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Make the DomTraversalContext own the SharedStyleContext and share it immutably across the traversal.
This allows us to get rid of a bunch of lifetimes and simplify a lot of code. It also lets us get rid of that nasty lifetime transmute, which is awesome. The situation with thread-local contexts is still suboptimal, but we fix that in subsequent patches.
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18 changed files with 329 additions and 323 deletions
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@ -5,74 +5,59 @@
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//! Traversals over the DOM and flow trees, running the layout computations.
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use construct::FlowConstructor;
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use context::{LayoutContext, SharedLayoutContext};
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use context::{LayoutContext, SharedLayoutContext, ThreadLocalLayoutContext};
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use context::create_or_get_local_context;
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use display_list_builder::DisplayListBuildState;
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use flow::{self, PreorderFlowTraversal};
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use flow::{CAN_BE_FRAGMENTED, Flow, ImmutableFlowUtils, PostorderFlowTraversal};
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use gfx::display_list::OpaqueNode;
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use script_layout_interface::wrapper_traits::{LayoutNode, ThreadSafeLayoutNode};
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use servo_config::opts;
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use std::mem;
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use std::rc::Rc;
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use style::atomic_refcell::AtomicRefCell;
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use style::context::{LocalStyleContext, SharedStyleContext, StyleContext};
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use style::context::{SharedStyleContext, StyleContext};
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use style::data::ElementData;
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use style::dom::{TElement, TNode};
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use style::selector_parser::RestyleDamage;
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use style::servo::restyle_damage::{BUBBLE_ISIZES, REFLOW, REFLOW_OUT_OF_FLOW, REPAINT};
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use style::traversal::{DomTraversalContext, recalc_style_at, remove_from_bloom_filter};
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use style::traversal::{DomTraversal, recalc_style_at, remove_from_bloom_filter};
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use style::traversal::PerLevelTraversalData;
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use wrapper::{GetRawData, LayoutNodeHelpers, LayoutNodeLayoutData};
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pub struct RecalcStyleAndConstructFlows<'lc> {
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context: LayoutContext<'lc>,
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pub struct RecalcStyleAndConstructFlows {
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shared: SharedLayoutContext,
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root: OpaqueNode,
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}
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#[allow(unsafe_code)]
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impl<'lc, N> DomTraversalContext<N> for RecalcStyleAndConstructFlows<'lc>
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where N: LayoutNode + TNode,
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N::ConcreteElement: TElement
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impl RecalcStyleAndConstructFlows {
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pub fn shared_layout_context(&self) -> &SharedLayoutContext {
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&self.shared
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}
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}
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{
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type SharedContext = SharedLayoutContext;
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#[allow(unsafe_code)]
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fn new<'a>(shared: &'a Self::SharedContext, root: OpaqueNode) -> Self {
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// FIXME(bholley): This transmutation from &'a to &'lc is very unfortunate, but I haven't
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// found a way to avoid it despite spending several days on it (and consulting Manishearth,
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// brson, and nmatsakis).
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//
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// The crux of the problem is that parameterizing DomTraversalContext on the lifetime of
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// the SharedContext doesn't work for a variety of reasons [1]. However, the code in
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// parallel.rs needs to be able to use the DomTraversalContext trait (or something similar)
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// to stack-allocate a struct (a generalized LayoutContext<'a>) that holds a borrowed
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// SharedContext, which means that the struct needs to be parameterized on a lifetime.
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// Given the aforementioned constraint, the only way to accomplish this is to avoid
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// propagating the borrow lifetime from the struct to the trait, but that means that the
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// new() method on the trait cannot require the lifetime of its argument to match the
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// lifetime of the Self object it creates.
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//
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// This could be solved with an associated type with an unbound lifetime parameter, but
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// that would require higher-kinded types, which don't exist yet and probably aren't coming
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// for a while.
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//
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// So we transmute. :-( This is safe because the DomTravesalContext is stack-allocated on
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// the worker thread while processing a WorkUnit, whereas the borrowed SharedContext is
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// live for the entire duration of the restyle. This really could _almost_ compile: all
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// we'd need to do is change the signature to to |new<'a: 'lc>|, and everything would
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// work great. But we can't do that, because that would cause a mismatch with the signature
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// in the trait we're implementing, and we can't mention 'lc in that trait at all for the
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// reasons described above.
