读写锁版本（推荐）：https://blog.csdn.net/yunandsha/article/details/80925429
参考网络循环缓冲区类源码，修改了作者的两个bug，经测试，可以实现多线程并发读写。数据准确无误。
多线程并行读写环形缓冲区源代码例子
代码例子下载：环形缓冲区VC+Qt的项目代码
理论如下：
源码如下：
CCycleBuffer.h
//环形缓冲区头文件
//环形缓冲区头文件
#ifndef CCycleBuffer_H
#define CCycleBuffer_H
class CCycleBuffer
{
public:
bool isFull();
bool isEmpty();
void empty();
int getLength();
CCycleBuffer(int size);
virtual~CCycleBuffer();
int write(char* buf, int count);
int read(char* buf, int count);
int getStart()
{
return m_nReadPos;
}
int getEnd()
{
return m_nWritePos;
}
private:
bool m_bEmpty, m_bFull;
char* m_pBuf;
int m_nBufSize;
int m_nReadPos;
int m_nWritePos;
int test;
};
#endif// CCycleBuffer_H
CCycleBuffer.c
//环形缓冲区源文件
//尽量用C运行时库代码，改变了原作者基于WindowsAPI的代码。
//修改了原作者的两处错误，1是read函数最后的else 少了一个leftcount
//第二个错误，是write函数中，m_nWritePos 变量，他重新定义了一个。这些错误编译不会出错。
//但是运行起来，要了亲命啊。
#include "CCycleBuffer.h"
#include <assert.h>
#include <memory.h>
#include <QDebug>
// 定义
CCycleBuffer::CCycleBuffer(int size)
{
m_nBufSize = size;
m_nReadPos = 0;
m_nWritePos = 0;
m_pBuf = newchar[m_nBufSize];
m_bEmpty = true;
m_bFull = false;
test = 0;
}
CCycleBuffer::~CCycleBuffer()
{
delete[] m_pBuf;
}
/************************************************************************/
/* 向缓冲区写入数据，返回实际写入的字节数 */
/************************************************************************/
int CCycleBuffer::write(char* buf, int count)
{
if (count <= 0)
return0;
m_bEmpty = false;
// 缓冲区已满，不能继续写入
if (m_bFull)
{
return0;
}
else if (m_nReadPos == m_nWritePos)// 缓冲区为空时
{
/* == 内存模型 ==
(empty) m_nReadPos (empty)
|----------------------------------|-----------------------------------------|
m_nWritePos m_nBufSize
*/
int leftcount = m_nBufSize - m_nWritePos;
if (leftcount > count)
{
memcpy(m_pBuf + m_nWritePos, buf, count);
m_nWritePos += count;
m_bFull = (m_nWritePos == m_nReadPos);
return count;
}
else
{
memcpy(m_pBuf + m_nWritePos, buf, leftcount);
m_nWritePos = (m_nReadPos > count - leftcount) ? count - leftcount : m_nWritePos;
memcpy(m_pBuf, buf + leftcount, m_nWritePos);
m_bFull = (m_nWritePos == m_nReadPos);
return leftcount + m_nWritePos;
}
}
else if (m_nReadPos < m_nWritePos)// 有剩余空间可写入
{
/* == 内存模型 ==
(empty) (data) (empty)
|-------------------|----------------------------|---------------------------|
m_nReadPos m_nWritePos (leftcount)
*/
// 剩余缓冲区大小(从写入位置到缓冲区尾)
int leftcount = m_nBufSize - m_nWritePos;
int test = m_nWritePos;
if (leftcount > count) // 有足够的剩余空间存放
{
memcpy(m_pBuf + m_nWritePos, buf, count);
m_nWritePos += count;
m_bFull = (m_nReadPos == m_nWritePos);
assert(m_nReadPos <= m_nBufSize);
assert(m_nWritePos <= m_nBufSize);
return count;
}
else // 剩余空间不足
{
// 先填充满剩余空间，再回头找空间存放
memcpy(m_pBuf + test, buf, leftcount);
m_nWritePos = (m_nReadPos >= count - leftcount) ? count - leftcount : m_nReadPos;
memcpy(m_pBuf, buf + leftcount, m_nWritePos);
m_bFull = (m_nReadPos == m_nWritePos);
assert(m_nReadPos <= m_nBufSize);
assert(m_nWritePos <= m_nBufSize);
return leftcount + m_nWritePos;
}
}
else
{
/* == 内存模型 ==
(unread) (read) (unread)
|-------------------|----------------------------|---------------------------|
m_nWritePos (leftcount) m_nReadPos
*/
int leftcount = m_nReadPos - m_nWritePos;
if (leftcount > count)
{
// 有足够的剩余空间存放
