stream: fold desired-size check into WHATWG backpressure update by mcollina · Pull Request #64451 · nodejs/node

mcollina · 2026-07-12T15:12:39Z

writableStreamUpdateBackpressure ran two release-mode assertions and took a precomputed backpressure value that every caller derived with a separate GetBackpressure/GetDesiredSize call pair. All callers already hold the writable, not-close-queued invariant the assertions checked, so the backpressure is now derived from the desired size inside the function, dropping the assertions and the helper. This runs up to twice per write.

writer.write() loop: +10% (local harness)
pipe-to: +4.6% avg over 16 configs, all positive (benchmark, 20 runs)

The first commit is #64431; only the last commit is new here.

The [[queue]] backing the controllers became a ring buffer, but the read and write request queues (readRequests, readIntoRequests, writeRequests) were left as plain arrays consumed with ArrayPrototypeShift, which is O(n) and, even for the single pending request of the await-each regime, far slower than an indexed head advance. Back them with the same Queue, materialized lazily from the shared empty queue so acquiring a reader or constructing a writer allocates no request storage until a read or write actually parks. pipe-to: +4.7% to +9.4% (all 16 configs, ***) readable-read type=byob: +2.3% (**) parked read loop: +15%, write loop: +11% (local harness) Follow-up to nodejs#64312. Signed-off-by: Matteo Collina <hello@matteocollina.com>

writableStreamUpdateBackpressure ran two release-mode assertions and took a precomputed backpressure value that every caller derived with a separate GetBackpressure/GetDesiredSize call pair. All callers already hold the 'writable', not-close-queued invariant the assertions checked, so derive the backpressure from the desired size inside the function and drop the assertions and the helper. This runs up to twice per write. writer.write() loop: +10%, pipe-to: +4.6% avg over 16 configs (local harness / benchmark, all configs positive). Signed-off-by: Matteo Collina <hello@matteocollina.com>

codecov · 2026-07-12T17:00:30Z

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.24%. Comparing base (8a3b11c) to head (3cb9f68).
⚠️ Report is 45 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #64451      +/-   ##
==========================================
- Coverage   90.24%   90.24%   -0.01%     
==========================================
  Files         741      741              
  Lines      241384   241610     +226     
  Branches    45480    45519      +39     
==========================================
+ Hits       217844   218041     +197     
- Misses      15097    15110      +13     
- Partials     8443     8459      +16

Files with missing lines	Coverage Δ
lib/internal/webstreams/readablestream.js	`98.19% <100.00%> (+<0.01%)`	⬆️
lib/internal/webstreams/util.js	`97.71% <100.00%> (+<0.01%)`	⬆️
lib/internal/webstreams/writablestream.js	`99.50% <100.00%> (-0.01%)`	⬇️

... and 47 files with indirect coverage changes

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nodejs-github-bot · 2026-07-13T20:49:57Z

CI: https://ci.nodejs.org/job/node-test-pull-request/74797/

mcollina · 2026-07-14T13:41:52Z

@trivikr can you review?

