lkml.org 
[lkml]   [2023]   [Feb]   [21]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
SubjectRe: [PATCH] rust: time: New module for timekeeping functions
Date
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


\
 
 \ /
  Last update: 2023-03-27 00:30    [W:0.160 / U:0.632 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site