NetNews Usenet Archive 1992 #31/NN_1992_31.iso/spool/comp/sys/mac/programm/20420

Text File | 1992-12-30 | 1.9 KB | 42 lines

Newsgroups: comp.sys.mac.programmer
Path: sparky!uunet!zaphod.mps.ohio-state.edu!uwm.edu!spool.mu.edu!umn.edu!csus.edu!netcom.com!upstill
From: [e-mail] (Steve Upstill)
Subject: Resource Manager Purging Wierdness
Message-ID: <[e-mail]>
Organization: Netcom - Online Communication Services  (408 241-9760 guest)
Distribution: usa
Date: Wed, 30 Dec 1992 07:00:04 GMT
Lines: 31

I know this is the brave new world of unlimited RAM, but here I am
struggling to live in the world of Mac Plus'es and SE's, so I make
everything in the world purgeable, including a variety of resources.
I dutifully call SetResPurge(TRUE) so that any changed resources
(yes, I change them too) get written to disk. But still, under
low-memory conditions my resources start disappearing on me
(i.e., they're read in at size 0), implying that they were written
to disk empty anyway.

Now, there are ominous hints here and there that if the resource map is
written to disk and a resource has been purged, then an empty resource
will be written because, regardless of whether the resource was written
out at purge-time, it's still empty in memory and so the map is incorrect.
Unfortunately, this is as deep as the discussion gets (??!?), leaving
only a tantalizing hint to the effect that "yes, we may destroy your data,
but we're not going to say for sure, or indicate exactly when it might happen."

So it looks like data gets trashed under the following scenario:

1) a purgeable resource gets purged.
2) another resource is marked as changed
3) UpdateResFile() is called (perhaps by CloseResFile()). Because the map
has changed, the file gets written. Because the resource from 1) was
purged, its handle is empty and thus gets written empty.

I can't believe that this can happen this way, yet I am at a loss to
otherwise explain the 0-length resources that keep cropping up. Any clues?

Thanks,
Steve Upstill