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style: Introduce StyleBloom
The idea is this will fix the bad behavior of the bloom filter in parallel traversal.
This commit is contained in:
Emilio Cobos Álvarez
Emilio Cobos Álvarez
parent
7d69f53794
commit
84a50ed5cb
7 changed files with 318 additions and 172 deletions
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@ -5,17 +5,16 @@
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//! Traversing the DOM tree; the bloom filter.
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use atomic_refcell::{AtomicRefCell, AtomicRefMut};
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use bloom::StyleBloom;
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use context::{LocalStyleContext, SharedStyleContext, StyleContext};
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use data::{ElementData, RestyleData, StoredRestyleHint};
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use dom::{OpaqueNode, StylingMode, TElement, TNode, UnsafeNode};
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use dom::{OpaqueNode, StylingMode, TElement, TNode};
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use matching::{MatchMethods, StyleSharingResult};
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use restyle_hints::{RESTYLE_DESCENDANTS, RESTYLE_LATER_SIBLINGS, RESTYLE_SELF};
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use selectors::bloom::BloomFilter;
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use selectors::matching::StyleRelations;
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use std::cell::RefCell;
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use std::marker::PhantomData;
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use std::sync::atomic::{AtomicUsize, ATOMIC_USIZE_INIT, Ordering};
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use tid::tid;
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use util::opts;
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/// Every time we do another layout, the old bloom filters are invalid. This is
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@ -27,125 +26,68 @@ pub type Generation = u32;
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pub static STYLE_SHARING_CACHE_HITS: AtomicUsize = ATOMIC_USIZE_INIT;
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pub static STYLE_SHARING_CACHE_MISSES: AtomicUsize = ATOMIC_USIZE_INIT;
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/// A pair of the bloom filter used for css selector matching, and the node to
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/// which it applies. This is used to efficiently do `Descendant` selector
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/// matches. Thanks to the bloom filter, we can avoid walking up the tree
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/// looking for ancestors that aren't there in the majority of cases.
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///
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/// As we walk down the DOM tree a thread-local bloom filter is built of all the
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/// CSS `SimpleSelector`s which are part of a `Descendant` compound selector
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/// (i.e. paired with a `Descendant` combinator, in the `next` field of a
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/// `CompoundSelector`.
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///
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/// Before a `Descendant` selector match is tried, it's compared against the
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/// bloom filter. If the bloom filter can exclude it, the selector is quickly
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/// rejected.
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///
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/// When done styling a node, all selectors previously inserted into the filter
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/// are removed.
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///
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/// Since a work-stealing queue is used for styling, sometimes, the bloom filter
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/// will no longer be the for the parent of the node we're currently on. When
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/// this happens, the thread local bloom filter will be thrown away and rebuilt.
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thread_local!(
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static STYLE_BLOOM: RefCell<Option<(Box<BloomFilter>, UnsafeNode, Generation)>> = RefCell::new(None));
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static STYLE_BLOOM: RefCell<Option<StyleBloom>> = RefCell::new(None));
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/// Returns the thread local bloom filter.
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///
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/// If one does not exist, a new one will be made for you. If it is out of date,
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/// it will be cleared and reused.
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pub fn take_thread_local_bloom_filter<E>(parent_element: Option<E>,
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root: OpaqueNode,
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context: &SharedStyleContext)
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-> Box<BloomFilter>
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where E: TElement {
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pub fn take_thread_local_bloom_filter(context: &SharedStyleContext)
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-> StyleBloom
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{
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debug!("{} taking bf", ::tid::tid());
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STYLE_BLOOM.with(|style_bloom| {
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match (parent_element, style_bloom.borrow_mut().take()) {
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// Root node. Needs new bloom filter.
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(None, _ ) => {
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debug!("[{}] No parent, but new bloom filter!", tid());
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Box::new(BloomFilter::new())
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}
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// No bloom filter for this thread yet.
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(Some(parent), None) => {
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let mut bloom_filter = Box::new(BloomFilter::new());
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insert_ancestors_into_bloom_filter(&mut bloom_filter, parent, root);
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bloom_filter
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}
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// Found cached bloom filter.
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(Some(parent), Some((mut bloom_filter, old_node, old_generation))) => {
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if old_node == parent.as_node().to_unsafe() &&
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old_generation == context.generation {
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// Hey, the cached parent is our parent! We can reuse the bloom filter.
