servo/components/style/sharing/mod.rs
Emilio Cobos Álvarez 311c403522
style: Move all the style sharing code outside matching.rs
This is just a code health change. I want to move it away to keep matching.rs as
simple as possible.
2017-05-21 02:30:51 +02:00

384 lines
14 KiB
Rust

/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
//! Code related to the style sharing cache, an optimization that allows similar
//! nodes to share style without having to run selector matching twice.
use Atom;
use bit_vec::BitVec;
use cache::{LRUCache, LRUCacheMutIterator};
use context::{CurrentElementInfo, SelectorFlagsMap, SharedStyleContext};
use data::{ComputedStyle, ElementData, ElementStyles};
use dom::{TElement, SendElement};
use matching::{ChildCascadeRequirement, MatchMethods};
use properties::ComputedValues;
use selectors::bloom::BloomFilter;
use selectors::matching::StyleRelations;
use sink::ForgetfulSink;
mod checks;
/// The amount of nodes that the style sharing candidate cache should hold at
/// most.
pub const STYLE_SHARING_CANDIDATE_CACHE_SIZE: usize = 8;
/// Controls whether the style sharing cache is used.
#[derive(Clone, Copy, PartialEq)]
pub enum StyleSharingBehavior {
/// Style sharing allowed.
Allow,
/// Style sharing disallowed.
Disallow,
}
/// Information regarding a style sharing candidate, that is, an entry in the
/// style sharing cache.
///
/// Note that this information is stored in TLS and cleared after the traversal,
/// and once here, the style information of the element is immutable, so it's
/// safe to access.
///
/// TODO: We can stick a lot more info here.
#[derive(Debug)]
pub struct StyleSharingCandidate<E: TElement> {
/// The element. We use SendElement here so that the cache may live in
/// ScopedTLS.
element: SendElement<E>,
/// The cached class names.
class_attributes: Option<Vec<Atom>>,
/// The cached result of matching this entry against the revalidation selectors.
revalidation_match_results: Option<BitVec>,
}
impl<E: TElement> PartialEq<StyleSharingCandidate<E>> for StyleSharingCandidate<E> {
fn eq(&self, other: &Self) -> bool {
self.element == other.element
}
}
/// A cache miss result.
#[derive(Clone, Debug)]
pub enum CacheMiss {
/// The parents don't match.
Parent,
/// One element was NAC, while the other wasn't.
NativeAnonymousContent,
/// The local name of the element and the candidate don't match.
LocalName,
/// The namespace of the element and the candidate don't match.
Namespace,
/// One of the element or the candidate was a link, but the other one
/// wasn't.
Link,
/// The element and the candidate match different kind of rules. This can
/// only happen in Gecko.
UserAndAuthorRules,
/// The element and the candidate are in a different state.
State,
/// The element had an id attribute, which qualifies for a unique style.
IdAttr,
/// The element had a style attribute, which qualifies for a unique style.
StyleAttr,
/// The element and the candidate class names didn't match.
Class,
/// The presentation hints didn't match.
PresHints,
/// The element and the candidate didn't match the same set of revalidation
/// selectors.
Revalidation,
}
/// The results of attempting to share a style.
pub enum StyleSharingResult {
/// We didn't find anybody to share the style with.
CannotShare,
/// The node's style can be shared. The integer specifies the index in the
/// LRU cache that was hit and the damage that was done. The
/// `ChildCascadeRequirement` indicates whether style changes due to using
/// the shared style mean we need to recascade to children.
StyleWasShared(usize, ChildCascadeRequirement),
}
/// An LRU cache of the last few nodes seen, so that we can aggressively try to
/// reuse their styles.
///
/// Note that this cache is flushed every time we steal work from the queue, so
/// storing nodes here temporarily is safe.
pub struct StyleSharingCandidateCache<E: TElement> {
cache: LRUCache<StyleSharingCandidate<E>>,
}
impl<E: TElement> StyleSharingCandidateCache<E> {
/// Create a new style sharing candidate cache.
pub fn new() -> Self {
StyleSharingCandidateCache {
cache: LRUCache::new(STYLE_SHARING_CANDIDATE_CACHE_SIZE),
}
}
/// Returns the number of entries in the cache.
pub fn num_entries(&self) -> usize {
self.cache.num_entries()
}
fn iter_mut(&mut self) -> LRUCacheMutIterator<StyleSharingCandidate<E>> {
self.cache.iter_mut()
}
/// Tries to insert an element in the style sharing cache.
///
/// Fails if we know it should never be in the cache.
pub fn insert_if_possible(&mut self,
element: &E,
style: &ComputedValues,
relations: StyleRelations,
revalidation_match_results: Option<BitVec>) {
let parent = match element.parent_element() {
Some(element) => element,
None => {
debug!("Failing to insert to the cache: no parent element");
return;
}
};
if element.is_native_anonymous() {
debug!("Failing to insert into the cache: NAC");
return;
}
// These are things we don't check in the candidate match because they
// are either uncommon or expensive.
if !checks::relations_are_shareable(&relations) {
debug!("Failing to insert to the cache: {:?}", relations);
return;
}
// Make sure we noted any presentational hints in the StyleRelations.
if cfg!(debug_assertions) {
let mut hints = ForgetfulSink::new();
element.synthesize_presentational_hints_for_legacy_attributes(&mut hints);
debug_assert!(hints.is_empty(),
"Style relations should not be shareable!");
}
let box_style = style.get_box();
if box_style.specifies_transitions() {
debug!("Failing to insert to the cache: transitions");
return;
}
if box_style.specifies_animations() {
debug!("Failing to insert to the cache: animations");
return;
}
debug!("Inserting into cache: {:?} with parent {:?}", element, parent);
self.cache.insert(StyleSharingCandidate {
element: unsafe { SendElement::new(*element) },
class_attributes: None,
revalidation_match_results: revalidation_match_results,
});
}
/// Touch a given index in the style sharing candidate cache.
pub fn touch(&mut self, index: usize) {
self.cache.touch(index);
}
/// Clear the style sharing candidate cache.
pub fn clear(&mut self) {
self.cache.evict_all()
}
/// Attempts to share a style with another node.
