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Every dependency edge was a full barrier: the cache collected all of a generator's chunks before its dependents started, so each stage of a build waited for the whole of the one before it. A generator can now set streamsInput: true to receive its dependency's output as an async iterable of chunks, read as they are produced. With one thread nothing runs alongside, so it still gets one array, and a dependency that doesn't stream arrives as a single chunk. Nothing sets it yet. The cache runs a streamed generator once, recording its chunks so any number of readers each read all of them, from the first, while it still runs. Once every reader has started, it lets go of a chunk as soon as all of them have read it, rather than holding the output until the last one is done. Assisted-by: Claude Opus 5.5 <noreply@anthropic.com> Assisted-by: Claude Sonnet 5.5 <noreply@anthropic.com>
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ovflowd
changed the title
Codecov Report❌ Patch coverage is Additional details and impacted files@@ Coverage Diff @@
## perf/stream-worker #1238 +/- ##
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+ Coverage 94.21% 94.35% +0.14%
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Files 291 293 +2
Lines 29366 30238 +872
Branches 2985 3076 +91
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+ Hits 27666 28531 +865
- Misses 1678 1685 +7
Partials 22 22 ☔ View full report in Codecov by Harness. 🚀 New features to boost your workflow:
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ovflowd
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November 3, 2026 20:39
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Description
This PR lets the cache stream a generator's output to the generators that read it, instead of collecting every chunk first. It's the second part of a stack that splits #1205.
Every dependency edge was a full barrier:
cache.consumecollected all of a generator's chunks before its dependent started, so each stage of a build waited for the whole of the one before it.streamsInput: trueto get its dependency's output as an async iterable of chunks, read as they're produced. With one thread nothing runs alongside, so it still gets one array, and a dependency that doesn't stream arrives as a single chunk. No generator sets it yet.createReplay: any number of readers each read all of its chunks, from the first, while it still runs. Once every reader has started, a chunk is let go as soon as all of them have read it, rather than when the last one is done.docs/creating-generators.mdhas a new Streaming Input section.Validation
Added tests for
createReplay(every reader gets every chunk in order, a reader that starts late, a chunk let go before a reader read it, a failure), for the cache (one run for streaming and collecting readers, chunks let go only once every reader has read them, a stream read only once, failures before and after the stream is read), and forrunGenerators(streaming to a generator that streams its input, and giving it the whole input with one thread). Built on 12 of Node.js's API docs at 1 and 4 threads, the output is byte-identical tomain's.Related Issues
Refs: #1205
Check List
node --run testand all tests passed.node --run format:check&node --run lint.