Re: Filters with multiple copies of pine running

On Tue, 6 Feb 2007, Steve Hubert wrote:
> I think we're talking about IMAP folders and Pine.

OK, the folders are all on one server, & Pine/PC-Pine accesses 
them via IMAP protocol. I covered that contingency, but maybe not 
completely.

> Pine talks to the server by using the IMAP protocol, so there 
> is no possibility of locking or anything like that.

Then there is no possibility of operating a multiuser login 
secure system. It will crash. That server must somehow lock 
files/records to allow a write or crash for multiuser. A write is 
required to create/update any message/file/record.

I will bet the server in some way protects itself & demands some 
type of locking process, & Pine is given the locking control via 
IMAP or the system will not work. Even is single user. The server 
more than likely *nix, is not stupid.

> The two clients accessing the folder on the server very likely 
> are coming from different hosts, so there is no possibility of 
> them knowing about each other.

Sort of irrelevant.

> There are definitely race conditions. For example, one client 
> can expunge a message and the other one won't know about that 
> for a while, or one could set the Delete flag and the other 
> wouldn't know (for a while).

No, the system will not work that way. In a multiuser system, 
where multiple users such as this access one database of 
messages/files/records, one user must be allowed to create/update 
message/file/records & other users see the change before being 
allowed to continue with access. That is the purpose of locking & 
updating. Pine must be able to deal with that or is not a 
multiuser program, & a crash will occur.

> The "Recent" flag is special. It isn't set by the clients, it is set by the 
> server. I believe it is supposed to be the case that each message is only 
> Recent for one client. So if two clients are both talking to a server about a 
> particular folder and a new message arrives, the message should only appear 
> as Recent to one of the clients. (It sounded like that was not true in the 
> original message of this thread.)

Irrelevant who sets the flags, for the server & Pine to function 
in a multiuser login environment, flags that could effect more 
than one login user must be accessable & function for all users. 
If the recent flag is only recent for the first login, that 
proves this is a single user login system only. Do not login with 
two simultaneous users. If another user accesses the same account 
& does not get a recent flag, that proves to me the system is not 
intended for multiuser login service.

I suspect all flags with an IMAP protocol, server based or 
otherwise, are controlled by Pine in a single user fashion. The 
server may change the recent flag, but as a result of client 
access. Pine functions with them that way. I remember reading in 
Pine help where Pine used via POP cannot update server flags, so 
I suspect Pine does update server flags via IMAP. But POP 
irrelevant for this as POP is a download only scheme really, & 
serves one client for sure. IMAP is a split update system that 
must sync to maintain correct flags, data, updates.

> The move-only-if-not-deleted option is an attempt to reduce the duplicate 
> message problem, but it is known that there is still a race that will cause 
> duplicates (because one client setting Delete won't show up in the other 
> client for a while).

This is not a multiuser system you describe, it does not operate 
"realtime". I repeat my suggestion, do not try to use it that 
way.

Can you use the different filter parameters suggestion I made? 
Split the IP numbers to avoid this problem.

If I may ask - why must two separate simultaneous logins, two 
separate Pine applications, perform the same filter process?

--
RossARR
[email protected]
mrossarr.nixsyspaus.org/
nixsyspaus.org=208.64.38.250
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