feat(rule): gate sync rule-result resolution behind runTypeASync flag#235
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chikara1608 wants to merge 1 commit into
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feat(rule): gate sync rule-result resolution behind runTypeASync flag#235chikara1608 wants to merge 1 commit into
chikara1608 wants to merge 1 commit into
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Resolving each rule's result via setTimeout(0) (Deque #1172) creates one
macrotask transition per rule (~335). On large DOMs with advance ON these
interleave with DevTools IPC (resource.getContent), ballooning the
per-rule resolve from ~8ms to ~180ms and inflating axe.run from ~14s to
~85s.
When axe._cache 'runTypeASync' is set (by a11y-engine-core run.js from the
a11yCoreConfig flag), resolve synchronously to eliminate the contention.
The flag defaults OFF, preserving the original deferred behaviour.
On the OFF path, instrument the schedule-to-fire delay of each yield and
accumulate {totalMs,count,maxMs} onto axe._typeASyncYield so every scan
reports how much wall-clock the async resolve costs — the exact time the
flag would recover. Read back into Type A telemetry by a11y-engine-core.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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rohitsahu-bstack
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Jun 4, 2026
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What
Gates per-rule result resolution on a new
runTypeASyncflag (set intoaxe._cachebya11y-engine-corefrom thea11yCoreConfig.runTypeASyncconfig field):resolve(ruleResult)synchronously.setTimeout(0)defer (Deque #1172), unchanged behaviour, plus lightweight yield-latency instrumentation.Why
The
setTimeout(0)wrapper aroundresolve(ruleResult)creates one macrotask transition per rule (~335). On large DOMs with advance ON, these interleave with concurrent DevTools IPC (resource.getContent), inflating the per-rule resolve from ~8ms to ~180ms andaxe.runfrom ~14s to ~85s (Savvas Realize investigation). Resolving synchronously eliminates the contention.We are shipping the fix behind a flag, default OFF, and want to measure which other customers exhibit the same pathology before enabling it for them.
Instrumentation (OFF path only)
Accumulates the schedule-to-fire delay of each resolve yield onto
axe._typeASyncYield{ totalMs, count, maxMs }.a11y-engine-corereads this back afteraxe.runand surfaces it in Type A telemetry.totalMs≈ the wall-clock the async resolve costs = the exact time the flag would recover.Cost / safety
setTimeoutthat already existed onmain. Event-loop behaviour on the OFF path is byte-for-byte identical to today.performance.now()+ a few arithmetic ops per rule ≈ ~1ms per scan; scales with rule count, not DOM size.Tagging
All changes carry
// [a11y-core]:per submodule convention.Test plan
build_axe.shcompiles clean;runTypeASync+_typeASyncYieldpresent in builtaxe.js.type_a_sync_yield_countreports 0.type_a_sync_yield_total_mspopulated on a large advance-ON scan.Paired with a11y-engine PR (flag extraction + telemetry surfacing + submodule bump).
🤖 Generated with Claude Code