Distinguish duration and idle TTL — Discover and trace

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

Calculate fixed expiry from a timeline

A cache entry is created at 10:00 with fixed duration 30 minutes. Reads occur at 10:10 and 10:25. In this exercise, reads do not refresh fixed expiry.

Creation plus duration gives expiry 10:30. The two reads leave that timestamp unchanged. At 10:29 the entry is eligible; at 10:31 it is expired under the stated policy. Eligibility is distinct from cleanup completion: expired bytes may still await removal. Calling every read a reset would turn this into idle expiry, a different policy.

Use the supplied case as a paper design exercise. WillowScript and these library integrations are proposed and unimplemented here; no interpreter or native host has checked the example. Preserve the source API spellings, label new policies as exercise-host contracts, and distinguish a predicted result from measured execution.

Worked reasoning and supplied artifact

// PAPER FIXTURE — Calculate fixed expiry from a timeline
// Manual worked artifact; comments below are not executable source.
// INPUT / CONTRACT: A cache entry is created at 10:00 with fixed duration 30 minutes. Reads occur at 10:10
// and 10:25. In this exercise, reads do not refresh fixed expiry.
// DERIVATION / EXPECTED ARTIFACT: Creation plus duration gives expiry 10:30. The two reads leave that
// timestamp unchanged. At 10:29 the entry is eligible; at 10:31 it is expired under the stated policy.
// Eligibility is distinct from cleanup completion: expired bytes may still await removal. Calling every
// read a reset would turn this into idle expiry, a different policy.

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.

Draw the same timeline for creation 11:05, duration 20 minutes and reads 11:15/11:23. Distinguish expiry decision and deletion confirmation.

What to produce

Draw the same timeline for creation 11:05, duration 20 minutes and reads 11:15/11:23. Distinguish expiry decision and deletion confirmation.

• 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.

• Calculate fixed expiry from a timeline
• A cache entry is created at 10:00 with fixed duration 30 minutes. Reads occur at 10:10 and 10:25. In this exercise, reads do not refresh fixed expiry.
• Separate source-backed behavior, host requirements and untested predictions.

One small recap task

Explain why “10:55” fails for the supplied case, then give one changed input that would require revisiting your conclusion.

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