服务器缓存数据处理的两种方式：循环写入读取和剪切写入读取

循环写入读取的原理：在分配的指定大小的内存空间上，首地址开始写入，超出范围之后（未超出整体范围，只是超出当前写入位置之后整体范围的剩余范围）连接超出的范围到缓存的首地址（因为之前的数据比较早，已经被读取），如此循环。

剪切写入读取的原理：在分配的指定大小的内存空间上，首地址开始写入，写入超出整体之后提示报错（缓存空间不足），未超出则正常写入，读取数据时，从当前写位置开始往前读取，读取完之后，将读取的数据从缓存数据中剪切走（将写指针往前指向读的数据长度）。

以下是两种方式的源文件和头文件：（其中还包括线程锁函数）

void *CLoopBuffer::InitLoopBuffer(unsigned long buff_len)
{
    LOOP_BUFFER * lb;
    lb =new  LOOP_BUFFER(); 
    if( lb!=NULL ) 
    {
        lb->MaxLength = buff_len;
        lb->Buffer =new  unsigned char[buff_len];
        if (lb->Buffer==NULL)
        {
            delete lb;
            return NULL;
        }
        lb_ptr = lb;
        ResetLoopBuffer();
    }
    return (void *)lb;
}

void CLoopBuffer::UnLockLoopBuffer()
{
    BufferLock.UnLock();
}

void CLoopBuffer::LockLoopBuffer()
{
    BufferLock.Lock();
}

void CLoopBuffer::FreeLoopBuffer()
{
    LOOP_BUFFER * lb = (LOOP_BUFFER *)lb_ptr;
    lb->WritePtr	= NULL;
    lb->ReadPtr		= NULL;
    delete []lb->Buffer;
    delete lb ;
    return;
}

void CLoopBuffer::ResetLoopBuffer()
{
    LOOP_BUFFER * lb = (LOOP_BUFFER *)lb_ptr;
    lb->CurWritePos = 0;
    lb->WritePtr = lb->Buffer;
    lb->CurReadPos = 0;
    lb->ReadPtr = lb->Buffer;
    UnLockLoopBuffer();
}

//取缓冲的写指针位置，该函数与WriteLoopBuffer配合使用来控制缓冲区的锁问题
//即：GetLoopBufferWritePos 置锁
//	  WriteLoopBuffer 写好后开锁
long	CLoopBuffer::GetLoopBufferWritePos()
{
    LOOP_BUFFER * lb = (LOOP_BUFFER *)lb_ptr;
    LockLoopBuffer();
    return lb->CurWritePos;
}

long	CLoopBuffer::WriteLoopBuffer(unsigned char *data,long len)
{
    try{
        LOOP_BUFFER * lb = (LOOP_BUFFER *)lb_ptr;
        unsigned char *ptr = lb->WritePtr,*s_ptr;
        long r_len,l_len;

        if( len + lb->CurWritePos > lb->MaxLength ) //buffer need loop
        {	
            if( len < lb->MaxLength) //added 20080325
            {
                r_len = lb->MaxLength - lb->CurWritePos;
                l_len = len - r_len;
                s_ptr=data;
                memcpy( ptr,s_ptr,r_len);
                s_ptr += r_len;
                ptr = lb->Buffer;
                memcpy( ptr,l_len);

                lb->WritePtr = lb->Buffer;
                lb->WritePtr += l_len;
                lb->CurWritePos =l_len;
            }
            else
                myTRACE(1,3,"WriteLoopBuffer len is Error !n");
        }
        else {	//buffer right enought for write,not loop
            memcpy( ptr,data,len );
            lb->WritePtr += len;
            lb->CurWritePos +=len;
        }
    }
    catch(...)
    {
        myTRACE(1,"WriteLoopBuffer Error !n");
    }
    UnLockLoopBuffer();
    return len;
}

//取缓冲中的数据，独立开、关锁
long	CLoopBuffer::GetLoopBufferData(long readpos,char *tagdata,long requestlen )
{
    if(requestlen<0)
		return -1;
    LOOP_BUFFER * lb = (LOOP_BUFFER *)lb_ptr;
    long pos=0,l_len=0,r_len=0;

