Linux IPC共享内存（多进程通信）

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JDSH0224 2022-09-19 13:40:50 博主文章分类：Linux IPC ©著作权

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1. ShareMem.h

#ifndef SHARE_MEM_H
#define SHARE_MEM_H

#include <sys/shm.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>


class CShareMem{
private:
  key_t m_key; //共享内存键值
  int m_iShmId; //共享内存ID
  void *m_pvAddr; //共享内存的起始地址
  int m_iTotalSize; //共享内存总大小
  int m_iUsageSize; //共享内存已使用
  
  //描述：共享内存初始化
  int ShmInit();
  
  //描述：附加到共享内存指定地址
  //返回：成功返回附加的地址，否则为NULL
  void *ShmAtt(); 
  
  //描述：分离到共享内存指定地址
  //返回：成功返回0，否则为-1
  int ShmDat();
  
public:
  CShareMem(int iTotalSize);  
  
  ~CShareMem();
  
  //描述：申请共享内存地址
  const char *NewShmAddr(int iAddrSize);
  
  //描述：删除共享内存地址
  int DelShmAddr();
};

//描述：共享内存初始化
//参数：@iTotalSize 共享内存大小
//返回：成功返回0，反之失败返回-1
int ShmInit(int iTotalSize);

//描述：分配共享内存
//参数：@iAddrSize 请求分配的共享内存大小
//返回：成功返回新内存地址，否则为NULL
const char *NewShmAddr(int iAddrSize);

//描述：释放共享内存
//返回：成功返回0，反之返回-1
int DelShmAddr();

#endif

2. ShareMem.cpp

#include <string.h>
#include "ShareMem.h"


CShareMem::CShareMem(int iTotalSize)
{
    m_iTotalSize = iTotalSize;
    m_iUsageSize = 0;
    m_key = 0x78746B6D; //"系统库映射"缩写字符，xtkm=0x78746B6D
    ShmInit();
    ShmAtt();
}   
    
CShareMem::~CShareMem()
{
    shmdt(m_pvAddr);
}

int CShareMem::ShmInit()
{
    //long page_size = sysconf(_SC_PAGESIZE);
    //int data_size =  (m_iMemTol + page_size - 1) & (~(page_size - 1));
    
    //printf("CShareMem::ShmInit(): System page size=%d, iMemTolSize=%d, Adjust iMemTolSize=%d.\n", page_size, m_iMemTol, page_size);
    //m_iMemTol = page_size;
    
    printf("ShmInit: m_iTotalSize(dec)=%d.\n", m_iTotalSize);
    
    if ((m_iShmId=shmget(m_key, m_iTotalSize, IPC_CREAT)) < 0)
    {
        if ((m_iShmId=shmget(m_key, m_iTotalSize, IPC_CREAT|IPC_EXCL|0666)) < 0)
            printf("CShareMem::ShmInit:shmget() %s\n", strerror(m_iShmId));
    }
    
    if (m_iShmId > 0)
        printf("CShareMem::ShmInit:shmget() key=0x%08x, ShmId=0x%08x\n", m_key, m_iShmId);
    
    return m_iShmId;  
}
}

//描述：附加到共享内存指定地址
//返回：成功返回附加的地址，否则为NULL
void *CShareMem::ShmAtt()
{
    m_pvAddr = shmat(m_iShmId, NULL, 0);
    if (m_pvAddr == NULL)
        printf("CShareMem::ShmAtt() m_pvAddr=NULL!\n");
    return m_pvAddr;
}

//描述：分离共享内存指定地址
//参数：@pvShmAddr 附加的共享内层地址
//返回：成功返回0，否则为-1
int CShareMem::ShmDat()
{
    return shmdt(m_pvAddr);
}
}

const char *CShareMem::NewShmAddr(int iNewSize)
{
    const char *pAddr = NULL;
    
    if (m_iUsageSize+iNewSize > m_iTotalSize)
    {
        printf("NewShmAddr: The length is too large, pAddr=%p, Offset=%d, iNewSize=%d!!!\n", pAddr, m_iUsageSize, iNewSize);
        return NULL;
    }
    
    pAddr = (char*)m_pvAddr + m_iUsageSize;
    printf("NewShmAddr: pAddr=%p, Offset=%d, iNewSize=%d\n", pAddr, m_iUsageSize, iNewSize);
    m_iUsageSize += iNewSize;
    return pAddr;
}


//描述：删除共享内存地址
int CShareMem::DelShmAddr()
{
    return shmctl(m_iShmId, IPC_RMID, 0);
}

//定义共享内存对象
static CShareMem *g_pCSM=NULL;

//描述：共享内存初始化
//参数：@iTotalSize 共享内存大小
//返回：成功返回0，反之失败返回-1
int ShmInit(int iTotalSize)
{
    if (g_pCSM == NULL)
    {
        if ((g_pCSM=new CShareMem(iTotalSize)) == NULL)
            return -1;
    }
    return 0;
}

//描述：分配共享内存
//参数：@iAddrSize 请求分配的共享内存大小
//返回：成功返回新内存地址，否则为NULL
const char *NewShmAddr(int iAddrSize)
{
    if (g_pCSM != NULL)
        return g_pCSM->NewShmAddr(iAddrSize);
    return NULL;
}

//描述：释放共享内存
//返回：成功返回0，反之返回-1
int DelShmAddr()
{
    if (g_pCSM != NULL)
    {
        if (g_pCSM->DelShmAddr() > 0)
        {
            delete g_pCSM;
            return 0;
        }
    }
    return -1;
}

