channel 的底层和 select

How one stock question fills forty minutes: the five-layer ladder

• L1 · Definition — what each term means, list the differences. Can't answer: you never learned it.
• L2 · Mechanism — which structure, which step actually produces that difference. Can't answer: you memorised the conclusion only.
• L3 · Numbers — by how much? How many microseconds, how many times, how many I/Os. Can't answer: you've never done it hands-on.
• L4 · Choice — given a concrete scenario, which one, at what cost, and when is that choice wrong. Can't answer: you can't apply it.
• L5 · Limits — under what conditions does everything you just said stop holding. Can't answer: you know it all, but you don't really understand it.

The bar: L4 is what passes an interview, L5 is what counts as really understanding it, and anything that stops at L1 is recorded as memorised.

Six scenes — the first and last are unique to this set

• In scene one it does not interrupt, comment or hint. You deliver the version you already have, start to finish, and it records that as your baseline. The silence is deliberate — it is listening, it just isn't correcting you yet.
• The middle four scenes work down the ladder; scene three, mechanism and numbers, is the main battleground.
• The last scene puts sixty seconds on the clock and makes you deliver it again, side by side with your opening version — because what an interview asks you to hand over isn't "I understand it", it's a sentence you can actually say out loud.

How to start

1. Pick one, open it, copy the prompt.
2. Paste it into a brand-new conversation, say nothing, and wait for its first question.
3. Then answer like you would in an interview: deliver your memorised version in one go. It's fine if it's rough — that's the baseline it compares against at the end.
4. After that it starts pressing. Running out of answers is a normal outcome: this isn't study material, it's a mock interview.

Five commands you can call out at any time

• 跳过 move to the next scene now
• 提示 give me a hint, not the answer
• 直说吧 spell the full answer out
• 重讲 jump straight to the last scene, re-record the sixty-second version and compare it with the opening one
• 复盘 jump to the wrap-up and print the review card

Three traps

• The prompt you copy has the answer key at the end — don't read it first. One of its columns is the "recital fingerprints": the exact sentences you're most likely to blurt out. Read them and there's nothing left to drill.
• Don't hand over adjectives where a number belongs. "Much faster", "barely any overhead" — it stops you and asks for the figure. A conclusion you can't put an order of magnitude on is recorded as memorised.
• The last two groups are language-bound: do the Java group if you write Java, the Go group if you write Go. They are not translations of each other — each picks its own questions — so there's no need to do both.