echo服务端-单线程+epoll

epoll的作用
- 实现IO多路复用，在单线程下同时与多个client建立连接，并行处理多个请求
- 注意这里不是并发，因为只有一个线程，仍然是顺序处理，不存在竞态条件，同时节约了多线程或多进程切换的开销
- 仅支持Linux环境
如果单线程下不使用epoll，那么
- 当前线程就会堵塞在serv_sock的accept函数上
- 只有来一个client请求，才会进入处理流程，等结束此连接，才能继续调用accept函数等待下一个client请求

echo_server.c

#include <stdio.h> //printf、fput
#include <stdlib.h> //atoi
#include <string.h> //memset
#include <unistd.h> //write、close
#include <arpa/inet.h> //sockaddr_in结构、INADDR_ANY
#include <sys/socket.h>
#include <sys/epoll.h> 
#define BUF_SIZE 100
#define EPOLL_SIZE 50

int main(int argc, char *argv[]) {
    char buf[BUF_SIZE];
    if (argc != 2) {
        printf("Usage: %s <port>\n", argv[0]);
        exit(1);
    }
    
    int serv_sock = socket(PF_INET, SOCK_STREAM, 0);
    if (serv_sock == -1) {
        fputs("socket() error", stderr);
        exit(1);
    }

    struct sockaddr_in serv_addr;
    memset(&serv_addr, 0, sizeof(serv_addr)); //全部位置0
    serv_addr.sin_family = AF_INET; //
    serv_addr.sin_addr.s_addr = htonl(INADDR_ANY); //等价于绑定到"0.0.0.0"
    serv_addr.sin_port = htons(atoi(argv[1])); //取1号参数作为端口

    if (bind(serv_sock, (struct sockaddr*) &serv_addr, sizeof(serv_addr)) == -1) {
        fputs("bind() error", stderr);
        exit(1);
    }

    if (listen(serv_sock, 5) == -1) {
        fputs("listen() error", stderr);
        exit(1);
    }

    int epfd = epoll_create(50); //创建

    struct epoll_event event;
    event.events = EPOLLIN;
    event.data.fd = serv_sock;
    epoll_ctl(epfd, EPOLL_CTL_ADD, serv_sock, &event); //注册

    struct epoll_event* ep_events;
    ep_events = malloc(sizeof(struct epoll_event) * EPOLL_SIZE);

    int event_cnt;
    while(1) {
        event_cnt = epoll_wait(epfd, ep_events, EPOLL_SIZE, -1);
        if (event_cnt == -1) {
            fputs("epoll_wait() error", stderr);
            break;
        }

        for (int i = 0; i < event_cnt; i++) {
            if (ep_events[i].data.fd == serv_sock) {
                struct sockaddr_in clnt_addr;
                socklen_t clnt_addr_size = sizeof(clnt_addr);
                int clnt_sock = accept(serv_sock, (struct sockaddr*) &clnt_addr, &clnt_addr_size);
                if (clnt_sock == -1) {
                    fputs("accept() error", stderr);
                    continue;
                }
                event.events = EPOLLIN;
                event.data.fd = clnt_sock;
                epoll_ctl(epfd, EPOLL_CTL_ADD, clnt_sock, &event);
            } else {
                int clnt_sock = ep_events[i].data.fd;
                int str_len = read(clnt_sock, buf, BUF_SIZE);
                if (str_len == 0) {
                    epoll_ctl(epfd, EPOLL_CTL_DEL, clnt_sock, NULL);
                    close(clnt_sock);
                    printf("close client sock: %d \n", clnt_sock);
                } else {
                    write(clnt_sock, buf, str_len); //echo
                }
            }
        }
    }
    
    close(serv_sock);
    close(epfd);
    return 0;
}

编译——需要在Linux环境执行
```
gcc echo_server.c -o eserver
```
执行
```
./eserver 8100
```

Keyboard shortcuts

echo服务端-单线程+epoll

echo_server.c