epoll程序示例

TCP server程序：

#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 


#define MAXEVENTS 64

//設置描述符為非阻塞模式；
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;

      s = bind (sfd, rp->ai_addr, rp->ai_addrlen);
      if (s == 0)
        {
          //綁定成功；
          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 (htons(argv[1]));
  //注意這裡要轉為網絡字節序
  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;//邊沿觸發（Level Triggered，電平觸發）
  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)
            {
               //監聽套接字可讀，說明要建立新連接；
                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);
                    }

                  //將已連接套接字描述符設為非阻塞模式，並添加到事件監聽鏈表中；
                  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
            {
              //已連接套接字上有數據到達，必須要完全讀出數據，因為這在邊沿觸發模式；
              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不代表錯誤，說明已讀到全部數據；
                      if (errno != EAGAIN)
                        {
                          perror ("read");
                          done = 1;
                        }
                      break;
                    }
                  else if (count == 0)
                    {
                      //EOF ，說明客戶端發來了FIN；
                      done = 1;
                      break;
                    }

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

              if (done)
                {//每次處理完一個客戶端的請求就關閉對應的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;
}

結構體epoll_event被用於注冊希望監聽的事件和反饋發生的事件，定義如下：

typedef union epoll_data {
void *ptr;
int fd;
__uint32_t u32;
__uint64_t u64;
} epoll_data_t;//保存觸發事件的某個文件描述符相關的數據

struct epoll_event {
__uint32_t events; /* epoll event */
epoll_data_t data; /* User data variable */
};