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debug!("[{}] Parent matches (={}). Reusing bloom filter.", tid(), old_node.0);
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} else {
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// Oh no. the cached parent is stale. I guess we need a new one. Reuse the existing
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// allocation to avoid malloc churn.
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bloom_filter.clear();
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insert_ancestors_into_bloom_filter(&mut bloom_filter, parent, root);
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}
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bloom_filter
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},
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}
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style_bloom.borrow_mut().take()
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.unwrap_or_else(|| StyleBloom::new(context.generation))
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})
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}
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pub fn put_thread_local_bloom_filter(bf: Box<BloomFilter>, unsafe_node: &UnsafeNode,
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context: &SharedStyleContext) {
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pub fn put_thread_local_bloom_filter(bf: StyleBloom) {
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debug!("[{}] putting bloom filter back", ::tid::tid());
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STYLE_BLOOM.with(move |style_bloom| {
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assert!(style_bloom.borrow().is_none(),
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"Putting into a never-taken thread-local bloom filter");
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*style_bloom.borrow_mut() = Some((bf, *unsafe_node, context.generation));
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debug_assert!(style_bloom.borrow().is_none(),
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"Putting into a never-taken thread-local bloom filter");
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*style_bloom.borrow_mut() = Some(bf);
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})
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}
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/// "Ancestors" in this context is inclusive of ourselves.
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fn insert_ancestors_into_bloom_filter<E>(bf: &mut Box<BloomFilter>,
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mut el: E,
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root: OpaqueNode)
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where E: TElement {
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debug!("[{}] Inserting ancestors.", tid());
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let mut ancestors = 0;
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loop {
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ancestors += 1;
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el.insert_into_bloom_filter(&mut **bf);
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el = match el.layout_parent_element(root) {
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None => break,
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Some(p) => p,
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};
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}
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debug!("[{}] Inserted {} ancestors.", tid(), ancestors);
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}
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pub fn remove_from_bloom_filter<'a, N, C>(context: &C, root: OpaqueNode, node: N)
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where N: TNode,
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/// Remove `element` from the bloom filter if it's the last element we inserted.
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///
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/// Restores the bloom filter if this is not the root of the reflow.
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///
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/// This is mostly useful for sequential traversal, where the element will
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/// always be the last one.
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pub fn remove_from_bloom_filter<'a, E, C>(context: &C, root: OpaqueNode, element: E)
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where E: TElement,
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C: StyleContext<'a>
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{
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let unsafe_layout_node = node.to_unsafe();
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debug!("[{}] remove_from_bloom_filter", ::tid::tid());
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let (mut bf, old_node, old_generation) =
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STYLE_BLOOM.with(|style_bloom| {
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style_bloom.borrow_mut()
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.take()
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.expect("The bloom filter should have been set by style recalc.")
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});
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// We may have arrived to `reconstruct_flows` without entering in style
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// recalc at all due to our optimizations, nor that it's up to date, so we
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// can't ensure there's a bloom filter at all.
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let bf = STYLE_BLOOM.with(|style_bloom| {
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style_bloom.borrow_mut().take()
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});
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assert_eq!(old_node, unsafe_layout_node);
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assert_eq!(old_generation, context.shared_context().generation);
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if let Some(mut bf) = bf {
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if context.shared_context().generation == bf.generation() {
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bf.maybe_pop(element);
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match node.layout_parent_element(root) {
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None => {
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debug!("[{}] - {:X}, and deleting BF.", tid(), unsafe_layout_node.0);
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// If this is the reflow root, eat the thread-local bloom filter.
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// If we're the root of the reflow, just get rid of the bloom
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// filter.
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//
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// FIXME: We might want to just leave it in TLS? You don't do 4k
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// allocations every day. Also, this just clears one thread's bloom
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// filter, which is... not great?
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if element.as_node().opaque() != root {
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put_thread_local_bloom_filter(bf);
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}
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}
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Some(parent) => {
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// Otherwise, put it back, but remove this node.
