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Fix memory leak in flow tree by adding weak refs.

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Cycles were being created in the flow tree since absolutely positioned
descendants had pointers to their containing blocks. This adds
WeakFlowRef (based on Weak<T>) and makes these backpointers weak
references. This also harmonizes our custom Arc<T>, FlowRef, to be
consistent with the upstream implementation.

Fixes #4915.
This commit is contained in:
Jack Moffitt 2015-03-12 16:32:49 -06:00
parent 660ea05ddb
commit 237150fa49
4 changed files with 147 additions and 18 deletions
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26
components/layout/flow.rs
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@ -31,7 +31,7 @@ use context::LayoutContext;
use display_list_builder::DisplayListBuildingResult;
use floats::Floats;
use flow_list::{FlowList, FlowListIterator, MutFlowListIterator};
use flow_ref::FlowRef;
use flow_ref::{FlowRef, WeakFlowRef};
use fragment::{Fragment, FragmentBorderBoxIterator, SpecificFragmentInfo};
use incremental::{self, RECONSTRUCT_FLOW, REFLOW, REFLOW_OUT_OF_FLOW, RestyleDamage};
use inline::InlineFlow;
@ -740,7 +740,9 @@ pub struct BaseFlow {
/// NB: Must be the first element.
///
/// The necessity of this will disappear once we have dynamically-sized types.
ref_count: AtomicUint,
strong_ref_count: AtomicUint,
weak_ref_count: AtomicUint,
pub restyle_damage: RestyleDamage,
@ -887,7 +889,8 @@ impl Encodable for BaseFlow {
#[unsafe_destructor]
impl Drop for BaseFlow {
fn drop(&mut self) {
if self.ref_count.load(Ordering::SeqCst) != 0 {
if self.strong_ref_count.load(Ordering::SeqCst) != 0 &&
self.weak_ref_count.load(Ordering::SeqCst) != 0 {
panic!("Flow destroyed before its ref count hit zero—this is unsafe!")
}
}
@ -948,7 +951,8 @@ impl BaseFlow {
damage.remove(RECONSTRUCT_FLOW);
BaseFlow {
ref_count: AtomicUint::new(1),
strong_ref_count: AtomicUint::new(1),
weak_ref_count: AtomicUint::new(1),
restyle_damage: damage,
children: FlowList::new(),
intrinsic_inline_sizes: IntrinsicISizes::new(),
@ -978,8 +982,12 @@ impl BaseFlow {
self.children.iter_mut()
}
pub unsafe fn ref_count<'a>(&'a self) -> &'a AtomicUint {
&self.ref_count
pub unsafe fn strong_ref_count<'a>(&'a self) -> &'a AtomicUint {
&self.strong_ref_count
}
pub unsafe fn weak_ref_count<'a>(&'a self) -> &'a AtomicUint {
&self.weak_ref_count
}
pub fn debug_id(&self) -> uint {
@ -1333,7 +1341,7 @@ impl MutableOwnedFlowUtils for FlowRef {
/// FIXME(pcwalton): I think this would be better with a borrow flag instead of `unsafe`.
pub struct ContainingBlockLink {
/// The pointer up to the containing block.
link: Option<FlowRef>,
link: Option<WeakFlowRef>,
}
impl ContainingBlockLink {
@ -1344,10 +1352,10 @@ impl ContainingBlockLink {
}
fn set(&mut self, link: FlowRef) {
self.link = Some(link)
self.link = Some(link.downgrade())
}
pub unsafe fn get<'a>(&'a mut self) -> &'a mut Option<FlowRef> {
pub unsafe fn get<'a>(&'a mut self) -> &'a mut Option<WeakFlowRef> {
&mut self.link
}