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From: gwyn@brl-tgr.ARPA (Doug Gwyn <gwyn>)
Newsgroups: net.news.b,net.bugs.4bsd
Subject: Re: alarm() bug in 4.2
Message-ID: <3166@brl-tgr.ARPA>
Date: Tue, 10-Jul-84 23:56:12 EDT
Article-I.D.: brl-tgr.3166
Posted: Tue Jul 10 23:56:12 1984
Date-Received: Fri, 13-Jul-84 03:09:47 EDT
References: <282@voder.UUCP>
Organization: Ballistics Research Lab
Lines: 44

The following fixes the round-down behavior of 4.2BSD alarm(3):

/*
	alarm -- system call emulation for 4.2BSD

	last edit:	14-Dec-1983	D A Gwyn
*/

extern int	_setitimer();

typedef struct
	{
	unsigned long	tv_sec;		/* seconds */
	long		tv_usec;	/* microseconds */
	}	timeval;

typedef struct
	{
	timeval		it_interval;	/* timer interval */
	timeval		it_value;	/* current value */
	}	itimerval;

unsigned
alarm( sec )
	unsigned	sec;		/* timeout in seconds */
	{
	itimerval	newit;		/* new interval data */
	itimerval	oldit;		/* old interval data */

	/* set alarm clock timeout interval (0 disables) */
	newit.it_value.tv_sec = (unsigned long)sec;
	newit.it_value.tv_usec = 0L;

	/* avoid retriggering once timer expires */
	newit.it_interval.tv_sec = 0L;
	newit.it_interval.tv_usec = 0L;

	if ( _setitimer( 0, &newit, &oldit ) < 0 )	/* real time */
		return -1;
	/* SIGALRM now pending */

	return (unsigned)oldit.it_value.tv_sec +
			(oldit.it_value.tv_usec > 500L ? 1 : 0);
	}