Font Caches Gone Wild

Friday, 25 March 2005

Thanks to a veritable avalanche of email regarding Monday’s piece on login delays caused by damaged font caches, I think I have a pretty good idea what’s going on.

One thing I know is that it wasn’t just me — an awful lot of people have been stricken with this problem, and in some cases, it was nearly crippling. One reader reported finding over 1 gigabyte of “fontTablesAnnex” files in /System/Library/Caches/; and in terms of login delays, designer Cameron Moll reported that his login time had grown to 14 minutes.

This is, clearly, a bug in Mac OS X 10.3. Specifically, it’s a bug in version 1.8.5 of the ATS framework.¹ Recall from Monday that “ATS” stands for “Apple Type Solution” (although several readers seconded my suspicion that it previously stood for “Apple Type Services”; regardless, all you need to know for this discussion is that ATS is the Mac OS X subsystem that handles fonts).

Version 1.8.5 shipped as part of the Mac OS X 10.3.6 update, the release notes for which mention several font-related bugs that were addressed in that release. So my guess is that this bug — where the “fontTablesAnnex” caches grow without bound, leading to severe login delays — was introduced as a side-effect of one of the bug fixes for ATS.framework in 10.3.6.²

10.3.6 was released in October, and that gibes with my suspicion that this is when the bug was introduced. It’s not a bug where boom, you’re hit and logging into your account suddenly takes a minute or longer. These font caches grow endlessly, but they tend to grow slowly, and so the adverse effects tend to sneak up on you. I began to suspect something was wrong around December; by February, I was highly annoyed.

ATS.framework has not changed in either 10.3.7 or 10.3.8; version 1.8.5 is still current, and thus, the bug is still present.

Most users haven’t been affected by this bug, or if they have been, it hasn’t been severe. I believe, but can’t prove, that the reason for this is that the bug is only triggered if you have PostScript fonts installed, or perhaps, certain kinds of PostScript fonts.

I believe this because:

1. Everyone who has written to me to say they too were hit by this bug has reported having at least several PostScript fonts installed.

2. Everyone I know who hasn’t been hit — no large font cache files, no delays when logging in to their accounts — has no PostScript fonts installed.

Group #2 includes everyone who runs with the stock set of fonts that ship with the system from Apple — Apple only ships TrueType fonts.

I’d be interested to hear from anyone who can contradict either of these suppositions; i.e. if you’ve been hit by this bug but have no PostScript fonts installed, or if you have many PostScript fonts installed in the system’s font folders, but haven’t been hit by the bug.

This is not to say there’s anything wrong with PostScript fonts. Or, if you’ve been hit, that there’s anything damaged or corrupt with your PostScript font files. This is a bug in Mac OS X, plain and simple.

My suspicion that the bug was introduced in 10.3.6 is further backed by the investigative work of Arton Ragsdale, who sent me this report by email:

The problem with ATSServer and the font caches is both old and new. I have experienced many variable problems throughout the life of OS X, particularly 10.3, that were easily solved by erasing font caches (repeatedly as various problems reappeared). I know you’ve always thought this was nonsense, but I can assure you it is not. It generally got better [through] 10.3.5, which seemed to clear up most of the problems.

The 10.3.6 update however, brought with it a new version of ATS.framework updating version 1.8.4 to 1.8.5. The major change in this update, which has yet to be addressed, is the behavior of scanning every single font in any of the three font folders (/System/Library/Fonts/, /Library/Fonts/, and ~/Library/Fonts/) regardless of whether they are activated or not. This takes an extremely long time if you have a large number of fonts.

The computers I set up have about 500 fonts and many of them are quite old and of various types, which I believe adds to the problem. I came to this conclusion by using a similar troubleshooting technique to the one you mentioned, using ssh to access the computer while it logged in. But in addition to using top to narrow down the problem to ATSServer, I used fs_usage to find out exactly which processes were accessing which files.³ I discovered ATSServer accessing every single font on the computer.

My solution to the problem is one of your big pet peeves, I replaced the ATS.framework hidden in /System/Library/Frameworks/ApplicationServices.framework/Versions/ A/Frameworks/ATS.framework with the older version from 10.3.5. Not the most elegant solution, but it has worked smoothly on 30 G5s loaded with all different kinds of graphics apps and I can keep the fonts where they belong, in the fonts folder. It has worked with every version released since 10.3.6 but I wouldn’t recommend it to anyone who doesn’t use many fonts.

Arton’s investigation was thorough, and but he’s also correct that I absolutely cannot endorse his solution of replacing version 1.8.5 of ATS.framework with version 1.8.4 from Mac OS X 10.3.5. That it worked for him is proof that it’s a bug in version 1.8.5 that is causing these problems; that doesn’t mean replacing OS components with versions from previous OS updates is a wise idea.

My Advice

Better is to wait for Apple to fix the bug, as I believe they will in Mac OS X 10.3.9 (and, one would hope, also in 10.4). For one thing, this is a severe bug. For another, even though it isn’t hitting everyone, it’s hitting a large number of users, and designers in particular. Designers are the hardest-hit demographic simply because they almost invariably have numerous PostScript fonts installed (and conversely, non-designers are less likely to install any PostScript fonts).

I have no first-hand knowledge that there will even be a 10.3.9 release, but the rumor mill says it’s imminent. Included in the release notes for the latest build released to developers, as reported by MacRumors.com, is this item:

• updated font management

And according to some site called Think Secret:

Mac OS X 10.3.9 will deliver dozens of other fixes and improvements when it is released, including improved startup times on systems with many fonts, FireWire audio performance fixes, an updated Kernel, improvements when waking from sleep, and more.

(I believe where Think Secret says “startup”, they mean “login”, although perhaps these caching problems affect both startup and login times.)

In the meantime, I believe this bug can be managed manually by keeping an eye on the size of your font caches. If your “fontTablesAnnex” files seem unduly large, or if the time it takes you to log in seems unduly long, trash your font caches and restart.

Update 17 April: 10.3.9 is out, and the fix is in:

Addresses an issue in which the startup time in Mac OS X 10.3.6 through 10.3.8 may be extended if a large number of PostScript fonts are installed.