threadsafety

Thread safety is the property of software components to function correctly when accessed by multiple threads concurrently. A thread-safe component ensures that its behavior remains correct and its data remains consistent regardless of the interleaving of thread execution, or it uses proper synchronization to control access. Thread safety is often achieved through immutability, confined usage within a single thread, or by synchronizing access with primitives such as mutexes or locks, atomic operations, or lock-free algorithms.

Common approaches include making objects immutable so their state cannot change after construction, restricting a resource to one thread (thread confinement), and using synchronization to guard critical sections. Atomic operations provide indivisible updates to shared values, while lock-free and wait-free data structures avoid explicit locking but rely on advanced techniques to ensure progress. In some environments, memory models require correct synchronization to guarantee visibility of writes across threads, ensuring that changes become observable in a defined order.

Thread safety is related to, but distinct from, reentrancy. A thread-safe function can be safely invoked by multiple threads concurrently; a reentrant function is safe to call again before a previous invocation completes, even if it has been interrupted. Reentrancy is a stronger requirement in some contexts, as it often implies independence from shared state.

Common pitfalls include data races, deadlocks, livelocks, and priority inversion. Thorough testing—including stress testing and dynamic data-race detection—helps verify thread safety. Libraries and components may advertise thread safety to indicate that they are designed to support concurrent use, whereas non-thread-safe code requires external synchronization to avoid incorrect behavior.