epoll 定时器

参考：

Linux下使用epoll监听定时器-CSDN博客

但是这个用的是gettimeofday。

本人使用的是

#include <stdlib.h>
#include<stdio.h>
#include <sys/timerfd.h>
#include <sys/epoll.h>
#include <unistd.h>
#include <sys/time.h>
#include <stdint.h>void timer_expires(void)
{struct timespec curr;static struct timespec start;static int first_call = 1;if (first_call){first_call = 0;if (clock_gettime(CLOCK_MONOTONIC, &start) == -1)perror("clock_gettime");}if (clock_gettime(CLOCK_MONOTONIC, &curr) == -1)perror("clock_gettime");int secs, nsecs;secs = curr.tv_sec - start.tv_sec;nsecs = curr.tv_nsec - start.tv_nsec;if (nsecs < 0){secs--;nsecs += 1000000000;}printf("%d.%03d \n", secs, (nsecs + 500000) / 1000000);  //四舍五入纳秒转换为毫秒
}int main(int argc, char const *argv[])
{int timefd = timerfd_create(CLOCK_MONOTONIC, 0);if (timefd == -1){perror("timerfd_create failed");}struct itimerspec new_value = {};new_value.it_value.tv_sec = 1;new_value.it_value.tv_nsec = 0;new_value.it_interval.tv_sec = 5;new_value.it_interval.tv_nsec = 0;if (timerfd_settime(timefd, 0, &new_value, NULL) == -1){perror("timerfd_settime failed");}printf("time start-----------\n");timer_expires();/*-------------------------------------------------------------------------*/struct epoll_event ev;ev.data.fd = timefd;ev.events = EPOLLIN; // 文件描述符可读的时候就触发int epollfd = epoll_create(EPOLL_CLOEXEC);if (epollfd == -1){perror("epoll_create failed");}epoll_ctl(epollfd, EPOLL_CTL_ADD, timefd, &ev);/* int epoll_wait（int epfd，struct epoll_event * events， int maxevents，int timeout）;epfd ：epoll文件描述符events ：接口的返回参数，一般都是一个数组，数组长度大于等于maxevents。maxevents：期望捕获的事件的个数。timeout ：超时时间(>=0)，单位是毫秒ms，-1表示阻塞，0表示不阻塞*/const int maxEvents = 1; // 必须大于1struct epoll_event events[maxEvents];int buf[2];int ret = 0;int i =0;while (1){int nfd = epoll_wait(epollfd, events, maxEvents, -1);if (nfd == -1)perror("epoll_wait failed");for (i = 0; i < nfd; ++i){ret = read(events[i].data.fd, buf, sizeof(buf));if (ret < 0)perror("epoll callback read error");timer_expires();}}return 0;
}

会发现有0.1 的输出，是因为四舍五入的原因，如果要很精确，建议用gettimeofday(未处理）

在Linux中常用的时间结构有struct timespec 和struct timeval 。
下面是两个结构的定义

struct timespec
{
    __time_t tv_sec;        /* Seconds. */
    long   tv_nsec;       /* Nanoseconds. */
};
struct timeval {
　　      time_t tv_sec;  
　　      suseconds_t tv_usec;
}; 

两者的区别是timespec的第二个参数是纳秒数，而timeval的第二个参数是毫秒数。