On Mon, 02 Aug 2010 15:49:08 -0500, "Yaakov (Cygwin/X)" wrote: > Here is an attempt to implement POSIX.1-2004+ Monotonic Clock: > > http://www.opengroup.org/onlinepubs/9699919799/functions/clock_getres.html > > In summary, I took hires_us and changed the resolution to nanoseconds. I > dropped systime() because the only place hires_us was being used is in > strace.cc which ignored it, and WRT POSIX monotonic clocks the absolute > value of the clock is meaningless. Since systime() has only 100ns > precision, using it would either force a loss in resolution or (if > multiplied by 100 to get ns) an early overflow. I also switched from > ENOSYS to EINVAL, as POSIX.1-2004 and 2008 dropped references to the > former (as noted in Change History). > > Patches for newlib, winsup/cygwin and winsup/doc attached. > > I have also attached an STC for the new functionality. FWIW, on my > machine, QueryPerformanceFrequency() returns just over 2.9 million, > resulting in a clock_getres(CLOCK_MONOTONIC) of 340ns. > > I would appreciate a careful review of this patch, both from the Cygwin > API and POSIX POVs. Is it really ok to use QueryPerformanceCounter() to implement this? Quote from <http://msdn.microsoft.com/en-us/library/ms644904%28VS.85%29.aspx>:
"On a multiprocessor computer, it should not matter which processor is called. However, you can get different results on different processors due to bugs in the basic input/output system (BIOS) or the hardware abstraction layer (HAL). To specify processor affinity for a thread, use the SetThreadAffinityMask function." This looks like you could get monotonic clock going backwards. -- VH
