libevent

libevent doc example

#include <event2/event.h>

void cb_func(evutil_socket_t fd, short what, void *arg)
{
        const char *data = arg;
        printf("Got an event on socket %d:%s%s%s%s [%s]",
            (int) fd,
            (what&EV_TIMEOUT) ? " timeout" : "",
            (what&EV_READ)    ? " read" : "",
            (what&EV_WRITE)   ? " write" : "",
            (what&EV_SIGNAL)  ? " signal" : "",
            data);
}

void main_loop(evutil_socket_t fd1, evutil_socket_t fd2)
{
        struct event *ev1, *ev2;
        struct timeval five_seconds = {5,0};
        struct event_base *base = event_base_new();

        /* The caller has already set up fd1, fd2 somehow, and make them
           nonblocking. */

        ev1 = event_new(base, fd1, EV_TIMEOUT|EV_READ|EV_PERSIST, cb_func,
           (char*)"Reading event");
        ev2 = event_new(base, fd2, EV_WRITE|EV_PERSIST, cb_func,
           (char*)"Writing event");

        event_add(ev1, &five_seconds);
        event_add(ev2, NULL);
        event_base_dispatch(base);
}

The event flags

EV_TIMEOUT

This flag indicates an event that becomes active after a timeout elapses.

The EV_TIMEOUT flag is ignored when constructing an event: you
can either set a timeout when you add the event, or not.  It is
set in the 'what' argument to the callback function when a timeout
has occurred.

EV_READ

This flag indicates an event that becomes active when the provided file descriptor is ready for reading.

EV_WRITE

This flag indicates an event that becomes active when the provided file descriptor is ready for writing.

EV_SIGNAL

Used to implement signal detection. See "Constructing signal events" below.

EV_PERSIST

Indicates that the event is persistent. See "About Event Persistence" below.

EV_ET

Indicates that the event should be edge-triggered, if the underlying event_base backend supports edge-triggered events. This affects the semantics of EV_READ and EV_WRITE.

若想将event当作参数传给回调函数，则可用使用event_self_cbarg函数（在2.1.1版本才引入）

#include <event2/event.h>

static int n_calls = 0;

void cb_func(evutil_socket_t fd, short what, void *arg)
{
    struct event *me = arg;

    printf("cb_func called %d times so far.
", ++n_calls);

    if (n_calls > 100)
       event_del(me);
}

void run(struct event_base *base)
{
    struct timeval one_sec = { 1, 0 };
    struct event *ev;
    /* We're going to set up a repeating timer to get called called 100
       times. */
    ev = event_new(base, -1, EV_PERSIST, cb_func, event_self_cbarg());
    event_add(ev, &one_sec);
    event_base_dispatch(base);
}

reference： http://www.wangafu.net/~nickm/libevent-book/Ref4_event.html