如何在 Linux 中检测系统时间的变化? [英] How to detect change of system time in Linux?
问题描述
有没有办法在从时间服务器更新系统时间或由于 DST 更改时收到通知?我在进行 API/系统调用或等效调用.
Is there a way to get notified when there is update to the system time from a time-server or due to DST change? I am after an API/system call or equivalent.
在不使用 SQL 的情况下,将类似于 SQL NOW() 的值的生成优化到小时粒度是我努力的一部分.
It is part of my effort to optimise generating a value for something similar to SQL NOW() to an hour granularity, without using SQL.
推荐答案
你可以使用timerfd_create(2) 创建一个定时器,然后在设置时用 TFD_TIMER_CANCEL_ON_SET
选项标记它.将其设置为将来不合理的时间,然后对其进行阻止(使用轮询/选择等)-如果系统时间发生更改,则计时器将被取消,您可以检测到.
You can use timerfd_create(2) to create a timer, then mark it with the TFD_TIMER_CANCEL_ON_SET
option when setting it. Set it for an implausible time in the future and then block on it (with poll/select etc.) - if the system time changes then the timer will be cancelled, which you can detect.
(这是 systemd 是如何做到的)
例如:
#include <sys/timerfd.h>
#include <limits.h>
#include <stdio.h>
#include <unistd.h>
#include <errno.h>
int main(void) {
int fd = timerfd_create(CLOCK_REALTIME, 0);
timerfd_settime(fd, TFD_TIMER_ABSTIME | TFD_TIMER_CANCEL_ON_SET,
&(struct itimerspec){ .it_value = { .tv_sec = INT_MAX } },
NULL);
printf("Waiting
");
char buffer[10];
if (-1 == read(fd, &buffer, 10)) {
if (errno == ECANCELED)
printf("Timer cancelled - system clock changed
");
else
perror("error");
}
close(fd);
return 0;
}
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