libevent EVLOOP_NO_EXIT_ON_EMPTY无法正常工作吗? [英] libevent EVLOOP_NO_EXIT_ON_EMPTY not working?

问题描述

我不明白EVLOOP_NO_EXIT_ON_EMPTY标志在libevent的2.1.x版本中应该如何工作.

I don't understand how the EVLOOP_NO_EXIT_ON_EMPTY flag is supposed to work in version 2.1.x of libevent.

如果我未在event_base中添加任何事件，则

If I don't add any events to my event_base the

event_base_loop(my_base, EVLOOP_NO_EXIT_ON_EMPTY);

通话返回 立即，这根本不是我认为应该做的.

call returns immediately which is not at all what I think it's supposed to do.

如果我添加一个事件，它将与该未决事件一起循环，直到该事件变为活动状态为止，然后退出该循环，而我希望不会发生这种情况.

If I add an event it loops with that pending event until it get's active but then the loop exits which I hoped would not happen.

目标:

打开一个命名管道，并在libevent中侦听读取. 每当我

Have a named pipe open and libevent listening for a read. Whenever I

echo "something" > pipe

应调用已注册的回调.如果回调已完成，则事件返回到待处理状态，循环将等待另一个回声.

the registered callback should be called. If the callback has finished the event get's back to pending and the loop waits for another echo.

这是我到目前为止所得到的:(省略了错误检查)

Here's what I got so far: (error checking omitted)

#include <fcntl.h>
#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <event.h>
#include <unistd.h>

#define PIPE "/tmp/ev_pipe"


void cb_func(evutil_socket_t fd, short what, void *arg)
{
  printf("foo\n");
}

int main(void)
{
  /* create & open named pipe */
  mkfifo(PIPE, 0666);
  int socket = open(PIPE, O_RDONLY | O_NONBLOCK);

  /* libevent specific stuff */
  struct event_base *ev_base = event_base_new();
  struct event *ev = event_new(ev_base, (evutil_socket_t) socket, EV_READ, cb_func, NULL);
  event_add(ev, NULL);

  /* loop forever */
  event_base_loop(ev_base, EVLOOP_NO_EXIT_ON_EMPTY);

  printf("a\n");

  /* clean up */
  unlink(PIPE);
  event_base_free(ev_base);
  close(socket);

  return 0;
}

我想念什么?第一次写入队列后，事件循环退出:/

What am I missing? The event loop exits after the first write to the queue :/

感谢您的帮助！

推荐答案

该功能的实现似乎有问题！我在2.1.x版本中也遇到过同样的问题.解决该问题的一种方法是@Wizzard指出.解决该问题的另一种方法是将标志EV_PERSIST与功能event_new的events参数相符:

The implementation of the feature looks buggy! I had faced the same issue with the 2.1.x version. One way to get around the issue is as @Wizzard has pointed out. Another way of getting around the issue is OR the flag EV_PERSIST to the events argument to the function event_new:

struct event *ev = event_new(ev_base, 
    (evutil_socket_t) socket, EV_READ|EV_PERSIST, cb_func, NULL);

这将防止事件被删除. https://github.com/libevent/libevent/blob/master /include/event2/event.h +872

This will prevent the event from being removed. https://github.com/libevent/libevent/blob/master/include/event2/event.h +872

请注意，管道上有数据时，您可能会得到多个回调.

Please be aware that you might get multiple callbacks when there is data on pipe.

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