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From: davel@hpcupt1.HP.COM (Dave Lennert)
Newsgroups: comp.unix.questions
Subject: Re: msleep
Message-ID: <6060001@hpcupt1.HP.COM>
Date: Mon, 16-Nov-87 23:26:24 EST
Article-I.D.: hpcupt1.6060001
Posted: Mon Nov 16 23:26:24 1987
Date-Received: Thu, 19-Nov-87 23:49:50 EST
References: <332@PT.CS.CMU.EDU>
Organization: Hewlett Packard, Cupertino
Lines: 21

> 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!)
> -- 
> In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 7690)
> Domain:	chris@mimsy.umd.edu	Path:	uunet!mimsy!chris
> ----------

In reality one would like every system call to accept a signal mask
(like what sigpause() does for pause()).  However, it is not impossible
to code reliably; setjmp()...longjmp() work acceptably.

You can't code reliably in the presense of signals (especially SIGALRM)
without using setjmp()...longjmp() (with the one exception of sigpause()).
If you timeout a system call other than sigpause() by arming SIGALRM and
then immediately invoking the system call (without setjmp()) you have a
race condition.

-Dave Lennert   HP   ihnp4!hplabs!hpda!davel