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Web Workers · 19 Timeouts and Duplicate Responses
Series contents · Technology map
Stage: Queues and Error Recovery · Editable example · Storage ID: web-workers-step-19
Goals and learning outcomes
- Learning outcome: explain the role of Time limit. Input cases: normal, delayed, and duplicate responses.
- Deliverable: per-request settlement counts and pending size. Explain the rationale for handling Single settlement, linking it to the code.
Prerequisites
Prepare the experiment results for Completion order and Index from Unit 18, “Restoring Result Order”.
Key concepts and explanations
Time limit
A timeout judges that a response is late. It does not automatically stop Worker computation.
Single settlement
Each request must settle only once. Discard late responses after a timeout.
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-19.js in a separate practice project, create per-request timers and settled checks, and inject late responses. Refer to the existing Unit 1·14·28 examples only as starting points.
- Input conditions: normal, delayed, and duplicate responses. Baseline: Long enough. Run under the baseline conditions, then record observations and errors in notes/day-19.md.
- Variable: Time limit; changed value: Shorter than the delay. Run again through the same input path. Deliverable to save: per-request settlement counts and pending size. Hypothesis to check: Failure is recorded once, and late responses are ignored. Compare it with the actual results, and record whether they agree and why they differ.
Variables to observe
| Variable | Baseline | Change | Expected change / hypothesis |
|---|---|---|---|
| Time limit | Long enough | Shorter than the delay | Failure is recorded once, and late responses are ignored. |
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: per-request settlement counts and pending size. 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: Time limit and Single settlement. For unexpected items, at least 1 cause or reason they remain unresolved is recorded.
Self-check
- Which processing stage does Time limit affect in this exercise? Input cases: normal, delayed, and duplicate responses.
- Variable: Time limit. Hypothesis to check: Failure is recorded once, and late responses are ignored. Did the actual results agree with the hypothesis? Explain the evidence in terms of Single settlement.
Official references
Linked example and execution scope
Example source · Runtime environments and limits
An interactive Timeouts and Duplicate Responses experiment with cleanup of the resources it uses.
Source code and records are not overwritten automatically. Resetting an existing example also preserves your notes.