FeatureNonlocking

FeatureNonlocking describes a class of software design choices that aim to perform operations without acquiring locks on shared data, thereby avoiding blocking and reducing contention under concurrent access. The core idea is to use non-blocking synchronization techniques such as atomic operations, compare-and-swap (CAS), or lock-free and wait-free data structures to maintain correctness without holding a mutex.

This approach is common in multithreaded libraries, real-time systems, high-throughput services, and user interfaces where latency spikes due to locking can degrade performance. Benefits include improved scalability, lower latency under high contention, and better responsiveness of interactive components.

Trade-offs include higher design and verification complexity, potential livelock or liveliness issues, and sometimes higher CPU utilization due to spinning; not all operations admit a non-blocking formulation. Implementation considerations include choosing appropriate non-blocking data structures, providing clear guarantees about progress (wait-free, lock-free, obstruction-free), considering memory models, and including thorough testing with concurrency stress tests.

Examples include non-blocking queues, atomic counters, and lock-free stacks. Software transactional memory can provide nonblocking semantics at a higher level. Related concepts include lock-based synchronization, optimistic versus pessimistic concurrency, and lock-free programming. The term is often used in product documentation or design discussions to denote a feature or component that avoids blocking behavior to improve concurrency and responsiveness.