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From: keegane@ittvax.UUCP (Edward Keegan)
Newsgroups: net.sources
Subject: Re: fsleep() -- sleep for fractional seconds (4.2 BSD)
Message-ID: <1659@ittvax.UUCP>
Date: Tue, 30-Apr-85 09:09:32 EDT
Article-I.D.: ittvax.1659
Posted: Tue Apr 30 09:09:32 1985
Date-Received: Thu, 2-May-85 00:47:12 EDT
References: <1432@utah-gr.UUCP>
Organization: ITT-ATC, Stratford Ct.
Lines: 205

> /*
s


s
s
  * fsleep( d ) -- Sleep for d seconds, where d is a double.  Like sleep()
>  *	but with a finer grain.  Uses the 4.2 BSD interval timer.
>  *
>  * Author:	Donn Seeley, UCSD Chemistry Dept., sdchema!donn
>  * Date:	Wed Apr 25 03:28:14 PST 1984
>  * Remarks:
>  *	If an alarm clock has gone off for the caller and alarms are being
>  *		blocked, the alarm is lost.  You'd think with all those new
>  *		system calls, there would be a way to find out what signals
>  *		have arrived without actually taking them...
>  *	You must define SLEEPBUG when compiling to get the 'feature' of
>  *		sleep() that signals other than alarms won't terminate
>  *		the sleep.
>  */
> 
> # include	<signal.h>
> # include	<sys/time.h>
> 
> # define	mask(s)		(1 << ((s) - 1))
> 
> # ifdef	SLEEPBUG
> static int	beep;
> # endif	SLEEPBUG
> 
> fsleep( d )
> 	double			d;
> {
> 	struct itimerval	oldalarm, newalarm;
> 	struct sigvec		oldvec, newvec;
> 	int			_fsleep_handler();
> 	int			savemask;
> 	int			wasblocked	= 0;
> 	int			alarmpending	= 0;
> 
> 	/*
> 	 * Sanity check.
> 	 */
> 	if ( d <= 0.0 )
> 		return;
> 
> 	/*
> 	 * Block the alarm signal.
> 	 */
> 	savemask	= sigblock( mask( SIGALRM ) );
> 	wasblocked	= savemask & mask( SIGALRM );
> 
> 	/*
> 	 * Get the old alarm time, set up the new one.
> 	 */
> 	newalarm.it_value.tv_sec	= (long) d;
> 	newalarm.it_value.tv_usec	=
> 		(long) ((d - (double) newalarm.it_value.tv_sec) * 1000000.0);
> 	timerclear( &newalarm.it_interval );
> 	if ( setitimer( ITIMER_REAL, &newalarm, &oldalarm ) < 0 ) {
> 		/*
> 		 * Illegal sleep time.
> 		 */
> 		(void) setitimer( ITIMER_REAL, &oldalarm, (struct itimerval *) 0 );
> 		(void) sigsetmask( savemask );
> 		return;
> 	}
> 
> 	/*
> 	 * Was there an alarm out there already?
> 	 */
> 	if ( timerisset( &oldalarm.it_value ) )
> 		++alarmpending;
> 	else if ( timerisset( &oldalarm.it_interval ) ) {
> 		/*
> 		 * Paranoia.
> 		 */
> 		++alarmpending;
> 		oldalarm.it_value.tv_usec	= 11000;
> 	}
> 
> 	/*
> 	 * If an old alarm would come while we slept, shorten the sleep.
> 	 */
> 	if ( alarmpending &&
> 	     ! timercmp( &oldalarm.it_value, &newalarm.it_value, > ) ) {
> 		(void) setitimer( ITIMER_REAL, &oldalarm, (struct itimerval *) 0 );
> 		if ( ! wasblocked ) {
> 			/*
> 			 * Just take the old alarm and return.
> 			 */
> 			sigpause( savemask );
> 			(void) sigsetmask( savemask );
> 			return;
> 		}
> 		/*
> 		 * Alarms are being blocked by the caller -- arrange to queue
> 		 * an alarm for the caller when the sleep finishes.
> 		 */
> 		newalarm.it_value	= oldalarm.it_value;
> 		{
> 			struct timeval	t;
> 
> 			timerclear( &t );
> 			t.tv_usec		= 11000;
> 			timevaladd( &oldalarm.it_value, &t );
> 		}
> 	}
> 
> 	/*
> 	 * Get the old signal handler, set up the new one.
> 	 */
> 	newvec.sv_handler	= _fsleep_handler;
> 	newvec.sv_mask		= savemask;
> 	newvec.sv_onstack	= 0;
> 	(void) sigvec( SIGALRM, &newvec, &oldvec );
> 
> 	/*
> 	 * Pause for the alarm.
> 	 */
> # ifdef	SLEEPBUG
> 	/*
> 	 * Duplicate disgusting sleep() behavior of only breaking for alarms.
> 	 */
> 	beep			= 0;
> 	while ( ! beep )
> # endif	SLEEPBUG
> 		sigpause( savemask & ~ mask( SIGALRM ) );
> 
> 	/*
> 	 * Reset the old signal handler and alarm.
> 	 */
> 	sigvec( SIGALRM, &oldvec, (struct sigvec *) 0 );
> 	if ( alarmpending ) {
> 		timevalsub( &oldalarm.it_value, &newalarm.it_value );
> 		(void) setitimer( ITIMER_REAL, (struct itimerval *) 0, &newalarm );
> 		timevaladd( &oldalarm.it_value, &newalarm.it_value );
> 		(void) setitimer( ITIMER_REAL, &oldalarm, (struct itimerval *) 0 );
> 	}
> 
> 	/*
> 	 * Reset the mask and return.  This unblocks the alarm if it was
> 	 *	unblocked previously, allowing any old alarm to arrive.
> 	 */
> 	(void) sigsetmask( savemask );
> 	return;
> }
> 
> 
> 
> /*
>  * _fsleep_handler() -- Dummy routine for handling alarms.
>  */
> int _fsleep_handler()
> {
> # ifdef	SLEEPBUG
> 	++beep;
> # endif	SLEEPBUG
> 	return 0;
> }
> 
> 
> 
> /*
>  * Add and subtract routines for timevals.
>  * Stolen from the kernel.
>  *
>  * N.B.: subtract routine doesn't deal with
>  * results which are before the beginning,
>  * it just gets very confused in this case.
>  * Caveat emptor.
>  */
> timevaladd(t1, t2)
> 	struct timeval *t1, *t2;
> {
> 
> 	t1->tv_sec += t2->tv_sec;
> 	t1->tv_usec += t2->tv_usec;
> 	timevalfix(t1);
> }
> 
> timevalsub(t1, t2)
> 	struct timeval *t1, *t2;
> {
> 
> 	t1->tv_sec -= t2->tv_sec;
> 	t1->tv_usec -= t2->tv_usec;
> 	timevalfix(t1);
> }
> 
> timevalfix(t1)
> 	struct timeval *t1;
> {
> 
> 	if (t1->tv_usec < 0) {
> 		t1->tv_sec--;
> 		t1->tv_usec += 1000000;
> 	}
> 	if (t1->tv_usec >= 1000000) {
> 		t1->tv_sec++;
> 		t1->tv_usec -= 1000000;
> 	}
> }

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