SIGUNBLOCK

SIGUNBLOCK is a conceptual toolkit and reference design for managing unblock operations in asynchronous and concurrent software systems. The term is used in theoretical discussions and some experimental libraries to address how blocked tasks, signals, or resources can be released without compromising correctness or performance.

Core concepts include a central unblock registry that tracks blockers, a policy engine that selects when and how unblocks occur, and adapters for common runtimes (POSIX threads, asyncio, event-driven architectures). Unblock operations may be cooperative (tasks periodically yield and check for unblock conditions) or preemptive (the runtime injects unblock events under defined policies). Safety mechanisms aim to avoid deadlocks, priority inversion, and livelock.

Implementation typically provides: an unblock request API, a set of unblock triggers (timeouts, I/O readiness, cancellation), a state machine for blocked/unblocked transitions, and instrumentation for debugging.

Applications include high-concurrency servers, real-time streaming, embedded systems, distributed simulations, and testing tools that need deterministic unblocking behavior. As SIGUNBLOCK is not a formal standard, its exact semantics vary across platforms and projects.

See also: asynchronous I/O, signal handling, non-blocking I/O, event loop, concurrency control.