clarify that time_ns is monotonic #57129
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stevengj
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LilithHafner
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Jan 22, 2025
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For reference, I also want link the discussion at w3c/hr-time#115 — it turns out that whether |
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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
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KristofferC
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Jan 30, 2025
| be monotonic (mod 2⁶⁴) while the system is running, and is unaffected by clock drift or changes to local calendar time, | ||
| but it may change arbitrarily across system reboots or suspensions. | ||
| (Although the returned time is always in nanoseconds, the timing resolution is platform-dependent.) |
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Why is this in its own paragraph with parenthesis? Seems like it is just as relevant as the other text.
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Because I thought it was kind of obvious that units ≠ resolution (i.e. precision ≠ accuracy), so this paragraph is just a gentle reminder / clarification (since the preceding paragraph already says that the units are ns)? But if you want to remove the parens that's fine with me.
Co-authored-by: Kristoffer Carlsson <kcarlsson89@gmail.com>
This was referenced Mar 11, 2025
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Assuming this is ready to be merged. |
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Backported PRs: - [x] #54840 <!-- Add boundscheck in speccache_eq to avoid OOB access due to data race --> - [x] #42080 <!-- recommend explicit `using Foo: Foo, ...` in package code (was: "using considered harmful") --> - [x] #58127 <!-- [DOC] Update installation docs: /downloads/ => /install/ --> - [x] #58202 <!-- [release-1.11] malloc: use jl_get_current_task to fix null check --> - [x] #58584 <!-- Make `Ptr` values static-show w/ type-information --> - [x] #58637 <!-- Make late gc lower handle insertelement of alloca use. --> - [x] #58837 <!-- fix null comparisons for non-standard address spaces --> - [x] #57826 <!-- Add a `similar` method for `Type{<:CodeUnits}` --> - [x] #58293 <!-- fix trailing indices stackoverflow in reinterpreted array --> - [x] #58887 <!-- Pkg: Allow configuring can_fancyprint(io::IO) using IOContext --> - [x] #58937 <!-- Fix nthreadpools size in JLOptions --> - [x] #58978 <!-- Fix precompilepkgs warn loaded setting --> - [x] #58998 <!-- Bugfix: Use Base.aligned_sizeof instead of sizeof in Mmap.mmap --> - [x] #59120 <!-- Fix memory order typo in "src/julia_atomics.h" --> - [x] #59170 <!-- Clarify and enhance confusing precompile test --> Need manual backport: - [ ] #56329 <!-- loading: clean up more concurrency issues --> - [ ] #56956 <!-- Add "mea culpa" to foreign module assignment error. --> - [ ] #57035 <!-- linux: workaround to avoid deadlock inside dl_iterate_phdr in glibc --> - [ ] #57089 <!-- Block thread from receiving profile signal with stackwalk lock --> - [ ] #57249 <!-- restore non-freebsd-unix fix for profiling --> - [ ] #58011 <!-- Remove try-finally scope from `@time_imports` `@trace_compile` `@trace_dispatch` --> - [ ] #58062 <!-- remove unnecessary edge from `exp_impl` to `pow` --> - [ ] #58157 <!-- add showing a string to REPL precompile workload --> - [ ] #58209 <!-- Specialize `one` for the `SizedArray` test helper --> - [ ] #58108 <!-- Base.get_extension & Dates.format made public --> - [ ] #58356 <!-- codegen: remove readonly from abstract type calling convention --> - [ ] #58415 <!-- [REPL] more reliable extension loading --> - [ ] #58510 <!-- Don't filter `Core` methods from newly-inferred list --> - [ ] #58110 <!