Help-optimal and Language-portable Lock-free Concurrent Data Structures
Rapport, 2016

Helping is the most common mechanism to guarantee lock-freedom in many concurrent data structures. An optimized helping strategy improves the overall performance of a lock-free algorithm. In this paper, we propose help-optimality, which essentially implies that no operation step is accounted for exclusive helping in the lock-free synchronization of concurrent operations. To describe the concept, we revisit the designs of a lock-free linked-list and a lock-free binary search tree and present improved algorithms. Our algorithms employ atomic single- word compare-and-swap (CAS) primitives and are linearizable. Additionally, we do not use a language/platform speci?c mechanism to modulate helping, speci?cally, we use neither bit-stealing from a pointer nor runtime type introspection of objects, making the algorithms language-portable. Further, to optimize the amortized number of steps per operation, if a CAS execution to modify a shared pointer fails, we obtain a fresh set of thread-local variables without restarting an operation from scratch. We use several micro-benchmarks in both C/C++ and Java to validate the e?ciency of our algorithms against existing state-of-the-art. The experiments show that the algorithms are scalable. Our implementations perform on a par with highly optimized ones and in many cases yield 10%-50% higher throughput.


concurrent data structure




binary search tree



Bapi Chatterjee

Chalmers, Data- och informationsteknik, Nätverk och system

Ivan Walulya

Chalmers, Data- och informationsteknik, Nätverk och system

Philippas Tsigas

Chalmers, Data- och informationsteknik, Nätverk och system


Informations- och kommunikationsteknik



Technical report - Department of Computer Science and Engineering, Chalmers University of Technology and Göteborg University

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