学步园

利用我的前一篇文章介绍的多线程无锁解决方案，很容易实现一个支持一个线程读，一个线程写的CycleBuffer。需要特别注意的是该CycleBuffer要求缓冲区长度为2的n次方。下面贴出代码：

class ZwAsynCount
{
public:
	ZwAsynCount(unsigned uSize)	//uSize必须为2的n次方
	{
		m_uReadCount = 0;
		m_uWriteCount = 0;
		m_uSize = uSize;
	}
	int Write(int nLen)			//返回元素位置 -1表示读失败
	{
		int nRet = -1;

		if (GetFree() >= nLen)
		{
			nRet = m_uWriteCount&(m_uSize-1);
		}
		return nRet;
	}
	void AddWrite(int nCount = 1)
	{
		m_uWriteCount += nCount;
	}
	int GetUsed()
	{
		return m_uWriteCount - m_uReadCount;
	}
	int GetFree()
	{
		return m_uSize - GetUsed();
	}
	int Read(int nLen)		//返回元素位置 -1表示写失败
	{
		int nRet = -1;

		if (GetUsed() <= nLen)
		{
			nRet = m_uReadCount&(m_uSize-1);
		}

		return nRet;
	}
	void AddRead(int nCount = 1)
	{
		m_uReadCount+= nCount;
	}
private:
	unsigned m_uSize;
	volatile unsigned m_uReadCount;
	volatile unsigned m_uWriteCount;
};

class CCycleBuffer
{
public:
	CCycleBuffer(int nSize):m_asynCount(nSize)
	{
		m_pBuf = new char[nSize];  
		m_nTalLen = nSize;
	}
	int GetFreeSpace()
	{
		return m_asynCount.GetFree();
	}
	int GetLength()
	{
		return m_asynCount.GetUsed();
	}
	~CCycleBuffer()
	{
		if (m_pBuf)
		{
			delete m_pBuf;
		}
	}
	bool Write(char* buf, int count)
	{
		bool bRet = false;
		int  nPos = m_asynCount.Write(count);

		if (nPos >=0)
		{
			if (m_nTalLen - nPos >=  count)
			{
				memcpy(m_pBuf + nPos, buf, count);
			}
			else
			{
				memcpy(m_pBuf + nPos, buf, m_nTalLen - nPos);
				memcpy(m_pBuf, buf + m_nTalLen - nPos, count - (m_nTalLen - nPos));
			}

			m_asynCount.AddWrite(count);
			bRet = true;
		}

		return bRet;
	}
	bool Read(char* buf, int count)
	{
		bool bRet = false;
		int  nPos = m_asynCount.Read(count);

		if (nPos >=0)
		{
			if (m_nTalLen - nPos >=  count)
			{
				memcpy(buf,m_pBuf + nPos,count);
			}
			else
			{
				memcpy(buf,m_pBuf + nPos, m_nTalLen - nPos);
				memcpy(buf + m_nTalLen - nPos,m_pBuf, count - (m_nTalLen - nPos));
			}

			m_asynCount.AddRead(count);
			bRet = true;
		}

		return bRet;
	}
private:
	char	*m_pBuf;
	int		m_nTalLen;
	ZwAsynCount m_asynCount;
};