fork前后创建socket对 udp server的影响

结论:

Linux上五元组关系由socket 维护的(但是mac 和linux 表现还不一样)

代码:

udp-client.c

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

#define DEST_PORT 8080
#define DSET_IP_ADDRESS  "127.0.0.1"


int do_main()
{
  /* socket文件描述符 */
  int sock_fd;

  /* 建立udp socket */
  sock_fd = socket(AF_INET, SOCK_DGRAM, 0);
  if(sock_fd < 0)
  {
    perror("socket");
    exit(1);
  }

  /* 设置address */
  struct sockaddr_in addr_serv;
  int len;
  memset(&addr_serv, 0, sizeof(addr_serv));
  addr_serv.sin_family = AF_INET;
  addr_serv.sin_addr.s_addr = inet_addr(DSET_IP_ADDRESS);
  addr_serv.sin_port = htons(DEST_PORT);
  len = sizeof(addr_serv);


  int send_num;
  int recv_num;
  char send_buf[20] = "hey, who are you?";
  char recv_buf[20];
  while (1) {
    printf("client send: %s\n", send_buf);

    send_num = sendto(sock_fd, send_buf, strlen(send_buf), 0, (struct sockaddr *)&addr_serv, len);

    if(send_num < 0)
    {
      perror("sendto error:");
      exit(1);
    }
    sleep(1);
  }
  recv_num = recvfrom(sock_fd, recv_buf, sizeof(recv_buf), 0, (struct sockaddr *)&addr_serv, (socklen_t *)&len);

  if(recv_num < 0)
  {
    perror("recvfrom error:");
    exit(1);
  }

  recv_buf[recv_num] = '\0';
  printf("client receive %d bytes: %s\n", recv_num, recv_buf);

  close(sock_fd);

  return 0;
}
int main() {
  for (int i =0; i < 4; i++) {
    if (fork() == 0) { // 子进程  
        do_main();  
        exit(EXIT_SUCCESS); // 子进程处理完请求后退出  
    }  
  }
  // 父进程等待子进程结束（可选）  
  while (waitpid(-1, NULL, 0) > 0); 
  return 0;
}

udp-server.c

#include <iostream>  
#include <sys/socket.h>  
#include <netinet/in.h>  
#include <string.h>  
#include <unistd.h>  
#include <fcntl.h>  
#include <cstdlib>  
#include <sys/types.h>  
#include <sys/wait.h>  
#include <arpa/inet.h>
#define PORT 8080  
#define BUF_SIZE 1024  
  
void handle_client(int server_fd) { 
  while(1){ 
    char buffer[BUF_SIZE];  
    struct sockaddr_in client_addr;  
    socklen_t client_len = sizeof(client_addr);  
  
    int n = recvfrom(server_fd, buffer, BUF_SIZE, 0, (struct sockaddr*)&client_addr, &client_len);  
    if (n < 0) {  
        perror("recvfrom");  
        exit(1);  
    }  
  
    std::cout << "Received from " << inet_ntoa(client_addr.sin_addr) << ":" << ntohs(client_addr.sin_port)  
              << " in process " << getpid() << std::endl;  
    // 可以选择发送响应给客户端  
    // sendto(server_fd, buffer, n, 0, (struct sockaddr*)&client_addr, client_len);  
    }
}  
  
int main() {  
    int server_fd, new_socket;  
    struct sockaddr_in address;  
    int opt = 1;  
    int addrlen = sizeof(address);  
  
    if ((server_fd = socket(AF_INET, SOCK_DGRAM, 0)) == 0) {  
        perror("socket failed");  
        exit(EXIT_FAILURE);  
    }  
  
    if (setsockopt(server_fd, SOL_SOCKET, SO_REUSEPORT, &opt, sizeof(opt))) {  
        perror("setsockopt (SO_REUSEPORT) failed");  
        exit(EXIT_FAILURE);  
    }  
  
    address.sin_family = AF_INET;  
    address.sin_addr.s_addr = INADDR_ANY;  
    address.sin_port = htons(PORT);  
  
    if (bind(server_fd, (struct sockaddr *)&address, sizeof(address)) < 0) {  
        perror("bind failed");  
        exit(EXIT_FAILURE);  
    }  
  
