Linux IO multiplexing epoll network programming

#include <unistd.h>
#include <sys/types.h> /* basic system data types */
#include <sys/socket.h> /* basic socket definitions */
#include <netinet/in.h> /* sockaddr_in{} and other Internet defns */
#include <arpa/inet.h> /* inet(3) functions */
#include <sys/epoll.h> /* epoll function */
#include <fcntl.h> /* nonblocking */
#include <sys/resource.h> /*setrlimit */
#include <stdlib.h>
#include <errno.h>
#include <stdio.h>
#include <string.h>
#define MAXEPOLLSIZE 10000
#define MAXLINE 10240
int handle(int connfd);
int setnonblocking(int sockfd)
{
  if (fcntl(sockfd, F_SETFL, fcntl(sockfd, F_GETFD, 0)|O_NONBLOCK) == -1) {
    return -1;
  }
  return 0;
}
int main(int argc, char **argv)
{
  int servPort = 6888;
  int listenq = 1024;
  int listenfd, connfd, kdpfd, nfds, n, nread, curfds, acceptCount = 0;
  struct sockaddr_in servaddr, cliaddr;
  socklen_t socklen = sizeof(struct sockaddr_in);
  struct epoll_event ev;
  struct epoll_event events[MAXEPOLLSIZE];
  struct rlimit rt;
  char buf[MAXLINE];
  /* Set the maximum number of files each process is allowed to open */
  rt.rlim_max = rt.rlim_cur = MAXEPOLLSIZE;
  if (setrlimit(RLIMIT_NOFILE, &rt) == -1) 
  {
    perror("setrlimit error");
    return -1;
  }
  bzero(&servaddr, sizeof(servaddr));
  servaddr.sin_family = AF_INET; 
  servaddr.sin_addr.s_addr = htonl (INADDR_ANY);
  servaddr.sin_port = htons(servPort);
  listenfd = socket(AF_INET, SOCK_STREAM, 0); 
  if (listenfd == -1) {
    perror("can't create socket file");
    return -1;
  }
  int opt ​​= 1;
  setsockopt(listenfd, SOL_SOCKET, SO_REUSEADDR, &opt, sizeof(opt));
  if (setnonblocking(listenfd) < 0) {
    perror("setnonblock error");
  }
  if (bind(listenfd, (struct sockaddr *) &servaddr, sizeof(struct sockaddr)) == -1) 
  {
    perror("bind error");
    return -1;
  } 
  if (listen(listenfd, listenq) == -1) 
  {
    perror("listen error");
    return -1;
  }
  /* Create an epoll handle and add the listening socket to the epoll set*/
  kdpfd = epoll_create(MAXEPOLLSIZE);
  ev.events = EPOLLIN | EPOLLET;
  ev.data.fd = listenfd;
  if (epoll_ctl(kdpfd, EPOLL_CTL_ADD, listenfd, &ev) < 0) 
  {
    fprintf(stderr, "epoll set insertion error: fd=%d\n", listenfd);
    return -1;
  }
  curfds = 1;
  printf("epollserver startup,port %d, max connection is %d, backlog is %d\n", servPort, MAXEPOLLSIZE, listenq);
  for (;;) {
    /* Wait for an event to occur */
    nfds = epoll_wait(kdpfd, events, curfds, -1);
    if (nfds == -1)
    {
      perror("epoll_wait");
      continue;
    }
    /* Handle all events */
    for (n = 0; n < nfds; ++n)
    {
      if (events[n].data.fd == listenfd) 
      {
        connfd = accept(listenfd, (struct sockaddr *)&cliaddr,&socklen);
        if (connfd < 0) 
        {
          perror("accept error");
          continue;
        }
        sprintf(buf, "accept form %s:%d\n", inet_ntoa(cliaddr.sin_addr), cliaddr.sin_port);
        printf("%d:%s", ++acceptCount, buf);

        if (curfds >= MAXEPOLLSIZE) {
          fprintf(stderr, "too many connections, more than %d\n", MAXEPOLLSIZE);
          close(connfd);
          continue;
        } 
        if (setnonblocking(connfd) < 0) {
          perror("setnonblocking error");
        }
        ev.events = EPOLLIN | EPOLLET;
        ev.data.fd = connfd;
        if (epoll_ctl(kdpfd, EPOLL_CTL_ADD, connfd, &ev) < 0)
        {
          fprintf(stderr, "add socket '%d' to epoll failed: %s\n", connfd, strerror(errno));
          return -1;
        }
        curfds++;
        continue;
      } 
      // Process client request if (handle(events[n].data.fd) < 0) {
        epoll_ctl(kdpfd, EPOLL_CTL_DEL, events[n].data.fd,&ev);
        curfds--;
      }
    }
  }
  close(listenfd);
  return 0;
}
int handle(int connfd) {
  int nread;
  char buf[MAXLINE];
  nread = read(connfd, buf, MAXLINE); //Read client socket stream if (nread == 0) {
    printf("client close the connection\n");
    close(connfd);
    return -1;
  } 
  if (nread < 0) {
    perror("read error");
    close(connfd);
    return -1;
  }  
  write(connfd, buf, nread); //respond to the client return 0;
}

gcc epollserver.c -o epollserver
./epollserver