epoll函数

1)、epoll_create函数
    函数声明：int epoll_create(int size)
   该函数生成一个epoll专用的文件描述符，其中的参数是指定生成描述符的最大范围。

2)、epoll_ctl函数
   函数声明：int epoll_ctl(int epfd, int op, int fd, struct epoll_event *event)
   该函数用于控制某个文件描述符上的事件，可以注册事件，修改事件，删除事件。
参数：
   epfd：由 epoll_create 生成的epoll专用的文件描述符；
   op：要进行的操作，可能的取值EPOLL_CTL_ADD 注册、EPOLL_CTL_MOD 修改、   EPOLL_CTL_DEL 删除；
   fd：关联的文件描述符；
   event：指向epoll_event的指针；
   如果调用成功则返回0，不成功则返回-1。

3)、epoll_wait函数
   函数声明：int epoll_wait(int epfd,struct epoll_event * events,int maxevents,int timeout)
   该函数用于轮询I/O事件的发生。
   参数：
   epfd：由epoll_create 生成的epoll专用的文件描述符；
   epoll_event：用于回传代处理事件的数组；
   maxevents：每次能处理的事件数；
   timeout：等待I/O事件发生的超时值；

 

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

#include <sys/types.h>
#include <sys/socket.h>
#include <sys/epoll.h>
#include <netdb.h>

#define MAXEVENTS 64

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; /* Return IPv4 and IPv6 choices */
    hints.ai_socktype = SOCK_STREAM; /* We want a TCP socket */
    hints.ai_flags = AI_PASSIVE; /* All interfaces */

    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)
        {
            /* We managed to bind */
            break;
        }

        close (sfd);
    }

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

    freeaddrinfo (result);

    return sfd;
}


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;
}


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;
    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)
            {
                /* We have a notification on the listening socket, which
                means one or more incoming connections. */

                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);
                    }

                    /* Make the incoming socket non-blocking and add it to the
                    list of fds to monitor. */
                    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
            {
                /* We have data on the fd waiting to be read. Read and
                display it. We must read whatever data is available
                completely, as we are running in edge-triggered mode
                and won't get a notification again for the same
                data. */
                int done = 0;

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

                    count = read (events[i].data.fd, buf, sizeof buf);
                    if (count == -1)
                    {
                        /* If errno == EAGAIN, that means we have read all
                        data. So go back to the main loop. */
                        if (errno != EAGAIN)
                        {
                            perror ("read");
                            done = 1;
                        }
                        break;
                    }
                    else if (count == 0)
                    {
                        /* End of file. The remote has closed the
                        connection. */
                        done = 1;
                        break;
                    }

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

                if (done)
                {
                    printf ("\nClosed 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;
}

main() first calls create_and_bind() which sets up the socket. It then makes the socket non-blocking, and then calls listen(2). It then creates an epoll instance in efd, to which it adds the listening socket sfd to watch for input events in an edge-triggered mode.

The outer while loop is the main events loop. It calls epoll_wait(2), where the thread remains blocked waiting for events. When events are available, epoll_wait(2) returns the events in the events argument, which is a bunch of epoll_event structures.