    // 创建多个进程来处理客户端请求  
    for (int i = 0; i < 4; ++i) { // 假设我们创建5个进程  
        if (fork() == 0) { // 子进程  
            handle_client(server_fd);  
            exit(EXIT_SUCCESS); // 子进程处理完请求后退出  
        }  
    }  
  
    // 父进程等待子进程结束（可选）  
    while (waitpid(-1, NULL, 0) > 0);  
  
    close(server_fd);  
    return 0;  
}

udp-server2.c

#include <iostream>  
#include <sys/socket.h>  
#include <netinet/in.h>  
#include <string.h>  
#include <unistd.h>  
#include <fcntl.h>  
#include <cstdlib>  
#include <sys/types.h>  
#include <sys/wait.h>  
#include <arpa/inet.h>
#define PORT 8080  
#define BUF_SIZE 1024  
  
void handle_client(int server_fd) { 
  while(1){ 
    char buffer[BUF_SIZE];  
    struct sockaddr_in client_addr;  
    socklen_t client_len = sizeof(client_addr);  
    std::cout << "ready recv:" << getpid() << std::endl;
    int n = recvfrom(server_fd, buffer, BUF_SIZE, 0, (struct sockaddr*)&client_addr, &client_len);  
    if (n < 0) {  
        perror("recvfrom");  
        exit(1);  
    }  
  
    std::cout << "Received from " << inet_ntoa(client_addr.sin_addr) << ":" << ntohs(client_addr.sin_port)  
              << " in process " << getpid() << std::endl;  
    // 可以选择发送响应给客户端  
    // sendto(server_fd, buffer, n, 0, (struct sockaddr*)&client_addr, client_len);  
    }
}  
  
int do_main() {  
    int server_fd, new_socket;  
    struct sockaddr_in address;  
    int opt = 1;  
    int addrlen = sizeof(address);  
  
    if ((server_fd = socket(AF_INET, SOCK_DGRAM, 0)) == 0) {  
        perror("socket failed");  
        exit(EXIT_FAILURE);  
    }  
  
    if (setsockopt(server_fd, SOL_SOCKET, SO_REUSEPORT, &opt, sizeof(opt))) {  
        perror("setsockopt (SO_REUSEPORT) failed");  
        exit(EXIT_FAILURE);  
    }  
  
    address.sin_family = AF_INET;  
    address.sin_addr.s_addr = INADDR_ANY;  
    address.sin_port = htons(PORT);  
  
    if (bind(server_fd, (struct sockaddr *)&address, sizeof(address)) < 0) {  
        perror("bind failed");  
        exit(EXIT_FAILURE);  
    }  
    handle_client(server_fd);
    // // 创建多个进程来处理客户端请求  
    // for (int i = 0; i < 4; ++i) { // 假设我们创建5个进程  
    //     if (fork() == 0) { // 子进程  
    //         handle_client(server_fd);  
    //         exit(EXIT_SUCCESS); // 子进程处理完请求后退出  
    //     }  
    // }  
  
    // 父进程等待子进程结束（可选）  
    // while (waitpid(-1, NULL, 0) > 0);  
  
    close(server_fd);  
    return 0;  
}

int main() {
  for (int i =0; i < 4; i++) {
    if (fork() == 0) { // 子进程  
        do_main();  
        exit(EXIT_SUCCESS); // 子进程处理完请求后退出  
    }  
  }
  // 父进程等待子进程结束（可选）  
  while (waitpid(-1, NULL, 0) > 0); 
  return 0;
}

过程:

结果: