readline: improve performance by mcollina · Pull Request #64585 · nodejs/node

mcollina · 2026-07-18T21:45:57Z

Speed up readline.createInterface(), which is on the hot path of every CLI tool that reads lines from a stream.

A CPU profile of interface construction showed three avoidable costs:

setupHistoryManager() accounted for ~43% of construction self time: every instance ran four ObjectDefineProperty calls, allocating six fresh closures and four descriptor objects each time. The accessors (history, historyIndex, historySize, isFlushing) are now defined from a module-level shared descriptor map with a single ObjectDefineProperties call. They remain own, enumerable, configurable properties, so observable semantics are unchanged.
The constructor assigned size, history and removeHistoryDuplicates onto the user-provided input stream to forward them to the history manager. It now passes a plain options object instead, so the user's stream is no longer observably mutated and doesn't go through extra hidden-class transitions. The legacy positional-arguments path is unchanged.
The Interface wrapper unconditionally read process.env.TERM (which goes through the env interceptor) to bind the dumb-terminal _ttyWrite. The check is now gated on this.terminal, since _ttyWrite is never invoked when the interface is not in terminal mode.

Results with the new benchmark (30 runs, interleaved via benchmark/compare.js):

                                                         confidence improvement accuracy (*)   (**)  (***)
readline/readline-createInterface.js terminal=0 n=100000        ***     63.81 %       ±1.94% ±2.59% ±3.38%
readline/readline-createInterface.js terminal=1 n=100000        ***     38.05 %       ±1.90% ±2.53% ±3.31%

Update: a second commit speeds up line throughput as well. [kNormalWrite] ran a regular-expression exec loop that allocated a match object and two index entries per line, then sliced each line out in JS. It now does a single split pass, and uses a plain string split on "\n" when the chunk contains none of the rare line endings (\r,  ,  ), which takes V8's fast string-split path.

Results for readline/readline-iterable.js (20 runs, interleaved):

                                                   confidence improvement accuracy (*)    (**)   (***)
readline/readline-iterable.js type='new' n=10             ***      5.18 %       ±1.91%  ±2.57%  ±3.38%
readline/readline-iterable.js type='new' n=100              *     13.16 %      ±12.52% ±16.89% ±22.48%
readline/readline-iterable.js type='new' n=1000           ***     32.94 %      ±11.25% ±15.31% ±20.66%
readline/readline-iterable.js type='new' n=10000          ***     47.44 %       ±4.83%  ±6.53%  ±8.70%
readline/readline-iterable.js type='new' n=100000         ***     70.71 %       ±2.18%  ±2.94%  ±3.91%
readline/readline-iterable.js type='new' n=1000000        ***     80.62 %       ±1.51%  ±2.05%  ±2.75%
readline/readline-iterable.js type='old' n=10             ***      4.92 %       ±1.50%  ±2.01%  ±2.66%
readline/readline-iterable.js type='old' n=100                    -5.79 %      ±10.40% ±13.97% ±18.46%
readline/readline-iterable.js type='old' n=1000                    1.39 %       ±6.82%  ±9.14% ±12.03%
readline/readline-iterable.js type='old' n=10000          ***     18.40 %       ±3.62%  ±4.85%  ±6.38%
readline/readline-iterable.js type='old' n=100000         ***     26.02 %       ±2.91%  ±3.93%  ±5.21%
readline/readline-iterable.js type='old' n=1000000        ***     31.42 %       ±2.00%  ±2.67%  ±3.52%

Event-based consumption (rl.on('line')) goes from 8.1M to 13.3M lines/s (+65%) in a microbenchmark of 32-byte lines.

