[英]linux - Can't get eventfd to work with epoll together
I'm writing a simple server class based on epoll. 我正在编写一个基于epoll的简单服务器类。 In order to wake up
epoll_wait()
, I decided to use an eventfd. 为了唤醒
epoll_wait()
,我决定使用eventfd。 It is said that it is better suited for simple event communication and I agree with that. 据说它更适合简单的事件通信,我同意这一点。 So I created my event and put a watch on it:
所以我创建了我的活动并对其进行了观察:
_epollfd = epoll_create1(0);
if (_epollfd == -1) throw ServerError("epoll_create");
_eventfd = eventfd(0, EFD_NONBLOCK);
epoll_event evnt = {0};
evnt.data.fd = _eventfd;
evnt.events = _events;
if (epoll_ctl(_epollfd, EPOLL_CTL_ADD, _eventfd, &evnt) == -1)
throw ServerError("epoll_ctl(add)");
later in the message waiting loop, on a separate thread: 稍后在消息等待循环中,在一个单独的线程上:
int count = epoll_wait(_epollfd, evnts, EVENTS, -1);
if (count == -1)
{
if (errno != EINTR)
{
perror("epoll_wait");
return;
}
}
for (int i = 0; i < count; ++i)
{
epoll_event & e = evnts[i];
if (e.data.fd == _serverSock)
connectionAccepted();
else if (e.data.fd == _eventfd)
{
eventfd_t val;
eventfd_read(_eventfd, &val);
return;
}
}
and, of course, the code that stop the server was: 当然,停止服务器的代码是:
eventfd_write(_eventfd, 1);
For reasons that I can't explain, I was unable to wake up the epoll_wait()
just by writing to the event. 由于我无法解释的原因,我无法通过写入事件来唤醒
epoll_wait()
。 Eventually, this worked in a few debugging sessions. 最终,这在一些调试会话中起作用。
Here is my workaround: knowing that EPOLLOUT
will trigger an event every time the fd is available for writing, I changed the stop code to 这是我的解决方法:知道每次fd可用于写入时
EPOLLOUT
将触发事件,我将停止代码更改为
epoll_event evnt = {0};
evnt.data.fd = _eventfd;
evnt.events = EPOLLOUT;
if (epoll_ctl(_epollfd, EPOLL_CTL_MOD, _eventfd, &evnt) == -1)
throw ServerError("epoll_ctl(mod)");
Now it works but It shouldn't be this way. 现在它可以工作,但不应该这样。
I don't believe this should be any difficult. 我不相信这应该是困难的。 What have I done wrong?
我做错了什么?
Thanks 谢谢
Works for me. 适合我。 For reference, here is the complete C code: it prints "eventfd_write", "1" and "DING: 1".
作为参考,这里是完整的C代码:它打印“eventfd_write”,“1”和“DING:1”。 Tested on Linux 2.6.35-30-generic #56-Ubuntu SMP.
在Linux 2.6.35-30-通用#56-Ubuntu SMP上测试。
#include <stdio.h>
#include <errno.h>
#include <sys/epoll.h>
#include <sys/eventfd.h>
#include <pthread.h>
#include <stdlib.h>
int _epollfd, _eventfd;
int init()
{
_epollfd = epoll_create1(0);
if (_epollfd == -1) abort();
_eventfd = eventfd(0, EFD_NONBLOCK);
struct epoll_event evnt = {0};
evnt.data.fd = _eventfd;
evnt.events = EPOLLIN | EPOLLET;
if (epoll_ctl(_epollfd, EPOLL_CTL_ADD, _eventfd, &evnt) == -1)
abort();
}
void *subprocess(void *arg)
{
static const int EVENTS = 20;
struct epoll_event evnts[EVENTS];
while (1) {
int count = epoll_wait(_epollfd, evnts, EVENTS, -1);
printf("%d\n", count);
if (count == -1)
{
if (errno != EINTR)
{
perror("epoll_wait");
return NULL;
}
}
int i;
for (i = 0; i < count; ++i)
{
struct epoll_event *e = evnts + i;
if (e->data.fd == _eventfd)
{
eventfd_t val;
eventfd_read(_eventfd, &val);
printf("DING: %lld\n", (long long)val);
return NULL;
}
}
}
}
int main()
{
pthread_t th;
init();
if (pthread_create(&th, NULL, subprocess, NULL) != 0)
abort();
sleep(2);
printf("eventfd_write\n");
eventfd_write(_eventfd, 1);
sleep(2);
}
If you're using multiple threads you have to chain your call to eventfd_write
at the end of each thread. 如果您使用多个线程,则必须在每个线程结束时将调用链接到
eventfd_write
。 This is only one option. 这只是一种选择。
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