Optimistic concurrency with OPTIK

Abstract

We introduce OPTIK, a new practical design pattern for designing and implementing fast and scalable concurrent data structures. OPTIK relies on the commonly-used technique of version numbers for detecting conflicting concurrent operations. We show how to implement the OPTIK pattern using the novel concept of OPTIK locks. These locks enable the use of version numbers for implementing very efficient optimistic concurrent data structures. Existing state-of-the-art lock-based data structures acquire the lock and then check for conflicts. In contrast, with OPTIK locks, we merge the lock acquisition with the detection of conflicting concurrency in a single atomic step, similarly to lock-free algorithms. We illustrate the power of our OPTIK pattern and its implementation by introducing four new algorithms and by optimizing four state-of-the-art algorithms for linked lists, skip lists, hash tables, and queues. Our results show that concurrent data structures built using OPTIK are more scalable than the state of the art.

A scalable lock on NUMA multicore

“…First, a thread trying to become a combiner has to contend for an additional global lock. Second, inserting a node into the list head has to make a version check, 40,41 which can incur significant cache coherence traffic. Finally, it spends extra cost on traversing the whole list to remove request nodes that have not been used to execute critical sections in a long time.…”