diff options
Diffstat (limited to 'library/alloc/src/sync.rs')
| -rw-r--r-- | library/alloc/src/sync.rs | 38 |
1 files changed, 28 insertions, 10 deletions
diff --git a/library/alloc/src/sync.rs b/library/alloc/src/sync.rs index 3183a6db410..a066e0b49e2 100644 --- a/library/alloc/src/sync.rs +++ b/library/alloc/src/sync.rs @@ -1346,18 +1346,19 @@ impl<T: ?Sized> Receiver for Arc<T> {} impl<T: Clone> Arc<T> { /// Makes a mutable reference into the given `Arc`. /// - /// If there are other `Arc` or [`Weak`] pointers to the same allocation, - /// then `make_mut` will create a new allocation and invoke [`clone`][clone] on the inner value - /// to ensure unique ownership. This is also referred to as clone-on-write. + /// If there are other `Arc` pointers to the same allocation, then `make_mut` will + /// [`clone`] the inner value to a new allocation to ensure unique ownership. This is also + /// referred to as clone-on-write. /// - /// Note that this differs from the behavior of [`Rc::make_mut`] which disassociates - /// any remaining `Weak` pointers. + /// However, if there are no other `Arc` pointers to this allocation, but some [`Weak`] + /// pointers, then the [`Weak`] pointers will be disassociated and the inner value will not + /// be cloned. /// - /// See also [`get_mut`][get_mut], which will fail rather than cloning. + /// See also [`get_mut`], which will fail rather than cloning the inner value + /// or diassociating [`Weak`] pointers. /// - /// [clone]: Clone::clone - /// [get_mut]: Arc::get_mut - /// [`Rc::make_mut`]: super::rc::Rc::make_mut + /// [`clone`]: Clone::clone + /// [`get_mut`]: Arc::get_mut /// /// # Examples /// @@ -1376,6 +1377,23 @@ impl<T: Clone> Arc<T> { /// assert_eq!(*data, 8); /// assert_eq!(*other_data, 12); /// ``` + /// + /// [`Weak`] pointers will be disassociated: + /// + /// ``` + /// use std::sync::Arc; + /// + /// let mut data = Arc::new(75); + /// let weak = Arc::downgrade(&data); + /// + /// assert!(75 == *data); + /// assert!(75 == *weak.upgrade().unwrap()); + /// + /// *Arc::make_mut(&mut data) += 1; + /// + /// assert!(76 == *data); + /// assert!(weak.upgrade().is_none()); + /// ``` #[cfg(not(no_global_oom_handling))] #[inline] #[stable(feature = "arc_unique", since = "1.4.0")] @@ -1441,7 +1459,7 @@ impl<T: ?Sized> Arc<T> { /// mutate a shared value. /// /// See also [`make_mut`][make_mut], which will [`clone`][clone] - /// the inner value when there are other pointers. + /// the inner value when there are other `Arc` pointers. /// /// [make_mut]: Arc::make_mut /// [clone]: Clone::clone |