Lock-Free and Wait-Free Alternatives

Advanced Strategy
Lock-free programming eliminates locks entirely using atomic operations. No locks means no deadlock. But it is much harder to get right.
Lock-Free vs Wait-Free
Lock-free: At least one thread always makes progress. No thread can block another forever. Deadlock impossible.
Wait-free: Every thread makes progress in bounded steps. Even stronger guarantee. Very hard to implement.
How It Works
Use Compare-And-Swap (CAS) operations. Read value, compute new value, atomically update if unchanged. If changed by another thread, retry. No locking needed.
Lock-Free Counter with CAS
Readold = counterComputenew = old + 1CASif counter==old:counter=new
Trade-offs
Pros: No deadlock possible. Often faster under low contention. No priority inversion.
Cons: Much harder to implement correctly. Subtle bugs. Under high contention, CAS retry loops may burn CPU. Limited to simple data structures.
When to Use
Use lock-free data structures from libraries (ConcurrentHashMap, AtomicInteger). Writing your own is expert-level. For most applications, well-designed locking is simpler and sufficient.
Practical Advice: Use lock-free collections from standard libraries. Avoid writing lock-free algorithms yourself unless you are an expert. Good locking is easier to get right than bad lock-free code.

💡 Key Takeaways

✓Lock-free: uses CAS instead of locks. At least one thread always progresses. No deadlock possible.

✓Wait-free: every thread completes in bounded steps. Stronger than lock-free, harder to achieve.

✓CAS pattern: read old, compute new, atomically swap if unchanged. Retry on conflict.

✓Trade-off: no deadlock, often fast, but very hard to implement correctly. Subtle bugs.

✓Use library lock-free structures (AtomicInteger, ConcurrentHashMap). Avoid DIY lock-free code.

📌 Examples

1AtomicInteger: incrementAndGet() uses CAS internally. Lock-free counter.

2ConcurrentHashMap: lock-free reads, fine-grained locking for writes. Deadlock-resistant by design.

3Lock-free queue: Michael-Scott queue using CAS for enqueue/dequeue. Classic but tricky to implement.

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