stream: cache minimum cursor count in share#63262
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Track the number of consumers at the cached minimum cursor in share() so the minimum is only recomputed when the last consumer at that cursor advances or detaches. This avoids scanning every consumer on each trim attempt when multiple consumers advance through a shared buffer. Signed-off-by: Kamat, Trivikram <16024985+trivikr@users.noreply.github.com> Assisted-by: openai:gpt-5.5
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I'd attempted making the same changes in broadcast. They were reverted since benchmarks showed regression confidence improvement accuracy (*) (**) (***)
streams/iter-throughput-broadcast.js n=5 datasize=1048576 consumers=1 api='classic' -4.72 % ±8.35% ±11.66% ±16.39%
streams/iter-throughput-broadcast.js n=5 datasize=1048576 consumers=1 api='iter' *** -17.21 % ±8.78% ±12.06% ±16.50%
streams/iter-throughput-broadcast.js n=5 datasize=1048576 consumers=1 api='webstream' *** -31.77 % ±12.75% ±17.99% ±25.68%
streams/iter-throughput-broadcast.js n=5 datasize=1048576 consumers=2 api='classic' -2.32 % ±5.56% ±7.76% ±10.90%
streams/iter-throughput-broadcast.js n=5 datasize=1048576 consumers=2 api='iter' ** -11.18 % ±6.34% ±8.72% ±11.95%
streams/iter-throughput-broadcast.js n=5 datasize=1048576 consumers=2 api='webstream' *** -22.39 % ±6.13% ±8.68% ±12.44%
streams/iter-throughput-broadcast.js n=5 datasize=1048576 consumers=4 api='classic' -5.51 % ±7.07% ±9.78% ±13.55%
streams/iter-throughput-broadcast.js n=5 datasize=1048576 consumers=4 api='iter' -1.68 % ±6.46% ±8.92% ±12.30%
streams/iter-throughput-broadcast.js n=5 datasize=1048576 consumers=4 api='webstream' *** -26.03 % ±4.97% ±6.88% ±9.54%
streams/iter-throughput-broadcast.js n=5 datasize=16777216 consumers=1 api='classic' * -4.21 % ±3.90% ±5.36% ±7.33%
streams/iter-throughput-broadcast.js n=5 datasize=16777216 consumers=1 api='iter' ** -10.27 % ±7.18% ±10.03% ±14.07%
streams/iter-throughput-broadcast.js n=5 datasize=16777216 consumers=1 api='webstream' ** -20.80 % ±11.70% ±16.63% ±24.05%
streams/iter-throughput-broadcast.js n=5 datasize=16777216 consumers=2 api='classic' -4.53 % ±5.56% ±7.70% ±10.66%
streams/iter-throughput-broadcast.js n=5 datasize=16777216 consumers=2 api='iter' *** -11.46 % ±5.39% ±7.40% ±10.13%
streams/iter-throughput-broadcast.js n=5 datasize=16777216 consumers=2 api='webstream' ** -12.59 % ±9.01% ±12.36% ±16.87%
streams/iter-throughput-broadcast.js n=5 datasize=16777216 consumers=4 api='classic' -4.09 % ±6.01% ±8.35% ±11.61%
streams/iter-throughput-broadcast.js n=5 datasize=16777216 consumers=4 api='iter' * -8.16 % ±6.54% ±8.98% ±12.27%
streams/iter-throughput-broadcast.js n=5 datasize=16777216 consumers=4 api='webstream' *** -8.95 % ±4.03% ±5.55% ±7.60% |
Renegade334
reviewed
May 12, 2026
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| #recomputeMinCursor() { | ||
| this.#cachedMinCursor = getMinCursor( | ||
| const [minCursor] = getMinCursor( |
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Suggested change
| const [minCursor] = getMinCursor( | |
| const { 0: minCursor } = getMinCursor( |
| } | ||
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| #recomputeMinCursor() { | ||
| const [minCursor, minCursorConsumers] = getMinCursor( |
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Suggested change
| const [minCursor, minCursorConsumers] = getMinCursor( | |
| const { 0: minCursor, 1: minCursorConsumers } = getMinCursor( |
| } | ||
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| #recomputeMinCursor() { | ||
| const [minCursor, minCursorConsumers] = getMinCursor( |
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Suggested change
| const [minCursor, minCursorConsumers] = getMinCursor( | |
| const { 0: minCursor, 1: minCursorConsumers } = getMinCursor( |
Renegade334
reviewed
May 12, 2026
Comment on lines
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| #deleteConsumerFromMin(consumer) { | ||
| if (consumer.cursor === this.#cachedMinCursor) { | ||
| this.#cachedMinCursorConsumers--; | ||
| } | ||
| } | ||
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| #deleteConsumer(consumer) { | ||
| if (this.#consumers.delete(consumer)) { | ||
| const wasAtMin = consumer.cursor === this.#cachedMinCursor; | ||
| this.#deleteConsumerFromMin(consumer); | ||
| return wasAtMin && this.#cachedMinCursorConsumers === 0; | ||
| } | ||
| return false; | ||
| } |
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Deduplication:
Suggested change
| #deleteConsumerFromMin(consumer) { | |
| if (consumer.cursor === this.#cachedMinCursor) { | |
| this.#cachedMinCursorConsumers--; | |
| } | |
| } | |
| #deleteConsumer(consumer) { | |
| if (this.#consumers.delete(consumer)) { | |
| const wasAtMin = consumer.cursor === this.#cachedMinCursor; | |
| this.#deleteConsumerFromMin(consumer); | |
| return wasAtMin && this.#cachedMinCursorConsumers === 0; | |
| } | |
| return false; | |
| } | |
| #deleteConsumerFromMin(consumer) { | |
| if (consumer.cursor === this.#cachedMinCursor) { | |
| this.#cachedMinCursorConsumers--; | |
| return true; | |
| } | |
| return false; | |
| } | |
| #deleteConsumer(consumer) { | |
| if (this.#consumers.delete(consumer) && | |
| this.#deleteConsumerFromMin(consumer) && | |
| this.#cachedMinCursorConsumers === 0) { | |
| return true; | |
| } | |
| return false; | |
| } |
Codecov Report❌ Patch coverage is
Additional details and impacted files@@ Coverage Diff @@
## main #63262 +/- ##
==========================================
- Coverage 90.04% 89.99% -0.05%
==========================================
Files 713 712 -1
Lines 225003 224250 -753
Branches 42536 42443 -93
==========================================
- Hits 202606 201821 -785
- Misses 14177 14297 +120
+ Partials 8220 8132 -88
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Description
This updates
share()andshareSync()to avoid recomputing the minimumconsumer cursor on every buffer trim attempt.
Instead of scanning all consumers each time, share now caches the current
minimum cursor and tracks how many consumers are positioned at that
cursor. The minimum is recomputed only when the last consumer at the
cached minimum advances or detaches.
The shared
getMinCursor()utility now returns both the minimum cursorand the number of consumers at that cursor.
Benchmark
Assisted-by: openai:gpt-5.5