stream: drop per-chunk Promise alloc in pipeTo#63572
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Codecov Report✅ All modified and coverable lines are covered by tests. Additional details and impacted files@@ Coverage Diff @@
## main #63572 +/- ##
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+ Coverage 90.33% 90.34% +0.01%
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Files 732 732
Lines 236454 236458 +4
Branches 44540 44530 -10
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+ Hits 213589 213635 +46
+ Misses 14581 14524 -57
- Partials 8284 8299 +15
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aduh95
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| // | ||
| // setPromiseHandled's job here is purely to silence the per-chunk | ||
| // unhandled-rejection event — the chain Promise + noop closure it | ||
| // would allocate are unobserved by anything else (errors propagate | ||
| // through writer.closed, which pipeTo monitors via watchErrored). | ||
| // markPromiseAsHandled sets V8's MarkAsHandled + MarkAsSilent flags | ||
| // directly, with no per-chunk allocation. The LAST state.currentWrite | ||
| // is awaited in waitForCurrentWrite during shutdown — markAsHandled | ||
| // does not affect that subsequent .then chain. |
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I don't think this comment will make much sense after this PR is merged
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| // | |
| // setPromiseHandled's job here is purely to silence the per-chunk | |
| // unhandled-rejection event — the chain Promise + noop closure it | |
| // would allocate are unobserved by anything else (errors propagate | |
| // through writer.closed, which pipeTo monitors via watchErrored). | |
| // markPromiseAsHandled sets V8's MarkAsHandled + MarkAsSilent flags | |
| // directly, with no per-chunk allocation. The LAST state.currentWrite | |
| // is awaited in waitForCurrentWrite during shutdown — markAsHandled | |
| // does not affect that subsequent .then chain. |
aduh95
reviewed
May 26, 2026
| kPending, | ||
| }, | ||
| getPromiseDetails, | ||
| markPromiseAsHandled, |
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Does it really make sense to import it just to re-export it? I don't like it, it makes it harder to realize it crosses the C++ boundary
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Signed-off-by: Matteo Collina <hello@matteocollina.com>
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Replace
setPromiseHandledwithmarkPromiseAsHandledat the two pipeTo per-chunk call sites inreadablestream.js. The.then(undefined, () => {})chain thatsetPromiseHandledallocates per chunk has no observer in pipeTo: errors already propagate throughwriter.closed(whichwatchErroredmonitors) and the laststate.currentWriteis awaited inwaitForCurrentWriteduring shutdown (markAsHandled does not affect that subsequent.then). The per-chunk chain Promise + noop closure exist solely to silence the unhandled-rejection event —markPromiseAsHandledsets V8'sMarkAsHandled+MarkAsSilentflags directly with no allocation.benchmark/webstreams/pipe-to.jsat HWM=1024: ~5% throughput improvement (728K vs 694K ops/s mean, 6 alternating samples), with substantially tighter run-to-run variance.WPT streams parity preserved: 1403 subtests passing, 0 unexpected failures.