libevent，动态添加或删除事件而无需更改事件循环

Question

我遇到的问题可能是误解了这句话的真正含义 "An application just needs to call event_dispatch() and then add or remove events dynamically without having to change the event loop." 或者我找不到正确的文档来说明如何操作。好吧，问题是我认为我应该能够在运行之后使用 event_dispatch() 将事件添加到事件循环中，但我无法让它工作。这是代码：

#include <event2/event.h>
#include <event2/buffer.h>
#include <event2/bufferevent.h>

#include <stdio.h>

static int n_calls = 0;
static int n_calls2 = 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", ++n_calls);

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

void cb_func2(evutil_socket_t fd, short what, void *arg)
{
    struct event *me = arg;

    printf("cb_func2 called %d times so far.\n", ++n_calls2);

    if (n_calls2 > 100)
       event_del(me);
}

int main(int argc, char const *argv[])
{
    struct event_base *base;
    enum event_method_feature f;

    base = event_base_new();
    if (!base) {
        puts("Couldn't get an event_base!");
    } else {
        printf("Using Libevent with backend method %s.",
            event_base_get_method(base));
        f = event_base_get_features(base);
        if ((f & EV_FEATURE_ET))
            printf("  Edge-triggered events are supported.");
        if ((f & EV_FEATURE_O1))
            printf("  O(1) event notification is supported.");
        if ((f & EV_FEATURE_FDS))
            printf("  All FD types are supported.");
        puts("");
    }

    struct timeval one_sec = { 1, 0 };
    struct timeval two_sec = { 2, 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, NULL);
    event_add(ev, &one_sec);

    event_base_dispatch(base);

    // This event (two_sec) is never fired if I add it after calling event_base_dispatch. 
    // If I add it before calling event_base_dispatch it works as the other event (one_sec) also does.
    ev = event_new(base, -1, EV_PERSIST, cb_func2, NULL);
    event_add(ev, &two_sec);

    return 0;
}

Answer 1

我现在明白了...我不知道为什么，但我认为事件循环是在另一个线程或类似线程中开始的运行。我现在明白我试图做的事毫无意义。您可以在回调中添加事件，即当循环为运行时。当你启动事件循环时，它永远不会 returns 所以之后的一切都不会被调用（除非你停止事件循环）

libevent，动态添加或删除事件而无需更改事件循环

Libevent, add or remove events dynamically without having to change the event loop

events

libevent

event-loop

ansi-c