Duration and TimePoint were introduced to map to the types in C++ (
http://en.cppreference.com/w/cpp/chrono).
Duration is negative so as not to surprise users when they do TimePoints A
- B and end up with a positive duration when B > A. You could imagine a
user of these writing code to check if their maintenance window is in the
past:
Duration remaining = Now - Scheduled;
if (remaining < 0) {
// Don't use offer.
} else {
// Still `remaining` time to use offer.
}
This logic would compile correctly and likely pass review because it is
intuitive; however, if duration was an absolute value, then it would be a
bug.
To represent infinity we currently wrap the Duration with an Option. The
None state represents infinity. You can find this in the protobufs.
—
*Joris Van Remoortere*
Mesosphere
On Wed, Mar 9, 2016 at 11:29 PM, Alexander Rojas <alexan...@mesosphere.io>
wrote:
> IMO durations should not be negative. The problem with having them define
> an infinite period is the following:
>
> Lets say you want to compute the duration between two durations A and B:
> C = A-B;
> if A < B, C is negative and it will be infinite.
>
> I one want’s to check for the case mentioned in [1] about sleeping 0
> marked with a negative duration, I think adding an explicit `if` is better
> since it reflects the intention.
>
> So in to conclude:
>
> 1. Duration operations should always be positive so A-B is effectively
> |A.underlying_type - B.underlying_type|.
> 2. We do need a constant or an specific trait to represent an infinite
> duration.
>
> > On 09 Mar 2016, at 17:20, Klaus Ma <klaus1982...@gmail.com> wrote:
> >
> > One case I can image is to use negative value for forever duration?
> >
> > ----
> > Da (Klaus), Ma (马达) | PMP® | Advisory Software Engineer
> > Platform OpenSource Technology, STG, IBM GCG
> > +86-10-8245 4084 | klaus1982...@gmail.com | http://k82.me
> >
> > On Wed, Mar 9, 2016 at 8:21 PM, Alex Rukletsov <a...@mesosphere.com>
> wrote:
> >
> >> Folks,
> >>
> >> I've recently realized that durations we use in mesos (stout's
> `Duration`
> >> and `DurationInfo` protobuf) are based on signed integers. Negative
> >> duration concept is a bit strange to me, so I googled around a bit and
> >> found an interesting thread [1].
> >>
> >> Was it an explicit intention to allow `Duration`s to be negative? Do we
> use
> >> this feature? If yes, maybe we can introduce a class representing time
> >> delta (can be negative) and base `Duration` on top of it guaranteeing
> it is
> >> always non-negative?
> >>
> >> My ultimate intention is to avoid boilerplate code that validates every
> >> single instance of `Duration` in the codebase. I'd rather have a class
> with
> >> guarantees certain invariants.
> >>
> >> [1]
> https://internals.rust-lang.org/t/unsigned-version-of-duration/893/2
> >>
>
>
