blocks|key|951430|text|CLOCK_REALTIME受到NTP的影响，可以向前和向后移动。CLOCK_MONOTONIC并非如此，它以每个节拍一个节拍的速度前进。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|951431|entityMap^0|0|E|X|F|0^^$0|@$1|2|3|4|5|6|7|H|8|@$9|I|A|J|B|C]|$9|K|A|L|B|C]]|D|@]|E|$]]|$1|F|3|-4|5|6|7|M|8|@]|D|@]|E|$]]]|G|$]]

<code>CLOCK_REALTIME</code> is affected by NTP, and can move forwards and backwards. <code>CLOCK_MONOTONIC</code> is not, and advances at one tick per tick.

blocks|key|951473|text|除了Ignacio's+answer之外，CLOCK_REALTIME还可以飞跃前进，偶尔也会后退。CLOCK_MONOTONIC两者都不做；它只是继续前进(尽管它可能会在重启时重置)。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|951474|一个健壮的应用程序需要能够容忍CLOCK_REALTIME偶尔向前跳跃(可能偶尔会非常轻微地向后跳跃，尽管这更多是一种边缘情况)。|951475|想象一下，当你挂起你的笔记本电脑时会发生什么--+CLOCK_REALTIME会在简历之后向前跳转，而CLOCK_MONOTONIC不会。在VM上试用它。|951476|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/a/3523482^0|L|E|1E|F|2|G|0|0|F|E|0|P|E|1F|F|0^^$0|@$1|2|3|4|5|6|7|R|8|@$9|S|A|T|B|C]|$9|U|A|V|B|C]]|D|@$9|W|A|X|1|Y]]|E|$]]|$1|F|3|G|5|6|7|Z|8|@$9|10|A|11|B|C]]|D|@]|E|$]]|$1|H|3|I|5|6|7|12|8|@$9|13|A|14|B|C]|$9|15|A|16|B|C]]|D|@]|E|$]]|$1|J|3|-4|5|6|7|17|8|@]|D|@]|E|$]]]|K|$L|$5|M|N|O|E|$P|Q]]]]

In addition to <a href="https://stackoverflow.com/a/3523482">Ignacio's answer</a>, <code>CLOCK_REALTIME</code> can go up forward in leaps, and occasionally backwards. <code>CLOCK_MONOTONIC</code> does neither; it just keeps going forwards (although it probably resets at reboot).

A robust app needs to be able to tolerate <code>CLOCK_REALTIME</code> leaping forwards occasionally (and perhaps backwards very slightly very occasionally, although that is more of an edge-case). 

Imagine what happens when you suspend your laptop - <code>CLOCK_REALTIME</code> jumps forwards following the resume, <code>CLOCK_MONOTONIC</code> does not. Try it on a VM.

blocks|key|951522|text|CLOCK_REALTIME表示机器对当前挂钟、一天中的时间的最佳猜测。正如Ignacio和MarkR所说，这意味着CLOCK_REALTIME可以随着系统时间时钟的改变而向前和向后跳转。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|951523|CLOCK_MONOTONIC表示自过去某个任意固定点以来经过的绝对挂钟时间。它不受系统时间时钟变化的影响。|951524|如果您希望计算在一台计算机上观察到的两个事件之间的运行时间，而不需要重新启动，则CLOCK_MONOTONIC是最佳选择。|951525|注意，在Linux上，CLOCK_MONOTONIC不会测量挂起所花费的时间，尽管根据POSIX的定义，它应该测量挂起时间。您可以将特定于Linux的CLOCK_BOOTTIME用于在挂起期间保持运行的单调时钟。|951526|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/questions/3523442/difference-between-clock-realtime-and-clock-monotonic/3523482#3523482|1|https://stackoverflow.com/questions/3523442/difference-between-clock-realtime-and-clock-monotonic/3523857#3523857^0|0|E|1M|E|12|7|0|1A|5|1|0|0|F|0|14|F|0|B|F|23|E|0^^$0|@$1|2|3|4|5|6|7|V|8|@$9|W|A|X|B|C]|$9|Y|A|Z|B|C]]|D|@$9|10|A|11|1|12]|$9|13|A|14|1|15]]|E|$]]|$1|F|3|G|5|6|7|16|8|@$9|17|A|18|B|C]]|D|@]|E|$]]|$1|H|3|I|5|6|7|19|8|@$9|1A|A|1B|B|C]]|D|@]|E|$]]|$1|J|3|K|5|6|7|1C|8|@$9|1D|A|1E|B|C]|$9|1F|A|1G|B|C]]|D|@]|E|$]]|$1|L|3|-4|5|6|7|1H|8|@]|D|@]|E|$]]]|M|$N|$5|O|P|Q|E|$R|S]]|T|$5|O|P|Q|E|$R|U]]]]

<code>CLOCK_REALTIME</code> represents the machine's best-guess as to the current wall-clock, time-of-day time. As <a href="https://stackoverflow.com/questions/3523442/difference-between-clock-realtime-and-clock-monotonic/3523482#3523482">Ignacio</a> and <a href="https://stackoverflow.com/questions/3523442/difference-between-clock-realtime-and-clock-monotonic/3523857#3523857">MarkR</a> say, this means that <code>CLOCK_REALTIME</code> can jump forwards and backwards as the system time-of-day clock is changed, including by NTP.

<code>CLOCK_MONOTONIC</code> 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.

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

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

blocks|key|1165698|text|CLOCK_REALTIME和MONOTONIC之间有一个很大的区别。CLOCK_REALTIME可以根据NTP向前或向后跳转。默认情况下，NTP允许时钟频率最多加快或减慢0.05%25，但NTP不能使单调时钟向前或向后跳跃。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1165699|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

There's one big difference between CLOCK_REALTIME and MONOTONIC. CLOCK_REALTIME can jump forward or backward according to NTP.
By default, NTP allows the clock rate to be speeded up or slowed down by up to 0.05%, but NTP cannot cause the monotonic clock to jump forward or backward.

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

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

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

Difference between CLOCK_REALTIME and CLOCK_MONOTONIC?

Linux

你能解释一下Linux上clock_gettime()返回的CLOCK_REALTIME和CLOCK_MONOTONIC时钟的区别吗？如果我需要计算外部源产生的时间戳和当前时间之间经过的时间，哪一个是更好的选择？最后，如果我有一个NTP守护进程定期调整系统时间，这些调整如何与CLOCK_REALTIME和CLOCK_M...

问CLOCK_REALTIME和CLOCK_MONOTONIC的区别是什么？
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