What is Livelock?

Definition
Livelock occurs when threads are not blocked, they keep running and responding to each other, but none of them make any real progress. It is like two polite people in a hallway who keep stepping aside for each other.
The Hallway Problem
Two people walking toward each other in a narrow hallway. Person A steps left to let B pass. Person B steps right (their left) to let A pass. They are now still blocking each other. So A steps right. B steps left. Still blocked. They keep dancing but nobody moves forward.
Threads do exactly this. Thread 1 detects a conflict, backs off, retries. Thread 2 detects the same conflict, backs off, retries. Both keep backing off and retrying in sync. Nobody makes progress.
Why Livelock Is Tricky
CPU stays busy: Unlike deadlock where threads are blocked and use no CPU, livelock burns CPU cycles constantly. Your monitoring shows 100% utilization. Everything looks active.
Hard to detect: Health checks pass because threads are responding. Logs show activity. But throughput is zero. The system is running in circles.
Often caused by recovery code: Ironically, livelock frequently happens when you try to be too clever about avoiding deadlock. You add backoff logic that all threads follow identically.
Common Livelock Patterns
Identical retry logic: All threads use same backoff timing, retry at same moment.
Symmetric conflict resolution: Both threads use same rule like "give up your lock if someone else wants it" - so both give up simultaneously.
Overly polite protocols: Each thread tries too hard to accommodate others.
Key Difference from Deadlock: In deadlock, threads are blocked waiting. In livelock, threads are running but accomplishing nothing. Deadlock is frozen. Livelock is spinning wheels.

💡 Key Takeaways

✓Livelock: threads keep running but make zero progress - spinning wheels

✓The hallway problem: two polite people stepping aside for each other forever

✓Burns 100% CPU while accomplishing nothing - hard to detect via monitoring

✓Often caused by identical retry/backoff logic that synchronizes threads

✓Key difference: deadlock is frozen waiting, livelock is active but useless

📌 Examples

1Network retry: two services keep backing off and retrying at the same intervals forever

2Lock acquisition: threads detect conflict, release locks, retry, conflict again - loop

3Message passing: both senders wait for other to go first, both send simultaneously, both back off

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