Linux IPC 信号量

1. 概念原理

​​ipc信号原理​​

2. Semphore.h

#ifndef SEMPHORE_H
#define SEMPHORE_H

#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<unistd.h>
#include<sys/types.h>
#include<sys/ipc.h>
#include<sys/sem.h>
#include "Typedef.h"

class CSem
{
private:
  key_t m_key;
  int m_semID;

public:
  CSem(){};
  ~CSem(){};
  
  int InitSem(BYTE bBankNo, BYTE bSectNo, BYTE bIdx, int iSemVal);
  
  void P();
  
  void V();
  
  void DelSem();
  
  int GetSemID(){return m_semID;};
};
  

#endif //SEMPHORE_H

3. Semphore.cpp

#include<sys/stat.h>
#include "Semphore.h"


//描述：初始化信号量
//参数：@bBankNo BANK索引号
//      @bSectNo SECT索引号
//      @bIdx 对应索引
//      @iSemVal 信号量值，默认为1
//返回：失败小于0，反之成功
int CSem::InitSem(BYTE bBankNo, BYTE bSectNo, BYTE bIdx, int iSemVal)
{
    m_key = (bBankNo<<16) | (bSectNo<<8) | bIdx;
    m_key += 1;
    
    if((m_semID=semget(m_key, 1, IPC_CREAT)) < 0)
    {
        if ((m_semID=semget(m_key, 1, IPC_CREAT|IPC_EXCL|0666)) < 0)
        {
            printf("InitSem: semget error!\n");
            exit(1);
        }
    }
    
    if (access("/tmp/InitSemFlg", F_OK) != 0) //处理多个进程各自初始化不统一
    {
        system("touch /tmp/InitSemFlg");
        semctl(m_semID, 0, SETVAL, iSemVal); //只能初始化一次
        printf("touch /tmp/InitSemFlg\n");
    }
    
    
    printf("m_key=0x%08x.\n", m_key);
    
    return m_semID;
}

//描述：获取信号量
void CSem::P()
{
    struct sembuf op;
    
    memset(&op, 0, sizeof(op));
    op.sem_num = 0;
    op.sem_op = -1;
    op.sem_flg = SEM_UNDO;
    semop(m_semID, &op, 1);
}

//描述：释放信号量
void CSem::V()
{
    struct sembuf op;
    
    memset(&op, 0, sizeof(op));
    op.sem_num = 0;
    op.sem_op = 1;
    op.sem_flg = SEM_UNDO;
    semop(m_semID, &op, 1);
}

void CSem::DelSem()
{
    semctl(m_semID, 0, IPC_RMID);
}

4. main()测试函数

#include<sys/stat.h>
#include "Semphore.h"

int main(int argc, char *argv[])
{
  int iThrdNo;
  
  if (argc != 2)
  {
    printf("main: argc must be equal to 2.\n");
    exit(-1);
  }
  iThrdNo = atoi(argv[1]);
  
  CSem *pCSem;
  
  pCSem = new CSem();
  if (pCSem == NULL)
  {
    printf("pCSem == NULL.\n");
    exit(-1);
  }
  pCSem->InitSem(1, 1, 0, 1);
  
  if (iThrdNo == 1)
  {
    printf("before getval: %d\n", semctl(pCSem->GetSemID(), 0, GETVAL));
    pCSem->P();
    printf("ThrdNo=%d, P.\n", iThrdNo);
    while (getchar() == 'c')
      break;
    pCSem->V();
    printf("ThrdNo=%d, V.\n", iThrdNo);
  }
  else
  {
    printf("before getval: %d\n", semctl(pCSem->GetSemID(), 0, GETVAL));
    pCSem->P();
    printf("ThrdNo=%d, P.\n", iThrdNo);
    pCSem->V();
    printf("ThrdNo=%d, V.\n", iThrdNo);
  }
}

5. 交叉编译

root@ubuntu:/data/# arm-linux-gnueabi-g++ -o Semphore  Semphore.cpp -ldl -lrt

6. 测试运行（同步运行）

6.1 运行1号进程

root@nxbb:/mnt/# ./Semphore 1
touch /tmp/InitSemFlg
m_key=0x00010101.
before getval: 1
ThrdNo=1, P.
c
ThrdNo=1, V.

6.2 运行2号进程

root@nxbb:/mnt# ./Semphore 2
m_key=0x00010101.
before getval: 0
iThrdNo=2, P.
iThrdNo=2, V.