Distinguish duration and idle TTL — Connect the previous skills

PART I

Warm-up

Reconnect with a useful idea before starting distinguish duration and idle ttl. In one or two sentences, describe the input, output or host boundary from the previous exercise that this lesson builds on. If you are arriving directly, skim the worked example first; there is no locked prerequisite.

A rough note is enough. You can revise it after the example.

PART II

Instruction & guided example

Connect refresh to concurrency

Two successful reads occur at18:10 and18:12 with10-minute idle expiry. A delayed write from the earlier event arrives last.

Correct last qualifying access is18:12, so expiry is18:22. Overwriting it with18:10 would shorten lifetime incorrectly. A host should preserve the latest qualifying access under its concurrency contract; no concrete locking API is supplied.

Write the intermediate states explicitly before proposing a code change. The example below remains an illustrative source anchor; this new case changes the inputs or the host requirement. WillowScript and these library services are proposed and unimplemented here. Treat new policies as supplied exercise contracts, and keep hand predictions distinct from native execution evidence.

Worked reasoning and supplied artifact

// PAPER FIXTURE — Connect refresh to concurrency
// Manual worked artifact; comments below are not executable source.
// INPUT / CONTRACT: Two successful reads occur at18:10 and18:12 with10-minute idle expiry. A delayed write
// from the earlier event arrives last.
// DERIVATION / EXPECTED ARTIFACT: Correct last qualifying access is18:12, so expiry is18:22. Overwriting it
// with18:10 would shorten lifetime incorrectly. A host should preserve the latest qualifying access under
// its concurrency contract; no concrete locking API is supplied.

Illustrative example from the proposed WillowScript design. The language and WUIX/WMATH/WDB/WAUDIO/WTMP services are not implemented in the supplied source. This site has no interpreter, VM or native host and does not execute or certify the snippet.

Try the guided change

Reconstruct the supplied worked case first: list its inputs, intermediate decisions and final artifact. Compare each row with the explanation and identify exactly where the rejected alternative fails. Then use the changed inputs in Part IV for independent work.

• Write the supplied inputs and initial state before following the example.
• Reconstruct each intermediate calculation or host decision, then compare with the worked artifact.
• Explain why the contrasting alternative fails before attempting the changed inputs in Part IV.

PART III

Take a breather

Step back after the guided example. Look away from the screen, stretch, or reread your prediction. This is an optional learning pause, not a timer or an assessment gate.

When you return, try to name the lesson’s key idea without copying its wording. If that feels difficult, return to Part II and trace one line rather than restarting the entire lesson.

PART IV

Independent practice

Project context: Bounded report cache. Build a small, understandable change around distinguish duration and idle ttl.

Trace arrival order18:12 then18:10 and write the required nondecreasing-access invariant.

What to produce

Trace arrival order18:12 then18:10 and write the required nondecreasing-access invariant.

• State the intended behavior in a sentence before editing.
• Use only source-backed syntax and the host services whose contract you have been given.
• Record a normal case and a boundary or unavailable-resource case.
• Label hand predictions separately from anything actually measured in a supplied toolchain.

Syntax colors are a reading aid, not a compiler. The line you are editing stays uncolored until you move to a different line; capitalization is never changed. Drafts stay on this browser and code is not executed.

import tmp;
const cache = tmp.create({
    name: "report-cache",
    storage: "ssd",
    maxSize: "2GB",
    lifetime: { duration: "30m", refreshOnAccess: true },
    cleanup: { automatic: true, onCrashRecovery: true }
});

PART V

Self-check

Use this check to notice what to revisit. It does not award a private course grade, block another page or claim to verify compiled code. Every answer has a learning explanation.

You may keep exploring even if you are unsure. Use the hint, compare the trace, and revise your explanation.

PART VI

Recap & small task

Bring the idea back to the mod feature you are building. A useful recap connects the mechanism to a decision you can make in your own code.

• Connect refresh to concurrency
• Two successful reads occur at18:10 and18:12 with10-minute idle expiry. A delayed write from the earlier event arrives last.
• Separate source-backed behavior, host requirements and untested predictions.

One small recap task

Change one input in this case and state which intermediate state or calculation must be recomputed. Explain why “18:20” is not justified.

This marks your personal practice record only. It is not a certification or an official workspace assessment.