Re: Timers and timing, was: MySQL Performance 6.0rc1

From: Daniel Eischen (deischen_at_freebsd.org)
Date: 10/29/05

  • Next message: Thomas Hurst: "Re: MySQL Performance 6.0rc1" 
    Date: Sat, 29 Oct 2005 10:38:20 -0400 (EDT)
To: David Xu <davidxu@freebsd.org>

    On Sat, 29 Oct 2005, David Xu wrote:

    > M. Warner Losh wrote:
    >
    > >Does this mean I can have a 1s wait, jump time back an hour and that
    > >the timeout will happen in a little under 1s?
    > >
    > >Warner
    > >
    > It is almost but not always, there is still a very small race window.

    POSIX also says that you are not guaranteed that your event
    occurred when you wake up (false wakeup) and that you should
    check for the event after waking up.

    Speaking of interfaces for time, Solaris has gethrtime() and
    gethrvtime():

      http://docs.sun.com/app/docs/doc/817-0692/6mgfnkuga?q=gethrtime&a=view

        The gethrtime() function returns the current high-resolution
        real time. Time is expressed as nanoseconds since some
        arbitrary time in the past; it is not correlated in any way to
        the time of day, and thus is not subject to resetting or
        drifting by way of adjtime(2) or settimeofday(3C). The hi-res
        timer is ideally suited to performance measurement tasks, where
        cheap, accurate interval timing is required.

        The gethrvtime() function returns the current high-resolution
        LWP virtual time, expressed as total nanoseconds of execution
        time. This function requires that micro state accounting be
        enabled with the ptime utility (see proc(1)).

        The gethrtime() and gethrvtime() functions both return an
        hrtime_t, which is a 64-bit (long long) signed integer.

    We've been using gethrtime() for timestamps in our Solaris
    applications for several years. As an API, the autoconf
    scripts might already detect it. 

    -- 
DE
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  • Next message: Thomas Hurst: "Re: MySQL Performance 6.0rc1"