Explain AtomicInteger and ABA problem
Company: PayPal
Role: Software Engineer
Category: Coding & Algorithms
Difficulty: Medium
Interview Round: Technical Screen
How does AtomicInteger implement atomic updates (e.g., via CAS using Unsafe or VarHandles)? What is the ABA problem in lock-free algorithms, how can it affect CAS-based structures, and what are common mitigations (such as version tagging, AtomicStampedReference, or hazard pointers)?
Quick Answer: This question evaluates understanding of lock-free concurrency primitives and atomic operations, specifically how AtomicInteger implements atomic updates and the correctness issue known as the ABA problem.