Java Concurrency Interview Questions

Concurrency Basics

1. What’s the difference between concurrency and parallelism?

2. What is thread safety?

3. What is deadlock? How to avoid deadlock?

4. What is livelock and starvation?

5. What’s the difference between process and thread?

6. What’s the difference between coroutine and thread?

synchronized

7. How does synchronized work internally?

8. What’s the difference when synchronized is used in different locations?

9. What are the lock optimization mechanisms of synchronized? (biased lock, lightweight lock, heavyweight lock)

10. What’s the difference between synchronized and ReentrantLock?

11. What is a reentrant lock?

volatile

12. What does the volatile keyword do?

13. How is volatile implemented internally? (memory barriers)

14. Can volatile guarantee atomicity?

15. What’s the difference between volatile and synchronized?

CAS

16. What is CAS?

17. How does CAS work internally?

18. What are the problems with CAS? (ABA problem, spin overhead, single variable only)

19. How to solve the ABA problem?

Locks

20. What are optimistic lock and pessimistic lock?

21. What are fair lock and unfair lock?

22. What are shared lock and exclusive lock?

23. What is a spin lock?

24. How does ReentrantLock work internally?

25. How does ReentrantReadWriteLock work internally?

26. What is StampedLock?

AQS

27. What is AQS?

28. How does AQS work internally?

29. What are the applications of AQS?

30. What’s the difference between CountDownLatch, CyclicBarrier and Semaphore?