Explain how multithreading works and when to use locks. Compare mutexes, semaphores, and read–write locks, including their pros/cons and appropriate use cases. Identify race conditions, deadlocks, livelocks, and starvation; outline concrete strategies to avoid them (e.g., lock ordering, timeouts, backoff, minimizing critical sections). Then design and implement a thread-safe bounded queue supporting multiple producers and consumers using condition variables, and describe how you would test it for correctness and performance.