trivikr

lgtm

nodejs-github-bot · 2026-07-16T06:41:31Z

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- Loading data for nodejs/node/pull/64451 ✔ Done loading data for nodejs/node/pull/64451 ----------------------------------- PR info ------------------------------------ Title stream: fold desired-size check into WHATWG backpressure update (#64451) Author Matteo Collina <matteo.collina@gmail.com> (@mcollina) Branch mcollina:webstream-perf-round9 -> nodejs:main Labels author ready, needs-ci, web streams Commits 2 - stream: use the ring buffer for WHATWG stream request queues - stream: fold desired-size check into WHATWG backpressure update Committers 1 - Matteo Collina <hello@matteocollina.com> PR-URL: https://github.com/nodejs/node/pull/64451 Reviewed-By: James M Snell <jasnell@gmail.com> Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com> ------------------------------ Generated metadata ------------------------------ PR-URL: https://github.com/nodejs/node/pull/64451 Reviewed-By: James M Snell <jasnell@gmail.com> Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com> -------------------------------------------------------------------------------- ℹ This PR was created on Sun, 12 Jul 2026 15:12:39 GMT ✔ Approvals: 2 ✔ - James M Snell (@jasnell) (TSC): https://github.com/nodejs/node/pull/64451#pullrequestreview-4680407396 ✔ - Trivikram Kamat (@trivikr): https://github.com/nodejs/node/pull/64451#pullrequestreview-4710339944 ✔ Last GitHub CI successful ℹ Last Full PR CI on 2026-07-13T20:49:57Z: https://ci.nodejs.org/job/node-test-pull-request/74797/ - Querying data for job/node-test-pull-request/74797/ ✔ Build data downloaded ✔ Last Jenkins CI successful -------------------------------------------------------------------------------- ✔ No git cherry-pick in progress ✔ No git am in progress ✔ No git rebase in progress -------------------------------------------------------------------------------- - Bringing origin/main up to date... From https://github.com/nodejs/node * branch main -> FETCH_HEAD 608112affa..874e96ee4c main -> origin/main ✔ origin/main is now up-to-date main is out of sync with origin/main. Mismatched commits: - d91a9207a0 stream: validate writer options signal - 874e96ee4c stream: validate writer options signal -------------------------------------------------------------------------------- HEAD is now at 874e96ee4c stream: validate writer options signal ✔ Reset to origin/main - Downloading patch for 64451 From https://github.com/nodejs/node * branch refs/pull/64451/merge -> FETCH_HEAD ✔ Fetched commits as 608112affae2..3cb9f689c486 -------------------------------------------------------------------------------- The previous cherry-pick is now empty, possibly due to conflict resolution. If you wish to commit it anyway, use:

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nodejs-github-bot · 2026-07-16T08:26:35Z

Commit Queue failed

- Loading data for nodejs/node/pull/64451 ✔ Done loading data for nodejs/node/pull/64451 ----------------------------------- PR info ------------------------------------ Title stream: fold desired-size check into WHATWG backpressure update (#64451) Author Matteo Collina <matteo.collina@gmail.com> (@mcollina) Branch mcollina:webstream-perf-round9 -> nodejs:main Labels author ready, needs-ci, web streams, commit-queue-squash Commits 2 - stream: use the ring buffer for WHATWG stream request queues - stream: fold desired-size check into WHATWG backpressure update Committers 1 - Matteo Collina <hello@matteocollina.com> PR-URL: https://github.com/nodejs/node/pull/64451 Reviewed-By: James M Snell <jasnell@gmail.com> Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com> ------------------------------ Generated metadata ------------------------------ PR-URL: https://github.com/nodejs/node/pull/64451 Reviewed-By: James M Snell <jasnell@gmail.com> Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com> -------------------------------------------------------------------------------- ℹ This PR was created on Sun, 12 Jul 2026 15:12:39 GMT ✔ Approvals: 2 ✔ - James M Snell (@jasnell) (TSC): https://github.com/nodejs/node/pull/64451#pullrequestreview-4680407396 ✔ - Trivikram Kamat (@trivikr): https://github.com/nodejs/node/pull/64451#pullrequestreview-4710339944 ✔ Last GitHub CI successful ℹ Last Full PR CI on 2026-07-16T06:41:31Z: https://ci.nodejs.org/job/node-test-pull-request/74797/ - Querying data for job/node-test-pull-request/74797/ ✔ Build data downloaded ✔ Last Jenkins CI successful -------------------------------------------------------------------------------- ✔ No git cherry-pick in progress ✔ No git am in progress ✔ No git rebase in progress -------------------------------------------------------------------------------- - Bringing origin/main up to date... From https://github.com/nodejs/node * branch main -> FETCH_HEAD ✔ origin/main is now up-to-date - Downloading patch for 64451 From https://github.com/nodejs/node * branch refs/pull/64451/merge -> FETCH_HEAD ✔ Fetched commits as 608112affae2..3cb9f689c486 -------------------------------------------------------------------------------- The previous cherry-pick is now empty, possibly due to conflict resolution. If you wish to commit it anyway, use:

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aduh95 · 2026-07-16T11:34:11Z

Landed in cf882a7

mcollina added 2 commits July 12, 2026 12:48

nodejs-github-bot added needs-ci PRs that need a full CI run. web streams labels Jul 12, 2026

jasnell approved these changes Jul 12, 2026

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trivikr added the author ready PRs that have at least one approval, no pending requests for changes, and a CI started. label Jul 14, 2026

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aduh95 merged commit cf882a7 into nodejs:main Jul 16, 2026
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stream: fold desired-size check into WHATWG backpressure update#64451

stream: fold desired-size check into WHATWG backpressure update#64451
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