    LockLoopBuffer();
    try{
        if( readpos >= lb->MaxLength ) 
            pos = readpos % lb->MaxLength;
        else 
            pos = readpos;

        char* ptr = (char *)lb->Buffer;
        ptr += pos;
        if( pos + requestlen > lb->MaxLength ) 
        {
            if( requestlen < lb->MaxLength) //added 20080325
            {
                r_len = lb->MaxLength - pos;
                l_len = requestlen - r_len;
                memcpy( tagdata,ptr,r_len );
                tagdata += r_len ;
                ptr = (char *)lb->Buffer;
                memcpy( tagdata,l_len );
            }
            else
                myTRACE(1,"GetLoopBufferData requestlen is Error !n");
        }
        else 
        {
            memcpy( tagdata,requestlen );
        }
    }
    catch(...)
    {

        myTRACE(1,"GetLoopBufferData Error !n");
		requestlen =-1;
    }

    UnLockLoopBuffer();
    return requestlen;
}

#if !defined(LOOP_BUFFER__H)
#define LOOP_BUFFER__H

#include "ThreadLock.h"

typedef struct {
	long PacketPos;										//this media packet position on MediaBuffer
	long PacketLenfth;									//this media packet length
}PACKET_PARSE;

typedef struct {
    long		MaxLength;
    long		CurWritePos;
    long		CurReadPos;
    unsigned char		*Buffer;
    unsigned char		*ReadPtr;
    unsigned char		*WritePtr;
}LOOP_BUFFER;

class CLoopBuffer
{
public:
    void	*InitLoopBuffer(unsigned long buff_len);
    void	FreeLoopBuffer();
    long	WriteLoopBuffer(unsigned char *data,long len);
    void	ResetLoopBuffer();
    long	GetLoopBufferWritePos();
    long	GetLoopBufferData(long readpos,long requestlen );
    //char	*GetLoopBufferAviliDataPtr(long startpos,long requestlen,long *ret_len);
    //void	GetLoopBufferAviliDataPtrEnd();
    void	LockLoopBuffer();
    void	UnLockLoopBuffer();

    void	*lb_ptr;

private :

    CThreadLock		BufferLock;
};
#endif

void *CCutBuffer::InitCutBuffer(long buff_len)
{
    CUT_BUFFER * cb;
    cb = new CUT_BUFFER();

    cb->MaxLength = buff_len;
    cb->Buffer = new char[buff_len];
    memset(cb->Buffer,buff_len);
    cb->CurWritePos = 0;
    cb->WritePtr = cb->Buffer;
    cb_ptr = (void *)cb;
    return (void *)cb;
}

void CCutBuffer::FreeCutBuffer()
{
    CUT_BUFFER * cb = (CUT_BUFFER *)cb_ptr;
    cb->WritePtr	= NULL;
    delete []cb->Buffer;
    delete cb;
    return;
}

void CCutBuffer::LockCutBuffer()
{
    BufferLock.Lock();
}
void CCutBuffer::UnLockCutBuffer()
{
    BufferLock.UnLock();
}

long	CCutBuffer::WriteCutBuffer(unsigned char  *data,long len)
{
    CUT_BUFFER * cb = (CUT_BUFFER *)cb_ptr;
    if(len<=0 || len> cb->MaxLength)  //added 20080325
    {
        myTRACE(1,"WriteCutBuffer len is Error !n");
        return -1;
    }

    BufferLock.Lock();
    unsigned char  *ptr = (unsigned char  *)cb->WritePtr;

    if( len + cb->CurWritePos > cb->MaxLength ) 	//buffer not enought for write
    {
        myTRACE(0,"WriteCutBuffer buffer not enought for write,Clear the Buffer n");
        cb->CurWritePos = 0;
        cb->WritePtr = cb->Buffer;
        BufferLock.UnLock();
        return -1;
    }
    else  	//buffer right enought for write,not loop
    {
        memcpy( ptr,len );
        cb->WritePtr += len;
        cb->CurWritePos +=len;
    }
    BufferLock.UnLock();
    return len;
}

unsigned char 	*CCutBuffer::GetCutBufferWritePtr(long *len)
{
    CUT_BUFFER * cb = (CUT_BUFFER *)cb_ptr;
    BufferLock.Lock();

    long al = cb->MaxLength - cb->CurWritePos;
    *len = al;

    if( al <= 0 )
    {
        BufferLock.UnLock();
    }   

    return (unsigned char  *)cb->WritePtr;
}

void CCutBuffer::UpdateCutBufferWrite(long len)
{
    if( len <= 0 ) {
        BufferLock.UnLock();
        return;
    }

