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Web Workers · 08 Transfer Ownership
Series contents · Technology map
Stage: Ownership and Cancellation · Editable example · Storage ID: web-workers-step-08
Goals and learning outcomes
- Learning outcome: explain the role of Transfer. Input cases: an Int32Array of length 16.
- Deliverable: byteLength before and after sending, and the received sum. Explain the rationale for handling No further access, linking it to the code.
Prerequisites
Prepare the experiment results for Separation and Baseline experiment from Unit 7, “Observing Main-Thread Responsiveness”.
Key concepts and explanations
Transfer
Putting an ArrayBuffer in the transfer list transfers ownership. The sender's buffer becomes detached.
No further access
Do not reuse the old view after transfer. Copy data you need to reuse or establish a return protocol.
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-8.js in a separate practice project, record byteLength before and after postMessage({buffer},[buffer]) and the received values. Refer to the existing Unit 1·14·28 examples only as starting points.
- Input conditions: an Int32Array of length 16. Baseline: Copy. Run under the baseline conditions, then record observations and errors in notes/day-8.md.
- Variable: Sending method; changed value: transfer. Run again through the same input path. Deliverable to save: byteLength before and after sending, and the received sum. Hypothesis to check: The sender's byteLength becomes 0 while the received data remains intact. Compare it with the actual results, and record whether they agree and why they differ.
Variables to observe
| Variable | Baseline | Change | Expected change / hypothesis |
|---|---|---|---|
| Sending method | Copy | transfer | The sender's byteLength becomes 0 while the received data remains intact. |
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: byteLength before and after sending, and the received sum. 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: Transfer and No further access. For unexpected items, at least 1 cause or reason they remain unresolved is recorded.
Self-check
- Which processing stage does Transfer affect in this exercise? Input cases: an Int32Array of length 16.
- Variable: Sending method. Hypothesis to check: The sender's byteLength becomes 0 while the received data remains intact. Did the actual results agree with the hypothesis? Explain the evidence in terms of No further access.
Official references
Linked example and execution scope
Example source · Runtime environments and limits
An interactive Transfer Ownership 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: Observing Main-Thread Responsiveness · Next: Transferring a Partial View