operating-systems hardware concurrency Definition Test-and-Set Test-and-set is a hardware instruction providing atomic read-modify-write access to a memory location. Essential for implementing mutual exclusion in multiprocessor environments. Implementation Spinlock // Global: int lock = 0; // Process Pi while (testset(&lock) == false); // Busy waiting // --- Critical Section --- lock = 0; // Release lock // --- Remainder Section --- Properties Simplicity Provides a simple entry protocol for critical sections. No Bounded Waiting Ensures mutual exclusion but does not guarantee bounded waiting — lock acquisition order depends on hardware arbitration, not a queue.