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Web Workers · 09 Transferring a Partial View
Series contents · Technology map
Stage: Ownership and Cancellation · Editable example · Storage ID: web-workers-step-09
Goals and learning outcomes
- Learning outcome: explain the role of Storage granularity. Input cases: the middle 8 elements of a large array.
- Deliverable: transferred storage size and the states of other views. Explain the rationale for handling Minimizing the boundary, linking it to the code.
Prerequisites
Prepare the experiment results for Transfer and No further access from Unit 8, “Transfer Ownership”.
Key concepts and explanations
Storage granularity
The transfer target is the ArrayBuffer, not the view. Sending a partial view may transfer the entire underlying storage.
Minimizing the boundary
You can copy only the needed portion into new storage. This trades copying cost against the scope of shared access.
Practice setup
First check the execution scope guidance on the example screen. The following describes the environment needed to extend the assignment in a separate project. The existing web-workers-01·02·03 are starting examples. Implement the new assignments in main.js and worker.js in a separate local HTTP project. Preserve CSP and iframe isolation. For SharedArrayBuffer, check COOP and COEP requirements on an external server you control; use the transfer path if they are not met. Measure performance yourself.
The linked example is a starting point. It does not implement every task below. Complete work beyond its supported scope in a separate project.
Practice tasks
- In src/day-9.js in a separate practice project, compare directly transferring subarray.buffer with transferring after slice. Refer to the existing Unit 1·14·28 examples only as starting points.
- Input conditions: the middle 8 elements of a large array. Baseline: Original buffer. Run under the baseline conditions, then record observations and errors in notes/day-9.md.
- Variable: Transfer range; changed value: Buffer containing a partial copy. Run again through the same input path. Deliverable to save: transferred storage size and the states of other views. Hypothesis to check: The small-copy path does not detach other views. Compare it with the actual results, and record whether they agree and why they differ.
Variables to observe
| Variable | Baseline | Change | Expected change / hypothesis |
|---|---|---|---|
| Transfer range | Original buffer | Buffer containing a partial copy | The small-copy path does not detach other views. |
Predictions in this table are not measured results. Change one condition at a time and record why the actual result differs.
Completion criteria
- Required deliverable: transferred storage size and the states of other views. Results are available for both the baseline and changed conditions, allowing comparison of 2 conditions; input values and the execution environment are recorded together.
- The explanation of differences between the two conditions connects both concepts: Storage granularity and Minimizing the boundary. For unexpected items, at least 1 cause or reason they remain unresolved is recorded.
Self-check
- Which processing stage does Storage granularity affect in this exercise? Input cases: the middle 8 elements of a large array.
- Variable: Transfer range. Hypothesis to check: The small-copy path does not detach other views. Did the actual results agree with the hypothesis? Explain the evidence in terms of Minimizing the boundary.
Official references
Linked example and execution scope
Example source · Runtime environments and limits
An interactive Transferring a Partial View experiment with cleanup of the resources it uses.
Source code and records are not overwritten automatically. Resetting an existing example also preserves your notes.