多路IO复用--Select-优快云博客

本文链接：https://blog.youkuaiyun.com/qq_43538607/article/details/138305824

本文介绍了如何利用`select`函数和`epoll`机制实现在一个服务器上同时处理多个客户端的正常连接，接收和发送数据，以及设置超时以优化性能。

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select

作用：实现多个客户端正常连接服务器，并且每个客户端正常的收发数据

api


#include <sys/select.h>
#include <sys/time.h>
#include <sys/types.h>
#include <unistd.h>
int select(int maxfdp, fd_set *readset, fd_set *writeset,fd_set *exceptset, struct timeval *timeout);

maxfdp：客户端IO的最大socekfd

readfds、writefds、exceptset：判读服务端IO是否可以读，可写，异常

timeout:用于设置select函数的超时时间

code

#include <fcntl.h>

#include <unistd.h>

#include <pthread.h>
#include <sys/epoll.h>
#include <string.h>


#define BUFFER_LENGTH	128
#define EVENTS_LENGTH	128

int main() {

    int listenfd = socket(AF_INET, SOCK_STREAM, 0);  //
    if (listenfd == -1) return -1;

    struct sockaddr_in servaddr;
    servaddr.sin_family = AF_INET;
    servaddr.sin_addr.s_addr = htonl(INADDR_ANY);
    servaddr.sin_port = htons(9999);

    if (-1 == bind(listenfd, (struct sockaddr*)&servaddr, sizeof(servaddr))) {
        return -2;
    }

    listen(listenfd, 10);
    fd_set rfds, wfds, rset, wset;

    FD_ZERO(&rfds);
    FD_SET(listenfd, &rfds);

    FD_ZERO(&wfds);

    int maxfd = listenfd;

    unsigned char buffer[BUFFER_LENGTH] = {0}; // 0
    int ret = 0;

    while (1) {
        rset = rfds;
        wset = wfds;
        int nready = select(maxfd+1, &rset, &wset, NULL, NULL);
        if (FD_ISSET(listenfd, &rset)) { 
            // map类型，在reset中查找listenfd所对应的值是否设置为1
            printf("listenfd --> \n");
            struct sockaddr_in client;
            socklen_t len = sizeof(client);
            int clientfd = accept(listenfd, (struct sockaddr*)&client, &len);
            
            FD_SET(clientfd, &rfds);
            if (clientfd > maxfd) maxfd = clientfd;
        }
        int i = 0;
        for (i = listenfd+1; i <= maxfd;i ++) {
            if (FD_ISSET(i, &rset)) { //
                ret = recv(i, buffer, BUFFER_LENGTH, 0);
                if (ret == 0) {
                    close(i);
                    FD_CLR(i, &rfds);
                } else if (ret > 0) {
                    printf("buffer : %s, ret: %d\n", buffer, ret);
                    FD_SET(i, &wfds);
                }
            } else if (FD_ISSET(i, &wset)) {
                ret = send(i, buffer, ret, 0); //
                FD_CLR(i, &wfds); //
                FD_SET(i, &rfds);
            }
        }
    }
 }