Messages in this thread | | | From | Thomas Gleixner <> | Subject | Re: [PATCH] rust: time: New module for timekeeping functions | Date | Tue, 21 Feb 2023 19:45:33 +0100 |
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On Wed, Feb 22 2023 at 01:31, Asahi Lina wrote: > On 22/02/2023 01.02, Thomas Gleixner wrote: >> I'm not rusty enough, but you really want two types: >> >> timestamp and timedelta >> >> timestamp is an absolute time on a specific clock which is read via >> now() and you can add time deltas to it. The latter is required for >> arming an absolute timer on the clock. >> >> timedelta is a relative time and completely independent of any >> clock. That's what you get when you subtract two timestamps, but you can >> also initialize it from a constant or some other source. timedelta can >> be used to arm a relative timer on any clock. > > If all clocks end up as the same `timestamp` though, then this isn't > fully safe, because you could subtract `timestamp`s that came from > different clocks and the result would be meaningless. That's why the > Rust std Instant is specifically tied to one and only one system clock > on each platform.
Fine, but do you agree that:
ts1 = tboot.now() ... ts2 = tboot.now()
xb = ts2 - ts1
then the result x1 cannot be the same data type as ts1, ts2.
From a typesafety perspective
ts1 = treal.now() ... ts2 = tboot.now()
x = ts2 - ts1
would be an invalid operation, but
ts1 = treal.now() ... ts2 = treal.now()
xr = ts2 - ts1
is obviously valid.
But xb abd xr are the same datatype because they represent a time delta.
That's the same the Rust std time semantics:
Duration = Instance - Instance valid Duration = Systemtime - SystemTime valid Duration = Systemtime - Instance invalid
No?
Thanks,
tglx
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