clarify that time_ns is monotonic #57129
Open
Conversation
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
stevengj
added
docs
LilithHafner
approved these changes
Jan 22, 2025
|
For reference, I also want link the discussion at w3c/hr-time#115 — it turns out that whether |
|
This should be backported to older versions, at least latest 1.10.x, not just its next minor version?! Specifically, and also pointing out, and asking about general doc policy, when it's not a new feature, but applied to the existing one, like here. |
IanButterworth
added
backport 1.10
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
Since
time_ns()is based onuv_hrtime, the docs should note that it is guaranteed to be monotonic (see also #2464 and this discourse thread). This PR also notes that you can't compare times across machines or reboots, and that the timing resolution is system-dependent.On Unix systems, it calls
clock_gettime(CLOCK_MONOTONIC, &t)and the GNU libc manual notes that the reference time "may change if the system is rebooted or suspended." On Windows, it callsQueryPerformanceCounter.(This docstring was last discussed in #54696.)
Also, I changed
To "The primary use is for measuring elapsed times during program execution" (emphasis added), since you don't want to use this to compare arbitrary "moments", e.g. from different runs of a program (that may span a system reboot).