Scaling Writes hard
In lock-free concurrency (e.g., utilizing Compare-And-Swap), what is the 'ABA Problem'?
- A Deadlock between three threads.
- B A thread reads Value A. Another thread changes it to B, then back to A. The first thread's CAS succeeds because it sees A, incorrectly assuming the state hasn't changed.
- C Memory leak.
- D Priority inversion.
Answer: B. A thread reads Value A. Another thread changes it to B, then back to A. The first thread's CAS succeeds because it sees A, incorrectly assuming the state hasn't changed.
CAS checks value equality, not history. The value 'A' looks the same, but the side effects (e.g., a pointer inside a stack) might have changed. Solved by using Versioned Pointers (A1, B2, A3).
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