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From: mishkin@apollo.uucp (Nathaniel Mishkin)
Newsgroups: comp.sys.apollo
Subject: Re: Concurrency at open - (nf)
Message-ID: <382e6a52.c366@apollo.uucp>
Date: Fri, 30-Oct-87 14:34:00 EST
Article-I.D.: apollo.382e6a52.c366
Posted: Fri Oct 30 14:34:00 1987
Date-Received: Wed, 4-Nov-87 22:48:14 EST
References: <41600002@uklirb.UUCP>
Reply-To: mishkin@apollo.UUCP (Nathaniel Mishkin)
Organization: Apollo Computer, Chelmsford, MA
Lines: 25

In article <41600002@uklirb.UUCP> joa@uklirb.UUCP writes:
>I have some difficulties using files for reading and writing at the
>same time. The problem is the following: I'd like to write to a file
>with some program and at the same time to display this file with
>the DM call 'cv <file>'. But if the writing program does the first
>access to the file, it is locked and can't be shown by the DM. The
>same happens if I try to read the file with a second program.
>
>All tries with stream calls (STREAM_$REDEFINE) changing the attribute 
>"concurrency at open" failed.

I'm afraid you're out of luck.  The DM wants "n-readers xor 1-writers"
concurrency rules and wants read access.  Its desire conflicts with the
existing open your program has for write access.  The DM is trying to
be a good citizen (some would say paternalistic) by ensuring that it
doesn't ever show you something that might not be the "truth".  Other
editors (perhaps "vi") are probably less obsessive in this area and perhaps
you could use them to view your file.  (Note that your writing program
still must use "cowriters" concurrency rules, which is what Unix
open/creat give you by default.)
-- 
                    -- Nat Mishkin
                       Apollo Computer Inc.
                       Chelmsford, MA
                       {decvax,mit-eddie,umix}!apollo!mishkin