What am I using to lock this?

What this operating-systems locking question tests

This is an easy foundational question about the hardware primitives that underpin synchronisation mechanisms in modern operating systems. It probes whether you understand the lowest-level building blocks that allow concurrent code to safely access shared resources.

To answer well, think about what capabilities a processor must expose to enable mutual exclusion—specifically, the atomic operations that let software construct higher-level abstractions like mutexes and spinlocks. The question rewards clear understanding of why certain hardware features are essential for lock implementation, rather than deep algorithmic complexity.

• Atomic operations and compare-and-swap semantics
• Memory barriers and ordering guarantees
• The difference between busy-waiting and blocking synchronisation