Programming Fundamentals › Concurrency & Async

Livelock

Tasks keep reacting to each other without making progress.

Backend Engineer · Senior Data Engineer · Senior

Also known as: livelock, live lock, busy retry loop

A livelock looks a lot like a deadlock from the outside — the system is stuck — but the difference is that the tasks are not blocked. They’re actively running, repeatedly changing state in response to each other, and yet making no real progress. It’s the two people in a corridor each stepping aside in the same direction, forever.

A: detects B waiting → releases its resource, backs off, retries
B: detects A waiting → releases its resource, backs off, retries
repeat forever — both are busy, neither finishes

Livelock most often comes from retry and backoff logic that’s too eager or too symmetric. Two processes detect contention, both politely yield, then both grab again at the same instant, detect contention again, yield again. Or a system retries a failing operation with the same timing as its peer, creating a synchronized loop.

The classic mistakes:

Diagnosing it as a deadlock. A deadlock shows blocked tasks and no CPU use; a livelock shows busy tasks burning CPU but no throughput. Checking whether the CPU is spinning or idle tells you which you have.
Symmetric backoff. If every contender waits the same amount and retries at the same time, they collide forever. Add randomised backoff (jitter) so contenders desynchronise.
Unbounded retries. Retrying a state that can’t succeed just spins. Add a retry limit and then fail or degrade (see circuit breaker).
No progress check. It’s easy to add “detect conflict, retry” and never notice the loop never exits. Instrument retries; a rising retry count with flat throughput is a livelock forming.

The fix is usually to break the symmetry and bound the loop: randomised delays, a retry cap, or an explicit tie-breaker that decides who goes first. Livelock is a cousin of starvation — both are about tasks not getting to finish, but a livelock involves active, wasted work rather than a task being consistently passed over.