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

In message: <43630215.9050700_at_freebsd.org>
            David Xu <davidxu_at_freebsd.org> writes:
: M. Warner Losh wrote:
: 
: >: thread libraries use clock_gettime, this becauses there is
: >: pthread_cond_timedwait and other synchronization objects
: >: like rwlock, and mutex all have a timeout version, I think
: >: pthread_cond_timedwait is mostly used in some applications,
: >: though normally, application is not looking for high accuracy.
: >: they will get benefit from the clock_gettime speed improvement.
: >
: >And unfortuantely, the argument that needs to be passed to abstime is
: >unspecified, at leas tin our man page.  Also unfortuantely,
: >CLOCK_REALTIME seems to be what's required here (our man page just
: >says 'if the system time reaches the time specified in abstime'),
: >rather than CLOCK_MONOTONIC so jumps in system time can cause
: >previously short timeouts to become rather large timeouts...  This is
: >a flaw in the API. :-(
: >
: >Warner
: >  
: >
: I would rather to think it is brokeness of POSIX thread API specification,
: in real world, nobody uses the timeout as an absolute timestamp,  almost
: all applications are doing relative timeout sleep, if implementor 100%
: respects POSIX spec,  he will break many applications.
: libthr supports pthread_condattr_setclock, you can select CLOCK_MONOTONIC
: for pthread_cond_timedwait, but internally, all absolute timeout waits are
: converted to relative.

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