st: CPU usage for Stata loops (Windows)

[Nick Winter <nwinter@virginia.edu>]

Hi,

On my Windows XP [fully up to date, legal IC Stata 11 :-) ], the 
following consumes 30-50% of my system CPU time, according to the 
Windows Task Manager:

while 1 {
  sleep 500
}

Whereas this consumes essentially 0 CPU time:

while 1 {
  sleep 501
}


(On one computer the first loop consumes 50%, i.e. the total that Stata 
can use on my Dual Core processor; on a different computer it takes 
"only" 30-ish percent.  But on both systems there's a sharp drop to 
essentially nothing in the second loop.

Any ideas why?


An aside on why I care:

I'm writing a program in which Stata calls an external program and waits 
for it to finish before continuing.  I'd like to handle this with 
-winexec- followed by watching for the creation of a file by the 
external program to signal that it's done, rather than using 'shell' to 
make Stata wait, because I want Stata to spawn several of these 
processes and then wait for them *all* to finish.

So my strategy is to do something like this:

	winexec "c:\usrdata\autoit\sttest.exe"
	sleep 500
	capture confirm file "c:\temp\xxx.txt"
	while _rc {
		sleep 500
		capture confirm file "c:\temp\xxx.txt"
	}
	di "done!!!"


- Nick Winter


--
--------------------------------------------------------------
Nicholas Winter                                 434.924.6994 t
Assistant Professor                             434.924.3359 f
Department of Politics                  nwinter@virginia.edu e
University of Virginia          faculty.virginia.edu/nwinter w
PO Box 400787, 100 Cabell Hall
Charlottesville, VA 22904

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