38 void w_lock() { 39 std::unique_lock<std::mutex> lck(mtx); 40 while (state == RLOCK || state == WLOCK) { 41 waiteForWrite++; 42 cv2.wait(lck); 43 } 44 state = WLOCK; 45 } 46 47 void w_unlock() { 48 std::unique_lock<std::mutex> lck(mtx); 49 state = NOLOCK; 50 cv1.notify_all(); 51 } 52 53 };
