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Web Workers · 10 Returning Buffers
Series contents · Technology map
Stage: Ownership and Cancellation · Editable example · Storage ID: web-workers-step-10
Goals and learning outcomes
- Learning outcome: explain the role of Round-trip ownership. Input cases: 2 buffers and consecutive requests.
- Deliverable: a table of owners and value changes for each request. Explain the rationale for handling Pool states, linking it to the code.
Prerequisites
Prepare the experiment results for Storage granularity and Minimizing the boundary from Unit 9, “Transferring a Partial View”.
Key concepts and explanations
Round-trip ownership
A Worker can transfer a received buffer back. Make explicit who owns it at each point.
Pool states
Distinguishing available and inFlight prevents duplicate use. The UI must not read the original view before the buffer returns.
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-10.js in a separate practice project, have the Worker update the array and return the buffer using transfer. Refer to the existing Unit 1·14·28 examples only as starting points.
- Input conditions: 2 buffers and consecutive requests. Baseline: 1 buffer. Run under the baseline conditions, then record observations and errors in notes/day-10.md.
- Variable: Buffer count; changed value: 2 buffers. Run again through the same input path. Deliverable to save: a table of owners and value changes for each request. Hypothesis to check: The number of buffers available for simultaneous use is limited. Compare it with the actual results, and record whether they agree and why they differ.
Variables to observe
| Variable | Baseline | Change | Expected change / hypothesis |
|---|---|---|---|
| Buffer count | 1 buffer | 2 buffers | The number of buffers available for simultaneous use is limited. |
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: a table of owners and value changes for each request. 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: Round-trip ownership and Pool states. For unexpected items, at least 1 cause or reason they remain unresolved is recorded.
Self-check
- Which processing stage does Round-trip ownership affect in this exercise? Input cases: 2 buffers and consecutive requests.
- Variable: Buffer count. Hypothesis to check: The number of buffers available for simultaneous use is limited. Did the actual results agree with the hypothesis? Explain the evidence in terms of Pool states.
Official references
Linked example and execution scope
Example source · Runtime environments and limits
An interactive Returning Buffers experiment with cleanup of the resources it uses.
Source code and records are not overwritten automatically. Resetting an existing example also preserves your notes.
Next learning
Previous: Transferring a Partial View · Next: Rejecting Stale Results