epoll使用(服务端代码讲解）

 下面这段代码是一个回射服务器，它会把客户端发送给它的信息再返回给客户端。

#include <unistd.h>
#include <sys/types.h>
#include <fcntl.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <signal.h>
#include <sys/wait.h>
#include <sys/epoll.h>

#include <stdlib.h>
#include <stdio.h>
#include <errno.h>
#include <string.h>

#include <vector>
#include <algorithm>
#include <iostream>

typedef std::vector<struct epoll_event> EventList;

#define ERR_EXIT(n) do{perror(n);exit(EXIT_FAILURE);}while(0)

int main(void){
    signal(SIGPIPE,SIG_IGN);
    signal(SIGCHLD,SIG_IGN);

    int idlefd=open("/dev/null",O_RDONLY | O_CLOEXEC);
    int listenfd;
    if((listenfd=socket(PF_INET,SOCK_STREAM,IPPROTO_TCP))<0)
        ERR_EXIT("socket");

    struct sockaddr_in servaddr;
    memset(&servaddr,0,sizeof(servaddr));
    servaddr.sin_family=AF_INET;
    servaddr.sin_port=htons(5188);
    servaddr.sin_addr.s_addr=htonl(INADDR_ANY);

    int on=1;
    if(setsockopt(listenfd,SOL_SOCKET,SO_REUSEADDR,&on,sizeof(on))<0)
        ERR_EXIT("setsockopt");
    if(listen(listenfd,SOMAXCONN)<0)
        ERR_EXIT("listen");

    std::vector<int> clients;
    int epollfd;
    epollfd=epoll_create1(EPOLL_CLOEXEC);

    struct epoll_event event;
    event.data.fd=listenfd;
    event.events=EPOLIN;
    epoll_ctl(epollfd,EPOLL_CTL_ADD,listenfd,&event);

    EventList events(16);
    struct sockaddr_in peeraddr;
    socklen_t peerlen;
    int connfd;

    int nready;
    while(1){
        nready=epoll_wait(epollfd,&*events.begin(),static_cast<int>(events.size()),-1);
        if(nready==-1){
            if(errno==EINTR)
                continue;

            ERR_EXIT("epoll_wait");
        }
        if(nready==0){//没有事件发生
            continue;
        }
        if((size_t)nready==events.size())
            events.resize(events.size()*2);

        for(int i=0;i<nready;++i){
            if(events[i].data.fd==listenfd){
                peerlen=sizeof(peeraddr);
                connfd=::accept(listenfd,(struct sockaddr*)&peeraddr,&peerlen);

                if(connfd=