memcpy(m_pBuf + m_nWritePos, buf, count);
m_nWritePos += count;
m_bFull = (m_nReadPos == m_nWritePos);
assert(m_nReadPos <= m_nBufSize);
assert(m_nWritePos <= m_nBufSize);
return count;
}
else
{
// 剩余空间不足时要丢弃后面的数据
memcpy(m_pBuf + m_nWritePos, buf, leftcount);
m_nWritePos += leftcount;
m_bFull = (m_nReadPos == m_nWritePos);
assert(m_bFull);
assert(m_nReadPos <= m_nBufSize);
assert(m_nWritePos <= m_nBufSize);
return leftcount;
}
}
}
/************************************************************************/
/* 从缓冲区读数据，返回实际读取的字节数 */
/************************************************************************/
int CCycleBuffer::read(char* buf, int count)
{
if (count <= 0)
return0;
m_bFull = false;
if (m_bEmpty) // 缓冲区空，不能继续读取数据
{
return0;
}
else if (m_nReadPos == m_nWritePos) // 缓冲区满时
{
/* == 内存模型 ==
(data) m_nReadPos (data)
|--------------------------------|--------------------------------------------|
m_nWritePos m_nBufSize
*/
int leftcount = m_nBufSize - m_nReadPos;
if (leftcount > count)
{
memcpy(buf, m_pBuf + m_nReadPos, count);
m_nReadPos += count;
m_bEmpty = (m_nReadPos == m_nWritePos);
return count;
}
else
{
memcpy(buf, m_pBuf + m_nReadPos, leftcount);
m_nReadPos = (m_nWritePos > count - leftcount) ? count - leftcount : m_nWritePos;
memcpy(buf + leftcount, m_pBuf, m_nReadPos);
m_bEmpty = (m_nReadPos == m_nWritePos);
return leftcount + m_nReadPos;
}
}
else if (m_nReadPos < m_nWritePos) // 写指针在前(未读数据是连接的)
{
/* == 内存模型 ==
(read) (unread) (read)
|-------------------|----------------------------|---------------------------|
m_nReadPos m_nWritePos m_nBufSize
*/
int leftcount = m_nWritePos - m_nReadPos;
int c = (leftcount > count) ? count : leftcount;
memcpy(buf, m_pBuf + m_nReadPos, c);
m_nReadPos += c;
m_bEmpty = (m_nReadPos == m_nWritePos);
assert(m_nReadPos <= m_nBufSize);
assert(m_nWritePos <= m_nBufSize);
return c;
}
else // 读指针在前(未读数据可能是不连接的)
{
/* == 内存模型 ==
(unread) (read) (unread)
|-------------------|----------------------------|---------------------------|
m_nWritePos m_nReadPos m_nBufSize
*/
int leftcount = m_nBufSize - m_nReadPos;
if (leftcount > count) // 未读缓冲区够大，直接读取数据
{
memcpy(buf, m_pBuf + m_nReadPos, count);
m_nReadPos += count;
m_bEmpty = (m_nReadPos == m_nWritePos);
assert(m_nReadPos <= m_nBufSize);
assert(m_nWritePos <= m_nBufSize);
return count;
}
else // 未读缓冲区不足，需回到缓冲区头开始读
{
memcpy(buf, m_pBuf + m_nReadPos, leftcount);
m_nReadPos = (m_nWritePos >= count - leftcount) ? count - leftcount : m_nWritePos;
memcpy(buf + leftcount, m_pBuf, m_nReadPos);
m_bEmpty = (m_nReadPos == m_nWritePos);
assert(m_nReadPos <= m_nBufSize);
assert(m_nWritePos <= m_nBufSize);
return leftcount + m_nReadPos;
}
}
}
/************************************************************************/
/* 获取缓冲区有效数据长度 */
/************************************************************************/
int CCycleBuffer::getLength()
{
if (m_bEmpty)
{
return0;
}
else if (m_bFull)
{
return m_nBufSize;
}
else if (m_nReadPos < m_nWritePos)
{
return m_nWritePos - m_nReadPos;
}
else
{
return m_nBufSize - m_nReadPos + m_nWritePos;
}
}
void CCycleBuffer::empty()
{
m_nReadPos = 0;
m_nWritePos = 0;
m_bEmpty = true;
m_bFull = false;
}
bool CCycleBuffer::isEmpty()
{
return m_bEmpty;
}
bool CCycleBuffer::isFull()
{
return m_bFull;
}