Linux Epool 使用学习笔记

头文件

#include 

接口和结构体

/* Creates an epoll instance.  Returns an fd for the new instance.
   The "size" parameter is a hint specifying the number of file
   descriptors to be associated with the new instance.  The fd
   returned by epoll_create() should be closed with close().  */
/*创建一个epool实例。为这个实例返回一个文件描述符。size参数是这个实例所关联的
文件描述符个数。返回的文件描述符应该被close接口关闭。*/
extern int epoll_create (int __size) __THROW;

/* Same as epoll_create but with an FLAGS parameter.  The unused SIZE
   parameter has been dropped.  */
/*和epool_create一样但是带着FLAGS参数。遗弃了size参数。*/
extern int epoll_create1 (int __flags) __THROW;

/* Valid opcodes ( "op" parameter ) to issue to epoll_ctl().  */
#define EPOLL_CTL_ADD 1 /* Add a file descriptor to the interface.  */
#define EPOLL_CTL_DEL 2 /* Remove a file descriptor from the interface.  */
#define EPOLL_CTL_MOD 3 /* Change file descriptor epoll_event structure.  */

/* Manipulate an epoll instance "epfd". Returns 0 in case of success,
   -1 in case of error ( the "errno" variable will contain the
   specific error code ) The "op" parameter is one of the EPOLL_CTL_*
   constants defined above. The "fd" parameter is the target of the
   operation. The "event" parameter describes which events the caller
   is interested in and any associated user data.  */
/*管理epfd代表的epool实例。如果成功返回0， 出错返回-1（出错码写入errno）。
op参数是上面定义的EPOLL_CTL_*中的一个。event参数包含调用者关心的的事件和对应的数据（触发类型，fd）*/
extern int epoll_ctl (int __epfd, int __op, int __fd,
              struct epoll_event *__event) __THROW;


/* Wait for events on an epoll instance "epfd". Returns the number of
   triggered events returned in "events" buffer. Or -1 in case of
   error with the "errno" variable set to the specific error code. The
   "events" parameter is a buffer that will contain triggered
   events. The "maxevents" is the maximum number of events to be
   returned ( usually size of "events" ). The "timeout" parameter
   specifies the maximum wait time in milliseconds (-1 == infinite).

   This function is a cancellation point and therefore not marked with
   __THROW.  */
/*等待发生在epfd表示的epool实例上的事件。返回值是在events参数中返回的event缓存的大小。
0或者-1代表出错，出错码保存在errno中。events参数指向包含触发数据的缓存。
maxevents表示返回缓存的最大数目。timeout参数指定最大等待时间（-1表示永久）。*/
extern int epoll_wait (int __epfd, struct epoll_event *__events,
               int __maxevents, int __timeout);

EPOLL_EVENTS

enum EPOLL_EVENTS
  {
    EPOLLIN = 0x001,
#define EPOLLIN EPOLLIN     
    EPOLLPRI = 0x002,
#define EPOLLPRI EPOLLPRI
    EPOLLOUT = 0x004,
#define EPOLLOUT EPOLLOUT
    EPOLLRDNORM = 0x040,
#define EPOLLRDNORM EPOLLRDNORM
    EPOLLRDBAND = 0x080,
#define EPOLLRDBAND EPOLLRDBAND
    EPOLLWRNORM = 0x100,
#define EPOLLWRNORM EPOLLWRNORM
    EPOLLWRBAND = 0x200,
#define EPOLLWRBAND EPOLLWRBAND
    EPOLLMSG = 0x400,
#define EPOLLMSG EPOLLMSG
    EPOLLERR = 0x008,
#define EPOLLERR EPOLLERR
    EPOLLHUP = 0x010,
#define EPOLLHUP EPOLLHUP
    EPOLLRDHUP = 0x2000,
#define EPOLLRDHUP EPOLLRDHUP
    EPOLLWAKEUP = 1u << 29,
#define EPOLLWAKEUP EPOLLWAKEUP
    EPOLLONESHOT = 1u << 30,
#define EPOLLONESHOT EPOLLONESHOT
    EPOLLET = 1u << 31
#define EPOLLET EPOLLET
  };

epoll_event 结构体

typedef union epoll_data
{
    void *ptr;
    int fd;
    uint32_t u32;
    uint64_t u64;
} epoll_data_t;

struct epoll_event
{
    uint32_t events;  /* Epoll events */
    epoll_data_t data;    /* User data variable */
} ;

实例代码

来自 :

http://blog.csdn.net/xiajun07061225/article/details/9250579

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

#define MAXEVENTS 64

//函数:
//功能:创建和绑定一个TCP socket
//参数:端口
//返回值:创建的socket
    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 successfully! */
            break;
        }

        close (sfd);
    }

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

    freeaddrinfo (result);

    return sfd;
}


//函数
//功能:设置socket为非阻塞的
    static int
make_socket_non_blocking (int sfd)
{
    int flags, s;

    //得到文件状态标志
    flags = fcntl (sfd, F_GETFL, 0);
    if (flags == -1)
    {
        perror ("fcntl");
        return -1;
    }

    //设置文件状态标志
    flags |= O_NONBLOCK;
    s = fcntl (sfd, F_SETFL, flags);
    if (s == -1)
    {
        perror ("fcntl");
        return -1;
    }

    return 0;
}

//端口由参数argv[1]指定
    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 ();
    }

    //除了参数size被忽略外,此函数和epoll_create完全相同
    efd = epoll_create1 (0);
    if (efd == -1)
    {
        perror ("epoll_create");
        abort ();
    }

    event.data.fd = sfd;
    event.events = EPOLLIN | EPOLLET;//读入,边缘触发方式
    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;
                        }
                    }

                    //将地址转化为主机名或者服务名
                    s = getnameinfo (&in_addr, in_len,
                            hbuf, sizeof hbuf,
                            sbuf, sizeof sbuf,
                            NI_NUMERICHOST | NI_NUMERICSERV);//flag参数:以数字名返回
                    //主机地址和服务地址

                    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 ("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;
}

运行方式：
在一个终端运行此程序：a.out PORT
另一个终端：telnet 127.0.0.1 PORT