From owner-freebsd-hackers@FreeBSD.ORG  Sun Mar 30 20:04:21 2003
Return-Path: <owner-freebsd-hackers@FreeBSD.ORG>
Delivered-To: freebsd-hackers@freebsd.org
Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125])
	by hub.freebsd.org (Postfix) with ESMTP id 6B15837B401
	for <hackers@freebsd.org>; Sun, 30 Mar 2003 20:04:18 -0800 (PST)
Received: from priv-edtnes10-hme0.telusplanet.net (outbound02.telus.net
	[199.185.220.221])
	by mx1.FreeBSD.org (Postfix) with ESMTP id CAC8C43FA3
	for <hackers@freebsd.org>; Sun, 30 Mar 2003 20:04:17 -0800 (PST)
	(envelope-from sh@planetquake.com)
Received: from REASON ([154.5.106.237])
	by priv-edtnes10-hme0.telusplanet.netSMTP
	<20030331040417.ERSR12335.priv-edtnes10-hme0.telusplanet.net@REASON>
	for <hackers@freebsd.org>; Sun, 30 Mar 2003 21:04:17 -0700
Message-ID: <009301c2f73a$98d2c970$0300000a@slugabed.org>
From: "Sean Hamilton" <sh@planetquake.com>
To: <hackers@freebsd.org>
References:
	<001101c2f71d$8d9e4fb0$0300000a@slugabed.org><20030331023856.GL74971@dan.emsphone.com><007e01c2f730$4b5863d0$0300000a@slugabed.org>
	<20030331033643.GO74971@dan.emsphone.com>
Date: Sun, 30 Mar 2003 20:04:15 -0800
MIME-Version: 1.0
Content-Type: text/plain;
	charset="iso-8859-1"
Content-Transfer-Encoding: 7bit
X-Priority: 3
X-MSMail-Priority: Normal
X-Mailer: Microsoft Outlook Express 6.00.2800.1106
X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1106
Subject: Re: wait()/alarm() race condition
X-BeenThere: freebsd-hackers@freebsd.org
X-Mailman-Version: 2.1.1
Precedence: list
List-Id: Technical Discussions relating to FreeBSD
	<freebsd-hackers.freebsd.org>
List-Unsubscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-hackers>,
	<mailto:freebsd-hackers-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/freebsd-hackers>
List-Post: <mailto:freebsd-hackers@freebsd.org>
List-Help: <mailto:freebsd-hackers-request@freebsd.org?subject=help>
List-Subscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-hackers>,
	<mailto:freebsd-hackers-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Mon, 31 Mar 2003 04:04:22 -0000

Dan Nelson wrote:
| In the last episode (Mar 30), Sean Hamilton said:
|| I'm concerned about this order of events:
||
|| - alarm()
|| - wait() returns successfully
|| - if (alarmed...) [false]
|| - SIGALRM is delivered, alarmed = true
|| - loop
|| - wait() waits indefinitely
|
| A cleaner solution would be to use ualarm(60000,1000) or setitimer()
| to do this (replacing the alarm(60) call outside the handler).

This looks like the way to go. "cleaner" is certainly relative here, but
it's quite likely this hack never comes up in the lifetime of the program.
I've inserted a printf just in case. (slight grin)

This is my first time dealing with signals... they seem to lack the elegance
most of Unix offers. Perhaps that's just my inexperience speaking.

sh