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Stabilize Arc::{increment,decrement}_strong_count #79285

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Jan 31, 2021
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Stabilize Arc::{increment,decrement}_strong_count #79285

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a55039d
Stabilize Arc::{incr,decr}_strong_count
yoshuawuyts Nov 22, 2020
fe4ac95
Bump stable version of arc_mutate_strong_count
m-ou-se Jan 30, 2021
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18 changes: 7 additions & 11 deletions library/alloc/src/sync.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -870,15 +870,13 @@ impl<T: ?Sized> Arc<T> {
/// # Examples
///
/// ```
/// #![feature(arc_mutate_strong_count)]
///
/// use std::sync::Arc;
///
/// let five = Arc::new(5);
///
/// unsafe {
/// let ptr = Arc::into_raw(five);
/// Arc::incr_strong_count(ptr);
/// Arc::increment_strong_count(ptr);
///
/// // This assertion is deterministic because we haven't shared
/// // the `Arc` between threads.
Expand All @@ -887,8 +885,8 @@ impl<T: ?Sized> Arc<T> {
/// }
/// ```
#[inline]
#[unstable(feature = "arc_mutate_strong_count", issue = "71983")]
pub unsafe fn incr_strong_count(ptr: *const T) {
#[stable(feature = "arc_mutate_strong_count", since = "1.50.0")]
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pub unsafe fn increment_strong_count(ptr: *const T) {
// Retain Arc, but don't touch refcount by wrapping in ManuallyDrop
let arc = unsafe { mem::ManuallyDrop::new(Arc::<T>::from_raw(ptr)) };
// Now increase refcount, but don't drop new refcount either
Expand All @@ -909,27 +907,25 @@ impl<T: ?Sized> Arc<T> {
/// # Examples
///
/// ```
/// #![feature(arc_mutate_strong_count)]
///
/// use std::sync::Arc;
///
/// let five = Arc::new(5);
///
/// unsafe {
/// let ptr = Arc::into_raw(five);
/// Arc::incr_strong_count(ptr);
/// Arc::increment_strong_count(ptr);
///
/// // Those assertions are deterministic because we haven't shared
/// // the `Arc` between threads.
/// let five = Arc::from_raw(ptr);
/// assert_eq!(2, Arc::strong_count(&five));
/// Arc::decr_strong_count(ptr);
/// Arc::decrement_strong_count(ptr);
/// assert_eq!(1, Arc::strong_count(&five));
/// }
/// ```
#[inline]
#[unstable(feature = "arc_mutate_strong_count", issue = "71983")]
pub unsafe fn decr_strong_count(ptr: *const T) {
#[stable(feature = "arc_mutate_strong_count", since = "1.50.0")]
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pub unsafe fn decrement_strong_count(ptr: *const T) {
unsafe { mem::drop(Arc::from_raw(ptr)) };
}

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4 changes: 2 additions & 2 deletions library/alloc/src/task.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -60,7 +60,7 @@ impl<W: Wake + Send + Sync + 'static> From<Arc<W>> for RawWaker {
fn raw_waker<W: Wake + Send + Sync + 'static>(waker: Arc<W>) -> RawWaker {
// Increment the reference count of the arc to clone it.
unsafe fn clone_waker<W: Wake + Send + Sync + 'static>(waker: *const ()) -> RawWaker {
unsafe { Arc::incr_strong_count(waker as *const W) };
unsafe { Arc::increment_strong_count(waker as *const W) };
RawWaker::new(
waker as *const (),
&RawWakerVTable::new(clone_waker::<W>, wake::<W>, wake_by_ref::<W>, drop_waker::<W>),
Expand All @@ -81,7 +81,7 @@ fn raw_waker<W: Wake + Send + Sync + 'static>(waker: Arc<W>) -> RawWaker {

// Decrement the reference count of the Arc on drop
unsafe fn drop_waker<W: Wake + Send + Sync + 'static>(waker: *const ()) {
unsafe { Arc::decr_strong_count(waker as *const W) };
unsafe { Arc::decrement_strong_count(waker as *const W) };
}

RawWaker::new(
Expand Down