目录
接上篇的共享内存的函数封装。
命令 ipcs -m ：
我们可以写个代码验证一下：我们创建出共享内存后休眠 2s，然后把共享内存挂接到进程中，再次休眠 5s，休眠结束后把共享内存从进程的地址空间中分离出来，注意只是分离出来，并没有删除共享内存。
#include"Comm.hpp"
#include<unistd.h>
int main()
{
key_t k=GetShmKeyOrDie(path,pro_jid);
cout<<" key:"<<ToHex(k)<<endl;//转为十六进制输出
int shmid=CreateShm(k,defaultsize);
cout<<" shmid:"<<shmid<<endl;
sleep(2);
char* addr=(char*)ShmAttach(shmid);
cout<<" Attach success, addr:"<<ToHex((uint64_t)addr)<<endl;
sleep(5);
ShmDetach(addr);
cout<<" Detach success "<<ToHex((uint64_t)addr)<<endl;
return 0;
}
命令 ipcrm -m shmid：
共享内存的通信：
创建出共享内存之后，我们就可以通信了。
为什么共享内存更高效？
代码：
ShmClient.cc：
#include"Comm.hpp"
#include<unistd.h>
int main()
{
key_t k=GetShmKeyOrDie(path,pro_jid);
cout<<" key:"<<ToHex(k)<<endl;//转为十六进制输出
int shmid=GetShm(k,defaultsize);
cout<<" shmid:"<<shmid<<endl;
char* addr=(char*)ShmAttach(shmid);
cout<<" Attach success, addr:"<<ToHex((uint64_t)addr)<<endl;
memset(addr,0,defaultsize);//初始化共享内存
for(char ch='A';ch<='Z';ch++)//写入
{
addr[ch-'A']=ch;
sleep(1);
}
ShmDetach(addr);
cout<<" Detach success "<<ToHex((uint64_t)addr)<<endl;
return 0;
}ShmServer.cc：
#include"Comm.hpp"
#include<unistd.h>
int main()
{
key_t k=GetShmKeyOrDie(path,pro_jid);
cout<<" key:"<<ToHex(k)<<endl;//转为十六进制输出
int shmid=CreateShm(k,defaultsize);
cout<<" shmid:"<<shmid<<endl;
char* addr=(char*)ShmAttach(shmid);
cout<<" Attach success, addr:"<<ToHex((uint64_t)addr)<<endl;
//读取数据
for(;;)
{
cout<<" shm content:"<<addr<<endl;
sleep(1);
}
ShmDetach(addr);
cout<<" Detach success "<<ToHex((uint64_t)addr)<<endl;
DeleteShm(shmid);
return 0;
}结果：
如何让共享内存实现同步？
我们利用管道来实现同步。
代码：
Comm.hpp
#pragma once
#include <iostream>
#include <sys/ipc.h>
#include <cstdlib>
#include <cerrno>
#include <string>
#include <cstring>
#include <sys/shm.h>
#include <sys/types.h>
using namespace std;
const char *path = "./shm_test";
const int pro_jid = 0x66;
const int defaultsize = 4096;
key_t GetShmKeyOrDie(const char *pathname, const int pro_jid)
{
key_t k = ftok(pathname, pro_jid); // 得到key值
if (k < 0)// 获取失败
{
cerr << " ftok failed,errno:" << errno << ", errstring:" << strerror(errno) << endl;
exit(1); // 直接终止程序
}
return k; // 获取成功
}
int CreateShmOrDie(key_t key, int size, int flag)
{
// 得到共享内存的shmid
int shmid = shmget(key, size, flag);
if (shmid < 0) // 创建失败
{
cerr << " shmget failed, errno:" << errno << ", errstring:" << strerror(errno) << endl;
exit(2);
}
return shmid; // 创建成功
}
int CreateShm(key_t key, int size)
{
// 创建一个新的共享内存，并设置权限
return CreateShmOrDie(key, size, IPC_CREAT | IPC_EXCL | 0666);
}
int GetShm(key_t key, int size)
{
return CreateShmOrDie(key, size, IPC_CREAT);
}
void DeleteShm(int shmid)
{
int n = shmctl(shmid, IPC_RMID, nullptr);
if (n < 0)
cerr << " Delete failed,errno:" << errno << ", errstring:" << strerror(errno) << endl;
else
cout << " Delete success, shmid:" << shmid << endl;
}
string ToHex(key_t k)//将 key 值转为十六进制
{
char buffer[1024];//用C语言方便用 %x 直接转为十六进制
snprintf(buffer,sizeof(buffer),"0x%x",k);
return buffer;
}
void DebugShm(int shmid)
{
struct shmid_ds shmds;
int n = shmctl(shmid, IPC_STAT, &shmds);
if (n < 0)
cerr << " shmctl failed " << endl;
else
{
std::cout << "shmds.shm_segsz: " << shmds.shm_segsz << std::endl;//共享内存的大小
