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Make FlowRef a newtype

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This creates a sharp distinction between `Arc<Flow>`s, which may be
owned by anyone, and `FlowRef`s, which may only be owned by the
traversal code. By checking the reference count, we ensure that a `Flow`
cannot be pointed to by `Arc`s and `FlowRef`s simultaneously.

This is not a complete fix for #6503, though it is a necessary start
(enforcing the no-aliasing rule of `FlowRef::deref_mut` will require far
more work).

Fixes #14014
This commit is contained in:
Michael Howell 2016-11-03 12:53:27 -07:00
parent 5b4cc9568d
commit 5f320bd2ca
10 changed files with 145 additions and 101 deletions
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14
components/layout/flow.rs
View file

@ -32,7 +32,7 @@ use display_list_builder::DisplayListBuildState;
use euclid::{Point2D, Size2D};
use floats::{Floats, SpeculatedFloatPlacement};
use flow_list::{FlowList, MutFlowListIterator};
use flow_ref::{self, FlowRef, WeakFlowRef};
use flow_ref::{FlowRef, WeakFlowRef};
use fragment::{Fragment, FragmentBorderBoxIterator, Overflow};
use gfx::display_list::{ClippingRegion, StackingContext};
use gfx_traits::{ScrollRootId, StackingContextId};
@ -212,7 +212,7 @@ pub trait Flow: fmt::Debug + Sync + Send + 'static {
fn fragment(&mut self,
layout_context: &LayoutContext,
_fragmentation_context: Option<FragmentationContext>)
-> Option<FlowRef> {
-> Option<Arc<Flow>> {
fn recursive_assign_block_size<F: ?Sized + Flow>(flow: &mut F, ctx: &LayoutContext) {
for child in mut_base(flow).children.iter_mut() {
recursive_assign_block_size(child, ctx)
@ -791,7 +791,7 @@ pub struct AbsoluteDescendantIter<'a> {
impl<'a> Iterator for AbsoluteDescendantIter<'a> {
type Item = &'a mut Flow;
fn next(&mut self) -> Option<&'a mut Flow> {
self.iter.next().map(|info| flow_ref::deref_mut(&mut info.flow))
self.iter.next().map(|info| FlowRef::deref_mut(&mut info.flow))
}
}
@ -1403,11 +1403,11 @@ impl MutableOwnedFlowUtils for FlowRef {
/// construction is allowed to possess.
fn set_absolute_descendants(&mut self, abs_descendants: AbsoluteDescendants) {
let this = self.clone();
let base = mut_base(flow_ref::deref_mut(self));
let base = mut_base(FlowRef::deref_mut(self));
base.abs_descendants = abs_descendants;
for descendant_link in base.abs_descendants.descendant_links.iter_mut() {
debug_assert!(!descendant_link.has_reached_containing_block);
let descendant_base = mut_base(flow_ref::deref_mut(&mut descendant_link.flow));
let descendant_base = mut_base(FlowRef::deref_mut(&mut descendant_link.flow));
descendant_base.absolute_cb.set(this.clone());
}
}
@ -1433,7 +1433,7 @@ impl MutableOwnedFlowUtils for FlowRef {
});
let this = self.clone();
let base = mut_base(flow_ref::deref_mut(self));
let base = mut_base(FlowRef::deref_mut(self));
base.abs_descendants = applicable_absolute_descendants;
for descendant_link in base.abs_descendants.iter() {
let descendant_base = mut_base(descendant_link);
@ -1464,7 +1464,7 @@ impl ContainingBlockLink {
}
fn set(&mut self, link: FlowRef) {
self.link = Some(Arc::downgrade(&link))
self.link = Some(FlowRef::downgrade(&link))
}
#[inline]