stream: drain WHATWG stream queues from a head index#64354
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Skip the size algorithm call and its result validation when the size algorithm is the default one, and stop re-running the full ShouldCallPull predicate at per-chunk call sites where its inputs are already established. readable-async-iterator type=normal: +16.6% (***) readable-read-buffered: +13.9% to +27.5% (**/***) pipe-to: +3.7% to +6.0% (15/16 configs significant) Signed-off-by: Matteo Collina <hello@matteocollina.com>
The default readable and writable controller queues were drained with ArrayPrototypeShift, which is O(queue length); reading a buffered queue one chunk at a time is therefore O(n^2). Dequeue through a moving head index instead so each read is O(1), dropping the consumed prefix in amortized O(1) once it reaches half of the backing array (past a small floor, so a short oscillating queue never pays a per-dequeue array mutation). readable-read-buffered: +14.8% to +35.4% (**/***) readable-async-iterator type=normal: +17.8% (***) pipe-to: +12.9% to +18.1% (all 16 configs ***) Signed-off-by: Matteo Collina <hello@matteocollina.com>
Codecov Report✅ All modified and coverable lines are covered by tests. Additional details and impacted files@@ Coverage Diff @@
## main #64354 +/- ##
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- Coverage 90.24% 90.23% -0.01%
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Files 741 741
Lines 240976 241059 +83
Branches 45408 45419 +11
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+ Hits 217477 217530 +53
- Misses 15070 15099 +29
- Partials 8429 8430 +1
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| // each dequeue O(1); the consumed prefix is dropped in amortized O(1) once | ||
| // it grows to at least half of the backing array (and past a small floor, | ||
| // so a short oscillating queue never pays a per-dequeue array mutation). | ||
| // Callers must treat `queue.length - queueHead`, not `queue.length`, as the |
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Perhaps we should have a helper function for that?
function queueLength(controller) {
const state = controller[kState];
return state.queue.length - state.queueHead;
}Or does that not get inlined as aggressively as we'd want?
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Drain the default readable and writable controller queues through a moving head index instead of
ArrayPrototypeShift(which is O(queue length), making a buffered drain O(n^2)). Each dequeue becomes O(1); the consumed prefix is dropped in amortized O(1).The first commit is #64320; only the last commit is new here.