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From: Ian Kelly <ian.g.kelly@gmail.com>
Date: Fri, 5 Dec 2014 10:04:54 -0700
Subject: Re: time.monotonic() roll over
To: Python <python-list@python.org>
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On Thu, Dec 4, 2014 at 3:44 PM, Marko Rauhamaa <marko@pacujo.net> wrote:
>
> Ian Kelly <ian.g.kelly@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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<div dir=3D"ltr">On Thu, Dec 4, 2014 at 3:44 PM, Marko Rauhamaa &lt;<a href=
=3D"mailto:marko@pacujo.net">marko@pacujo.net</a>&gt; wrote:<br>&gt;<br>&gt=
; Ian Kelly &lt;<a href=3D"mailto:ian.g.kelly@gmail.com">ian.g.kelly@gmail.=
com</a>&gt;:<br>&gt;<br>&gt; &gt; It&#39;s not clear to me whether those ca=
ses are relevant to the rollover<br>&gt; &gt; concern anyway. I wouldn&#39;=
t be shocked if the GetTickCount() function<br>&gt; &gt; simply stopped inc=
reasing while the system is suspended, since after<br>&gt; &gt; all it&#39;=
s not &quot;ticking&quot; during that time.<br>&gt;<br>&gt; So, what&#39;s =
the semantics of time.sleep(), select.select() et al wrt<br>&gt; process or=
 machine suspension?<br><br><div>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 sle=
ep call would normally have ended.</div><div><br></div><div>&gt;&gt;&gt; im=
port time</div><div><div>&gt;&gt;&gt; def test():</div><div>... =C2=A0 t1 =
=3D time.time()</div><div>... =C2=A0 m1 =3D time.monotonic()</div><div>... =
=C2=A0 time.sleep(60)</div><div>... =C2=A0 t2 =3D time.time()</div><div>...=
 =C2=A0 m2 =3D time.monotonic()</div><div>... =C2=A0 return t2 - t1, m2 - m=
1</div></div><div>...</div><div>&gt;&gt;&gt; test()</div><div>(84.926424598=
69386, 60.002399999999994)<br></div><div><br></div><div>As you can see, the=
 sleep call and the monotonic time elapsed both appear to exclude the perio=
d when the VM was paused.</div><div><br></div><div>Then I tried the same wi=
th a MacBook and putting the system to sleep instead of pausing a VM:</div>=
<div><br></div><div>&gt;&gt;&gt; test()</div><div>(59.889225006103516, 60.0=
0102640298428)</div><div><br></div><div>Reducing the sleep time to 10 secon=
ds and suspending the process with Ctrl-Z produces a similar result on the =
MacBook:</div><div>(10.000508069992065, 10.000266332994215)<br></div><div><=
br></div><div>But the story is different in Linux. Here&#39;s what I got wi=
th the same Ctrl-Z test:</div><div>(16.000478506088257, 16.000478034024127)=
<br></div><div><br></div><div>I think the relative roundness of those numbe=
rs is just coincidence. I tried a second time and got:</div><div>(12.613622=
903823853, 12.613622067990946)<br></div><div><br></div><div>So it seems tha=
t it can go either way depending on the OS and perhaps the mechanism of sus=
pension.</div></div>

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