Linux TCP communication concurrency

Multiple processes

client

#include <stdio.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <string.h>
#include <stdlib.h>
int main() {
    //Create socket
    int lfd = socket(AF_INET, SOCK_STREAM, 0);
    if(lfd == -1) {
        perror("socket");
        exit(-1);
    }
    //connect to the server
    struct sockaddr_in serveraddr;
    inet_pton(AF_INET, "192.168.245.129", & amp;serveraddr.sin_addr.s_addr);
    serveraddr.sin_family = AF_INET;
    serveraddr.sin_port = htons(9999);
    int ret = connect(lfd, (struct sockaddr *) & amp;serveraddr, sizeof(serveraddr));
    if(ret == -1) {
        perror("connect");
        _exit(-1);
    }
    //communication
    int i = 0;
    char receiveBuf[1024] = {0};
    while(1) {
        sprintf(receiveBuf, "data: %d\\
", i + + );

        write(lfd, receiveBuf, strlen(receiveBuf));
        sleep(1);
        
        int len = read(lfd, receiveBuf, sizeof(receiveBuf));
        if(len == -1) {
            perror("read");
            exit(0);
        } else if(len > 0) {
            printf("receive server data: %s\\
", receiveBuf);
        } else if (len == 0) {
            printf("server closed...");
        }
        
    }
    

    close(lfd);
}

Service-Terminal

#define _XOPEN_SOURCE
#include<stdio.h>
#include<unistd.h>
#include<arpa/inet.h>
#include<string.h>
#include<stdlib.h>
#include<signal.h>
#include<wait.h>
#include<errno.h>

void recyleChild(int arg) {
    while(1) {
        int ret = waitpid(-1, NULL, WNOHANG);
        if(ret == -1) {
            break;
        } else if (ret == 0) {
            break;
        } else if (ret > 0) {
            printf("pid %d is resaved\\
", ret);
        }
    }
}

int main() {

    //Register signal capture function
    struct sigaction act;
    act.sa_flags = 0;
    sigemptyset( & amp;act.sa_mask);
    act.sa_handler = recyleChild;
    sigaction(SIGCHLD, &act, NULL);


    //Create socket
    int lfd = socket(AF_INET, SOCK_STREAM, 0);
    if(lfd == -1) {
        perror("socket");
        exit(0);
    }
    struct sockaddr_in saddr;
    saddr.sin_family = AF_INET;
    saddr.sin_port = htons(9999);
    saddr.sin_addr.s_addr = INADDR_ANY;

    //Bind
    int ret = bind(lfd, (struct sockaddr*) & amp;saddr, sizeof(saddr));
    if(ret == -1) {
        perror("bind");
        exit(0);
    }

    //monitor
    ret = listen(lfd, 128);
    if(ret == -1) {
        perror("listen");
        exit(0);
    }

    //Accept link
    while(1) {
        struct sockaddr_in cliaddr;
        int len = sizeof(cliaddr);
        
        int cfd = accept(lfd, (struct sockaddr*) & amp;cliaddr, & amp;len);
        if(cfd == -1) {
            if(errno == EINTR) {
                continue;
            }
            perror("accept");
            exit(-1);
        }

        //For each connection, create a child process
        pid_t pid = fork();
        if(pid == 0) {
            char clientIP[16];
            inet_ntop(AF_INET, & cliaddr.sin_addr.s_addr, clientIP, 16);
            unsigned short cliPort = ntohs(cliaddr.sin_port);
            printf("Client Port is %d, client addr is %s\\
", cliPort, clientIP);

            char recvBuf[1024] = {0};
            while(1) {
                int len = read(cfd, & amp;recvBuf, sizeof(recvBuf));
                if(len == -1) {
                    perror("read");
                    return 0;
                } else if(len > 0) {
                    printf("recv client data : %s \\
", recvBuf);
                    
                } else {
                    printf("closed....");
                }

                write(cfd, & amp;recvBuf, sizeof(recvBuf));
            }
            close(cfd);
            exit(0);
        }
    }
    close(lfd);
    return 0;
}

