diff --git a/library/alloc/src/sync.rs b/library/alloc/src/sync.rs index 22d34ecba845..cb4b364f0862 100644 --- a/library/alloc/src/sync.rs +++ b/library/alloc/src/sync.rs @@ -1489,6 +1489,34 @@ impl Arc { ptr } + /// Consumes the `Arc`, returning the wrapped pointer and allocator. + /// + /// To avoid a memory leak the pointer must be converted back to an `Arc` using + /// [`Arc::from_raw_in`]. + /// + /// # Examples + /// + /// ``` + /// #![feature(allocator_api)] + /// use std::sync::Arc; + /// use std::alloc::System; + /// + /// let x = Arc::new_in("hello".to_owned(), System); + /// let (ptr, alloc) = Arc::into_raw_with_allocator(x); + /// assert_eq!(unsafe { &*ptr }, "hello"); + /// let x = unsafe { Arc::from_raw_in(ptr, alloc) }; + /// assert_eq!(&*x, "hello"); + /// ``` + #[must_use = "losing the pointer will leak memory"] + #[unstable(feature = "allocator_api", issue = "32838")] + pub fn into_raw_with_allocator(this: Self) -> (*const T, A) { + let this = mem::ManuallyDrop::new(this); + let ptr = Self::as_ptr(&this); + // Safety: `this` is ManuallyDrop so the allocator will not be double-dropped + let alloc = unsafe { ptr::read(Self::allocator(&this)) }; + (ptr, alloc) + } + /// Provides a raw pointer to the data. /// /// The counts are not affected in any way and the `Arc` is not consumed. The pointer is valid for @@ -2724,6 +2752,45 @@ impl Weak { result } + /// Consumes the `Weak`, returning the wrapped pointer and allocator. + /// + /// This converts the weak pointer into a raw pointer, while still preserving the ownership of + /// one weak reference (the weak count is not modified by this operation). It can be turned + /// back into the `Weak` with [`from_raw_in`]. + /// + /// The same restrictions of accessing the target of the pointer as with + /// [`as_ptr`] apply. + /// + /// # Examples + /// + /// ``` + /// #![feature(allocator_api)] + /// use std::sync::{Arc, Weak}; + /// use std::alloc::System; + /// + /// let strong = Arc::new_in("hello".to_owned(), System); + /// let weak = Arc::downgrade(&strong); + /// let (raw, alloc) = weak.into_raw_with_allocator(); + /// + /// assert_eq!(1, Arc::weak_count(&strong)); + /// assert_eq!("hello", unsafe { &*raw }); + /// + /// drop(unsafe { Weak::from_raw_in(raw, alloc) }); + /// assert_eq!(0, Arc::weak_count(&strong)); + /// ``` + /// + /// [`from_raw_in`]: Weak::from_raw_in + /// [`as_ptr`]: Weak::as_ptr + #[must_use = "losing the pointer will leak memory"] + #[unstable(feature = "allocator_api", issue = "32838")] + pub fn into_raw_with_allocator(self) -> (*const T, A) { + let this = mem::ManuallyDrop::new(self); + let result = this.as_ptr(); + // Safety: `this` is ManuallyDrop so the allocator will not be double-dropped + let alloc = unsafe { ptr::read(Self::allocator(&this)) }; + (result, alloc) + } + /// Converts a raw pointer previously created by [`into_raw`] back into `Weak` in the provided /// allocator. ///