KON & BAL'S PUZZLE PAGE: Folder Fun

Konstantin Othmer and Bruce Leak

See if you can solve this programming puzzle, presented in the
form of a dialog between Konstantin Othmer (KON) and Bruce Leak
(BAL). The dialog gives clues to help you. Keep guessing until you're
done; your score is the number to the left of the clue that gave you
the correct answer. Even if you never run into the particular
problems being solved here, you'll learn some valuable debugging
techniques that will help you solve your own programming
conundrums. And you'll also learn interesting Macintosh trivia.

KON It's you again.

BAL It seems our bid for drumming up Puzzle Page authors
hasn't gone well.

KON I guess everyone's waiting for the Mac OS 8 release.
From what I hear, they'll be waiting quite a while.

BAL I've got a lot of work to do. Can we get on with this?

KON OK. Have you ever heard of Retrospect Remote?

BAL Yeah, we run it. It's that backup program. It slows
your machine to a crawl when it's doing its thing, but we've
never had a problem with it. Our engineers don't allow it on
their machines, though.

KON Apparently someone went around one morning and installed it
while we were all sleeping. It's been running great for the
last year, but suddenly one of the machines started showing
an execution error.

BAL Easy enough. Go check out the logs and see what it's
complaining about.

100 KON It says folders are nested too deep on that machine. Sure
enough, the machine has a folder called "<unknown name>,"
and inside that folder is another called "<unknown name>,"
and so on. It was mixed in with our project files.

BAL What system are you running?

KON A Power Mac 7100/66 with 32 MB of RAM and an 800 MB
hard disk, running system version 7.1.2 -- the "last trusted
system," according to Chris Derossi.

BAL What happens when you use the Finder to get info on the
folder?

90 KON It says there are 99 items inside this one for zero K of disk
space.

BAL Go in a level and try the same thing. Still 99 items?

KON Yep.

BAL Go in a few more levels and rename one of the folders. Come
back out and go back in. Anything unusual?

KON Nope. The renamed folder kept its new name. The Finder tells
you there are 99 items inside it.

BAL Just keep opening folders. How deep does it go?

80 KON After opening folders for a few minutes, you get too bored to
continue.

BAL Rename every tenth folder or so, to create some landmarks.
Dig down doing this. Can you Command-click on the window
title and see the whole hierarchy?

KON Yes. You're doing one heck of a test on the pop-up menu
manager.

BAL So, what happens?

70 KON After you do this about 150 times, the Finder displays the
familiar "out of memory" message. It says you might try
closing some windows to make more memory available. I have
the feeling this might be one case where that advice actually
works!

BAL Do a Get Info on the hard drive. How many items does it have?

KON 16,774 items on disk.

BAL Somehow I was expecting a larger number! Try copying the
folder.

KON We crash.

BAL Where? Any clues?

KON In CopyDoubler.

BAL That sounds like a subject for another column. Hold down the
Control key when copying the folder to tell CopyDoubler to
stay out of it.

60 KON The Finder puts up the copy dialog, waits about two minutes,
advances the thermometer the entire way in about three
seconds, and then waits another two minutes before finishing.
The copy dialog says there are 100 items to be copied. You
now have two folder hierarchies.

BAL That's interesting. I've seen the Finder copy way more than
100 items at one time, but somehow its knowledge of folder
nesting is limited to 99 or 100. Do a Get Info on the drive
again and see how many new items were created.

KON Now there are 18,679 items on disk -- 1,905 new ones.

BAL Copy it to a file server.

55 KON OK. Now the Finder does the copy the same as before, except
after the thermometer is finished, the dialog stays up,
waiting for a long time.

BAL How long?

KON Suppose we go to a long dinner at the Peppermill Lounge.
When we come back it still won't be done.

BAL Look at the folder hierarchy on the network from another
Mac.

KON While it's still copying?

BAL Sure.

50 KON You see a bunch of folders, as you'd expect, except the
network is really slow. Apparently the Finder is generating a
lot of network traffic trying to create all those directories.

BAL Stop that file copy.

45 KON The Stop button in the copy dialog is highlighted (indicating
that you pressed it), and the network is back to normal, but
the copy dialog doesn't go away.

BAL Reboot and look at the folders in Standard File.

KON No new clues. How deep do you want do go?

BAL Hmm. Try running Norton Utilities on the disk.

KON There were a few bundle bits that are wrong. But once those
are fixed, Norton says the disk is fine.

BAL Try DropStuffing the folder.

KON DropStuff crashes.

BAL Try Disk First Aid.

40 KON It tells you that the folder nesting exceeds the
Finder-recommended nesting of 100. But other than that, it
says the disk is fine.

BAL I guess those folders are really there. The system is running
into a bunch of boundary conditions trying to deal with them.
The question is how they got there, and I'm not sure how we
figure that out given that all we have is a smoking gun.

KON Wait a second...the column isn't supposed to end this way!

BAL OK. I've got an idea. I'll try looking at these folders from
MPW with afiles -r -c command.
>

35 KON MPW prints out a bunch of folders and then crashes. The
interesting thing is that it crashed right after printing out
the 100th level down, which we know from the "rename
every tenth folder" exercise we did earlier.

