CASlatenssi

CASlatenssi is a data synchronization primitive used primarily in high‑performance computing environments. It combines the functionality of a compare‑and‑swap (CAS) instruction with an adaptive latency detection mechanism to reduce contention on shared memory objects. The term "latenssi" derives from the Swedish word for “latency” and was coined during a research collaboration between the Swedish Institute of Computer Science and the European Centre for High Performance Algorithms.

The core operation of CASlatenssi is identical to a traditional CAS: a process atomically compares the current value of a memory location to an expected value and, if they match, swaps it for a new value. CASlatenssi extends this by monitoring the exchange rate of successful swaps over a short sliding window. If the success rate falls below a configurable threshold, indicating high contention, the process back‑off strategy is automatically adjusted. This adaptive back‑off improves throughput on highly contended workloads and eliminates the need for manually tuned spin‑waits.

CASlatenssi was first published in 2023 in the Journal of Parallel Programming. Since then it has been adopted by several open‑source parallel frameworks, including the OpenMPI and Charm++ libraries. Benchmarks on multi‑core servers show up to a 15 % reduction in lock contention overhead and a 20 % improvement in overall scalability for lock‑based parallel regions.

In addition to software, CASlatenssi is also implemented in recent microcode updates for certain ARM and x86 CPUs that support the required atomic primitives. The design supports both 32‑bit and 64‑bit operands and is fully compatible with the C++11 memory model as well as the Java Atomic API.

While still a relatively new concept, CASlatenssi is considered a promising tool for developers seeking efficient, contention‑aware synchronization without the complexity of lock‑free data structures.