1139824 - improve tracking of harfbuzz objects for font tables, to avoid inadvertent leaks

Status: RESOLVED FIXED

(Core :: Graphics: Text, defect)

Description

[Jonathan Kew [:jfkthame]]

See bug 1139646. We were leaking a font table reference, but this only showed up under WinXP because not all font backends keep track of the hb_blob objects created to hold tables.

The proposal here is to add constructor/destructor tracking (MOZ_COUNT_CTOR/MOZ_COUNT_DTOR) to the currently-untracked objects we attach to userData in the hb_blobs. This should make any such problems show up across all platforms in the future, and hence be easier to debug. (Bug 1139646 took me a while to track down largely because it was only happening on WinXP jobs.)

We might also want to do the same for other refcounted hb_* objects we're not currently tracking, such as hb_font and hb_face.

Comment 1

[Jonathan Kew [:jfkthame]]

Attachment: Track construction/destruction of the font table wrappers attached to hb_blob objects, to enable leak detection

I've confirmed locally that with this patch (and without the leak fix from bug 1139646), running vertical-text reftests will report a bunch of leaked font tables; and that the patch in bug 1139646 fixes them all as expected. If we'd had this in place, we'd have noticed the problem much sooner, instead of only seeing a mysterious WinXP orange when I tried to land bug 1134598.

Comment 2

[Jonathan Kew [:jfkthame]]

Attachment: Track construction/destruction of the font table wrappers attached to hb_blob objects, to enable leak detection

Minor update, adding 'explicit' to the FontTableRec constructor to make static analysis happy.

Comment 3

[Jonathan Kew [:jfkthame]]

https://hg.mozilla.org/integration/mozilla-inbound/rev/3b88e051558b

Comment 4

[Wes Kocher (:KWierso) (Not reading bugmail; email directly if needed)]

https://hg.mozilla.org/mozilla-central/rev/3b88e051558b