///
/// This method is unsafe because it depends on the
/// `style_sharing_candidate_cache` having only live nodes in it, and we
/// have no way to guarantee that at the type system level yet.
pub unsafe fn share_style_if_possible(
&mut self,
shared_context: &SharedStyleContext,
current_element_info: &mut CurrentElementInfo,
selector_flags_map: &mut SelectorFlagsMap<E>,
bloom_filter: &BloomFilter,
element: E,
data: &mut ElementData
) -> StyleSharingResult {
if shared_context.options.disable_style_sharing_cache {
debug!("{:?} Cannot share style: style sharing cache disabled",
element);
return StyleSharingResult::CannotShare
}
if element.parent_element().is_none() {
debug!("{:?} Cannot share style: element has no parent", element);
return StyleSharingResult::CannotShare
}
if element.is_native_anonymous() {
debug!("{:?} Cannot share style: NAC", element);
return StyleSharingResult::CannotShare;
}
if element.style_attribute().is_some() {
debug!("{:?} Cannot share style: element has style attribute",
element);
return StyleSharingResult::CannotShare
}
if element.get_id().is_some() {
debug!("{:?} Cannot share style: element has id", element);
return StyleSharingResult::CannotShare
}
let mut should_clear_cache = false;
for (i, candidate) in self.iter_mut().enumerate() {
let sharing_result =
Self::test_candidate(
element,
candidate,
&shared_context,
bloom_filter,
current_element_info,
selector_flags_map
);
match sharing_result {
Ok(shared_style) => {
// Yay, cache hit. Share the style.
// Accumulate restyle damage.
debug_assert_eq!(data.has_styles(), data.has_restyle());
let old_values = data.get_styles_mut()
.and_then(|s| s.primary.values.take());
let child_cascade_requirement =
element.accumulate_damage(
&shared_context,
data.get_restyle_mut(),
old_values.as_ref().map(|v| &**v),
shared_style.values(),
None
);
// We never put elements with pseudo style into the style
// sharing cache, so we can just mint an ElementStyles
// directly here.
//
// See https://bugzilla.mozilla.org/show_bug.cgi?id=1329361
let styles = ElementStyles::new(shared_style);
data.set_styles(styles);
return StyleSharingResult::StyleWasShared(i, child_cascade_requirement)
}
Err(miss) => {
debug!("Cache miss: {:?}", miss);
// Cache miss, let's see what kind of failure to decide
// whether we keep trying or not.
match miss {
// Cache miss because of parent, clear the candidate cache.
CacheMiss::Parent => {
should_clear_cache = true;
break;
},
// Too expensive failure, give up, we don't want another
// one of these.
CacheMiss::PresHints |
CacheMiss::Revalidation => break,
_ => {}
}
}
}
}
debug!("{:?} Cannot share style: {} cache entries", element,
self.cache.num_entries());
if should_clear_cache {
self.clear();
}
StyleSharingResult::CannotShare
}
fn test_candidate(element: E,
candidate: &mut StyleSharingCandidate<E>,
shared: &SharedStyleContext,
bloom: &BloomFilter,
info: &mut CurrentElementInfo,
selector_flags_map: &mut SelectorFlagsMap<E>)
-> Result<ComputedStyle, CacheMiss> {
macro_rules! miss {
($miss: ident) => {
return Err(CacheMiss::$miss);
}
}
// Check that we have the same parent, or at least the same pointer
// identity for parent computed style. The latter check allows us to
// share style between cousins if the parents shared style.
let parent = element.parent_element();
let candidate_parent = candidate.element.parent_element();
if parent != candidate_parent &&
!checks::same_computed_values(parent, candidate_parent) {
miss!(Parent)
}
if element.is_native_anonymous() {
debug_assert!(!candidate.element.is_native_anonymous(),
"Why inserting NAC into the cache?");
miss!(NativeAnonymousContent)
}
if *element.get_local_name() != *candidate.element.get_local_name() {
miss!(LocalName)
}
if *element.get_namespace() != *candidate.element.get_namespace() {
miss!(Namespace)
}
if element.is_link() != candidate.element.is_link() {
miss!(Link)
}
if element.matches_user_and_author_rules() !=
candidate.element.matches_user_and_author_rules() {
miss!(UserAndAuthorRules)
}
if element.get_state() != candidate.element.get_state() {
miss!(State)
}
if element.get_id() != candidate.element.get_id() {
miss!(IdAttr)
}
if element.style_attribute().is_some() {
miss!(StyleAttr)
}
if !checks::have_same_class(element, candidate) {
miss!(Class)
}
if checks::has_presentational_hints(element) {
miss!(PresHints)
}
if !checks::revalidate(element, candidate, shared, bloom, info,
selector_flags_map) {
miss!(Revalidation)
}
let data = candidate.element.borrow_data().unwrap();
debug_assert!(element.has_current_styles(&data));
debug!("Sharing style between {:?} and {:?}",
element, candidate.element);
Ok(data.styles().primary.clone())
}
}