Path: utzoo!utgpu!attcan!uunet!graphon!dc
From: dc@graphon.UUCP (Darren Croke)
Newsgroups: comp.windows.x
Subject: Re: Memory utilisation in X11 systems
Summary: Hopefully all clients will be capable of handling exposure events.
Keywords: storage backing-store
Message-ID: <219@graphon.UUCP>
Date: 7 Jan 89 02:09:17 GMT
References: <601@acorn.co.uk>
Organization: GraphOn Corp., San Jose, CA
Lines: 28



In reply to John Bowlers article on servers running out of memory. 
(posted Tue, Jan 3). I was disturbed to read the following comment.

> But writing a client which deals with resource exhaustion may well mean
> implementing the same thing twice - for example once using backing store
> (no redraw required on expose events) and once using explicit redraw if
> the backing store isn't available.  I cannot believe that such an application
> would achieve acceptable performance in both cases (else why bother with
> the backing store implementation) so effectively the application doesn't
> work unless sufficient backing store is available.  So much for portability.

The X11R3 protocol spec clearly states on page 33 that selecting 
backing-store for a window informs the server that maintaining contents 
would be beneficial. 
         ----------
The spec goes on to say that "the server may stop maintaining contents 
at any time", which, correct me if I'm wrong, means that your client
will receive expose events.

Hopefully writers of clients will cater for expose events even when 
backing-store is advertised.  Failure to do this will result in clients 
that won't run on most of the low end X terminals which don't have 
virtual memory and obviously have a finite limit as to how much 
backing-store they can maintain.

Darren Croke.