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Web Workers · 23 Shared Memory Requirements
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Stage: Validating Throughput and Responsiveness · Editable example · Storage ID: web-workers-step-23
Goals and learning outcomes
- Learning outcome: explain the role of Isolation. Input cases: isolated and non-isolated environments.
- Deliverable: a table of headers, crossOriginIsolated, and the selected path. Explain the rationale for handling Fallback, linking it to the code.
Prerequisites
Prepare the experiment results for Partitioning and Combining from Unit 22, “Splitting and Merging Data”.
Key concepts and explanations
Isolation
SharedArrayBuffer depends on browser security requirements. Check COOP, COEP, and crossOriginIsolated in an external project you control.
Fallback
Use the transfer path in an environment without isolation. Do not weaken the existing iframe CSP or isolation.
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-23.js in a separate practice project, display support requirements in an external project and implement a transfer fallback branch. Refer to the existing Unit 1·14·28 examples only as starting points.
- Input conditions: isolated and non-isolated environments. Baseline: Non-isolated. Run under the baseline conditions, then record observations and errors in notes/day-23.md.
- Variable: Environment; changed value: Controlled isolated server. Run again through the same input path. Deliverable to save: a table of headers, crossOriginIsolated, and the selected path. Hypothesis to check: Shared memory is used only when the requirements are met. Compare it with the actual results, and record whether they agree and why they differ.
Variables to observe
| Variable | Baseline | Change | Expected change / hypothesis |
|---|---|---|---|
| Environment | Non-isolated | Controlled isolated server | Shared memory is used only when the requirements are met. |
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 headers, crossOriginIsolated, and the selected path. 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: Isolation and Fallback. For unexpected items, at least 1 cause or reason they remain unresolved is recorded.
Self-check
- Which processing stage does Isolation affect in this exercise? Input cases: isolated and non-isolated environments.
- Variable: Environment. Hypothesis to check: Shared memory is used only when the requirements are met. Did the actual results agree with the hypothesis? Explain the evidence in terms of Fallback.
Official references
Linked example and execution scope
Example source · Runtime environments and limits
An interactive Shared Memory Requirements 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: Splitting and Merging Data · Next: Atomics and Synchronization