http://blog.csdn.net/raomeng1/article/details/7685421

一、使用互斥鎖和條件變量實現讀寫鎖：

class readwrite_lock { public:readwrite_lock(): stat(0){}void readLock(){mtx.lock();while (stat < 0)cond.wait(mtx);++stat;mtx.unlock();}void readUnlock(){mtx.lock();if (--stat == 0)cond.notify_one(); // 叫醒一個等待的寫操作mtx.unlock();}void writeLock(){mtx.lock();while (stat != 0)cond.wait(mtx);stat = -1;mtx.unlock();}void writeUnlock(){mtx.lock();stat = 0;cond.notify_all(); // 叫醒所有等待的讀和寫操作mtx.unlock();}private:mutex mtx;condition_variable cond;int stat; // == 0 無鎖；> 0 已加讀鎖個數；< 0 已加寫鎖 };
二、使用2個互斥鎖實現讀寫鎖：

class readwrite_lock { public:readwrite_lock(): read_cnt(0){}void readLock(){read_mtx.lock();if (++read_cnt == 1)write_mtx.lock();read_mtx.unlock();}void readUnlock(){read_mtx.lock();if (--read_cnt == 0)write_mtx.unlock();read_mtx.unlock();}void writeLock(){write_mtx.lock();}void writeUnlock(){write_mtx.unlock();}private:mutex read_mtx;mutex write_mtx;int read_cnt; // 已加讀鎖個數 };

用mutex和conditon實現寫優先的讀寫鎖

class RWLock { private:pthread_mutex_t mxt;pthread_cond_t cond;int rd_cnt;//等待讀的數量int wr_cnt;//等待寫的數量public:RWLock() :rd_cnt(0), wr_cnt(0) {pthread_mutex_init(&mxt,NULL);pthread_cond_init(&cond,NULL);}void readLock() {pthread_mutex_lock(&mxt);++rd_cnt;while(wr_cnt > 0)pthread_mutex_wait(&cond, &mxt);pthread_mutex_unlock(&mxt);}void readUnlock() {pthread_mutex_lock(&mxt);--rd_cnt;if (rd_cnt == 0 )pthread_cond_signal(&cond);pthread_mutex_unlock(&mxt);}void writeLock() {pthread_mutex_lock(&mxt);++wr_cnt;while (wr_cnt + rd_cnt >=2)pthread_cond_wait(&cond, &mxt);pthread_mutex_unlock(&mxt);}void writerUnlock() {pthread_mutex_lock(&mxt);--wr_cnt;if(wr_cnt==0)pthread_cond_signal(&cond);pthread_mutex_unlock(&mxt);} };

總結

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