Unix domain socket 或者 IPC socket是一种终端,可以使同一台操作系统上的两个或多个进程进行数据通信。提供 UDP 和 TCP 两种通信机制。 因为一些原因,项目现有软件架

Unix domain socket 或者 IPC socket是一种终端,可以使同一台操作系统上的两个或多个进程进行数据通信。提供 UDP 和 TCP 两种通信机制。

因为一些原因,项目现有软件架构采用的都是 IPC sockte 中的 TCP 通信机制,虽然保证了通信的可靠性,但近期需要对该程序进行热迁移(基于 criu ),有连接的 IPC 套接字状态很难被保存和恢复,而 无连接的 UDP 只需要保证服务端先冻结、先恢复即可实现程序整体状态迁移,因此写下本文,记录迁移过程,最后提供示例程序,可以自行通过 BCompare 等文本对比工具对比差异。

模式差异

至于两种通信机制的差异,除了在创建套接字时声明的差异,具体的通信流程也有差异,在这里找到 CSDN @frank909 的两张图片,感觉很有代表性,在这里引用一下。

首先是 TCP的:

https://imagehost-cdn.frytea.com/images/2021/01/13/202101131815253d04d69f377dae01.png

https://imagehost-cdn.frytea.com/images/2021/01/13/202101131815253d04d69f377dae01.png

接下来是 UDP 的:

https://imagehost-cdn.frytea.com/images/2021/01/13/2021011318145069f28463e2e1709c.png

二者的差异,主要是这几点:

  • 服务端:

(1)TCP连接在 bind() 之后需要 listen() ,而UDP不需要。

(2)TCP连接在 bind()listen() 后还需要 accept(),用来得到客户端连接描述符,而UDP不需要。

(3)收发数据,TCP使用 recv() , send() , 而 UDP 使用 recvfrom(), sendto()

(4)释放连接,TCP在客户端释放连接后需先释放 accept() 得到的客户端连接描述符,再 close(socket) ,而UDP直接 close(socket)

  • 客户端:

(1)TCP连接在bind()后需要 connect(),而UDP不需要。

(2)收发数据,TCP使用 recv() , send() , 而 UDP 使用 recvfrom(), sendto()

具体的差异可以查看下方的示例程序。

参考程序

TCP-Server

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/*************************************************************************
> File Name: ipc_tcp_server.cpp
> Author: TianLun Song
> Mail: songtianlun@frytea.com
> Blog: https://blog.frytea.com
> Created Time: Wed 13 Jan 2021 09:53:06 AM CST
************************************************************************/
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/un.h>
#include <memory.h>
#include <unistd.h>
#include <stdio.h>
#include <iostream>

using namespace std;
const char* server_file = "/tmp/ipc_tcp_server.sock";

int main(int argc,char** argv)
{
int socket_fd = socket(AF_UNIX,SOCK_STREAM,0);
if (socket_fd < 0)
{
perror("socket");
return -1;
}
struct sockaddr_un addr;
memset(&addr,0,sizeof(addr));
addr.sun_family = AF_UNIX;
strcpy(addr.sun_path,server_file);
if (access(addr.sun_path,0) != -1)
{
remove(addr.sun_path);
}
if (bind(socket_fd,(sockaddr*)&addr,sizeof(addr)) < 0)
{
perror("bind");
return -1;
}
/* --------DIFF, ipc tcp only------------ */
if (listen(socket_fd,12) < 0)
{
perror("listen");
return -1;
}
/* ---------------end------------ */
struct sockaddr_un clientaddr;
socklen_t addrlen = sizeof(clientaddr);
char msg_buf[1024];
/* --------DIFF, ipc tcp only------------ */
int newcon = -1;
newcon = accept(socket_fd,(sockaddr*)&clientaddr,&addrlen);
if (newcon < 0)
{
perror("accept");
return -1;
}
/* ---------------end------------ */
while (1)
{
memset(msg_buf,'\0',1024);
int rsize = recv(newcon,msg_buf,sizeof(msg_buf),0);
if (rsize < 0)
{
perror("server recv error!");
break;
}
cout << "I'm Unix socket(TCP) server, recv a msg:" << msg_buf << " from: " << clientaddr.sun_path << endl;
strcpy(msg_buf, "OK,I got it!");
int ssize = send(newcon, msg_buf, sizeof msg_buf, 0);
if (ssize < 0)
{
perror("server send error!");
break;
}
sleep(1);
}
/* --------DIFF, ipc tcp only------------ */
if (close(newcon) < 0)
{
perror("close accept");
return -1;
}
/* ---------------end------------ */
if (close(socket_fd) < 0)
{
perror("close socket");
return -1;
}
return 0;
}

TCP-Client

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/*************************************************************************
> File Name: ipc_tcp_client.cpp
> Author: TianLun Song
> Mail: songtianlun@frytea.com
> Blog: https://blog.frytea.com
> Created Time: Wed 13 Jan 2021 10:14:09 AM CST
************************************************************************/
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/un.h>
#include <memory.h>
#include <unistd.h>
#include <stdio.h>
#include <iostream>

using namespace std;

const char* server_file = "/tmp/ipc_tcp_server.sock";
const char* client_file = "/tmp/ipc_tcp_client.sock";

int main(int argc,char** argv)
{
int socket_fd = socket(AF_UNIX,SOCK_STREAM,0);
if (socket_fd < 0)
{
perror("client socket");
return -1;
}
struct sockaddr_un client_addr;
memset(&client_addr,0,sizeof(client_addr));
client_addr.sun_family = AF_UNIX;
strcpy(client_addr.sun_path,client_file);

