Concurrency and Thread Safety

When multiple threads touch shared mutable state, interleavings cause race conditions: lost updates, torn reads, corrupted data. Thread safety means correctness under any interleaving. Locks/mutexes enforce mutual exclusion (pessimistic); optimistic concurrency checks for conflicts at commit and retries (compare-and-swap, version columns). Atomic operations avoid locks for simple updates. Deadlock arises when locks are acquired in conflicting orders. Applied-AI interviews probe it because inference servers, batching queues, and shared caches are all concurrent, and the classic double-increment bug still shows up in production.