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From: cpcahil@virtech.uucp (Conor P. Cahill)
Newsgroups: news.software.nn,comp.unix.questions
Subject: Re: robust locking
Message-ID: <1990Aug29.122152.1600@virtech.uucp>
Date: 29 Aug 90 12:21:52 GMT
References: <2320@cirrusl.UUCP>
Reply-To: cpcahil@virtech.UUCP (Conor P. Cahill)
Organization: Virtual Technologies Inc., Sterling VA
Lines: 21

In article <2320@cirrusl.UUCP> dhesi%cirrusl@oliveb.ATC.olivetti.com (Rahul Dhesi) writes:
>A very simple mechanism can be used to ensure that such race conditions
>don't occur. Create a lock file that contains both process id and host
>name.  If a second process wants to create the same lock, it checks any
>existing lock file.  If the lock file exists, and the host name in it
>is that of the current host, then the process id in it can be tested to
>see if it is that of an existing process (and if not, that process
>crashed and the lock file can be superseded).  But if the host name in
>the lock file is that of a different host, we refuse to supersede the
>lock.

But if you allow both processes to run on different hosts, you need to 
modify the other parts of rn that deal with the .newsrc and other related
status/setup files.  You will run into real problems when two processes 
try to write out different .newsrc files.


-- 
Conor P. Cahill            (703)430-9247        Virtual Technologies, Inc.,
uunet!virtech!cpcahil                           46030 Manekin Plaza, Suite 160
                                                Sterling, VA 22170