Multi-threading

server

#define _XOPEN_SOURCE
#include<stdio.h>
#include<unistd.h>
#include<arpa/inet.h>
#include<string.h>
#include<stdlib.h>
#include<errno.h>
#include<pthread.h>


struct sockinfo {
    int fd;
    struct sockaddr_in saddr;
    pthread_t tid;
};

struct sockinfo sockinfos[128];

void* working(void* arg) {

    struct sockinfo* pinfo = (struct sockinfo*) arg;
    char clientIP[16];
    inet_ntop(AF_INET, & amp;pinfo->saddr.sin_addr.s_addr, clientIP, 16);
    unsigned short cliPort = ntohs(pinfo->saddr.sin_port);
    printf("Client Port is %d, client addr is %s\\
", cliPort, clientIP);

    char recvBuf[1024] = {0};
    while(1) {
        int len = read(pinfo->fd, & amp;recvBuf, sizeof(recvBuf));
        if(len == -1) {
            perror("read");
            return 0;
        } else if(len > 0) {
            printf("recv client data : %s \\
", recvBuf);
                    
        } else {
            printf("closed....");
        }

        write(pinfo->fd, & amp;recvBuf, sizeof(recvBuf));
    }
    close(pinfo->fd);
    exit(0);
    return NULL;
}

int main() {
 //Create socket
    int lfd = socket(AF_INET, SOCK_STREAM, 0);
    if(lfd == -1) {
        perror("socket");
        exit(0);
    }
    struct sockaddr_in saddr;
    saddr.sin_family = AF_INET;
    saddr.sin_port = htons(9999);
    saddr.sin_addr.s_addr = INADDR_ANY;

    //Bind
    int ret = bind(lfd, (struct sockaddr*) & amp;saddr, sizeof(saddr));
    if(ret == -1) {
        perror("bind");
        exit(0);
    }

    //monitor
    ret = listen(lfd, 128);
    if(ret == -1) {
        perror("listen");
        exit(0);
    }

    //Initialization data
    int max = sizeof(sockinfos) / sizeof(sockinfos[0]);
    for(int i = 0; i < max; i + + ) {
        memset( & amp;sockinfos[i], 0, sizeof(sockinfos[i]));
        sockinfos[i].fd = -1;
        sockinfos[i].tid = -1;
    }

    //Accept link
    while(1) {
        struct sockaddr_in cliaddr;
        int len = sizeof(cliaddr);
        
        int cfd = accept(lfd, (struct sockaddr*) & amp;cliaddr, & amp;len);
        if(cfd == -1) {
            perror("accept");
            exit(-1);
        }

        struct sockinfo *pinfo;
        for(int i = 0; i < max; i + + ) {
            if(sockinfos[i].fd == -1) {
                pinfo = &sockinfos[i];
                break;
            }
            if(i == max - 1) {
                sleep(1);
                i--;
            }
        }

        pinfo->fd = cfd;
        memcpy( & amp;pinfo->saddr, & amp;cliaddr, len);


        //For each connection, create a child process

        pthread_create( & amp;pinfo->tid, NULL, working, pinfo);

        pthread_detach(pinfo->tid);
    }
    close(lfd);
    return 0;
}

client

#include <stdio.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <string.h>
#include <stdlib.h>
int main() {
    //Create socket
    int lfd = socket(AF_INET, SOCK_STREAM, 0);
    if(lfd == -1) {
        perror("socket");
        exit(-1);
    }
    //connect to the server
    struct sockaddr_in serveraddr;
    inet_pton(AF_INET, "192.168.245.129", & amp;serveraddr.sin_addr.s_addr);
    serveraddr.sin_family = AF_INET;
    serveraddr.sin_port = htons(9999);
    int ret = connect(lfd, (struct sockaddr *) & amp;serveraddr, sizeof(serveraddr));
    if(ret == -1) {
        perror("connect");
        _exit(-1);
    }
    //communication
    int i = 0;
    char receiveBuf[1024] = {0};
    while(1) {
        sprintf(receiveBuf, "data: %d\\
", i + + );

        write(lfd, receiveBuf, strlen(receiveBuf));
        sleep(1);
        
        int len = read(lfd, receiveBuf, sizeof(receiveBuf));
        if(len == -1) {
            perror("read");
            exit(0);
        } else if(len > 0) {
            printf("receive server data: %s\\
", receiveBuf);
        } else if (len == 0) {
            printf("server closed...");
        }
        
    }
    

    close(lfd);
}