    CUT_BUFFER * cb = (CUT_BUFFER *)cb_ptr;
    cb->CurWritePos += len;
    cb->WritePtr += len;

    BufferLock.UnLock();
}

unsigned char 	*CCutBuffer::GetCutBufferReadPtr(long *len)
{
    CUT_BUFFER * cb = (CUT_BUFFER *)cb_ptr;

    BufferLock.Lock();

    *len = cb->CurWritePos;

    if( cb->CurWritePos <= 0 )
    {
        cb->CurWritePos = 0;
        cb->WritePtr = cb->Buffer; //added 20080325

        BufferLock.UnLock();
    }

    return (unsigned char  *)cb->Buffer;
}

void CCutBuffer::UpdateCutBufferRead(long len)
{
    if( len <= 0 ) {
        BufferLock.UnLock();
        return;
    }

    CUT_BUFFER * cb = (CUT_BUFFER *)cb_ptr;
    if( cb->CurWritePos > len ) {
        unsigned char* sptr = (unsigned char  *)cb->Buffer;
        unsigned char* tptr = (unsigned char  *)cb->Buffer;

        sptr += len;
        memcpy( tptr,sptr,cb->CurWritePos - len );//memmove保险些，memcpy效率高些
    }
    cb->CurWritePos -= len;
    cb->WritePtr -= len;

    BufferLock.UnLock();
}

void CCutBuffer::ResetCutBuffer()
{
    CUT_BUFFER * cb = (CUT_BUFFER *)cb_ptr;

    cb->CurWritePos = 0;
    cb->WritePtr = cb->Buffer;
    BufferLock.UnLock();
}

bool CCutBuffer::NoData() 
{ 
    CUT_BUFFER * cb = (CUT_BUFFER *)cb_ptr;
    if( cb->CurWritePos == 0 ) 
        return true;
    return false;
}

#if !defined(CUT_BUFFER_H)
#define CUT_BUFFER_H

#include "ThreadLock.h"


typedef struct {
	long		MaxLength;
	long		CurWritePos;
	char		*Buffer;
	char		*WritePtr;
}CUT_BUFFER;

class CCutBuffer
{
public:
void	LockCutBuffer();
void	UnLockCutBuffer();
void	*InitCutBuffer(long buff_len);
void	FreeCutBuffer();
long	WriteCutBuffer(unsigned char  *data,long len);
//long	DirectWriteCutBuffer(unsigned char *data,long len);
unsigned char 	*GetCutBufferWritePtr(long *len);
void	UpdateCutBufferWrite(long len);
unsigned char 	*GetCutBufferReadPtr(long *len);
void	UpdateCutBufferRead(long len);
void	ResetCutBuffer();
bool	NoData();
void *cb_ptr;
private:
    
	CThreadLock		BufferLock;
};
#endif

#include "StdAfx.h"
#include "ThreadLock.h"
//#include "stream_svr.h"

CThreadLock::CThreadLock(void)
{
#ifdef WIN32
    ThreadLockHandle = CreateMutex (NULL,FALSE,NULL);
#else
	pthread_mutex_init(&ThreadLockHandle,NULL);
#endif
}

CThreadLock::~CThreadLock(void)
{
#ifdef WIN32
    CloseHandle(ThreadLockHandle);
#else
    pthread_mutex_destroy(&ThreadLockHandle);
#endif
}

void CThreadLock::Lock()
{
#ifdef WIN32
	WaitForSingleObject(ThreadLockHandle,INFINITE); 
#else
	pthread_mutex_lock(&ThreadLockHandle); 
#endif
}
void CThreadLock::UnLock()
{
#ifdef WIN32
	ReleaseMutex(ThreadLockHandle);
#else
	pthread_mutex_unlock(&ThreadLockHandle); 
#endif
}

#ifndef THREAD_LOCK_H
#define THREAD_LOCK_H
//#include "stream_svr.h"
#ifndef WIN32
#include <pthread.h>
#endif
class CThreadLock
{
public:
	CThreadLock(void);
	~CThreadLock(void);
	void Lock();
	void UnLock();
#ifdef WIN32
	HANDLE             ThreadLockHandle;
#else
    pthread_mutex_t    ThreadLockHandle;
#endif

};
#endif