c++实现读写共享锁

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(); // 叫醒一个等待的写操作
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(); // 叫醒所有等待的读和写操作
mtx.unlock();
}

private:

mutex mtx;

condition_variable cond;

int stat; // == 0 无锁；> 0 已加读锁个数；< 0 已加写锁

};

二、使用2个互斥锁实现读写锁：

[cpp] view plain copy

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; // 已加读锁个数

};

用mutex和conditon实现写优先的读写锁

[cpp] view plain copy

class RWLock {

private:

pthread_mutex_t mxt;

pthread_cond_t cond;

int rd_cnt;//等待读的数量

int wr_cnt;//等待写的数量

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);
}

};

zhuan http://blog.csdn.net/sunmenggmail/article/details/8207141