Tracking issue for 'checked_duration_since' feature #58402

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1. jonas-schievink

   added

   T-libs-api[DEPRECATED; DO NOT USE][DEPRECATED; DO NOT USE]

   C-feature-requestCategory: A feature request, i.e: not implemented / a PR.Category: A feature request, i.e: not implemented / a PR.

   on Feb 12, 2019
2. dtolnay commented on Feb 15, 2019

   

   dtolnay

   on Feb 15, 2019

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   Some use cases from @vi:

   Most recent example from my code:

   let rtt4 = if now >= send_time { now - send_time } else { Duration::from_secs(999)};

   now.saturating_duration_since(send_time) would probably be OK for this, or a checked_duration_since with more explicit fallback.

   The comparison was added when I suddenly encountered a panic.

   A close call nearby:

   if now < deadline {
       sleeper.sleep(deadline - now);
   }

   Although readable as is, using saturating_duration_since would be almost equally good.

   That comparison is easy to miss, leading to panic when under load. Seeing checked/saturating analogues nearby in documentation puts one in "here be dragonsoverflows" mode and suggests care.
3. vi

   changed the title [-]No non-panicking analogue for Instant::duration_since[/-] [+]Tracking issue for 'checked_duration_since' feature[/+] on Feb 17, 2019
4. vi commented on Feb 20, 2019

   

   vi

   on Feb 20, 2019 · Hidden as resolved

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5. dtolnay

   added

   B-unstableBlocker: Implemented in the nightly compiler and unstable.Blocker: Implemented in the nightly compiler and unstable.

   C-tracking-issueCategory: An issue tracking the progress of sth. like the implementation of an RFCCategory: An issue tracking the progress of sth. like the implementation of an RFC

   and removed

   C-feature-requestCategory: A feature request, i.e: not implemented / a PR.Category: A feature request, i.e: not implemented / a PR.

   on Feb 20, 2019
6. faern commented on Mar 22, 2019

   

   faern

   on Mar 22, 2019

   Last edited by faern

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   I just had good use for Instant::checked_duration_since. It's a good method to have when working with deadlines, as compared to timeouts. I get a deadline: Instant handed to me, and I need to figure out how far into the future it is without risking a panic:

   deadline.checked_duration_since(Instant::now())
   
7. faern commented on Apr 3, 2019

   

   faern

   on Apr 3, 2019

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   I do like checked_duration_since, and I would like that function stabilized. It both lowers the amount of code needed and lowers the risk of screwing up some check and ending up with a panic. It's already used by parking_lot here and here. And it can use it in even more places when it's stable.

   However, I personally don't see the benefit of saturating_duration_since. It's a small convenience, but it does not help the user avoid panics like checked_duration_since does.

   In the example posted above, regarding saturating_duration_since:

   if now < deadline {
       sleeper.sleep(deadline - now);
   }

   The author hint that they would like to shorten it to:

   sleeper.sleep(deadline.saturating_duration_since(now));

   But it feels wasteful* to call sleep when we don't want to sleep, and I would personally have used:

   if let Some(time_left) = deadline.checked_duration_since(now) {
       sleeper.sleep(time_left);
   }

   If someone really want a saturating computation it's not that many extra characters to type deadline.checked_duration_since(now).unwrap_or(Duration::new(0, 0)).

   *: Assuming sleeper. means std::thread::, some platforms (Windows and CloudABI from what I can see) don't have any check if the duration is non-zero, and will actually perform the syscall even if the duration is zero.

   👍React with 👍1Reacted by Jeff VanDyke
8. vi

   added a commit that references this issue on Jul 21, 2019

   Stabilize checked_duration_since for 1.38.0

   ...

   This issue will close once commit 01d9e57 is merged into the 'master' branch.

   01d9e57
9. Centril

   added

   I-nominated

   on Jul 26, 2019
10. Centril

    added a commit that references this issue on Aug 9, 2019

    Rollup merge of rust-lang#62860 - vi:stabilize_checked_duration_since…

    ...

    This issue will close once commit 1b3e7fb is merged into the 'master' branch.

    1b3e7fb
11. alexcrichton commented on Sep 4, 2019

    

    alexcrichton

    on Sep 4, 2019

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    Removing nomination since this is covered by #62860
12. alexcrichton

    removed

    I-nominated

    on Sep 4, 2019
13. Centril

    added 2 commits that reference this issue on Sep 5, 2019

    Rollup merge of rust-lang#62860 - vi:stabilize_checked_duration_since…

    ...

    This issue will close once commit f062076 is merged into the 'master' branch.

    f062076

    Rollup merge of rust-lang#62860 - vi:stabilize_checked_duration_since…

    ...

    This issue will close once commit ee437eb is merged into the 'master' branch.

    ee437eb
14. bors

    closed this as completedin 843fba3on Sep 5, 2019
15. Centril

    added 2 commits that reference this issue on Mar 8, 2020

    Rollup merge of rust-lang#69561 - JohnTitor:clean-up-unstable-book, r…

    ...

    12920f4

    Rollup merge of rust-lang#69561 - JohnTitor:clean-up-unstable-book, r…

    ...

    d4860fc