Path: utzoo!utgpu!news-server.csri.toronto.edu!clyde.concordia.ca!uunet!pcrat!rick
From: rick@pcrat.uucp (Rick Richardson)
Newsgroups: comp.windows.x
Subject: Re: XtAddTimeOut() and Timed Interrupts.
Message-ID: <1990Aug25.171200.8440@pcrat.uucp>
Date: 25 Aug 90 17:12:00 GMT
References: <9008231943.AA01202@crc.skl.dnd.ca> <141292@sun.Eng.Sun.COM>
Reply-To: rick@pcrat.UUCP (Rick Richardson)
Organization: PC Research, Inc., Tinton Falls, NJ
Lines: 57

In article <141292@sun.Eng.Sun.COM> argv@turnpike.Eng.Sun.COM (Dan Heller) writes:
>In article <9008231943.AA01202@crc.skl.dnd.ca> jgraham@CRC.SKL.DND.CA (Jay Graham) writes:
>>     We are developing an application on 386/ix and will need time
>>     interrupts in the 10s of milleseconds range, however when using
>>     XtAddTimeOut() with a 10ms interval we seem to be actually getting
>>     around a 20ms interval.  We assume that maybe there are communication

>Don't try to develop something similar -- this is the best resolution
>you're going to get, all things considered.  XtAddTimeOut() is closely
>tied to the select() system call.

On 386/ix, the STREAMS function poll() takes an argument in milliseconds,
but the actual resolution is 10 msecs.  I don't know what the select()
function uses, since I can't find any documentation for it.  I haven't
any knowledge of which one 386/ix uses for X, but my guess is that it
isn't poll, since you should be able to get down to 10 msecs.

Here is a little test program you can use to check the resolution
of poll().  Usage: polltest msecs.  The test should take 10 seconds
unless you specify an msecs value smaller than the resolution allowed.

-Rick

#include <sys/types.h>
#include <sys/times.h>
#include <sys/param.h>
#include <stropts.h>
#include <poll.h>

#define	SECS	10

/*
 *	Test program to verify timeout resolution of poll(2)
 *	Usage: polltest [ timeout_in_msecs ]
 */
main(argc, argv)
char	*argv[];
{
	struct tms	tms_dummy;
	struct pollfd	poll_dummy;
	int	i, msecs, ticks;
	long	start, end;

	msecs = (argc > 1) ? atoi(argv[1]) : 10;
	ticks = (SECS*1000)/msecs;
	start = times(&tms_dummy);
	for (i = 0; i < ticks; ++i)
		poll(&poll_dummy, 0, msecs);
	end = times(&tms_dummy);
	printf("%d sec. test took %f secs.\n", SECS, ((float) end-start)/HZ);
}

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