if (access(client_addr.sun_path,0) != -1)
{
remove(client_addr.sun_path);
}

if(bind(socket_fd,(sockaddr*)&client_addr,sizeof(client_addr)) < 0)
{
perror("client bind");
return -1;
}
struct sockaddr_un serveraddr;
memset(&serveraddr,0,sizeof(serveraddr));
socklen_t addrlen = sizeof(serveraddr);
serveraddr.sun_family = AF_UNIX;
strcpy(serveraddr.sun_path,server_file);
char msg_buf[1024];
/* --------DIFF, ipc tcp only------------ */
int newcon = -1;
newcon = connect(socket_fd,(sockaddr*)&serveraddr,addrlen);
if (newcon < 0){
perror("client connect");
}
/* ---------------end------------ */
while(1)
{
strcpy(msg_buf, "How are you !!!");
int ssize = send(socket_fd, msg_buf, sizeof msg_buf, 0);
if (ssize < 0)
{
perror("client send");
continue;
}
int rsize = recv(socket_fd, msg_buf, sizeof(msg_buf), 0);
if (rsize < 0)
{
perror("client recv");
continue;
}
cout << "I'm Unix socket(TCP) client,receive a msg :" << msg_buf << endl;
sleep(1);
}
if (close(socket_fd) < 0)
{
perror("close");
return -1;
}
return 0;
}

UDP-Server

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/*************************************************************************
> File Name: ipc_udp_server.cpp
> Author: TianLun Song
> Mail: songtianlun@frytea.com
> Blog: https://blog.frytea.com
> Created Time: Wed 13 Jan 2021 09:53:06 AM CST
************************************************************************/
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/un.h>
#include <memory.h>
#include <unistd.h>
#include <stdio.h>
#include <iostream>

using namespace std;
const char* server_file = "/tmp/ipc_udp_server.sock";

int main(int argc,char** argv)
{
int socket_fd = socket(AF_UNIX,SOCK_DGRAM,0);
if (socket_fd < 0)
{
perror("socket");
return -1;
}
struct sockaddr_un addr;
memset(&addr,0,sizeof(addr));
addr.sun_family = AF_UNIX;
strcpy(addr.sun_path,server_file);
if (access(addr.sun_path,0) != -1)
{
remove(addr.sun_path);
}
if (bind(socket_fd,(sockaddr*)&addr,sizeof(addr)) < 0)
{
perror("bind");
return -1;
}
struct sockaddr_un clientaddr;
socklen_t addrlen = sizeof(clientaddr);
char msg_buf[1024];
while (1)
{
memset(msg_buf,'\0',1024);
int rsize = recvfrom(socket_fd,msg_buf,sizeof(msg_buf),0,(sockaddr*)&clientaddr,&addrlen);
if (rsize < 0)
{
perror("server recv error!");
break;
}
cout << "I'm Unix socket(UDP) server, recv a msg: " << msg_buf << " from: " << clientaddr.sun_path << endl;
strcpy(msg_buf, "OK,I got it!");
int ssize = sendto(socket_fd, msg_buf, sizeof msg_buf,0,(sockaddr*)&clientaddr,addrlen);
if (ssize < 0)
{
perror("server send error!");
break;
}
sleep(1);
}
if (close(socket_fd) < 0)
{
perror("close socket");
return -1;
}
return 0;
}

UDP-Client

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/*************************************************************************
> File Name: ipc_udp_client.cpp
> Author: TianLun Song
> Mail: songtianlun@frytea.com
> Blog: https://blog.frytea.com
> Created Time: Wed 13 Jan 2021 10:14:09 AM CST
************************************************************************/
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/un.h>
#include <memory.h>
#include <unistd.h>
#include <stdio.h>
#include <iostream>

using namespace std;

const char* server_file = "/tmp/ipc_udp_server.sock";
const char* client_file = "/tmp/ipc_udp_client.sock";

int main(int argc,char** argv)
{
int socket_fd = socket(AF_UNIX,SOCK_DGRAM,0);
if (socket_fd < 0)
{
perror("client socket");
return -1;
}
struct sockaddr_un client_addr;
memset(&client_addr,0,sizeof(client_addr));
client_addr.sun_family = AF_UNIX;
strcpy(client_addr.sun_path,client_file);

if (access(client_addr.sun_path,0) != -1)
{
remove(client_addr.sun_path);
}

if(bind(socket_fd,(sockaddr*)&client_addr,sizeof(client_addr)) < 0)
{
perror("client bind");
return -1;
}
struct sockaddr_un serveraddr;
memset(&serveraddr,0,sizeof(serveraddr));
socklen_t addrlen = sizeof(serveraddr);
serveraddr.sun_family = AF_UNIX;
strcpy(serveraddr.sun_path,server_file);
char msg_buf[1024];
while(1)
{
strcpy(msg_buf, "How are you !!!");
int ssize = sendto(socket_fd, msg_buf, sizeof msg_buf, 0, (sockaddr*)&serveraddr,addrlen);
if (ssize < 0)
{
perror("client sendto");
continue;
}
int rsize = recvfrom(socket_fd, msg_buf, sizeof(msg_buf), 0,(sockaddr*)&serveraddr, &addrlen);
if (rsize < 0)
{
perror("client recv");
continue;
}
cout << "I'm Unix socket(TCP) client,receive a msg :" << msg_buf << endl;
sleep(1);
}
if (close(socket_fd) < 0)
{
perror("close");
return -1;
}
return 0;
}

源文件

ipc_test.zip

参考文献