diff options
| -rw-r--r-- | library/alloc/src/sync.rs | 39 |
1 files changed, 16 insertions, 23 deletions
diff --git a/library/alloc/src/sync.rs b/library/alloc/src/sync.rs index 4377edeee87..fc000cce8f8 100644 --- a/library/alloc/src/sync.rs +++ b/library/alloc/src/sync.rs @@ -1980,33 +1980,26 @@ impl<T: ?Sized> Weak<T> { // We use a CAS loop to increment the strong count instead of a // fetch_add as this function should never take the reference count // from zero to one. - let inner = self.inner()?; - - // Relaxed load because any write of 0 that we can observe - // leaves the field in a permanently zero state (so a - // "stale" read of 0 is fine), and any other value is - // confirmed via the CAS below. - let mut n = inner.strong.load(Relaxed); - - loop { - if n == 0 { - return None; - } - - // See comments in `Arc::clone` for why we do this (for `mem::forget`). - if n > MAX_REFCOUNT { - abort(); - } - + self.inner()? + .strong // Relaxed is fine for the failure case because we don't have any expectations about the new state. // Acquire is necessary for the success case to synchronise with `Arc::new_cyclic`, when the inner // value can be initialized after `Weak` references have already been created. In that case, we // expect to observe the fully initialized value. - match inner.strong.compare_exchange_weak(n, n + 1, Acquire, Relaxed) { - Ok(_) => return Some(unsafe { Arc::from_inner(self.ptr) }), // null checked above - Err(old) => n = old, - } - } + .fetch_update(Acquire, Relaxed, |n| { + // Any write of 0 we can observe leaves the field in permanently zero state. + if n == 0 { + return None; + } + // See comments in `Arc::clone` for why we do this (for `mem::forget`). + if n > MAX_REFCOUNT { + abort(); + } + Some(n + 1) + }) + .ok() + // null checked above + .map(|_| unsafe { Arc::from_inner(self.ptr) }) } /// Gets the number of strong (`Arc`) pointers pointing to this allocation. |