std::cout << "shmds.shm_nattch:" << shmds.shm_nattch << std::endl;//有多少个进程挂接
std::cout << "shmds.shm_ctime:" << shmds.shm_ctime << std::endl;//上一次挂接或取消挂接的时间
std::cout << "shmds.shm_perm.__key:" << ToHex(shmds.shm_perm.__key) << std::endl;//对应的key
}
}
void *ShmAttach(int shmid)
{
void* addr=shmat(shmid,nullptr,0);
if((long long int)addr==-1)
{
//挂接失败
cerr<<" attach failed,errno:"<<errno<<", errstring:"<<strerror(errno)<<endl;
return nullptr;
}
else
{
//挂接成功
return addr;
}
}
void ShmDetach(void *addr)
{
int n=shmdt(addr);
if(n<0)
{
cerr<<" Detach failed,errno:"<<errno<<", errstring:"<<strerror(errno)<<endl;
}
}Fifo.hpp
#ifndef __COMM_HPP__
#define __COMM_HPP__
#include <iostream>
#include <string>
#include <cerrno>
#include <cstring>
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
#include <fcntl.h>
#include <cassert>
using namespace std;
#define Mode 0666
#define Path "./fifo"
class Fifo
{
public:
Fifo(const string &path = Path) : _path(path)
{
umask(0);
int n = mkfifo(_path.c_str(), Mode);
if (n == 0)
{
cout << "mkfifo success" << endl;
}
else
{
cerr << "mkfifo failed, errno: " << errno << ", errstring: " << strerror(errno) << endl;
}
}
~Fifo()
{
int n = unlink(_path.c_str());
if (n == 0)
{
cout << "remove fifo file " << _path << " success" << endl;
}
else
{
cerr << "remove failed, errno: " << errno << ", errstring: " << strerror(errno) << endl;
}
}
private:
string _path; // 文件路径+文件名
};
class Sync
{
public:
Sync():rfd(-1),wfd(-1)
{ }
void OpenReadOrDie()
{
rfd=open(Path,O_RDONLY);
if(rfd<0)
exit(1);
}
void OpenWriteOrDie()
{
wfd=open(Path,O_WRONLY);
if(wfd<0)
exit(1);
}
bool Wait()
{
//读端
bool ret=true;
uint32_t c=0;
ssize_t n=read(rfd,&c,sizeof(uint32_t));
if(n==sizeof(uint32_t))
{
cout<<" server wakeup, begin read shm..." << endl;
}
else if(n==0)
{
return false;
}
else
{
return false;
}
return true;
}
void Wakeup()
{
//写端
uint32_t c=0;
ssize_t n=write(wfd,&c,sizeof(c));
assert(n==sizeof(uint32_t));
cout<<" Wakeup server "<<endl;
}
~Sync()
{ }
private:
int rfd;
int wfd;
};
#endifShmClient.cc
#include"Comm.hpp"
#include"Fifo.hpp"
#include<unistd.h>
int main()
{
key_t k=GetShmKeyOrDie(path,pro_jid);
cout<<" key:"<<ToHex(k)<<endl;//转为十六进制输出
int shmid=GetShm(k,defaultsize);
cout<<" shmid:"<<shmid<<endl;
char* addr=(char*)ShmAttach(shmid);
cout<<" Attach success, addr:"<<ToHex((uint64_t)addr)<<endl;
Sync sync;
sync.OpenWriteOrDie();//打开写端
memset(addr,0,defaultsize);//初始化共享内存
sleep(5);
for(char ch='A';ch<='Z';ch++)//写入
{
addr[ch-'A']=ch;
sleep(1);
sync.Wakeup();//写完了
}
ShmDetach(addr);
cout<<" Detach success "<<ToHex((uint64_t)addr)<<endl;
return 0;
}ShmServer.cc
#include"Comm.hpp"
#include"Fifo.hpp"
#include<unistd.h>
int main()
{
key_t k=GetShmKeyOrDie(path,pro_jid);
cout<<" key:"<<ToHex(k)<<endl;//转为十六进制输出
int shmid=CreateShm(k,defaultsize);
cout<<" shmid:"<<shmid<<endl;
char* addr=(char*)ShmAttach(shmid);
cout<<" Attach success, addr:"<<ToHex((uint64_t)addr)<<endl;
Fifo fifo;
Sync sync;
sync.OpenReadOrDie();//打开读端
//读取数据
for(;;)
{
if(!sync.Wait()) break;
//写端写完了，读端可以读了
cout<<" shm content:"<<addr<<endl;
sleep(1);
}
ShmDetach(addr);
cout<<" Detach success "<<ToHex((uint64_t)addr)<<endl;
DeleteShm(shmid);
return 0;
}结果：
