我正在写一个基于epoll的简单服务器类.为了唤醒epoll_wait(),我决定使用eventfd.据说它更适合于简单的事件交流,对此我表示同意.因此,我创建了活动并对其进行监视：

_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)");

稍后在消息等待循环中的另一个线程上：

    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;
        }
    }

当然,停止服务器的代码是：

eventfd_write(_eventfd, 1);

由于我无法解释的原因,我无法仅通过写入事件来唤醒epoll_wait().最终,这在几个调试会话中起作用.

这是我的解决方法：知道每次fd可供写入时EPOLLOUT都会触发一个事件,因此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)");

现在可以了,但是不应该这样.

我不认为这应该很困难.我做错了什么？

谢谢

解决方法:

为我工作.作为参考,下面是完整的C代码：它输出“ eventfd_write”,“ 1”和“ DING：1”.在Linux 2.6.35-30(通用#56-Ubuntu SMP)上进行了测试.

#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);
}