【linux进程间通信(二)】共享内存详解以及进程互斥概念

#pragma once
#include<iostream>
#include<string>
#include<unistd.h>
#include<cstdio>
#include<sys/shm.h>
#include<sys/ipc.h>
#include<sys/types.h>
#include<cassert>
#include<cstring>
#include<sys/stat.h>
#include<fcntl.h>
using namespace std;
#define PATHNAME "/home/kwy"  //形成key值的字符串
#define PROJ_ID 0x666  //形成key值的整数
#define SHM_SIZE 4096 //共享内存的大小最好是页(PAGE : 4096)的整数倍

#include"common.hpp"
int main()
{
    //获取key
    key_t k = ftok(PATHNAME, PROJ_ID);
    if (k < 0)
    {
        perror("ftok");
        exit(1);
    }
    cout<<"creat key success: "<<k<<endl;
    // 获取共享内存
    int shmid = shmget(k, SHM_SIZE, 0);
    if(shmid < 0)
    {
        perror("shmget");
        exit(2);
    }
    cout<<"get shard success: "<<shmid<<endl;
    //挂接共享内存
    char *shmaddr = (char *)shmat(shmid, nullptr, 0);
    if(shmaddr == nullptr)
    {
       perror("shmat");
        exit(3);
    }
    cout<<"attach success!"<<endl;
    //将共享内存看作数组,写入数据
    char ch ='a';
    for(;ch<='z';ch++)
    {
        snprintf(shmaddr,SHM_SIZE-1,"hello server,i am other proc,mypid: %d ,inc: %c",getpid(),ch);
        sleep(2);
    }
    // 去关联
    int n = shmdt(shmaddr);
    assert(n != -1);
    cout<<"detach success!"<<endl;
    // client 要不要chmctl删除呢？不需要！！
    return 0;
}

#include"common.hpp"
int main()
{
    //创建公共的key的值
    key_t key = ftok(PATHNAME,PROJ_ID);
    cout<<"server key: "<<TransToHex(key)<<endl;
    assert(key!=-1);
    //创建共享内存(全新的共享内存)
    int shmid = shmget(key,SHM_SIZE,IPC_CREAT | IPC_EXCL | 0666);
    if(shmid==-1)
    {
        perror("shmid");
        exit(1);
    }
    cout<<"creat shmid: "<<shmid<<endl;
    //将创建好的共享内容挂接到虚拟地址
    char* shmaddr = (char*)shmat(shmid,nullptr,0);//shmat的返回值是void*,与malloc相似要强转
    cout<<"attach success!"<<endl;
    //使用共享内存,将共享内存当作一个大字符串
    //使用完共享内存后,将指定的内存与进程去关联
    int n1 = shmdt(shmaddr);
    if(n1==-1)
        perror("shmdt");
    else
        cout<<"detach success!"<<endl;
    //最后用代码删除共享内存
    int n2 = shmctl(shmid,IPC_RMID,nullptr);
    assert(n2!=-1);
    cout<<"delete shared memory: "<<shmid<<endl;
    return 0;
}