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Auto merge of #115546 - SUPERCILEX:patch-2, r=Amanieu

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Weaken needlessly restrictive orderings on Arc::*_count

Follow up to https://github.com/rust-lang/rust/pull/95183 from this zulip: https://rust-lang.zulipchat.com/#narrow/stream/219381-t-libs/topic/Why.20does.20Arc.3A.3Astrong_count.20use.20Acquire.20instead.20of.20Relaxed.3F/near/386213850

I'd like to use the strong_count for a lockless algorithm I'm writing, but I don't need acquire semantics so that's pointlessly restrictive on arm/risc-v.
This commit is contained in:
bors 2023-09-30 02:15:19 +00:00
commit 4efd65571e
1 changed files with 4 additions and 4 deletions
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8
library/alloc/src/sync.rs
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@ -1618,7 +1618,7 @@ impl<T: ?Sized, A: Allocator> Arc<T, A> {
#[must_use]
#[stable(feature = "arc_counts", since = "1.15.0")]
pub fn weak_count(this: &Self) -> usize {
let cnt = this.inner().weak.load(Acquire);
let cnt = this.inner().weak.load(Relaxed);
// If the weak count is currently locked, the value of the
// count was 0 just before taking the lock.
if cnt == usize::MAX { 0 } else { cnt - 1 }
@ -1648,7 +1648,7 @@ impl<T: ?Sized, A: Allocator> Arc<T, A> {
#[must_use]
#[stable(feature = "arc_counts", since = "1.15.0")]
pub fn strong_count(this: &Self) -> usize {
this.inner().strong.load(Acquire)
this.inner().strong.load(Relaxed)
}
/// Increments the strong reference count on the `Arc<T>` associated with the
@ -2803,7 +2803,7 @@ impl<T: ?Sized, A: Allocator> Weak<T, A> {
#[must_use]
#[stable(feature = "weak_counts", since = "1.41.0")]
pub fn strong_count(&self) -> usize {
if let Some(inner) = self.inner() { inner.strong.load(Acquire) } else { 0 }
if let Some(inner) = self.inner() { inner.strong.load(Relaxed) } else { 0 }
}
/// Gets an approximation of the number of `Weak` pointers pointing to this
@ -2822,7 +2822,7 @@ impl<T: ?Sized, A: Allocator> Weak<T, A> {
pub fn weak_count(&self) -> usize {
if let Some(inner) = self.inner() {
let weak = inner.weak.load(Acquire);
let strong = inner.strong.load(Acquire);
let strong = inner.strong.load(Relaxed);
if strong == 0 {
0
} else {