time.monotonic() roll over

[Ian Kelly]

On Thu, Dec 4, 2014 at 3:44 PM, Marko Rauhamaa <marko at pacujo.net> wrote:
>
> Ian Kelly <ian.g.kelly at gmail.com>:
>
> > It's not clear to me whether those cases are relevant to the rollover
> > concern anyway. I wouldn't be shocked if the GetTickCount() function
> > simply stopped increasing while the system is suspended, since after
> > all it's not "ticking" during that time.
>
> So, what's the semantics of time.sleep(), select.select() et al wrt
> process or machine suspension?

Rather than continue to speculate, I just tested this. I ran the following
script in a Windows 7 VM and paused the VM for part of the duration of the
sleep call. I unpaused well before the sleep call would normally have ended.

>>> import time
>>> def test():
...   t1 = time.time()
...   m1 = time.monotonic()
...   time.sleep(60)
...   t2 = time.time()
...   m2 = time.monotonic()
...   return t2 - t1, m2 - m1
...
>>> test()
(84.92642459869386, 60.002399999999994)

As you can see, the sleep call and the monotonic time elapsed both appear
to exclude the period when the VM was paused.

Then I tried the same with a MacBook and putting the system to sleep
instead of pausing a VM:

>>> test()
(59.889225006103516, 60.00102640298428)

Reducing the sleep time to 10 seconds and suspending the process with
Ctrl-Z produces a similar result on the MacBook:
(10.000508069992065, 10.000266332994215)

But the story is different in Linux. Here's what I got with the same Ctrl-Z
test:
(16.000478506088257, 16.000478034024127)

I think the relative roundness of those numbers is just coincidence. I
tried a second time and got:
(12.613622903823853, 12.613622067990946)

So it seems that it can go either way depending on the OS and perhaps the
mechanism of suspension.
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