From: Harold Hausman <hhausman@...>
Date: 2007-04-28T00:57:26+09:00
Subject: Re: 10 millisecond delay/callback

On 4/27/07, Phrogz <gavin@refinery.com> wrote:
> On Apr 26, 2:06 pm, khai...@enigo.com wrote:
> > On Fri, 27 Apr 2007, Earle Clubb wrote:
> > > I need to perform a task every 10ms.  I've been using
> > > kernel.sleep(0.01), but sleep seems to be slow and erratic at sub-second
> > > resolutions.  Here's a test I ran along with the results:
> [snip]
> > Try select()
> [snip]
>
> No such glory on Windows:
>
> [snip]

I think Time.now.usec on windows is just whack. :P

Here's a quick c extension for windows that can do super accurate waiting:
///////////////////////////////////
#include "ruby.h"
#include "windows.h"

VALUE rb_cHotwait;
__int64 Hotwait_freq;

VALUE Hotwait_wait( VALUE inSelf, VALUE inWaitTime )
{
	__int64 theStartTime;
	__int64 theCounter;
	__int64 theDifference=0;
	double theWaitTime = NUM2DBL(inWaitTime);
	theWaitTime *= Hotwait_freq;
	QueryPerformanceCounter( &theStartTime );
	while( theDifference < theWaitTime )
	{
		QueryPerformanceCounter( &theCounter );
		theDifference = theCounter - theStartTime;
		Sleep(0);
	}
	
	return rb_float_new( (float)theDifference / (float)Hotwait_freq );
}

void Init_hotwait()
{
	QueryPerformanceFrequency( &Hotwait_freq );
	rb_cHotwait = rb_define_class( "Hotwait", rb_cObject );
	rb_define_singleton_method( rb_cHotwait, "wait", Hotwait_wait, 1 );
}
///////////////////////////////////

Used like this:
############
require 'hotwait'

10.times {
	puts "Time.now.usec   : #{Time.now.usec/1000}"
	puts "QueryPerfCounter: #{"%.4f"%Hotwait.wait( 0.01 )}"
}
############

It produces this:
Time.now.usec   : 718
QueryPerfCounter: 0.0100
Time.now.usec   : 718
QueryPerfCounter: 0.0100
Time.now.usec   : 734
QueryPerfCounter: 0.0100
Time.now.usec   : 750
QueryPerfCounter: 0.0100
Time.now.usec   : 750
QueryPerfCounter: 0.0100
Time.now.usec   : 765
QueryPerfCounter: 0.0100
Time.now.usec   : 781
QueryPerfCounter: 0.0100
Time.now.usec   : 796
QueryPerfCounter: 0.0100
Time.now.usec   : 796
QueryPerfCounter: 0.0100
Time.now.usec   : 812
QueryPerfCounter: 0.0100

And now it's past my bedtime. (:

-Harold