Lock-Free Algorithms for Thread Safe Programming

An object is lock-free if it guarantees that in a system where multiple threads are manipulating the object, some thread will complete its operation on the object in a finite number of steps, no matter what happens to other threads. More practically, lock-free programming is a technique to achieve thread safety without the use of locks, which are the current standard. Lock-free objects (LFOs) have a number of useful properties that make them more broadly useful than locked objects, and also tend to perform well under high contention (being accessed by many threads at once). Though lock-free objects are not very common in practice, there is an opportunity for this to change. Lock-free algorithms (LFAs) are notoriously difficult to design and prove correct, and implementing them presents a number of technical challenges, but over the course of around ten years several commonly used data structures have been developed. This paper approaches lock-free objects from a practical standpoint. It addresses their features and problems, along with specific implementation issues. This paper also summarizes a large set of useful lock-free algorithms that would be broadly useful. Finally, it reports on the author’s efforts to implement a collection of lock-free data structures (LFDS) for general use.