Speed up Interface construction: - Hoist the history accessor property descriptors to module scope and define them with a single ObjectDefineProperties call, instead of allocating six closures and four descriptor objects per instance. - Stop assigning the history options onto the input stream. This avoids hidden class transitions on the user provided stream and no longer mutates it observably. - Only check process.env.TERM for a dumb terminal when the interface is in terminal mode. Reading process.env goes through the environment interceptor and is comparatively expensive, and _ttyWrite is never called when terminal is false. Signed-off-by: Matteo Collina <hello@matteocollina.com>

nodejs-github-bot · 2026-07-18T21:46:01Z

Review requested:

@nodejs/performance

Replace the per-line regular expression exec loop with a single split pass, and use a plain string split on "\n" when the chunk contains none of the rare line endings (\r, \u2028, \u2029). This avoids allocating a match object and two index entries per line and lets the common case use the fast string split path. readline/readline-iterable.js type='new' improves by up to 80% and the event based line consumption by up to 65%. Signed-off-by: Matteo Collina <hello@matteocollina.com>

codecov · 2026-07-18T23:37:33Z

Codecov Report

❌ Patch coverage is 98.59155% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 90.12%. Comparing base (4f844f4) to head (0fd92a9).
⚠️ Report is 56 commits behind head on main.

Files with missing lines	Patch %	Lines
lib/internal/readline/interface.js	98.52%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #64585      +/-   ##
==========================================
- Coverage   90.13%   90.12%   -0.02%     
==========================================
  Files         741      741              
  Lines      241976   241994      +18     
  Branches    45543    45551       +8     
==========================================
- Hits       218116   218101      -15     
- Misses      15379    15410      +31     
- Partials     8481     8483       +2

Files with missing lines	Coverage Δ
lib/readline.js	`95.80% <100.00%> (+0.01%)`	⬆️
lib/internal/readline/interface.js	`93.21% <98.52%> (+<0.01%)`	⬆️

... and 30 files with indirect coverage changes

🚀 New features to boost your workflow:

❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

nodejs-github-bot · 2026-07-20T14:46:25Z

CI: https://ci.nodejs.org/job/node-test-pull-request/74905/

nodejs-github-bot · 2026-07-24T10:42:58Z

Commit Queue failed

- Loading data for nodejs/node/pull/64585 ✔ Done loading data for nodejs/node/pull/64585 ----------------------------------- PR info ------------------------------------ Title readline: improve performance (#64585) Author Matteo Collina <matteo.collina@gmail.com> (@mcollina) Branch mcollina:readline-createinterface-perf -> nodejs:main Labels readline, author ready, needs-ci Commits 2 - readline: reduce createInterface overhead - readline: speed up line splitting in normal write Committers 1 - Matteo Collina <hello@matteocollina.com> PR-URL: https://github.com/nodejs/node/pull/64585 Reviewed-By: James M Snell <jasnell@gmail.com> Reviewed-By: Rafael Gonzaga <rafael.nunu@hotmail.com> Reviewed-By: Yagiz Nizipli <yagiz@nizipli.com> Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com> Reviewed-By: Gürgün Dayıoğlu <hey@gurgun.day> ------------------------------ Generated metadata ------------------------------ PR-URL: https://github.com/nodejs/node/pull/64585 Reviewed-By: James M Snell <jasnell@gmail.com> Reviewed-By: Rafael Gonzaga <rafael.nunu@hotmail.com> Reviewed-By: Yagiz Nizipli <yagiz@nizipli.com> Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com> Reviewed-By: Gürgün Dayıoğlu <hey@gurgun.day> -------------------------------------------------------------------------------- ℹ This PR was created on Sat, 18 Jul 2026 21:45:57 GMT ✔ Approvals: 5 ✔ - James M Snell (@jasnell) (TSC): https://github.com/nodejs/node/pull/64585#pullrequestreview-4731050691 ✔ - Rafael Gonzaga (@RafaelGSS) (TSC): https://github.com/nodejs/node/pull/64585#pullrequestreview-4731061804 ✔ - Yagiz Nizipli (@anonrig) (TSC): https://github.com/nodejs/node/pull/64585#pullrequestreview-4731326110 ✔ - Benjamin Gruenbaum (@benjamingr) (TSC): https://github.com/nodejs/node/pull/64585#pullrequestreview-4731378980 ✔ - Gürgün Dayıoğlu (@gurgunday): https://github.com/nodejs/node/pull/64585#pullrequestreview-4734487326 ✔ Last GitHub CI successful ℹ Last Full PR CI on 2026-07-20T14:46:25Z: https://ci.nodejs.org/job/node-test-pull-request/74905/ - Querying data for job/node-test-pull-request/74905/ ✔ 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 64585 From https://github.com/nodejs/node * branch refs/pull/64585/merge -> FETCH_HEAD ✔ Fetched commits as c558c8e81a7c..0fd92a96ca87 -------------------------------------------------------------------------------- [main 5fe0cee5e7] readline: reduce createInterface overhead Author: Matteo Collina <hello@matteocollina.com> Date: Sat Jul 18 23:45:16 2026 +0200 3 files changed, 63 insertions(+), 27 deletions(-) create mode 100644 benchmark/readline/readline-createInterface.js [main 07a3f277aa] readline: speed up line splitting in normal write Author: Matteo Collina <hello@matteocollina.com> Date: Sun Jul 19 00:03:28 2026 +0200 1 file changed, 34 insertions(+), 26 deletions(-) ✔ Patches applied There are 2 commits in the PR. Attempting autorebase. (node:352) [DEP0190] DeprecationWarning: Passing args to a child process with shell option true can lead to security vulnerabilities, as the arguments are not escaped, only concatenated. (Use `node --trace-deprecation ...` to show where the warning was created) Rebasing (2/4) Executing: git node land --amend --yes --------------------------------- New Message ---------------------------------- readline: reduce createInterface overhead

