Subject: Re: Multiple sessions viewing a mailbox

From: Mark Crispin <[email-masked]>
Date: Tue, 1 Nov 1994 20:00:09 -0800

This would work if you use tenex format with a delivery program such as
tmail (available on our FTP server) to write to it. 

There is a general misunderstanding as to exactly what, and why, read-only
is with the standard UNIX mbox format.  Read-only in mbox format means 
that Pine has taken an in-memory snapshot of that folder.  After it takes 
the snapshot of the folder, it no longer looks at the disk.  Messages can 
be deleted and expunged, and Pine would not know.

The fact that messages can be deleted and expunged, or that messages can
be moved around (because of writing the Status:/X-Status:) header, means
that a Pine process can not update its in-memory snapshot, unless it was
the entity that did the manipulation of the folder.  If some other process
sloshes messages around, Pine no longer knows where anything is in the
file.  The only way to reconcile is to toss out everything it may have
known about the file and read it all in again; that's just about what you
do when you quit Pine and restart it. 

There is a lock that says ``I declare that I may slosh messages around in
the folder.'' If a Pine process has this lock, it is called ``normal
access''.  If not, it is called ``read-only access'' and it punts on 
trying to keep track of what the disk copy is doing.

Tenex format exploits certain technical aspects to permit many Pine 
processes to read the folder at the same time, yet each is able to 
reconcile the in-Pine state with the disk (Tenex format does not require 
a complete snapshot of the folder, just pointers to where all the 
messages are).  So, using Tenex format, you can have lots of people 
reading the same file, and seeing changes as they happen, even if they 
only have read permission to the file.

The downside to Tenex format is that it is incompatible from the ordinary 
UNIX mbox format, so other tools such as Elm can not read folders in this 
format.

-- Mark --

On Tue, 1 Nov 1994, Mike Roch wrote:

> 
> We are considering using a dummy username's inbox as our incoming fault 
> report conduit. The idea is that lots of people could have a window open 
> running		pine -if /var/spool/mail/dummy_username
> 
> These lots of people have  group read permission on the spool file.
> 
> It works up to a point, but new arrivals are not reflected in the 
> read-only sessions. If a session is read-only, why shouldn't pine 
> periodically check the mail spool for changes? The person with the r/o 
> session isn't changing anything ...
> 
> Mike
> 
> ==============================================================================
> Mike Roch, Computer Services Centre,                          Tel: 0734 318430
> The University, Whiteknights, Reading, RG6 2AF                Fax: 0734 753094
>

---

From: Mike Roch <[email-masked]>
Date: Tue, 1 Nov 1994 23:18:09 GMT

Mike