读者作家锁

Question

我正在执行这里提到的多个读/写锁 MultiplereadersWriterLock

这里的EnterReader代码是

void EnterReader(void)
    {
        EnterCriticalSection(&m_csWrite);
        EnterCriticalSection(&m_csReaderCount);
        if (++m_cReaders == 1)
            ResetEvent(m_hevReadersCleared);
        LeaveCriticalSection(&m_csReaderCount);
        LeaveCriticalSection(&m_csWrite);
    }

根据我对这个锁的理解，我们解决了我们可以通过多个线程读取共享资源的问题。这意味着多个线程可以调用EnterReader函数而不会阻塞它们可以继续读取。

示例

Thread T1 calls EnterReader()
It acquires m_csWrite
It acquires m_csReaderCount
Interrupted by CPU and thread T2 starts

    Thread T2 calls EnterReader()
    Since m_csWrite already acquired by T1 so how thread T2 can perform read. 
T2 cannot proceed further since m_csWrite is already acquired that means T2 reader thread is blocked and waiting for T1 to get finish.

我很困惑这个实现如何解决多个读者访问共享资源的问题。

Answer 1

EnterReader只是快速锁定以增加读者的数量。注意它在返回之前释放锁。在阅读时，m_csWrite不会像EnterReader和LeaveReader之间那样在EnterWriter和LeaveWriter来电之间保持锁定。

用法示例：

lock->EnterReader();
/*Do the reading*/ //No locks here. m_csReaderCount is blocking writes.
lock->LeaveReader();