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From: guy@auspex.auspex.com (Guy Harris)
Newsgroups: comp.unix.questions
Subject: Re: Are terminal writes atomic?
Message-ID: <2541@auspex.auspex.com>
Date: 9 Oct 89 20:25:44 GMT
References: <-286379999@hpcupt1.HP.COM> <1118@cs.yale.edu> <186@promark.UUCP> <19972@mimsy.UUCP> <191@promark.UUCP>
Reply-To: guy@auspex.auspex.com (Guy Harris)
Organization: Auspex Systems, Santa Clara
Lines: 13

>Indeed I should have qualified my statement, however almost everyone is
>familiar with Rochkind's _Advanced Unix Programming_ book, and they are
>aware it is a SYSTEM V book, not a 4BSD Unix book.
>Under System V, it is a known undocumented item.  By undocumented, I mean
>it was left out of the documentation and under ALL true Unix System V systems,
>atomic writes at the system call level are guaranteed.

And you believe that, in fact, *terminal* writes are atomic on S5?  I
don't - and I've checked the S5R3 code.  While S5 *does*, in fact, lock
the inode on "read"s and "write"s in some cases - as does 4.3BSD, in
fact - neither of them do so if the file is a character special file,
which terminals are.  Chris Torek's scenario appears to apply to S5 as
well.