BAL Well, there are some mysteries that we should be able to
solve. Clearly, some software on this machine created the
folder called "<unknown name>," probably when a directory
with a null name or some other exception condition was
encountered.

KON OK.

BAL It's probably the Finder, the File Manager, or one of the
applications that's commonly used on the machine. Let's ask
Paul Mercer if he knows anything about it.

30 Paul First of all, the Finder isn't going to rename a folder on you.
And second, even if it did, no one on the Finder team would
give the folder a name that contains an angle bracket -- that's
just too unpleasant aesthetically. Maybe the File Manager
would do such a thing, though.

KON We could try Dave Feldman. I'm not sure he'd have the same
issues with angle brackets that Paul has.

25 Dave No issue with angle brackets here! But the File Manager
doesn't ever attempt to detect or fix damaged catalog info. It
will rebuild the volume bitmap (that long pause when
remounting a disk after a system crash), but it leaves
everything else alone. No matter how much it's abused by the
Finder, the File Manager will never surreptitiously set a
folder to "<unknown name>." Tell Paul I said what does he
know, he's been gone from Apple long enough to have forgotten
what little he once knew about the File Manager.
Furthermore, the File Manager doesn't care how deep you
nest folders; that's a Finder problem.

BAL Well, the system hasn't changed much since either of those
guys left Apple, so it's probably something else. Maybe you
can get someone at Apple to search all the system sources and
see if they can come up with a hit on "unknown name."

20 KON I talked to Jim Luther about it and he said it shows up in only
one place -- the Alias Manager. Apparently the Alias Manager
will store the name of the user who created the alias as part
of the alias record. If a user who logs on as a guest creates an
alias, the name of the alias creator is set to "unknown name,"
but there are no angle brackets.

BAL Let's grep the hard disk and see if we can find any hits on
"<unknown name>."

KON How do you propose we do that?

BAL Have you seen AltaVista?

KON You mean the search engine on the Internet? Totally awesome.
When you do a query they can instantly give you a list of the
top hits from any Web site. But what does that have to do with
this puzzle?

BAL Well, I figure they can search huge amounts of data way
faster than we could ever do it on our local machine. So we
dump the entire contents of the hard disk to a Web page,
register it with AltaVista, and perform the search.

KON A little unrealistic, but not a bad idea.

BAL Ron Avitzur thought it up.

KON For those keeping score, you're approaching 15.

BAL OK, OK. I'll use Norton Disk Editor and search the whole
volume for the string "<unknown name>."

15 KON The first hit is in the catalog. I get the feeling you're going to
find at least 1905 of these on this disk, probably more since
you duplicated the folders so many times.

BAL OK. Try it on one of your other development machines.

10 KON The string is found in a bunch of places but the sectors aren't
owned by a file. But then the needle in the haystack pokes
your probing finger -- you find the string in the MPW Shell
application.

BAL Open up MPW Shell with ResEdit and find out which resource
it's in.

KON Duh! Wrong tool for the job! ResEdit can't search the entire
resource fork.

BAL OK. Use Resorcerer.

KON You find the string in CODE resource 27, called %A5Init.

BAL So, it sounds like we should contact someone in MPW land and
see if they know what's going on. Here's Alex McKale; maybe
he can help us.

5 Alex Sure enough, Projector will create folders with the name
"<unknown name>." CheckOutDir creates a folder hierarchy
that matches the project hierarchy.

BAL The project hierarchy on this machine is only three or four
levels deep, not 1905! Any explanation for that?

Alex Did the machine ever crash while checking out? Maybe some
script got in an infinite loop, and you hit the reset button or
crashed after some time. This would mean the depth of the
hierarchy is based on how long the machine was running in
the loop, rather than on some magic number, such as
everyone's favorite year plus 1.

KON It happened on Richard's machine. He says his Mac crashes all
the time, and he'd be hard pressed to tell you what it was
doing during any particular crash.

BAL Hmm. I guess we just need a plausible explanation. Any ideas,
Alex?

Alex Your guess is as good as mine. CheckOutDir does very little
error checking, so if the project tree got munged -- for
example, if there was no terminator in the project folder
hierarchy -- it would keep creating folders called "<unknown
name>" until it hit a terminator. Give me a reproducible case,
and this thing is dead meat.

KON No can do. I guess the exact cause will remain a mystery,
along with the true nature of consciousness, the details of
Jimmy Hoffa's demise, and the location of my other red sock.
Well, at least we managed to narrow it down to Projector, so
we can point both our accusatory fingers in the same
direction. If nothing else, maybe this will get the Projector
folks to add a little more error checking to CheckOutDir.

BAL Nasty.

KON Yeah.

SCORING

KONSTANTIN OTHMER AND BRUCE LEAK are cashing in on the enormous
popularity of the Puzzle Page by starting their own online magazine. After rejecting
titles like MacsBug Life and Dead Mackerel, they've settled on Mired as the name for
their daily diary of debugging. The first issue will include hard-hitting articles like
"MacsBug: The Best Command-Line Interface for the Mac?" and "Celebrity dcmds."
Watch for it soon in your local cybernews shop!*

Thanks to Chris Derossi, Dave Feldman, Jim Luther, Alex McKale, and Paul Mercer
for reviewing this column.*