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From: michael@stb.UUCP (Michael)
Newsgroups: comp.sys.amiga
Subject: Re: PIPE:... should it buffer at all?
Message-ID: <130@stb.UUCP>
Date: Mon, 7-Sep-87 00:42:21 EDT
Article-I.D.: stb.130
Posted: Mon Sep  7 00:42:21 1987
Date-Received: Tue, 8-Sep-87 06:35:45 EDT
References: <571@sugar.UUCP> <92@stb.UUCP> <628@sugar.UUCP>
Reply-To: michael@stb.UUCP (Michael)
Organization: STB BBS, LA, CA, USA, 90402, (213) 459-7231
Lines: 58
Keywords: PIPE: buffer UNIX pipes

In article <628@sugar.UUCP> peter@sugar.UUCP (Peter da Silva) writes:
>> >Alternatively, how about making PIPE: act like the UNIX pipe? That is, you
>> >can open it and write as much as you please without waiting until you fill
>       ^^^^^^^^^^^
>> >it up. You can have multiple writers but only one reader. The pipe hangs
>                       ^^^^^^^^^^^^^^^^
>> >around as long as a single writer *or* reader wants it. And finally you can
>> >reopen it without losing data.
>   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>> 
>> Gee, thats how I thought PIPE: worked.
>
>Nope. If you open it, you currently wait for the reader to open it too. You
>can also only have one writer. And if the writer closes it and the reader
>closes it it goes away even if there's still data in it. This makes it
>useless as a printer buffer (the obvious application for it: you open
>PIPE:spool and write your data. Have a program read from PIPE:spool and
>write to PRT:. Make PIPE:spool 16K long. Instant buffer.)

Okay, lets look at unix pipes. I assume you mean Named Fifo's (pipe files
in file space vs. pipe(2) sys call). 
#1. 4K buffer--after that, you wait until someone else reads it.
#2. The system I have makes the writer wait until a reader shows up.
#3. Both multiple readers and writers are allowed (remember: The dup() call
will work for anything in unix, and fork implicitly dups every file
descriptor).
#4. You cannot reopen without losing data.

Which system are you thinkin of? 4.3? (I'm using sys3). If I understand
correctly, that system does not guarantee any atomicy of writes to pipes.

>> Besides, I like P:, which can have multiple readers.
>
>I find it hard to fathom the use of multiple readers to a single pipe. Perhaps
>you can describe an application you've used this feature for.

Look at the "tee" command in unix. P: will send identical copies of data to
a file, such as a CON: window, or another pipe (to another program), so
one program's output will go to two destination programs.

>> : Copy protection? Just say Pirate! (if its worth pirating)
>
>How are people supposed to take you seriously if you say things like this?
>-- 
>-- Peter da Silva `-_-' ...!seismo!soma!uhnix1!sugar!peter
>--                  U   <--- not a copyrighted cartoon :->

Gee, I suppose very. Seriously, I am strongly opposed to copy protection and
"machine takeovers"; I will not willingly buy any program with either. I
bought "Hex" thinking it wasn't protected, but I see now I need a better test
for protected before I buy. But, I have changed my .signature now. And when
I learn enough 68000 and amiga assembly, I will change it again.

			Michael.

-- 
: Michael Gersten		seismo!scgvaxd!stb!michael
: Copy protection? Just say "Off site backup"