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Path: utzoo!linus!philabs!cmcl2!seismo!lll-crg!dual!qantel!ihnp4!laidbak!dpb
From: dpb@laidbak.UUCP (Darryl Baker)
Newsgroups: net.bugs.uucp
Subject: A better way to check lockfiles for HoneyDANBER.
Message-ID: <247@laidbak.UUCP>
Date: Tue, 8-Oct-85 14:21:29 EDT
Article-I.D.: laidbak.247
Posted: Tue Oct  8 14:21:29 1985
Date-Received: Fri, 11-Oct-85 08:23:56 EDT
Reply-To: dpb@laidbak.UUCP (Darryl Baker)
Organization: LAI Chicago
Lines: 25


In looking at justifing the cost of us getting HoneyDANBER uucp for our
4.2BSD system I found it still used timestamps on the lock file to see
if the lock was old. On System V systems HoneyDANBER uses kill(0,pid)
to see if the process who created the lock file still exists. Well on
4.2 systems it could do the same sort of thing using the getpriority()
system call since it allows anyone to get the priority of a process.
The usage would be:

		errno = 0;		/* the kernel also clear this */
		getpriority(PRIO_PROCESS, pid);/* returns the priority of */
					       /* but who cares and -1 is */
					       /* a valid priority */
		if(errno == ESRCH){
			remove lockfile
		} else {
			lock valid
		}

Using this would eliminate the problem of getting two processes doing
things at the same time.
-- 
				from the sleepy terminal of
				Darryl Baker
				[ihnp4!]laidbak!dpb