perf(server): replace quadratic task queue drain with index-based FIFO - #37464
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mturac wants to merge 1 commit into
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perf(server): replace quadratic task queue drain with index-based FIFO#37464mturac wants to merge 1 commit into
mturac wants to merge 1 commit into
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The browser server stream scheduler used Array.shift() to dequeue callbacks one at a time. shift() moves every remaining element on each call, making a burst of n scheduled tasks O(n²) to drain. Replace with a head-index that advances in O(1). Null out consumed slots so the callbacks can be collected, and compact the underlying array when the consumed prefix exceeds both 1024 entries and half the array length, keeping amortized memory bounded. Fixes react#37453
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Summary
Fixes #37453 — the browser server stream scheduler stores pending callbacks in an array and removes one per
MessageChanneldelivery withArray.shift(). Each shift copies every remaining element, making queue draining O(n²) in the number of scheduled tasks during a burst.Fix: Replace
shift()with a head-index that advances in O(1). Consumed slots are nulled out so callbacks can be garbage-collected. When the consumed prefix exceeds both 1024 entries and half the array length, the live tail is compacted into a fresh array. This preserves FIFO ordering, supports reentrant scheduling, and keeps amortized memory bounded.Changed files
packages/react-server/src/ReactServerStreamConfigBrowser.js— replaceshift()with indexed dequeue and periodic compactionTest plan
ReactDOMFizzServer-test.js— 183/183 passed (core SSR streaming tests)packages/react-server/— 2/3 suites passed (1 pre-existing snapshot failure inReactFlightAsyncDebugInfo-test.js, unrelated to this change — confirmed by running on unmodifiedmain)