6.4 检查事件状态

    2. #include <stdio.h>
    4. /* Change the callback and callback_arg of 'ev', which must not be
    5.  * pending. */
    6. int replace_callback(struct event *ev, event_callback_fn new_callback,
    7.     void *new_callback_arg)
    8. {
    9.     struct event_base *base;
    12.     int pending;
    14.     pending = event_pending(ev, EV_READ|EV_WRITE|EV_SIGNAL|EV_TIMEOUT,
    15.                             NULL);
    16.     if (pending) {
    17.         /* We want to catch this here so that we do not re-assign a
    18.          * pending event.  That would be very very bad. */
    19.         fprintf(stderr,
    20.         return -1;
    21.     }
    23.     event_get_assignment(ev, &base, &fd, &events,
    24.                          NULL /* ignore old callback */ ,
    25.                          NULL /* ignore old callback argument */);
    27.     event_assign(ev, base, fd, events, new_callback, new_callback_arg);
    28.     return 0;