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Re^2: Anything better than 'times' ?

by oshalla (Deacon)
on Sep 17, 2008 at 18:18 UTC ( #712087=note: print w/ replies, xml ) Need Help??

in reply to Re: Anything better than 'times' ?
in thread Anything better than 'times' ?

I had tried Time::HiRes::clock(), but that gives the same resolution as times. So I thought that was a dead end.

However, I went back and read again. There are Time::HiRes::clock_gettime($which) and Time::HiRes::getres($which). Where the $which is the name of a POSIX high resolution timer. I confess I had assumed that this was wall-clock.

The POSIX timer CLOCK_REALTIME claims a resolution of 1E-9 on my machine. Hurrah :-) However, that is wall-clock. Boo :-(

The Time::HiRes hints that there may be other timers... so, I went digging in the POSIX documentation. I found CLOCK_PROCESS_CPUTIME_ID, which does what the name suggests, and also claims a resolution of 1E-9 on my machine. Hurrah !

Conclusion, yes: turns out that Time::HiRes is the answer -- thank you. To know that, however, you need to know that:

  • there is a "clock" called CLOCK_PROCESS_CPUTIME_ID -- provided you have a POSIX compliant system, and _POSIX_CPUTIME is defined (which is discovered using getconf).
  • that you use can import that name from Time::HiRes and use it with Time::HiRes::clock_gettime($which) and Time::HiRes::getres($which) to access the timer.
  • there is also a "clock" called CLOCK_THREAD_CPUTIME_ID, which is available if _POSIX_THREAD_CPUTIME is defined.
So, for my purposes:
use Time::HiRes qw(clock_gettime CLOCK_PROCESS_CPUTIME_ID) ; $start = clock_gettime(CLOCK_PROCESS_CPUTIME_ID) ; # replaces $start + = (times)[0] ... $end = clock_gettime(CLOCK_PROCESS_CPUTIME_ID) ; # replaces $end + = (times)[0]
is the trick -- which I note in case it's of use to anyone like me who knew nothing of it until today.

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