Speed up Interface construction:

Hoist the history accessor property descriptors to module scope and
define them with a single ObjectDefineProperties call, instead of
allocating six closures and four descriptor objects per instance.
Stop assigning the history options onto the input stream. This avoids
hidden class transitions on the user provided stream and no longer
mutates it observably.
Only check process.env.TERM for a dumb terminal when the interface is
in terminal mode. Reading process.env goes through the environment
interceptor and is comparatively expensive, and _ttyWrite is never
called when terminal is false.

Signed-off-by: Matteo Collina <hello@matteocollina.com>
PR-URL: #64585
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Rafael Gonzaga <rafael.nunu@hotmail.com>
Reviewed-By: Yagiz Nizipli <yagiz@nizipli.com>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Gürgün Dayıoğlu <hey@gurgun.day>

[detached HEAD 7dd44d226b] readline: reduce createInterface overhead
Author: Matteo Collina <hello@matteocollina.com>
Date: Sat Jul 18 23:45:16 2026 +0200
3 files changed, 63 insertions(+), 27 deletions(-)
create mode 100644 benchmark/readline/readline-createInterface.js
Rebasing (3/4)
Rebasing (4/4)
Executing: git node land --amend --yes
--------------------------------- New Message ----------------------------------
readline: speed up line splitting in normal write

Replace the per-line regular expression exec loop with a single split
pass, and use a plain string split on "\n" when the chunk contains none
of the rare line endings (\r, \u2028, \u2029). This avoids allocating a
match object and two index entries per line and lets the common case
use the fast string split path.

readline/readline-iterable.js type='new' improves by up to 80% and
the event based line consumption by up to 65%.

Signed-off-by: Matteo Collina <hello@matteocollina.com>
PR-URL: #64585
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Rafael Gonzaga <rafael.nunu@hotmail.com>
Reviewed-By: Yagiz Nizipli <yagiz@nizipli.com>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Gürgün Dayıoğlu <hey@gurgun.day>

[detached HEAD 1ba3425011] readline: speed up line splitting in normal write
Author: Matteo Collina <hello@matteocollina.com>
Date: Sun Jul 19 00:03:28 2026 +0200
1 file changed, 34 insertions(+), 26 deletions(-)
Successfully rebased and updated refs/heads/main.

