diff options
| -rw-r--r-- | library/alloc/src/rc.rs | 12 |
1 files changed, 11 insertions, 1 deletions
diff --git a/library/alloc/src/rc.rs b/library/alloc/src/rc.rs index 7dbdc8f6017..1a2dfd28882 100644 --- a/library/alloc/src/rc.rs +++ b/library/alloc/src/rc.rs @@ -329,9 +329,10 @@ impl<T> Rc<T> { /// to upgrade the weak reference before this function returns will result /// in a `None` value. However, the weak reference may be cloned freely and /// stored for use at a later time. - #[inline] #[unstable(feature = "arc_new_cyclic", issue = "75861")] pub fn new_cyclic(data_fn: impl FnOnce(&Weak<T>) -> T) -> Rc<T> { + // Construct the inner in the "uninitialized" state with a single + // weak reference. let uninit_ptr: NonNull<_> = Box::leak(box RcBox { strong: Cell::new(0), weak: Cell::new(1), @@ -343,6 +344,12 @@ impl<T> Rc<T> { let weak = Weak { ptr: init_ptr }; + // It's important we don't give up ownership of the weak pointer, or + // else the memory might be freed by the time `data_fn` returns. If + // we really wanted to pass ownership, we could create an additional + // weak pointer for ourselves, but this would result in additional + // updates to the weak reference count which might not be necessary + // otherwise. let data = data_fn(&weak); unsafe { @@ -355,6 +362,9 @@ impl<T> Rc<T> { } let strong = Rc::from_inner(init_ptr); + + // Strong references should collectively own a shared weak reference, + // so don't run the destructor for our old weak reference. mem::forget(weak); strong } |