Pin transaction-critical data — Connect the previous skills

PART I

Warm-up

Reconnect with a useful idea before starting pin transaction-critical data. 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 retention to concurrent readers

A resource becomes transaction-critical because unfinished work depends on it. The retention obligation needs an owner and a release boundary; an indefinite label without an owner can leak storage. Describe this as a host retention contract rather than assuming the source supplies concrete pin/unpin methods.

Exercise transaction T edits a mod configuration. It needs old snapshot S(20 MiB), pending new version N(30 MiB) and journal J(5 MiB) until commit/abort resolves. Derived preview P(15 MiB) is regenerable. Budget is 80 MiB. Only P is eviction-eligible while T is unresolved.

Supplied case: T commits N; reader R started earlier and still reads S under the host snapshot contract.

Worked reasoning: S remains needed until R releases its snapshot, even though N is canonical for new readers. Commit and last-reader release are separate lifecycle events. Resource accounting must include both versions during overlap.

Contrast and diagnosis: Releasing S at the commit event alone violates the read contract for R.

Worked reasoning and supplied artifact

// Disposable exercise fixture / host-contract notes; not executable API syntax.
// Supplied input: T commits N; reader R started earlier and still reads S under the host snapshot contract.
// Worked prediction: S remains needed until R releases its snapshot, even though N is canonical for new readers. Commit and last-reader release are separate lifecycle events. Resource accounting must include both versions during overlap.
// Rejected alternative: Releasing S at the commit event alone violates the read contract for R.

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: Resource budget dashboard. Build a small, understandable change around pin transaction-critical data.

Draw old-reader start→commit N→new-reader start→old-reader finish. State which version each reader sees and when S may be reclaimed.

What to produce

Draw old-reader start→commit N→new-reader start→old-reader finish. State which version each reader sees and when S may be reclaimed. Include input → intermediate decision/state → predicted outcome, with any required host rule stated explicitly.

• 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 retention to concurrent readers
• Explain the decision for the supplied case, then independently work the changed fixture.
• Separate source-backed behavior, host requirements and untested predictions.

One small recap task

In one or two sentences, name the decisive rule in “Connect retention to concurrent readers” and predict the outcome of one changed input from your independent fixture. State which host behavior still needs real verification.

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