CODEWITHSUNDEEP
wpfwindowscachingfontstext-rendering
quetzalcoatl
quetzalcoatl

Reputation: 33556

WPF application freezes when rendering text (wpfgfx issues)

TL;DR:

Background:

I have built a WPF application on .Net 3.5. I've checked the application on various machines with different OS, ranging from Windows XP up to Windows 7 - and it runs fine, no bugs, etc. It also works fine on my client's several target machines, XP and W7 included again.

However, on one machine, it suddenly ceased to work. My client sent me the machine so I can investigate. From the files on its drives, I can see there were older versions, and they were used by the client for a few months. I also see that the newest version is not installed yet on this machine. So, I tried running the old versions first, to see what's the problem.

What user sees:

Technical bits, just FYI:

Tracing and observations:

I've focused on the TextBox part, since it's more granular.
I've got the app to freeze again, and checked the threads with ProcessHacker.
Except for typical threads, one thread that was sitting and busy-spinning at:

 wpfgfx_v0300.dll MilGlyphRun SetGeometryAtRenderTime
 wpfgfx_v0300.dll MilGlyphRun SetGeometryAtRenderTime
 ...
 wpfgfx_v0300.dll MilContent DetachFromHWND

That's certainly problem with the WPF layer itself. The DetachFromHWND tells me close to nothing, but MilGlyphRun is surely about the text rendering. It freezes while trying to render the text. I've checked the black-screens on older versions of the applications, but I couldn't catch it, since the apps were not frozen, just black.

So..

No changes, still black screen, still freezing.

So, focusing back to the problem. It failed to render a text. Sounds obvious, since it deadlocked when user entered a character into a textbox, but it's damn not obvious! The user was presented with tons of different TextBoxes until he finally got to the PasswordBox. All TextBoxes worked OK, only this one fails. And why old verions of the app display black screen and the new version displays the "welcome" screen properly? How can be those issues related?

Upvotes: 7

Views: 2985

Answers (1)

quetzalcoatl
quetzalcoatl

Reputation: 33556

The connection is: Windows Presentation Foundation Font Cache service.

Sources:

WPF uses a Font-Cache service, running as a separate process, for, well, caching fonts. Whenever your WPF app needs to draw some text, it might ask the cache service for fonts. Once in a while the font cache might get corrupted and it then will/may randomly impact any WPF application.

Unfortunatelly, restarting the service is not enough. When this happens, you must delete all FontCache files that this service keeps on the disk. Before deleting them, you must stop the "Windows Presentation Foundation Font Cache service (or whatever it's called in your languge, for example Usługa buforowania czcionek platformy Windows Presentation Foundation in Polish..). Then, go to

  • Win7: %systemdrive%\Windows\ServiceProfiles\LocalService\AppData\Local\
  • Vista: %systemdrive%\Windows\ServiceProfiles\LocalService\AppData\Local\
  • WinXP: %systemdrive%\Documents and Settings\LocalService\Local Settings\Application Data

and remove all files looking like FontCache.dat. The source articles mentioned only one file (FontCache3.0.0.0.dat, but in my case there were around 8 files with similar naming convention).

After deleing them and restarting the service, all versions of my application were running properly again. No black screens, no freezing on textbox.

Upvotes: 7

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