CLOCK_REALTIME和CLOCK_MONOTONIC之间的区别? [英] Difference between CLOCK_REALTIME and CLOCK_MONOTONIC?

问题描述

您能解释一下Linux上clock_gettime()返回的CLOCK_REALTIME和CLOCK_MONOTONIC时钟之间的区别吗?

Could you explain the difference between CLOCK_REALTIME and CLOCK_MONOTONIC clocks returned by clock_gettime() on Linux?

如果我需要计算外部源产生的时间戳与当前时间之间的经过时间，哪个是更好的选择?

Which is a better choice if I need to compute elapsed time between timestamps produced by an external source and the current time?

最后，如果我有一个NTP守护程序定期调整系统时间，这些调整如何与CLOCK_REALTIME和CLOCK_MONOTONIC中的每一个相互作用?

Lastly, if I have an NTP daemon periodically adjusting system time, how do these adjustments interact with each of CLOCK_REALTIME and CLOCK_MONOTONIC?

推荐答案

CLOCK_REALTIME代表机器对于当前壁钟时间的最佳猜测.如 Ignacio 和MarkR 说，这意味着CLOCK_REALTIME可以在系统中前后跳转时间时钟已更改，包括通过NTP更改.

CLOCK_REALTIME represents the machine's best-guess as to the current wall-clock, time-of-day time. As Ignacio and MarkR say, this means that CLOCK_REALTIME can jump forwards and backwards as the system time-of-day clock is changed, including by NTP.

CLOCK_MONOTONIC表示自过去某个固定点以来经过的绝对时间.不受系统时间时钟变化的影响.

CLOCK_MONOTONIC represents the absolute elapsed wall-clock time since some arbitrary, fixed point in the past. It isn't affected by changes in the system time-of-day clock.

如果要计算在一台计算机上观察到的两个事件之间的间隔时间，而又不进行重新引导，那么CLOCK_MONOTONIC是最佳选择.

If you want to compute the elapsed time between two events observed on the one machine without an intervening reboot, CLOCK_MONOTONIC is the best option.

请注意，在Linux上，CLOCK_MONOTONIC不会衡量挂起所花费的时间，尽管它应该由POSIX定义.您可以使用特定于Linux的CLOCK_BOOTTIME来使单调时钟在挂起期间保持运行.

Note that on Linux, CLOCK_MONOTONIC does not measure time spent in suspend, although by the POSIX definition it should. You can use the Linux-specific CLOCK_BOOTTIME for a monotonic clock that keeps running during suspend.

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