Network programming sockets (6) - a multi-process version of a simple TCP network program

In the last blog, we implemented a single-process version of a simple TCP network program. This program can only connect to one client at a time, which has limitations. So now let's implement a multi-process version of a simple TCP network program that supports multiple connections by creating child processes.

server.c:

#include <stdio.h>
#include<sys/socket.h>
#include<netinet/in.h>
#include<unistd.h>
#include<string.h>
#include<sys/types.h>
#include<arpa/inet.h>
#include<stdlib.h>

#define MAX 128

int Startup(char* ip,int port){
    int sock = socket (AF_INET, SOCK_STREAM, 0);
    if(sock < 0){
        printf("socket error!\n");
        exit(2);
    }
    struct sockaddr_in local;
    local.sin_family = AF_INET;
    local.sin_addr.s_addr = inet_addr(ip);
    local.sin_port = htons(port);

    if(bind(sock,(struct sockaddr*)&local,sizeof(local)) < 0){
        printf("bind error!\n");
        exit(3);
    }
    
    if(listen(sock,5) < 0){
        printf("listen error!\n");
        exit(4);
    }

    return sock;
}

void service(int sock,char* ip,int port){
    char buf[MAX];
    while(1){
        buf[0] = 0;
        ssize_t s = read(sock,buf,sizeof(buf)-1);
        if(s > 0){
            buf[s] = 0;
            printf("[%s:%d] say# %s\n",ip,port,buf);
            write(sock,buf,strlen(buf));
        }
        else if(s == 0){
            printf("client [%s:%d] quit!\n",ip,port);
            break;
        }
        else{
            printf("read error!\n");
            break;
        }
    }
}

int main(int argc,char* argv[]){
    if(argc != 3){
        printf("Usage:%s [ip] [port]\n",argv[0]);
        return 1;
    }
    int listen_sock = Startup(argv[1],atoi(argv[2]));
    
    struct sockaddr_in peer;
    char ipBuf[24];
    for(;;){
        ipBuf[0] = 0;
        socklen_t len = sizeof(peer);
        int new_sock = accept(listen_sock,(struct sockaddr*)&peer,&len);
        if(new_sock < 0){
            printf("accept error!\n");
            continue;
        }
        inet_ntop(AF_INET,(const void*)&peer.sin_addr,ipBuf,sizeof(ipBuf));
        int p = ntohs(peer.sin_port);
        printf("get a new connect,[%s:%d]\n",ipBuf,p);

        pid_t id = fork();
        if(id == 0){//child
            close(listen_sock);
            if(fork() > 0){
                exit(0);
            }
            service(new_sock,ipBuf,p);
            close(new_sock);
            exit(0);
        }
        else if(id > 0){//father
            close(new_sock);
            waitpid(id,NULL,0);
        }
        else{
            printf("fork error!\n");
            continue;
        }
    }
    return 0;
}

client.c:

#include <stdio.h>
#include<sys/socket.h>
#include<netinet/in.h>
#include<unistd.h>
#include<string.h>
#include<sys/types.h>
#include<stdlib.h>
#include<string.h>

#define MAX 128

int main(int argc,char* argv[]){
    if(argc != 3){
        printf("Usage:%s [ip] [port]\n",argv[0]);
        return 1;
    }
    int sock = socket (AF_INET, SOCK_STREAM, 0);
    if(sock < 0){
        printf("socket error!\n");
        return 2;
    }

    struct sockaddr_in server;
    server.sin_family = AF_INET;
    server.sin_port = htons(atoi(argv[2]));
    server.sin_addr.s_addr = inet_addr(argv[1]);

    if(connect(sock,(struct sockaddr*)&server,sizeof(server)) < 0){
        printf("connect error!\n");
        return 3;
    }

    char buf[MAX];
    while(1){
        printf("please Enter# ");
        fflush(stdout);
        ssize_t s = read(0,buf,sizeof(buf)-1);
        if(s > 0){
        buf[s-1] = 0;
        if(strcmp("quit",buf) == 0){
            printf("client quit!\n");
            break;
        }
        write(sock,buf,strlen(buf));
        s = read(sock,buf,sizeof(buf)-1);
        buf[s] = 0;
        printf("server Echo# %s\n",buf);
        }
    }
    close(sock);
    return 0;
}

When receiving a request, the server first creates a child process, and then the child process creates a grandchild process, and the grandchild process completes the interaction with the client.

• Advantages and disadvantages of the multi-process version
  

advantage:

    (1) Can handle multiple user requests;

    (2) The code is relatively simple and the writing cycle is short;

    (3) Due to the independence of the process, the stability of the multi-process server is strong.

shortcoming:

    (1) The child process is created only when the connection arrives, and creating a child process takes time and affects performance;

    (2) Each process of the multi-process server occupies resources, resulting in a limited number of customers that it can serve;

    (3) As the number of multi-process servers increases, the pressure on the CPU will increase, and the time required for CPU scheduling will become longer, which will affect performance.