ℹ Add commit-queue-squash label to land the PR as one commit, or commit-queue-rebase to land as separate commits.

https://github.com/nodejs/node/actions/runs/30086846509

Speed up Interface construction: - Hoist the history accessor property descriptors to module scope and define them with a single ObjectDefineProperties call, instead of allocating six closures and four descriptor objects per instance. - Stop assigning the history options onto the input stream. This avoids hidden class transitions on the user provided stream and no longer mutates it observably. - Only check process.env.TERM for a dumb terminal when the interface is in terminal mode. Reading process.env goes through the environment interceptor and is comparatively expensive, and _ttyWrite is never called when terminal is false. Signed-off-by: Matteo Collina <hello@matteocollina.com> PR-URL: #64585 Reviewed-By: James M Snell <jasnell@gmail.com> Reviewed-By: Rafael Gonzaga <rafael.nunu@hotmail.com> Reviewed-By: Yagiz Nizipli <yagiz@nizipli.com> Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com> Reviewed-By: Gürgün Dayıoğlu <hey@gurgun.day>

avivkeller · 2026-07-24T16:09:17Z

Landed in 9041ad0

nodejs-github-bot added needs-ci PRs that need a full CI run. readline Issues and PRs related to the built-in readline module. labels Jul 18, 2026

mcollina changed the title ~~readline: reduce createInterface overhead~~ readline: improve performance Jul 18, 2026

mcollina requested review from anonrig and jasnell July 19, 2026 10:22

jasnell approved these changes Jul 19, 2026

View reviewed changes

RafaelGSS approved these changes Jul 19, 2026

View reviewed changes

anonrig approved these changes Jul 19, 2026

View reviewed changes

benjamingr approved these changes Jul 19, 2026

View reviewed changes

mcollina added the request-ci Add this label to start a Jenkins CI on a PR. label Jul 20, 2026

github-actions Bot removed the request-ci Add this label to start a Jenkins CI on a PR. label Jul 20, 2026

This comment was marked as outdated.

Sign in to view

gurgunday approved these changes Jul 20, 2026

View reviewed changes

trivikr added the author ready PRs that have at least one approval, no pending requests for changes, and a CI started. label Jul 21, 2026

mcollina added the commit-queue Add this label to land a pull request using GitHub Actions. label Jul 24, 2026

nodejs-github-bot added commit-queue-failed An error occurred while landing this pull request using GitHub Actions. and removed commit-queue Add this label to land a pull request using GitHub Actions. labels Jul 24, 2026

avivkeller closed this Jul 24, 2026

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

Uh oh!

Uh oh!

readline: improve performance#64585

readline: improve performance#64585
mcollina wants to merge 2 commits into
nodejs:mainfrom
mcollina:readline-createinterface-perf

mcollina commented Jul 18, 2026 •

edited

Loading

Uh oh!

nodejs-github-bot commented Jul 18, 2026

Uh oh!

codecov Bot commented Jul 18, 2026 •

edited

Loading

Uh oh!

This comment was marked as outdated.

nodejs-github-bot commented Jul 20, 2026

Uh oh!

nodejs-github-bot commented Jul 24, 2026

[detached HEAD 1ba3425011] readline: speed up line splitting in normal write
Author: Matteo Collina <hello@matteocollina.com>
Date: Sun Jul 19 00:03:28 2026 +0200
1 file changed, 34 insertions(+), 26 deletions(-)
Successfully rebased and updated refs/heads/main.

Uh oh!

avivkeller commented Jul 24, 2026

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

9 participants

Uh oh!

Uh oh!

Conversation

mcollina commented Jul 18, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

nodejs-github-bot commented Jul 18, 2026

Uh oh!

codecov Bot commented Jul 18, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Codecov Report

Uh oh!

This comment was marked as outdated.

nodejs-github-bot commented Jul 20, 2026

Uh oh!

nodejs-github-bot commented Jul 24, 2026

[detached HEAD 1ba3425011] readline: speed up line splitting in normal write Author: Matteo Collina <hello@matteocollina.com> Date: Sun Jul 19 00:03:28 2026 +0200 1 file changed, 34 insertions(+), 26 deletions(-) Successfully rebased and updated refs/heads/main.

Uh oh!

avivkeller commented Jul 24, 2026

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

9 participants

mcollina commented Jul 18, 2026 •

edited

Loading

codecov Bot commented Jul 18, 2026 •

edited

Loading

[detached HEAD 1ba3425011] readline: speed up line splitting in normal write
Author: Matteo Collina <hello@matteocollina.com>
Date: Sun Jul 19 00:03:28 2026 +0200
1 file changed, 34 insertions(+), 26 deletions(-)
Successfully rebased and updated refs/heads/main.