I confirmed that we're actually using this codepath by manually testing
<input type=color>: it works with the patch, but if I comment out the
call to nsHTMLCSSStyleSheet::PseudoElementRulesMatching from
nsStyleSet::RuleNodeWithReplacement, then the color swatch breaks, which
proves that we're depending on the code.
I think I included this in the queue because it is needed for patch 22,
although I've forgotten the full reasoning.
Note that this means that when we start transitions, we post restyles
that are processed during the current restyling operation, rather than
in a later phase. This depends on patch 11, which makes the transition
manager skip style changes that it posts while starting transitions, to
ensure that this doesn't lead to an infinite loop. This also depends on
patch 16, which only consumes restyle data for the primary frame, to
ensure that the animation restyles posted are processed properly. It
also depends on patch 14, which makes us retain data on finished
transitions, to avoid triggering extra transitions on descendants when
both an ancestor and a descendant transition an inherited property, and
the descendant does so faster.
This fixes a known failure in layout/style/test/test_animations.html and
test_animations_omta.html (as visible in the patch). I believe this is
because this patch changes us to compute keyframe values for animations
on top of a style context *with* animation data rather than one without,
which means what we're computing them on top of changes each time. (The
purpose of patch 3 was to avoid this in the case where avoiding it
matters, i.e., implicit 0% and 100% keyframes.)
This allows nsStyleSet::RuleNodeWithReplacement to call it without
constructing an entire (and unnecessary) ElementRuleProcessorData, which
will happen in patch 3.
Note that this removes the Reset method and the mURL and mDocument
members (and arguments to set them) from nsHTMLCSSStyleSheet.
On the other hand, from nsHTMLStyleSheet it only removes mURL (and
equivalent arguments), and nsHTMLStyleSheet keeps the SetOwningDocument
method that was previously part of nsIStyleSheet (but no longer virtual).
This patch enables sharing of an nsAttrValue's MiscContainer between nodes for style rules. MiscContainers of type eCSSStyleRule are now refcounted (with some clever struct packing to ensure that the amount of memory allocated for MiscContainer remains unchanged on 32 and 64 bit). This infrastructure can be used to share most MiscContainer types in the future if we find advantages to sharing other types than just eCSSStyleRuley. A cache mapping strings to MiscContainers has been added to nsHTMLCSSStyleSheet. MiscContainers can be shared between nsAttrValues when one nsAttrValue is SetTo another nsAttrValue or when there is a cache hit in this cache. This patch also adds the ability to tell a style rule that it belongs to an nsHTMLCSSStyleSheet, with appropriate accessor functions to separate that from the existing case of belonging to an nsCSSStyleSheet.
The primary use case is to reduce memory use for pages that have lots of inline style attributes with the same value. This can happen easily with large pages that are automatically generated. An (admittedly pathological) testcase in Bug 686975 sees over 250 MB of memory savings with this change. Reusing the same MiscContainer for multiple nodes saves the overhead of maintaining separate copies of the string containing the serialized value of the style attribute and of creating separate style rules for each node. Eliminating duplicate style rules enables further savings in layout through style context sharing. The testcase sees the amount of memory used by style contexts go from over 250 MB to 10 KB.
Because the cache is based on the text value of the style attribute, it will not handle attributes that have different text values but are parsed into identical style rules. We also do not attempt to share MiscContainers when the node's base URI differs from the document URI. The effect of these limitations is expected to be low.
L. David Baron
Jonathan Watt
Birunthan Mohanathas
Cameron McCormack
Ehsan Akhgari
Arnaud Bienner
Robert O'Callahan
Catalin Iacob
Ms2ger
David Zbarsky
Kyle Huey
Randell Jesup
Aryeh Gregor
Gervase Markham
Nicholas Nethercote
Matheus Kerschbaum
Michael Wu
Craig Topper
Boris Zbarsky
Zack Weinberg
Markus Stange
Daniel Holbert