Path: utzoo!attcan!uunet!cbmvax!andy
From: andy@cbmvax.UUCP (Andy Finkel)
Newsgroups: comp.sys.amiga.tech
Subject: Re: Protect Failed
Message-ID: <5157@cbmvax.UUCP>
Date: 1 Nov 88 01:27:39 GMT
References: <8810281416.AA01431@decwrl.dec.com> <5147@cbmvax.UUCP> <9968@swan.ulowell.edu>
Reply-To: andy@cbmvax.UUCP (Andy Finkel)
Organization: Commodore Technology, West Chester, PA
Lines: 58

In article <9968@swan.ulowell.edu> page@swan.ulowell.edu (Bob Page) writes:
>[followups to comp.sys.amiga.tech]
>
>andy@cbmvax.UUCP (Andy Finkel) wrote:
>>Any file currently in use can't have its protection bits changes
>>(under 1.1, 1.2, 1.3)  Locks (ie Assigns) count as 'in use'.
>
>So why can't you look at "in use" file system resources?
>
>This has always seemed arbitrary to me, especially something as
>harmless as poking attribute bits in the fileheader when another
>process is reading the data in the file.

I specified it as carefully as I did precisely because it
may change in the future.  We're not locked into having it work
precisely the way it does now; on the other hand, we like to
have a pretty good idea of the full implications of a change before we
make it.

>
>But the real reason is I want to do the Unix equivalent of
>
>datagenerator >>logfile
>tail -f file
>
>Sure, I can say
>	datagenerator | tee >>logfile
>but that begs the question.  I'm sure the answer can't be "because we
>want to avoid race conditions" when you have something as notorious as
>ExNext() out there.

What a peculiar statement; possibly the running the source groups
(BTW, you seem to be doing a great job so far) is effecting your
mind. :-)  Are you saying that because we have one area of vunerability,
additional ones are OK ?

Anyway, back to the request:

You can do this now; there are dangers, certainly, but the worst
that should happen is the file will get corrupted if you have
2 writers.  It will be made safer in the future.

(Using 1.3 AmigaShell you can do this on an existing file, ie

echo >logfile
datagenerator >>logfile
tail -f logfile

assuming, of course, that your tail doesn't want exclusive access.
-- 
andy finkel		{uunet|rutgers|amiga}!cbmvax!andy
Commodore-Amiga, Inc.

"I first began to lose faith in software engineering when I found out
 that no two printers were compatible."

Any expressed opinions are mine; but feel free to share.
I disclaim all responsibilities, all shapes, all sizes, all colors.