Have done this on the HP1000 to emulate message files and circular files. Non-extensible file. Keep two record pointers, first record and last record.  First record is the oldest, and gets sent for a read. Last record is oldest; increment it (with wraparound) before writing an new record to where it points. When "file" is empty set them both to zero. For consistency, use the same error values as would MPE to report error conditions. It doesn't take a lot of code unless you want to emulate open/close and #readers/#writers protocols. You can easily implement non-destructive reads and file info.

-Dave D




[log in to unmask] on 11/26/2001 05:56:00 AM
To:     [log in to unmask]@Internet
cc:      (bcc: David T Darnell/CO/KAIPERM)
Subject:        Re: [HP3000-L] Named pipes vs. MSG files

Gavin Scott wrote:
>
> Once again, pipes turn out to make rather lousy Message Files.
>
> G.
>

Yes.  This is an opportunity.  The way of Unix is to create
tools that provide better building blocks for all.  Someone
could implement much of the MPE Message concept on Unix by taking
a pair of named pipes with a program (deamon) in the middle
to handle the FIFO buffering of data to disk.  The same deamon
could be used to handle any number of "message pipes" and be very
general.

Richard
--
Richard L Gambrell, Senior Information Technology Consultant and
Director of Computing Systems and Networks
Information Technology Division, University of Tennessee at Chattanooga
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