An Improved Lock-Free Binary Search Tree

We investigated the binary search tree data structure proposed in the publication, Efficient Lock-Free Binary Search Trees by Bapi Chatterjee, Nhan Nguyen and Philipas Tsigas. We will explore its correctness, progression factor, and the linearizability of its operations and report our findings. With a lock-free algorithm, software engineers will be able to use a thread-safe binary search tree that is capable of the many different operations that are normally available on a binary search tree. This includes the basic, primitive operations of Add(), Contains(), and Remove(), without the performance loss of using a binary search tree that uses object locking. An implementation of a binary search tree that uses locks to promote thread-safety takes a performance loss due to the threads waiting when another thread holds the lock and causing contention. The approach outlined in the aforementioned paper claims to have several key fundamental improvements over existing lock-free binary search tree algorithms. This implementation of the binary search tree eliminates contention in Contains() operations where, if a node was modified while a Contains() operation took place, the program would restart any current operation from the root of the tree. This happens because the thread can no longer reliably confide in the traversal of the tree and must restart its search. This is taxing to the performance of a binary search tree and an inefficient design can underperform a sequential implementation. Among other improvements, the authors of this paper claim that their algorithm is linearizable and has improved disjoint-access parallelism compared to similar existing algorithms.