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Hoist the style parts of parallel.rs into style/.
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4 changed files with 148 additions and 130 deletions
142
components/style/parallel.rs
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142
components/style/parallel.rs
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/* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
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//! Implements parallel traversal over the DOM tree.
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//!
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//! This code is highly unsafe. Keep this file small and easy to audit.
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#![allow(unsafe_code)]
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use dom::{OpaqueNode, TNode, UnsafeNode};
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use std::mem;
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use std::sync::atomic::Ordering;
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use traversal::DomTraversalContext;
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use util::workqueue::{WorkQueue, WorkUnit, WorkerProxy};
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#[allow(dead_code)]
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fn static_assertion(node: UnsafeNode) {
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unsafe {
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let _: UnsafeNodeList = ::std::intrinsics::transmute(node);
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}
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}
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pub type UnsafeNodeList = (Box<Vec<UnsafeNode>>, OpaqueNode);
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pub const CHUNK_SIZE: usize = 64;
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pub struct WorkQueueData(usize, usize);
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pub fn run_queue_with_custom_work_data_type<To, F, SharedContext: Sync>(
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queue: &mut WorkQueue<SharedContext, WorkQueueData>,
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callback: F,
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shared: &SharedContext)
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where To: 'static + Send, F: FnOnce(&mut WorkQueue<SharedContext, To>) {
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let queue: &mut WorkQueue<SharedContext, To> = unsafe {
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mem::transmute(queue)
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};
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callback(queue);
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queue.run(shared);
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}
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pub fn traverse_dom_preorder<'ln, N, C>(
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root: N,
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queue_data: &C::SharedContext,
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queue: &mut WorkQueue<C::SharedContext, WorkQueueData>)
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where N: TNode<'ln>, C: DomTraversalContext<'ln, N> {
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run_queue_with_custom_work_data_type(queue, |queue| {
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queue.push(WorkUnit {
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fun: top_down_dom::<N, C>,
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data: (box vec![root.to_unsafe()], root.opaque()),
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});
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}, queue_data);
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}
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/// A parallel top-down DOM traversal.
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#[inline(always)]
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fn top_down_dom<'ln, N, C>(unsafe_nodes: UnsafeNodeList,
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proxy: &mut WorkerProxy<C::SharedContext, UnsafeNodeList>)
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where N: TNode<'ln>, C: DomTraversalContext<'ln, N> {
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let context = C::new(proxy.user_data(), unsafe_nodes.1);
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let mut discovered_child_nodes = Vec::new();
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for unsafe_node in *unsafe_nodes.0 {
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// Get a real layout node.
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let node = unsafe { N::from_unsafe(&unsafe_node) };
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// Perform the appropriate traversal.
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context.process_preorder(node);
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let child_count = node.children_count();
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// Reset the count of children.
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{
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let data = node.mutate_data().unwrap();
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data.parallel.children_count.store(child_count as isize,
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Ordering::Relaxed);
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}
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// Possibly enqueue the children.
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if child_count != 0 {
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for kid in node.children() {
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discovered_child_nodes.push(kid.to_unsafe())
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}
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} else {
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// If there were no more children, start walking back up.
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bottom_up_dom::<N, C>(unsafe_nodes.1, unsafe_node, proxy)
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}
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}
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for chunk in discovered_child_nodes.chunks(CHUNK_SIZE) {
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proxy.push(WorkUnit {
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fun: top_down_dom::<N, C>,
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data: (box chunk.iter().cloned().collect(), unsafe_nodes.1),
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});
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}
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}
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/// Process current node and potentially traverse its ancestors.
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///
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/// If we are the last child that finished processing, recursively process
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/// our parent. Else, stop. Also, stop at the root.
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///
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/// Thus, if we start with all the leaves of a tree, we end up traversing
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/// the whole tree bottom-up because each parent will be processed exactly
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/// once (by the last child that finishes processing).
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///
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/// The only communication between siblings is that they both
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/// fetch-and-subtract the parent's children count.
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fn bottom_up_dom<'ln, N, C>(root: OpaqueNode,
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unsafe_node: UnsafeNode,
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proxy: &mut WorkerProxy<C::SharedContext, UnsafeNodeList>)
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where N: TNode<'ln>, C: DomTraversalContext<'ln, N> {
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let context = C::new(proxy.user_data(), root);
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// Get a real layout node.
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let mut node = unsafe { N::from_unsafe(&unsafe_node) };
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loop {
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// Perform the appropriate operation.
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context.process_postorder(node);
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let parent = match node.layout_parent_node(root) {
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None => break,
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Some(parent) => parent,
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};
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let parent_data = unsafe {
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&*parent.borrow_data_unchecked().unwrap()
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};
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if parent_data
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.parallel
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.children_count
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.fetch_sub(1, Ordering::Relaxed) != 1 {
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// Get out of here and find another node to work on.
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break
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}
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// We were the last child of our parent. Construct flows for our parent.
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node = parent;
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}
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}
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