862222 - Allow to circumvent caching of platform instantiations of webfonts

Status: RESOLVED FIXED

(Core :: Layout: Text and Fonts, defect)

Description

[Sebastian Zartner [:sebo]]

Bug 816483 implemented caching for webfonts instantiations.
This avoids unnecessary work to be done when the font is reused somewhere.
Though it is counter-productive for web developers, because there is no way to circumvent this cache to be able to see and analyze those requests.

Therefore I think caching webfonts should consider the browser's cache setting and reloading the page via Ctrl+F5.

Test case:
1. Open the Web Console on http://jeroenhoek.nl/jquery/twice.html (Ctrl+Shift+K)
2. Delete the browser cache
3. Reload the page

=> The request to the font http://jeroenhoek.nl/jquery/dejavu_sans/dejavusans-webfont.woff is not shown while it should be shown.

FWIW Chrome 26.0.1410.64 does this already.

Sebastian

Comment 1

[Jonathan Kew [:jfkthame]]

Yes, there really should be a way to circumvent this, but right now it's very awkward (and slow, as you have to wait for font instances to expire even after leaving the page) to work around it.

Comment 3

[Jonathan Kew [:jfkthame]]

Attachment: bypass the webfont cache when force-reloading the page

This seems to work OK to make Shift-Reload bypass the webfont cache; it checks for the BYPASS_CACHE flag in the docshell's loadType, and just skips the cache lookup if this is set.

Comment 4

[Jonathan Kew [:jfkthame]]

I suspect Shift-Reload is probably the most convenient tool for authors who want to ensure they're seeing the latest version of their font during development (for example). However, it'd probably make sense to also watch for the Clear Cache notification and forget the cached fonts in that case, too.

Comment 5

[Sebastian Zartner [:sebo]]

Just to be clear:
With "Shift-Reload" do you mean clicking the reload button while pressing Shift, Ctrl+F5, or both?

Sebastian

Comment 6

[Jonathan Kew [:jfkthame]]

I mean whatever UI action triggers a "force-reload" operation, bypassing the usual http cache... Holding Shift while clicking the Reload button does this on OS X (and presumably on all platforms); I don't usually work on Windows, but it looks like Ctrl-F5 does the same there, so AFAIK either one would cause this patch to also bypass the webfont cache.

Comment 7

[Jonathan Kew [:jfkthame]]

Attachment: pt 2 - empty the webfont cache in response to cacheservice:empty-cache notification

I think it also makes sense that the webfont cache should be included among the caches that are cleared by "Clear Recent History" if the Cache option is selected. So this patch adds a simple observer to handle this case.

Comment 8

[Robert O'Callahan (:roc) (email my personal email if necessary)]

Comment on attachment 752231 [details] [diff] [review]
pt 2 - empty the webfont cache in response to cacheservice:empty-cache notification

Review of attachment 752231 [details] [diff] [review]:
-----------------------------------------------------------------

::: gfx/thebes/gfxUserFontSet.cpp
@@ +795,5 @@
> +        nsCOMPtr<nsIObserverService> obs =
> +            mozilla::services::GetObserverService();
> +        if (obs) {
> +            obs->AddObserver(new Flusher, NS_CACHESERVICE_EMPTYCACHE_TOPIC_ID,
> +                             false);

I think you need a matching RemoveObserver call somewhere or we leak.

Comment 9

[Jonathan Kew [:jfkthame]]

Do we? I thought that this idiom would give the observer service the only reference to the observer, and it'd release it on shutdown. But if that's not correct, I'll fix it tomorrow. :)

Comment 10

[Robert O'Callahan (:roc) (email my personal email if necessary)]

I think you're right :-)

Comment 11

[Jonathan Kew [:jfkthame]]

https://hg.mozilla.org/integration/mozilla-inbound/rev/e1ef6c994470
https://hg.mozilla.org/integration/mozilla-inbound/rev/58ce67a325e6

Comment 12

[Ryan VanderMeulen [:RyanVM]]

https://hg.mozilla.org/mozilla-central/rev/e1ef6c994470
https://hg.mozilla.org/mozilla-central/rev/58ce67a325e6

Comment 13

[Sebastian Zartner [:sebo]]

I can now see the requests for web fonts again when pressing Ctrl+F5 or Shift+clicking the reload button. Thanks for that!

Though it seems setting browser.cache.disk.enable and browser.cache.memory.enable to false (i.e. disabling the browser cache) don't affect font caching. At least not constantly. Can you confirm that?

1. Opened https://getfirebug.com in a new tab
2. Set the prefs mentioned above to false
3. Opened the Web Console (Ctrl+Shift+K)
4. Reloaded the page twice

=> There are no requests listed for the web fonts, while they should be there due to the browser cache being disabled.

Sebastian