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From: chris@umcp-cs.UUCP (Chris Torek)
Newsgroups: net.unix-wizards
Subject: Re: sub-second sleeps on BSD 4.2
Message-ID: <5173@umcp-cs.UUCP>
Date: Wed, 24-Apr-85 23:36:37 EST
Article-I.D.: umcp-cs.5173
Posted: Wed Apr 24 23:36:37 1985
Date-Received: Sat, 27-Apr-85 00:08:55 EST
References: <408@psivax.UUCP>
Organization: U of Maryland, Computer Science Dept., College Park, MD
Lines: 28

Your code is one big race condition.  If you aren't interested in
preserving the old interval timer, then use this (I've deleted the
unchanged code):

delay()
{
	int omask, nmask;
#define mask(x) (1 << ((x) - 1))

	signal(SIGALRM, nullfunc);
	wakeup = 0;
	omask = sigblock(mask(SIGALRM));
	nmask = omask & ~mask(SIGALRM);
	if (setitimer(ITIMER_REAL, &tm, (struct timeval *)NULL))
		exit(1);
	while (wakeup == 0)
		sigpause(nmask);
	sigsetmask(omask);
}

I'm assuming that sigpause() restores the signal mask that was in
effect before it's call; there is some very bogus-looking code in
the 4.2BSD kernel that is intended to do that, but I've never tested
it....
-- 
In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 4251)
UUCP:	{seismo,allegra,brl-bmd}!umcp-cs!chris
CSNet:	chris@umcp-cs		ARPA:	chris@maryland