Wait-Free Weak Reference Counting
Matthew Parkinson, Sylvan Clebsch, Ben Simner · 2023
Reference counting is a common approach to memory management. One challenge with reference counting is cycles that prevent objects from being deallocated. Systems such as the C++ and Rust standard libraries introduce two types of reference: strong and weak. A strong reference allows access to the object and prevents the object from being deallocated, while a weak reference only prevents deallocation. A weak reference can be upgraded to provide a strong reference provided there are other strong references to the object. Hence, the upgrade operation is partial, and may fail dynamically. The classic implementation of this upgrade operation is not wait-free, that is, it can take arbitrarily long to complete if there is contention on the reference count.