sleep()ing less than a second

[Marc Frajola]

In article <2754 at servax0.essex.ac.uk> peter at essex.ac.uk (Allott P) writes:
>In article <89348.231211BACON at MTUS5.BITNET> BACON at MTUS5.BITNET (Jeffery Bacon) writes:
>>Given sleep(arg); unsigned arg. Nothing new.
>>But what if you want to sleep for less than one second, say, 0.5?
>
>It is possible to "sleep" for less than one second by doing a
>selcect(.......) with an appropriate value in the timeval (5th param I think)
>and with no channels to check (2nd through 4th params I think).
>See the documentation for full details.

Hi...

    Some time ago, I was posed with the problem of doing the equivalent
of nap() on BSD. Since SysV had nap(), I decided to implement nap()
with BSD primitives. I've used it in one of my programs for the last
two years without problems (so it is SOMEWHAT tested). I distribute it
in nap.c and only compile it on BSD systems; SysV already has nap()
somewhere in a library.

    Following is my version of nap() -- please e-mail me if you make
useful enhancements/changes... Bon Appetit!

...Marc...
--
Marc Frajola, Tektronix Inc., Beaverton, OR
Phone: (503) 627-4340 (Tek) or (503) 643-5203 (Home)
InterNet-Style Address: marc at tekig3.PEN.TEK.COM
UUCP: ..!tektronix.TEK.COM!tekig3.PEN.TEK.COM!marc (Tek - Lab Scopes)
      ..!tektronix.TEK.COM!tessi.UUCP!escargot!marc (Home System e-mail)

---------- Cut here for 'nap.shar' -------------------------------------
#! /bin/sh
# This is a shell archive, meaning:
# 1. Remove everything above the #! /bin/sh line.
# 2. Save the resulting text in a file.
# 3. Execute the file with /bin/sh (not csh) to create the files:
#	nap.c
# This archive created: Tue Dec 19 15:39:41 1989
export PATH; PATH=/bin:$PATH
echo shar: extracting "'nap.c'" '(2496 characters)'
if test -f 'nap.c'
then
	echo shar: will not over-write existing file "'nap.c'"
else
sed 's/^X//' << \SHAR_EOF > 'nap.c'
X/*
X * Implementation of System-V style nap() on BSD Unix (4.2 and after)
X *
X * Copyright (C) 1987, 1988, 1989 by Marc A. Frajola
X *
X * Permission to use, copy, modify, and distribute this software and
X * its documentation for any purpose and without fee is hereby
X * granted, provided that the above copyright notice appear in all
X * copies and that both that copyright notice and this permission
X * notice appear in supporting documentation. This software is
X * provided "as is" without express or implied warranty.
X *
X * The nap() function under SysV may be implemented quite differently,
X * but the idea here is to delay a specified number of milliseconds
X * since sleep()'s granularity is only every second.
X *
X * This code is provided here is for BSD, and will function ONLY on a
X * 4.2bsd or later UNIX system.
X *
X * WARNING: This function will blow away any previous alarm setting if
X * the alarm() function uses setitimer().
X *
X * By Marc A. Frajola, 08/20/87
X *
X * $Header: nap.c,v 1.6 89/12/19 14:21:33 marc Exp $
X */
X
X#include <sys/time.h>
X#include <signal.h>
X
Xstatic int napwakeup();		/* Forward reference for wakeup function */
Xstatic int napdone;		/* Flag if nap() call is done */
X
X/*
X * Function for emulating System-V like nap() behavior using BSD
X * setitimer()
X */
Xnap(msec)
X    int msec;			/* Number of milliseconds to nap */
X{
X    struct itimerval value;	/* Timer value structure for setitimer() */
X    long usec;			/* Number of microseconds before alarm */
X    int (*oldsig)();		/* Old signal condition */
X
X    /* Set the timer reload values for no followup SIGALRMs: */
X    value.it_interval.tv_sec = 0;
X    value.it_interval.tv_usec = 0;
X
X    /* Set the current timer for the desired number of milliseconds: */
X    usec = msec * 1000;
X    value.it_value.tv_sec = msec / 1000;
X    value.it_value.tv_usec = usec % 1000000;
X
X    /*
X     * Set the timer, done flags, and wakeup procedure:
X     */
X    napdone = 0;
X    oldsig = signal(SIGALRM, napwakeup);
X    if (setitimer(ITIMER_REAL, &value, (struct itimerval *)0) < 0) {
X	perror("setitimer");
X	return;
X    }
X
X    /* Block the process until a SIGALRM comes in: */
X    do {
X	pause();
X    } while (napdone != 1);
X
X    /* Reset signal() state back to original condition: */
X    signal(SIGALRM, oldsig);
X
X    return;
X}
X
X/*
X * This function only gets executed so that pause() will unblock the
X * process.
X */
Xstatic
Xnapwakeup()
X{
X    /* Set flag so nap() knows the SIGALRM has actually come in: */
X    napdone = 1;
X
X    return;
X}
SHAR_EOF
if test 2496 -ne "`wc -c < 'nap.c'`"
then
	echo shar: error transmitting "'nap.c'" '(should have been 2496 characters)'
fi
fi # end of overwriting check
#	End of shell archive
exit 0