ABA Problem in Lock-free Code

Understanding the ABA problem in lock-free concurrent programming

This question tests your grasp of a fundamental pitfall in lock-free synchronization—one that appears in technical interviews at firms building high-performance systems where mutex contention is unacceptable. The ABA problem is subtle: it can break supposedly correct lock-free algorithms in ways that are hard to detect and reproduce.

To answer well, you need to explain the specific sequence of events that makes certain compare-and-swap (CAS) based algorithms fail, why traditional mutual exclusion does not suffer from it, and what the practical consequences are for data structures like lock-free queues and stacks. Interviewers often follow up by asking how to detect or mitigate the issue in real code.

• Compare-and-swap (CAS) and atomic operations
• Memory ordering and visibility in concurrent systems
• Pragmatic solutions: versioning, hazard pointers, and garbage collection