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//
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// [1] For example, the WorkQueue type needs to be parameterized on the concrete type of
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// DomTraversalContext::SharedContext, and the WorkQueue lifetime is similar to that of the
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// LayoutThread, generally much longer than that of a given SharedLayoutContext borrow.
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let shared_lc: &'lc SharedLayoutContext = unsafe { mem::transmute(shared) };
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impl RecalcStyleAndConstructFlows {
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/// Creates a traversal context, taking ownership of the shared layout context.
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pub fn new(shared: SharedLayoutContext, root: OpaqueNode) -> Self {
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RecalcStyleAndConstructFlows {
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context: LayoutContext::new(shared_lc),
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shared: shared,
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root: root,
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}
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}
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/// Consumes this traversal context, returning ownership of the shared layout
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/// context to the caller.
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pub fn destroy(self) -> SharedLayoutContext {
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self.shared
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}
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}
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#[allow(unsafe_code)]
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impl<N> DomTraversal<N> for RecalcStyleAndConstructFlows
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where N: LayoutNode + TNode,
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N::ConcreteElement: TElement
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{
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type ThreadLocalContext = ThreadLocalLayoutContext;
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fn process_preorder(&self, node: N, traversal_data: &mut PerLevelTraversalData) {
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// FIXME(pcwalton): Stop allocating here. Ideally this should just be
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// done by the HTML parser.
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@ -81,12 +66,19 @@ impl<'lc, N> DomTraversalContext<N> for RecalcStyleAndConstructFlows<'lc>
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if !node.is_text_node() {
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let el = node.as_element().unwrap();
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let mut data = el.mutate_data().unwrap();
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recalc_style_at::<_, _, Self>(&self.context, traversal_data, el, &mut data);
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let tlc = create_or_get_local_context(&self.shared);
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let context = StyleContext {
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shared: &self.shared.style_context,
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thread_local: &tlc.style_context,
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};
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recalc_style_at(self, traversal_data, &context, el, &mut data);
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}
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}
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fn process_postorder(&self, node: N) {
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construct_flows_at(&self.context, self.root, node);
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let tlc = create_or_get_local_context(&self.shared);
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let context = LayoutContext::new(&self.shared, &*tlc);
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construct_flows_at(&context, self.root, node);
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}
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fn text_node_needs_traversal(node: N) -> bool {
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@ -107,8 +99,12 @@ impl<'lc, N> DomTraversalContext<N> for RecalcStyleAndConstructFlows<'lc>
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element.as_node().clear_data();
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}
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fn local_context(&self) -> &LocalStyleContext {
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self.context.local_context()
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fn shared_context(&self) -> &SharedStyleContext {
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&self.shared.style_context
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}
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fn create_or_get_thread_local_context(&self) -> Rc<ThreadLocalLayoutContext> {
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create_or_get_local_context(&self.shared)
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}
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}
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@ -121,7 +117,9 @@ pub trait PostorderNodeMutTraversal<ConcreteThreadSafeLayoutNode: ThreadSafeLayo
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/// The flow construction traversal, which builds flows for styled nodes.
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#[inline]
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#[allow(unsafe_code)]
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fn construct_flows_at<'a, N: LayoutNode>(context: &'a LayoutContext<'a>, root: OpaqueNode, node: N) {
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fn construct_flows_at<'a, N>(context: &LayoutContext<'a>, root: OpaqueNode, node: N)
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where N: LayoutNode,
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{
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debug!("construct_flows_at: {:?}", node);
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// Construct flows for this node.
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@ -146,7 +144,7 @@ fn construct_flows_at<'a, N: LayoutNode>(context: &'a LayoutContext<'a>, root: O
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el.mutate_data().unwrap().persist();
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unsafe { el.unset_dirty_descendants(); }
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remove_from_bloom_filter(context, root, el);
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remove_from_bloom_filter(&context.shared.style_context, root, el);
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}
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}
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