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From: chris@mimsy.UUCP (Chris Torek)
Newsgroups: comp.lang.c,comp.unix.questions
Subject: Re: msleep
Message-ID: <9310@mimsy.UUCP>
Date: Wed, 11-Nov-87 20:18:41 EST
Article-I.D.: mimsy.9310
Posted: Wed Nov 11 20:18:41 1987
Date-Received: Sat, 14-Nov-87 06:01:38 EST
References: <332@PT.CS.CMU.EDU>
Organization: U of Maryland, Dept. of Computer Science, Coll. Pk., MD 20742
Lines: 37
Keywords: sleep millisecs
Xref: mnetor comp.lang.c:5384 comp.unix.questions:4885

In article <332@PT.CS.CMU.EDU> edw@IUS1.CS.CMU.EDU (Eddie Wyatt) writes:
>/**************************************************************************
> *                                                                        *
> *                        msleep                                          *
> *                                                                        *
> **************************************************************************
>
>   Purpose :   What you all been waiting for -- A sleep that works in
>	     microseconds!!!.  Actually it depends on the granularity
>	     of the interrupt timer, but at least its better than
>	     the second wait.

... followed by code that uses setitimer.

0) Only certain 4BSD-based operating systems *have* setitimer.
   (What this *really* means is that if you need a sleep that works
   in milliseconds or microseconds or whatever, using a routine
   like msleep is imperative.  Then the victim, er, user, of your
   code need rewrite only msleep.)

1) you can (and, I think, should) avoid the critical section by using
   sigblock and sigsetmask (see man 2 sigblock).

2) using setitimer is more expensive than calling select with three
   `(fd_set *)0' arguments.  Select does have one problem: like
   sigpause, it is interrupted by signals; unlike sigpause, it does
   not take a signal mask, so it sometimes has unavoidable critical
   sections.  (Yes, I want a sixth argument to select!)

3) The actual granularity of interval timers (including select timers):

	system				granularity
	4.[23]BSD Vax			10 ms
	Sun[23] running SunOS 3.x	20 ms
-- 
In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 7690)
Domain:	chris@mimsy.umd.edu	Path:	uunet!mimsy!chris