libevent，动态添加或删除事件，无需更改事件循环

Posted 2023-02-16

【中文标题】libevent，动态添加或删除事件，无需更改事件循环

【英文标题】：Libevent, add or remove events dynamically without having to change the event loop

【发布时间】：2015-03-19 10:12:05

【问题描述】：

我遇到的问题可能是对这句话真正含义的误解“应用程序只需要调用 event_dispatch()，然后动态添加或删除事件，而无需更改事件循环。”或者我找不到有关如何操作的正确文档。 好吧，问题是我认为我应该能够在使用 event_dispatch() 运行事件循环后将事件添加到事件循环中，但我无法让它工作。代码如下：

#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;

【参考方案1】：

我现在看到了...我不知道为什么，但我认为事件循环开始在另一个线程或类似的东西中运行。我现在看到我试图做的事情毫无意义。您可以在回调中添加事件，即在循环运行时。当您启动事件循环时，它永远不会返回，因此之后的所有内容都不会被调用（除非您停止事件循环）