Re: timeBeginPeriod considered harmful

[Christopher Faylor <me at cgf dot cx>]

On Sun, Nov 13, 2005 at 10:37:50PM -0500, Pierre A. Humblet wrote:
>At 06:16 PM 11/12/2005 -0500, Christopher Faylor wrote:
>>On Fri, Nov 11, 2005 at 05:47:17PM -0500, Pierre A. Humblet wrote:
>>>I worked on the resolution issue a while back, to insure the following
>>>Posix behavior (exim relies on it):
>>>If you 1) call time() or equivalent, 2) sleep() or alarm() for some
>>>interval, 3) call time() again, then the difference between the times in
>>>3) and 1) cannot be smaller than the interval in 2).  Insuring that is
>>>easier if the resolution is known.
>>>I am not sure if Cygwin still behaves that way, insuring it requiring
>>>rounding up at various places.
>>
>>I was thinking about the above in the thinking room today and it
>>occurred to me that the right way (tm) to fix this problem would be to
>>modify sleep/alarm so that the above is true.  alarm might be slightly
>>trickier than sleep but I don't think it would be unbelievably hard.  It
>>seems like adding a low_priority_sleep loop to nanosleep and alarm which
>>waits until the time delta was >= what was expected would be preferable
>>to forcing the resolution to 1ms for the whole program forever.
>
>I was just indicating what I had done with the time routines, this is not
>directly related to the 1 ms resolution (it was there before, as I recall).
>No matter what the resolution is, it should be possible to get it and do
>the right thing, for example in nanosleep:
>  DWORD resolution = gtod.resolution ();
>  DWORD req = ((rqtp->tv_sec * 1000 + (rqtp->tv_nsec + 999999) / 1000000
>                + resolution - 1) / resolution) * resolution;
>Your approach can surely also be made to work.
>I will take another look this week, on WinME and XP.

Ah.  I thought you were saying that you were relying on the 1ms
behavior.  I should have known better, though, since I have looked at
nanosleep recently.

I am not convinced that trying to factor in the resolution into the amount
of time to sleep is going to always do the right thing but I'm not overly
worried about it, I guess.  If the above expression is right then it should
continue to work even when the resolution is != 1ms, AFAICT.

cgf