8234397: add OS uptime information to os::print_os_info output

[Baesken, Matthias]

Hi Lutz,  I adjusted the days calculation,  new webrev :

http://cr.openjdk.java.net/~mbaesken/webrevs/8234397.2/

Best regards, Matthias



> Matthias,
> 
> your change looks good to me overall. Please note: I'm not a Reviewer!
> 
> I feel the urge to complain about one thing, though:
> When calculating the uptime in days, you divide the time retrieved from the
> system (usually seconds or milliseconds) by a large number. Why do you
> force that number to be a float? I would prefer the denominator to be an
> "int" value.
> 
> Rationale: floats (32bits) are very limited in precision, only y6 to 7 decimal
> digits. At least in the windows case, where you obtain milliseconds from the
> system, your denominator is 86,400,000. At first glance, that does not fit into
> a float mantissa. What saves you here are the prime factors "2" (10 in total).
> As a result, you only need 17 mantissa bits to represent the denominator.
> 
> Thanks,
> Lutz
> 
> On 25.11.19, 09:06, "hotspot-dev on behalf of Baesken, Matthias" <hotspot-
> dev-bounces at openjdk.java.net on behalf of matthias.baesken at sap.com>
> wrote:
> 
>     >
>     > The comment in the posix code mentions that it doesn't work on macOS
> but
>     > doesn't say anything about Linux. Has it been tested on Solaris?
>     >
> 
>     Hi David,  it works on Solaris .
>     I think I should adjust the comment (saying macOS AND Linux) .
> 
>     Best regards, Matthias
> 
> 
>     > >
>     > > One example that occurred last week  -  my colleague Christoph and me
>     > were browsing through an hs_err  file of a crash on AIX .
>     > > When looking into the hs_err  we wanted to know the  uptime because
>     > our latest  fontconfig - patches   (for getting rid of the crash)    needed a
>     > reboot too to really work .
>     > > Unfortunately we  could not find the info , and we were  disappointed
> (
>     > then we noticed the crash is from  OpenJDK and not our internal JVM ).
>     > >
>     > >
>     > >>> Bug/webrev :
>     > >>> https://bugs.openjdk.java.net/browse/JDK-8234397
>     > >>> http://cr.openjdk.java.net/~mbaesken/webrevs/8234397.1/
>     > >>
>     > >> Can Linux not use the POSIX version?
>     > >>
>     > >
>     > > Unfortunately the posix code does not give the desired result  on Linux
> (at
>     > least on my test machines).
>     >
>     > The comment in the posix code mentions that it doesn't work on macOS
> but
>     > doesn't say anything about Linux. Has it been tested on Solaris?
>     >
>     > I'm really unsure about this code and am hoping someone more
>     > knowledgeable in this areas can chime in. I'd be less concerned if there
>     > was a single POSIX implementation that worked everywhere. :( Though I
>     > have my general concern about adding yet another potential point of
>     > failure in the error reporting logic.
>     >
>     > Thanks,
>     > David
>     >
>     > > Best regards, Matthias
>     > >
>