blog: the missing structured concurrency guarantees in k6's JavaScript runtime#1114
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blog: the missing structured concurrency guarantees in k6's JavaScript runtime#1114
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Document how @effectionx/k6 solves 20+ open k6 issues related to structured concurrency gaps: context loss, resource leaks, silent failures, unpredictable shutdown, and race conditions. References: - Sobek PR #115: grafana/sobek#115 - Effectionx PR #156: thefrontside/effectionx#156 Session-ID: ses_39d99b9c2ffeSKxHPZAk9P7E1O
commit: |
Replace generic JS hook with k6-specific group/tag drift framing and align examples with k6 maintainer analysis in grafana/k6#2728. Session-ID: ses_39d99b9c2ffeSKxHPZAk9P7E1O
taras
changed the title
Remove absolution/blame-shift phrasing, make the two guarantees explicit, and keep maintainer discussion to paraphrase plus a single anchored quote. Session-ID: ses_39d99b9c2ffeSKxHPZAk9P7E1O
Restructure the post around: 1. The familiar k6 symptom (group/tag drift) 2. Why group() can't fix it (try/finally model + stack unwinding) 3. The two structured concurrency guarantees 4. Five categories of missing guarantees with issue links 5. Before/after example showing scope ownership 6. ECMAScript spec conformance and Sobek PR #115 7. What the conformance suite tests (what Sobek already has vs the one gap) 8. CTA for users and maintainers Voice: paraphrase + one anchored quote per section, neutral attribution, no absolution/blame-shift, explicit two guarantees. Session-ID: ses_39d99b9c2ffeSKxHPZAk9P7E1O
Reframe opening and key transitions around 'your expectations': - sync group() works the way you expect; async breaks that - structured concurrency aligns async with those expectations - scope owns async the same way it owns sync Session-ID: ses_39d99b9c2ffeSKxHPZAk9P7E1O
Update featured image to show async deforming the call stack: a then() callback runs on the next tick with restored tags, so group attribution changes. Add a short bridge paragraph tying the diagram to k6 tag behavior. Session-ID: ses_39d99b9c2ffeSKxHPZAk9P7E1O
Use "future tick" language consistently in the diagram and bridge paragraph. Session-ID: ses_39d99b9c2ffeSKxHPZAk9P7E1O
Session-ID: ses_39d99b9c2ffeSKxHPZAk9P7E1O
Explain that k6 reads current tags from the sync stack, but async callbacks run on a future tick after group() has unwound and restored tags. Session-ID: ses_39d99bc2ffeSKxHPZAk9P7E1O
Session-ID: w0t1p0:529AE7AB-BFCA-4B51-9880-FDF1D759DFBE
Session-ID: w0t1p0:529AE7AB-BFCA-4B51-9880-FDF1D759DFBE
- Cut 45-line GitHub issue list - Add bridge paragraph (universal async problem) - Combine technical sections - Tighten to ~650 words
- Replace fake delay() with http.asyncRequest() - Use until() instead of call() for promises - Rename section to 'Universal solution' - Clarify guarantees match sync expectations
- Add transition paragraph before code examples - Add 'Why Effection for k6?' section explaining polyfill design - Include Rosetta Stone link - Frame as easy/safe choice until JS runtime adds guarantees - Note additive adoption without Sobek changes beyond ECMAScript
- Replace abstract 'Lifetime is structural' with concrete code comparison - Rename Sobek section to 'Missing ECMAScript compliance' - Add link to conformance suite gist showing 80% compatibility - Link to ECMAScript spec for Generator.prototype.return - Show that only async cleanup was missing
- Replace incorrect npm install instructions with Docker-based setup - Redesign SVG to show vertical execution sequence with animated tag state - Left side shows async/await losing tags before .then() runs - Right side shows structured concurrency preserving tags through async - Animation highlights when tag state changes (the key insight)
- Left-align all headings - Update title: 'Missing Structured Concurrency Guarantees in Sobek' - Left-align step text (remove awkward centered comments) - Widen tag pills to fit 'group: coolgroup' text - Add result summary labels at bottom of each card - Fix card containers and spacing
- Remove CSS animations that caused content to be invisible on load - Make all content static and visible by default - Fix shadow filter bounds (use objectBoundingBox) - Adjust card heights to prevent overlap with result labels - Remove 'When the invariant holds, async stops lying' closing line (needs more thought, will revisit later)
- Fix animation by using proper keyframe timing - Steps appear sequentially over 8-second cycle - Left tag changes from green 'coolgroup' to red '(lost)' at step 4 - Right tag stays green 'coolgroup' through async, then '(done)' - Result summaries appear after all steps - Smooth loop with reset phase
- Add explicit audience callout for k6 users debugging flaky tests - Reference k6 issues #2848, #5435, #5249, #5524 as evidence of the pattern
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Summary
Add a new blog post documenting how
@effectionx/k6solves structured concurrency problems in k6.Motivation
k6 has 20+ open issues that trace back to missing structured concurrency guarantees:
group()doesn't work with async calls (#2728, #2848)This post:
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