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Use a different sentinel value to lock the free list.

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We're going to use null to indicate that the final GC has already
occurred.
This commit is contained in:
Bobby Holley 2017-06-29 23:30:33 -07:00
parent 654661df36
commit 67cd974636
1 changed files with 7 additions and 3 deletions
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10
components/style/rule_tree/mod.rs
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@ -122,6 +122,10 @@ impl StyleSource {
/// The root node doesn't have a null pointer in the free list, but this value.
const FREE_LIST_SENTINEL: *mut RuleNode = 0x01 as *mut RuleNode;
/// A second sentinel value for the free list, indicating that it's locked (i.e.
/// another thread is currently adding an entry). We spin if we find this value.
const FREE_LIST_LOCKED: *mut RuleNode = 0x02 as *mut RuleNode;
impl RuleTree {
/// Construct a new rule tree.
pub fn new() -> Self {
@ -1395,7 +1399,7 @@ impl Drop for StrongRuleNode {
return;
}
// Ensure we "lock" the free list head swapping it with a null pointer.
// Ensure we "lock" the free list head swapping it with FREE_LIST_LOCKED.
//
// Note that we use Acquire/Release semantics for the free list
// synchronization, in order to guarantee that the next_free
@ -1404,11 +1408,11 @@ impl Drop for StrongRuleNode {
let mut old_head = free_list.load(Ordering::Relaxed);
loop {
match free_list.compare_exchange_weak(old_head,
ptr::null_mut(),
FREE_LIST_LOCKED,
Ordering::Acquire,
Ordering::Relaxed) {
Ok(..) => {
if !old_head.is_null() {
if old_head != FREE_LIST_LOCKED {
break;
}
},