What is a deadlock, in one interview story?
PICTURE THIS: HOW TO EXPLAIN IT
Simple meaning
Thread A holds lock L1 and waits for L2, while thread B holds L2 and waits for L1, so both wait forever.
WHY — Concurrency instead of guessing?
Why interviewers care about Concurrency:
who only read docs from people who shipped.
and tied to Backend work.
Name the idea, why it exists, then one short example.
End with when you use it and one common pitfall.
STEPS — What happens step by step?
Before you speak the answer, walk the interviewer through these steps:
- 1Thread A holds lock
L1 and waits for L2, while thread B holds L2 and waits for L1, so both wait forever.
- 2It also happens with
more than two locks if the wait-for graph has a cycle.
- 3Campus interviews often want
the four Coffman conditions: mutual exclusion, hold and wait, no preemption, and circular wait.
- 4Give an example
One tiny concrete case you can say aloud.
- 5Common mistake
What juniors usually get wrong.
- 6Close
When you pick this over the alternative.
EXAMPLE — See it in action
Here's a short line you can speak, broken into clear beats:
Note: Adapt this scaffold to your own project — keep it under 60–90 seconds.
Key takeaway
Thread A holds lock L1 and waits for L2, while thread B holds L2 and waits for L1, so both wait forever. It also happens with more than two locks if the wait-for graph has a cycle.