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node.as_element().map(|x| x.remove_from_bloom_filter(&mut *bf));
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let unsafe_parent = parent.as_node().to_unsafe();
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put_thread_local_bloom_filter(bf, &unsafe_parent, &context.shared_context());
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},
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};
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}
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}
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pub trait DomTraversalContext<N: TNode> {
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@ -258,27 +200,19 @@ pub fn style_element_in_display_none_subtree<'a, E, C, F>(element: E,
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#[inline]
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#[allow(unsafe_code)]
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pub fn recalc_style_at<'a, E, C, D>(context: &'a C,
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root: OpaqueNode,
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dom_depth: Option<usize>,
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element: E)
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where E: TElement,
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C: StyleContext<'a>,
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D: DomTraversalContext<E::ConcreteNode>
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{
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// Get the style bloom filter.
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//
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// FIXME(bholley): We need to do these even in the StylingMode::Stop case
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// to handshake with the unconditional pop during servo's bottom-up
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// traversal. We should avoid doing work here in the Stop case when we
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// redesign the bloom filter.
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let mut bf = take_thread_local_bloom_filter(element.parent_element(), root, context.shared_context());
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let mode = element.styling_mode();
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let should_compute = element.borrow_data().map_or(true, |d| d.get_current_styles().is_none());
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debug!("recalc_style_at: {:?} (should_compute={:?} mode={:?}, data={:?})",
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element, should_compute, mode, element.borrow_data());
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let (computed_display_none, propagated_hint) = if should_compute {
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compute_style::<_, _, D>(context, element, &*bf)
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compute_style::<_, _, D>(context, dom_depth, element)
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} else {
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(false, StoredRestyleHint::empty())
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};
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@ -294,25 +228,24 @@ pub fn recalc_style_at<'a, E, C, D>(context: &'a C,
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preprocess_children::<_, _, D>(context, element, propagated_hint,
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mode == StylingMode::Restyle);
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}
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let unsafe_layout_node = element.as_node().to_unsafe();
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// Before running the children, we need to insert our nodes into the bloom
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// filter.
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debug!("[{}] + {:X}", tid(), unsafe_layout_node.0);
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element.insert_into_bloom_filter(&mut *bf);
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// NB: flow construction updates the bloom filter on the way up.
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put_thread_local_bloom_filter(bf, &unsafe_layout_node, context.shared_context());
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}
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fn compute_style<'a, E, C, D>(context: &'a C,
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element: E,
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bloom_filter: &BloomFilter) -> (bool, StoredRestyleHint)
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dom_depth: Option<usize>,
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element: E) -> (bool, StoredRestyleHint)
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where E: TElement,
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C: StyleContext<'a>,
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D: DomTraversalContext<E::ConcreteNode>
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{
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let shared_context = context.shared_context();
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let mut bf = take_thread_local_bloom_filter(shared_context);
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// Ensure the bloom filter is up to date.
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bf.insert_parents_recovering(element,
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dom_depth,
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shared_context.generation);
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bf.assert_complete(element);
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let mut data = unsafe { D::ensure_element_data(&element).borrow_mut() };
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debug_assert!(!data.is_persistent());
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@ -324,7 +257,7 @@ fn compute_style<'a, E, C, D>(context: &'a C,
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StyleSharingResult::CannotShare
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} else {
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unsafe { element.share_style_if_possible(style_sharing_candidate_cache,
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context.shared_context(), &mut data) }
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shared_context, &mut data) }
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};
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// Otherwise, match and cascade selectors.
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@ -337,7 +270,7 @@ fn compute_style<'a, E, C, D>(context: &'a C,
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}
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// Perform the CSS selector matching.
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match_results = element.match_element(context, Some(bloom_filter));
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match_results = element.match_element(context, Some(bf.filter()));
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if match_results.primary_is_shareable() {
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Some(element)
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} else {
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@ -379,6 +312,13 @@ fn compute_style<'a, E, C, D>(context: &'a C,
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clear_descendant_data(element, &|e| unsafe { D::clear_element_data(&e) });
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}
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// TODO(emilio): It's pointless to insert the element in the parallel
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// traversal, but it may be worth todo it for sequential restyling. What we
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// do now is trying to recover it which in that case is really cheap, so
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// we'd save a few instructions, but probably not worth given the added
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// complexity.
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put_thread_local_bloom_filter(bf);
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(display_none, data.as_restyle().map_or(StoredRestyleHint::empty(), |r| r.hint.propagate()))
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}
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