3. main.cpp

#include <string.h>
#include "ShareMem.h"

#define SHARE_MEM_SIZE    (20*1024*1024)  //20M
#define SHARE_MEM_USAGE   (10*1024)   //10K

int main(int argc, char *argv[])
{
  const char *pvAddr0, *pvAddr1, *pvAddr2;
  int iCnt;
  int iRdWr;
  
  if (argc != 2)
    exit(0);
  
  iRdWr = atoi(argv[1]);
  printf("iRdWr = %d.\n", iRdWr);
  
  //1.共享内存初始化
  ShmInit(SHARE_MEM_SIZE);

  //2.申请共享内存1
  pvAddr0 = NewShmAddr(SHARE_MEM_USAGE);
  if (pvAddr0 == NULL)
    printf("pvAddr0=%p\n", pvAddr0);
  
  //3.申请共享内存2
  pvAddr1 = NewShmAddr(SHARE_MEM_USAGE);
  if (pvAddr1 == NULL)
    printf("pvAddr1=%p\n", pvAddr1);
  
  //4.申请共享内存3
  pvAddr2 = NewShmAddr(SHARE_MEM_USAGE);
  if (pvAddr2 == NULL)
    printf("pvAddr2=%p\n", pvAddr2);
  
  iCnt = 0;
  while(1)
  {
    if (iRdWr == 0)
    {
      sprintf((char*)pvAddr0, "hello world! iCnt=%d", iCnt++);
      printf("Write pvAddr0=%p, %s\n", pvAddr0, pvAddr0);
      
      sprintf((char*)pvAddr1, "hello world! iCnt=%d", iCnt++);
      printf("Write pvAddr1=%p, %s\n", pvAddr1, pvAddr1);
  
      sprintf((char*)pvAddr2, "hello world! iCnt=%d", iCnt++);
      printf("Write pvAddr2=%p, %s\n", pvAddr2, pvAddr2);
      
      sleep(1); //1s
    }
    else
    {
      printf("Read pvAddr0=%p, %s\n", pvAddr0, pvAddr0);
      
      printf("Read pvAddr1=%p, %s\n", pvAddr1, pvAddr1);
      
      printf("Read pvAddr2=%p, %s\n", pvAddr2, pvAddr2);
      
      usleep(500*1000); //500ms
    }
  }
  
  //4.释放共享内存
  DelShmAddr();
}

4. 编译

arm-linux-gnueabi-g++ ShareMem.cpp -o ShareMem

5. 测试

编译的可执行程序ShareMem通过传入不同的参数0（写）或1（读）控制；

进程1（写）

root@NXBB:/mnt/# ./ShareMem 0
iRdWr = 0.
ShmInit: m_iTotalSize(dec)=20971520.
NewShmAddr: pAddr=0xb5887000, Offset=0, iNewSize=10240
NewShmAddr: pAddr=0xb5889800, Offset=10240, iNewSize=10240
NewShmAddr: pAddr=0xb588c000, Offset=20480, iNewSize=10240
Write pvAddr0=0xb5887000, hello world! iCnt=0
Write pvAddr1=0xb5889800, hello world! iCnt=1
Write pvAddr2=0xb588c000, hello world! iCnt=2
Write pvAddr0=0xb5887000, hello world! iCnt=3
Write pvAddr1=0xb5889800, hello world! iCnt=4
Write pvAddr2=0xb588c000, hello world! iCnt=5

进程2（读）

root@NXBB:/mnt/# ./ShareMem 1
iRdWr = 1.
ShmInit: m_iTotalSize(dec)=20971520.
NewShmAddr: pAddr=0xb5832000, Offset=0, iNewSize=10240
NewShmAddr: pAddr=0xb5834800, Offset=10240, iNewSize=10240
NewShmAddr: pAddr=0xb5837000, Offset=20480, iNewSize=10240
Read pvAddr0=0xb5832000, hello world! iCnt=3
Read pvAddr1=0xb5834800, hello world! iCnt=4
Read pvAddr2=0xb5837000, hello world! iCnt=5
Read pvAddr0=0xb5832000, hello world! iCnt=3
Read pvAddr1=0xb5834800, hello world! iCnt=4
Read pvAddr2=0xb5837000, hello world! iCnt=5
Read pvAddr0=0xb5832000, hello world! iCnt=3
Read pvAddr1=0xb5834800, hello world! iCnt=4
Read pvAddr2=0xb5837000, hello world! iCnt=5

进程3（读）

root@NXBB:/mnt/# ./ShareMem 1
iRdWr = 1.
ShmInit: m_iTotalSize(dec)=20971520.
NewShmAddr: pAddr=0xb5832000, Offset=0, iNewSize=10240
NewShmAddr: pAddr=0xb5834800, Offset=10240, iNewSize=10240
NewShmAddr: pAddr=0xb5837000, Offset=20480, iNewSize=10240
Read pvAddr0=0xb5832000, hello world! iCnt=3
Read pvAddr1=0xb5834800, hello world! iCnt=4
Read pvAddr2=0xb5837000, hello world! iCnt=5
Read pvAddr0=0xb5832000, hello world! iCnt=3
Read pvAddr1=0xb5834800, hello world! iCnt=4
Read pvAddr2=0xb5837000, hello world! iCnt=5
Read pvAddr0=0xb5832000, hello world! iCnt=3
Read pvAddr1=0xb5834800, hello world! iCnt=4
Read pvAddr2=0xb5837000, hello world! iCnt=5