-- relax dispatch for the `IteratorSize` method for `Generator` --> - [ ] #58965 <!-- Fix `hygienic-scope`s in inner macro expansions --> - [ ] #58971 <!-- Fix alignment of failed precompile jobs on CI --> - [ ] #59066 <!-- build: Also pass -fno-strict-aliasing for C++ --> Contains multiple commits, manual intervention needed: - [ ] #55877 <!-- fix FileWatching designs and add workaround for a stat bug on Apple --> - [ ] #56755 <!-- docs: fix scope type of a `struct` to hard --> - [ ] #57809 <!-- Fix fptrunc Float64 -> Float16 rounding through Float32 --> - [ ] #57398 <!-- Make remaining float intrinsics require float arguments --> - [ ] #56351 <!-- Fix `--project=@script` when outside script directory --> - [ ] #57129 <!-- clarify that time_ns is monotonic --> - [ ] #58134 <!-- Note annotated string API is experimental in Julia 1.11 in HISTORY.md --> - [ ] #58401 <!-- check that hashing of types does not foreigncall (`jl_type_hash` is concrete evaluated) --> - [ ] #58435 <!-- Fix layout flags for types that have oddly sized primitive type fields --> - [ ] #58483 <!-- Fix tbaa usage when storing into heap allocated immutable structs --> - [ ] #58512 <!-- Make more types jl_static_show readably --> - [ ] #58012 <!-- Re-enable tab completion of kwargs for large method tables --> - [ ] #58683 <!-- Add 0 predecessor to entry basic block and handle it in inlining --> - [ ] #59112 <!-- Add builtin function name to add methods error --> Non-merged PRs with backport label: - [ ] #59329 <!-- aotcompile: destroy LLVM context after serializing combined module --> - [ ] #58848 <!-- Set array size only when safe to do so --> - [ ] #58535 <!-- gf.c: include const-return methods in `--trace-compile` --> - [ ] #58038 <!-- strings/cstring: `transcode`: prevent Windows sysimage invalidation --> - [ ] #57604 <!-- `@nospecialize` for `string_index_err` --> - [ ] #57366 <!-- Use ptrdiff_t sized offsets for gvars_offsets to allow large sysimages --> - [ ] #56890 <!-- Enable getting non-boxed LLVM type from Julia Type --> - [ ] #56823 <!-- Make version of opaque closure constructor in world --> - [ ] #55958 <!-- also redirect JL_STDERR etc. when redirecting to devnull --> - [ ] #55956 <!-- Make threadcall gc safe --> - [ ] #55534 <!-- Set stdlib sources as read-only during installation --> - [ ] #55499 <!-- propagate the terminal's `displaysize` to the `IOContext` used by the REPL --> - [ ] #55458 <!-- Allow for generically extracting unannotated string --> - [ ] #55457 <!-- Make AnnotateChar equality consider annotations --> - [ ] #55220 <!-- `isfile_casesensitive` fixes on Windows --> - [ ] #53957 <!-- tweak how filtering is done for what packages should be precompiled --> - [ ] #51479 <!-- prevent code loading from lookin in the versioned environment when building Julia --> - [ ] #50813 <!-- More doctests for Sockets and capitalization fix --> - [ ] #50157 <!-- improve docs for `@inbounds` and `Base.@propagate_inbounds` --> --------- Co-authored-by: Kiran Pamnany <kpamnany@users.noreply.github.com> Co-authored-by: adienes <51664769+adienes@users.noreply.github.com> Co-authored-by: Gabriel Baraldi <baraldigabriel@gmail.com> Co-authored-by: Keno Fischer <keno@juliacomputing.com> Co-authored-by: Simeon David Schaub <simeon@schaub.rocks> Co-authored-by: Jameson Nash <vtjnash@gmail.com> Co-authored-by: Alex Arslan <ararslan@comcast.net> Co-authored-by: Fons van der Plas <fonsvdplas@gmail.com> Co-authored-by: Ian Butterworth <i.r.butterworth@gmail.com> Co-authored-by: JonasIsensee <jonas.isensee@web.de> Co-authored-by: Curtis Vogt <curtis.vogt@gmail.com> Co-authored-by: Dilum Aluthge <dilum@aluthge.com> Co-authored-by: DilumAluthgeBot <43731525+DilumAluthgeBot@users.noreply.github.com> Co-authored-by: DilumAluthge <5619885+DilumAluthge@users.noreply.github.com>
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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).