Linux网络编程基础（四） select多路复用

 TCP虽然可以实现 IO非阻塞操作，但在实际应用时会对资源是否准备完毕进行循环测试，增加了不必要的CPU占用。

 

    为了解决这种问题，应用多路复用的知识，select()监听信号。相关知识可以参考 linux文件读写 文件锁 select poll。

 

         服务端：

 

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

#define PORT                4321
#define MAX_QUE_CONN_NM         5
#define MAX_SOCK_FD         FD_SETSIZE
#define BUFFER_SIZE         1024

int main(){
    struct sockaddr_in server_sockaddr, client_sockaddr;
    int sin_size, count;
    fd_set inset, tmp_inset;
    int sockfd, client_fd, fd;
    char buf[BUFFER_SIZE];

    if ((sockfd = socket(AF_INET, SOCK_STREAM, 0)) == -1){
        perror("socket");
        exit(1);
    }

    server_sockaddr.sin_family = AF_INET;
    server_sockaddr.sin_port = htons(PORT);
    server_sockaddr.sin_addr.s_addr = INADDR_ANY;
    bzero(&(server_sockaddr.sin_zero), 8);

    int i = 1;
    //设置socket的属性
    setsockopt(sockfd, SOL_SOCKET, SO_REUSEADDR, &i, sizeof(i));
    if (bind(sockfd, (struct sockaddr *)&server_sockaddr, sizeof(struct sockaddr)) == -1){
        perror("bind");
        exit(1);
    }

    if(listen(sockfd, MAX_QUE_CONN_NM) == -1){
        perror("listen");
        exit(1);
    }
    printf("listening....\n");
    //清空select集合
    FD_ZERO(&inset);
   //将要检测的文件符加入
   FD_SET(sockfd, &inset);

    while(1){
        tmp_inset = inset;
        sin_size=sizeof(struct sockaddr_in);
        memset(buf, 0, sizeof(buf));
        printf("run while...\n");
        //程序在此阻塞，select返回一个文件符，并将其他文件符清空
        if (!(select(MAX_SOCK_FD, &tmp_inset, NULL, NULL, NULL) > 0)){
            perror("select");
            close(sockfd);
            exit(1);
        }
        printf("run for...\n");
        for (fd = 0; fd < MAX_SOCK_FD; fd++){
            if (FD_ISSET(fd, &tmp_inset) > 0) {
                printf("fd is %d ,socket is %d\n",fd,sockfd);
                if (fd == sockfd){
                    if ((client_fd = accept(sockfd, (struct sockaddr *)&client_sockaddr, &sin_size))== -1){
                        perror("accept");
                        exit(1);
                    }

                    FD_SET(client_fd, &inset);
                    printf("New connection from %d(socket)\n", client_fd);
                }else{
                    if ((count = recv(fd, buf, BUFFER_SIZE, 0)) > 0){
                        printf("Received a message from %d: %s\n", fd, buf);
                    }else{
                        close(fd);
                        FD_CLR(fd, &inset);
                        printf("Client %d(socket) has left\n", fd);
                    }
                }
            } /* end of if FD_ISSET*/
        } /* end of for fd*/
    } /* end if while while*/

    close(sockfd);
    exit(0);
}

 

     客户端：

 

<span style="font-size:18px;">#include <sys/types.h>
#include <sys/socket.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/ioctl.h>
#include <unistd.h>
#include <netdb.h>
#include <netinet/in.h>

#define PORT    4321
#define BUFFER_SIZE 1024

int main(int argc, char *argv[]){
    int sockfd, sendbytes;
    char buf[BUFFER_SIZE];
    struct hostent *host;
    struct sockaddr_in serv_addr;

    if(argc < 3){
        fprintf(stderr,"USAGE: ./client Hostname(or ip address) Text\n");
        exit(1);
    }

    if ((host = gethostbyname(argv[1])) == NULL){
        perror("gethostbyname");
        exit(1);
    }

    memset(buf, 0, sizeof(buf));
    sprintf(buf, "%s", argv[2]);

    if ((sockfd = socket(AF_INET,SOCK_STREAM,0)) == -1){
        perror("socket");
        exit(1);
    }

    serv_addr.sin_family = AF_INET;
    serv_addr.sin_port = htons(PORT);
    serv_addr.sin_addr = *((struct in_addr *)host->h_addr);
    bzero(&(serv_addr.sin_zero), 8);

    if(connect(sockfd,(struct sockaddr *)&serv_addr, sizeof(struct sockaddr))== -1){
        perror("connect");
        exit(1);
    }

    if ((sendbytes = send(sockfd, buf, strlen(buf), 0)) == -1){
        perror("send");
        exit(1);
    }
    sleep(30);
    close(sockfd);
    exit(0);
}