epoll程序示范

TCP server程序：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netdb.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/epoll.h>
#include <errno.h>
#include <netinet/in.h>


#define MAXEVENTS 64

//设置描述符为非阻塞模式；
static int make_socket_non_blocking (int sfd)
{
  int flags, s;

  flags = fcntl (sfd, F_GETFL, 0);
  if (flags == -1)
    {
      perror ("fcntl");
      return -1;
    }

  flags |= O_NONBLOCK;
  s = fcntl (sfd, F_SETFL, flags);
  if (s == -1)
    {
      perror ("fcntl");
      return -1;
    }

  return 0;
}

static int create_and_bind (char *port)
{
  struct addrinfo hints;
  struct addrinfo *result, *rp;
  int s, sfd;


  memset (&hints, 0, sizeof (struct addrinfo));
  hints.ai_family = AF_UNSPEC;     //IPv4 IPv6通用
  hints.ai_socktype = SOCK_STREAM; /* We want a TCP socket */
  hints.ai_flags = AI_PASSIVE;     //监听套接字；


  s = getaddrinfo (NULL, port, &hints, &result);
  if (s != 0)
    {
      fprintf (stderr, "getaddrinfo: %s\n", gai_strerror (s));
      return -1;
    }


  for (rp = result; rp != NULL; rp = rp->ai_next)
    {
      sfd = socket (rp->ai_family, rp->ai_socktype, rp->ai_protocol);
      if (sfd == -1)
        continue;


      s = bind (sfd, rp->ai_addr, rp->ai_addrlen);
      if (s == 0)
        {
          //绑定成功；
          break;
        }


      close (sfd);
    }


  if (rp == NULL)
    {
      fprintf (stderr, "Could not bind\n");
      return -1;
    }


  freeaddrinfo (result);


  return sfd;
}

int main (int argc, char *argv[])
{
  int sfd, s;
  int efd;
  struct epoll_event event;
  struct epoll_event *events;

  if (argc != 2)
    {
      fprintf (stderr, "Usage: %s [port]\n", argv[0]);
      exit (EXIT_FAILURE);
    }

  sfd = create_and_bind(argv[1]);
  
  if (sfd == -1)
    abort ();

  s = make_socket_non_blocking (sfd);
  if (s == -1)
    abort ();

  s = listen (sfd, SOMAXCONN);
  if (s == -1)
    {
      perror ("listen");
      abort ();
    }

  efd = epoll_create1 (0);
  if (efd == -1)
    {
      perror ("epoll_create");
      abort ();
    }

  event.data.fd = sfd;
  event.events = EPOLLIN | EPOLLET;//边沿触发（Level Triggered，电平触发）
  s = epoll_ctl (efd, EPOLL_CTL_ADD, sfd, &event);
  if (s == -1)
    {
      perror ("epoll_ctl");
      abort ();
    }

  /* Buffer where events are returned */
  events = calloc (MAXEVENTS, sizeof event);

  /* The event loop */
  while (1)
    {
      int n, i;

      n = epoll_wait (efd, events, MAXEVENTS, -1);
      for (i = 0; i < n; i++)
        {
          if ((events[i].events & EPOLLERR) ||
              (events[i].events & EPOLLHUP) ||
              (!(events[i].events & EPOLLIN)))
            {
              /* An error has occured on this fd, or the socket is not
                 ready for reading (why were we notified then?) */
              fprintf (stderr, "epoll error\n");
              close (events[i].data.fd);
              continue;
            }

          else if (sfd == events[i].data.fd)
            {
               //监听套接字可读，说明要建立新连接；
                while (1)
                {
                  struct sockaddr in_addr;
                  socklen_t in_len;
                  int infd;
                  char hbuf[NI_MAXHOST], sbuf[NI_MAXSERV];

                  in_len = sizeof in_addr;
                  infd = accept (sfd, &in_addr, &in_len);
                  if (infd == -1)
                    {
                      if ((errno == EAGAIN) ||
                          (errno == EWOULDBLOCK))
                        {
                          /* We have processed all incoming connections. */
                          break;
                        }
                      else
                        {
                          perror ("accept");
                          break;
                        }
                    }

                  s = getnameinfo (&in_addr, in_len,hbuf, sizeof hbuf,sbuf, sizeof sbuf,NI_NUMERICHOST | NI_NUMERICSERV);
                  //
                  if (s == 0)
                    {
                      printf("Accepted connection on descriptor %d (host=%s, port=%s)\n", infd, hbuf, sbuf);
                    }

                  //将已连接套接字描述符设为非阻塞模式，并添加到事件监听链表中；
                  s = make_socket_non_blocking (infd);
                  if (s == -1)
                    abort ();

                  event.data.fd = infd;
                  event.events = EPOLLIN | EPOLLET;
                  s = epoll_ctl (efd, EPOLL_CTL_ADD, infd, &event);
                  if (s == -1)
                    {
                      perror ("epoll_ctl");
                      abort ();
                    }
                }
              continue;
            }
          else
            {
              //已连接套接字上有数据到达，必须要完全读出数据，因为这在边沿触发模式；
              int done = 0;

              while (1)
                {
                  ssize_t count;
                  char buf[512];

                  count = read (events[i].data.fd, buf, sizeof buf);
                  if (count == -1)
                    {

                        //在非阻塞模式下errno == EAGAIN不代表错误，说明已读到全部数据；
                      if (errno != EAGAIN)
                        {
                          perror ("read");
                          done = 1;
                        }
                      break;
                    }
                  else if (count == 0)
                    {
                      //EOF ，说明客户端发来了FIN；
                      done = 1;
                      break;
                    }

                  /* Write the buffer to standard output */
                  s = write (1, buf, count);
                  if (s == -1)
                    {
                      perror ("write");
                      abort ();
                    }
                }

              if (done)
                {//每次处理完一个客户端的请求就关闭对应的connfd；
                  printf ("Closed connection on descriptor %d\n", events[i].data.fd);

                  /* Closing the descriptor will make epoll remove it
                     from the set of descriptors which are monitored. */
                  close (events[i].data.fd);
                }
            }
        }
    }

  free (events);

  close (sfd);

  return EXIT_SUCCESS;
}

---

  #include <sys/socket.h>

  #include <netdb.h>

  int getnameinfo(const struct sockaddr *sa, socklen_t salen,

                      char *host, size_t hostlen,

                      char *serv, size_t servlen, int flags);

getnameinfo函数以协议无关的方式从套接字地址格式得到字符展现形式

NI_NUMERICHOST，NI_NUMERICSERV 分别以数字的形式得到主机地址和服务端口

-------

#include<netdb.h>

int getaddrinfo( const char *hostname, const char *service, const struct addrinfo *hints, struct addrinfo **result );

参数说明

hostname:一个主机名或者地址串(IPv4的点分十进制串或者IPv6的16进制串)

service：服务名可以是十进制的端口号，也可以是已定义的服务名称，如ftp、http等

hints：可以是一个空指针，也可以是一个指向某个addrinfo结构体的指针，调用者在这个结构中填入关于期望返回的信息类型的暗示

result：本函数通过result指针参数返回一个指向addrinfo结构体链表的指针。