libevent（二）event_assign

信号或套接字都可以作为一个event的监听对象，并且一个信号或套接字可同时加入到多个event。
结构体struct event_base

结构体struct event：

struct event {
    struct event_callback ev_evcallback;

    /* for managing timeouts */
    union {
        TAILQ_ENTRY(event) ev_next_with_common_timeout;
        size_t min_heap_idx;
    } ev_timeout_pos;//管理定时器事件
    evutil_socket_t ev_fd;//监听对象套接字或信号

    struct event_base *ev_base;//所属event_base

    union {13
        /* used for io events */
        struct {
            LIST_ENTRY (event) ev_io_next;
            struct timeval ev_timeout;
        } ev_io;//套接字对象


        /* used by signal events */
        struct {
            LIST_ENTRY (event) ev_signal_next;
            short ev_ncalls;
            /* Allows deletes in callback */
            short *ev_pncalls;
        } ev_signal;//信号对象
    } ev_;


    short ev_events;//监听事件类型EV_READ...
    short ev_res;  //**事件类型     /* result passed to event callback */
    struct timeval ev_timeout;//定时器超时值
};

struct event_callback {
    TAILQ_ENTRY(event_callback) evcb_active_next;//**队列
    short evcb_flags;
    ev_uint8_t evcb_pri;//event的优先级    /* smaller numbers are higher priority */
    ev_uint8_t evcb_closure;
    /* allows us to adopt for different types of events */
        union {
        void (*evcb_callback)(evutil_socket_t, short, void *);
        void (*evcb_selfcb)(struct event_callback *, void *);
        void (*evcb_evfinalize)(struct event *, void *);
        void (*evcb_cbfinalize)(struct event_callback *, void *);
    } evcb_cb_union;//回调函数
    void *evcb_arg;//回调函数参数
};

创建event

struct event *
event_new(struct event_base *base, evutil_socket_t fd, short events, void (*             
cb)(evutil_socket_t, short, void *), void *arg)
{
    struct event *ev;
    ev = mm_malloc(sizeof(struct event));
    if (ev == NULL)
        return (NULL);
    if (event_assign(ev, base, fd, events, cb, arg) < 0) {
        mm_free(ev);
        return (NULL);
    }


    return (ev);
}

int
event_assign(struct event *ev, struct event_base *base, evutil_socket_t fd, short
events, void (*callback)(evutil_socket_t, short, void *), void *arg)
{
    if (!base)
        base = current_base;//current_base为全局指针，被初始化为NULL
    if (arg == &event_self_cbarg_ptr_)//event_self_cbarg_ptr_为全局指针，初始化为NULL
        arg = ev;


    if (!(events & EV_SIGNAL))
        event_debug_assert_socket_nonblocking_(fd);//如果event不是信号，判断套接字是否为非阻塞
    event_debug_assert_not_added_(ev);//判断此event是否是没有被"add"


    ev->ev_base = base;


    ev->ev_callback = callback;
    ev->ev_arg = arg;
    ev->ev_fd = fd;
    ev->ev_events = events;
    ev->ev_res = 0;
    ev->ev_flags = EVLIST_INIT;
    ev->ev_ncalls = 0;
    ev->ev_pncalls = NULL;


    if (events & EV_SIGNAL) {
        if ((events & (EV_READ|EV_WRITE|EV_CLOSED)) != 0) {
            event_warnx("%s: EV_SIGNAL is not compatible with "
                "EV_READ, EV_WRITE or EV_CLOSED", __func__);
            return -1;
        }
        ev->ev_closure = EV_CLOSURE_EVENT_SIGNAL;//如果event标志是信号，则判断是否还有EV_READ等标志，有就会出错，最后初始化ev_closure。
    } else {
        if (events & EV_PERSIST) {
            evutil_timerclear(&ev->ev_io_timeout);
            ev->ev_closure = EV_CLOSURE_EVENT_PERSIST;
       } else {
            ev->ev_closure = EV_CLOSURE_EVENT;
        }
    }//如果event为套接字（文件描述符）标志，则判断event是否设置EV_PERSIST标志，并设置ev_closure为对应宏


    min_heap_elem_init_(ev);


    if (base != NULL) {
        /* by default, we put new events into the middle priority */
        ev->ev_pri = base->nactivequeues / 2;//初始优先级
    }


    event_debug_note_setup_(ev);//加入event到全局队列global_debug_map


    return 0;
}

event_assign初始化中，会将ev_flag初始化为EVLIST_INIT。

event2/event_struct.h

#define EVLIST_TIMEOUT      0x01//event从属于定时器队列或者时间堆
#define EVLIST_INSERTED     0x02//event从属于注册队列
#define EVLIST_SIGNAL       0x04//没有使用
#define EVLIST_ACTIVE       0x08//event从属于活动队列
#define EVLIST_INTERNAL     0x10//该event是内部使用的。信号处理时有用到
#define EVLIST_ACTIVE_LATER 0x20
#define EVLIST_FINALIZING   0x40
#define EVLIST_INIT     0x80//event已经被初始化了
    
#define EVLIST_ALL          0xff//所有标志。这个不能取