[Python-Dev] cpython: Issue #10278: Add an optional strict argument to time.steady(), False by default

Tue Mar 20 08:33:51 CET 2012

I believe we should make a monotonic_time method that assures monotonicity
and be done with it. Forward steadiness can not be guaranteed. No
parameters.
On Mar 20, 2012 2:56 PM, "Steven D&apos;Aprano" <steve at pearwood.info> wrote:
> On Mon, Mar 19, 2012 at 01:35:49PM +0100, Victor Stinner wrote:
>> > Said differently: time.steady(strict=True) is always monotonic (*),
> > whereas time.steady() may or may not be monotonic, depending on what
> > is avaiable.
> >
> > time.steady() is a best-effort steady clock.
> >
> > (*) time.steady(strict=True) relies on the OS monotonic clock. If the
> > OS provides a "not really monotonic" clock, Python cannot do better.
>> I don't think that is true. Surely Python can guarantee that the clock
> will never go backwards by caching the last value. A sketch of an
> implementation:
>> def monotonic(_last=[None]):
> t = system_clock() # best effort, but sometimes goes backwards
> if _last[0] is not None:
> t = max(t, _last[0])
> _last[0] = t
> return t
>> Overhead if done in Python may be excessive, in which case do it in C.
>> Unless I've missed something, that guarantees monotonicity -- it may not
> advance from one call to the next, but it will never go backwards.
>> There's probably even a cleverer implementation that will not repeat the
> same value more than twice in a row. I leave that as an exercise :)
>> As far as I can tell, "steady" is a misnomer. We can't guarantee that
> the timer will tick at a steady rate. That will depend on the quality of
> the hardware clock.
>>> --
> Steven
>> _______________________________________________
> Python-Dev mailing list
> Python-Dev at python.org
> http://mail.python.org/mailman/listinfo/python-dev
> Unsubscribe:
> http://mail.python.org/mailman/options/python-dev/anacrolix%40gmail.com
>-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.python.org/pipermail/python-dev/attachments/20120320/08533aa7/attachment.html>