libevent(十一)event

libevent使用event表示一个事件，结构如下:

struct event {
    TAILQ_ENTRY(event) ev_active_next;
    TAILQ_ENTRY(event) ev_next;
    /* for managing timeouts */
    union {
        TAILQ_ENTRY(event) ev_next_with_common_timeout;
        int min_heap_idx;
    } ev_timeout_pos;
    evutil_socket_t ev_fd;

    struct event_base *ev_base;

    union {
        /* used for io events */
        struct {
            TAILQ_ENTRY(event) ev_io_next;
            struct timeval ev_timeout;
        } ev_io;

        /* used by signal events */
        struct {
            TAILQ_ENTRY(event) ev_signal_next;
            short ev_ncalls;
            /* Allows deletes in callback */
            short *ev_pncalls;
        } ev_signal;
    } _ev;

    short ev_events;
    short ev_res;        /* result passed to event callback */
    short ev_flags;
    ev_uint8_t ev_pri;    /* smaller numbers are higher priority */
    ev_uint8_t ev_closure;
    struct timeval ev_timeout;

    /* allows us to adopt for different types of events */
    void (*ev_callback)(evutil_socket_t, short, void *arg);
    void *ev_arg;
};

有两个成员变量值得注意:

ev_events，描述事件类型，主要有以下几种:

#define EV_TIMEOUT  0x01
#define EV_READ     0x02
#define EV_WRITE    0x04
#define EV_SIGNAL   0x08
#define EV_PERSIST  0x10
#define EV_ET       0x20

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ev_flags，描述事件状态，主要有以下几种：

#define EVLIST_TIMEOUT  0x01
#define EVLIST_INSERTED 0x02
#define EVLIST_SIGNAL   0x04
#define EVLIST_ACTIVE   0x08
#define EVLIST_INTERNAL 0x10
#define EVLIST_INIT     0x80