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Reuse unlocked buffers in os.write - #9107

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youknowone merged 3 commits into
RustPython:mainfrom
1ndahous3:os_write_borrow_bytes
Oct 14, 2026
Merged

Reuse unlocked buffers in os.write#9107
youknowone merged 3 commits into
RustPython:mainfrom
1ndahous3:os_write_borrow_bytes

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@1ndahous3

@1ndahous3 1ndahous3 commented Oct 14, 2026 •
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Summary

  • Avoid allocating and copying immutable buffers before os.write.
  • Borrow storage owned by bytes, including memoryviews; snapshot other exporters, including readonly views over mutable raw memory, before releasing the interpreter thread.

Performance

Debian 13 amd64

os.write to /dev/null, median of seven samples, release build.

Workload Before After Speedup
64 KiB bytes 2.48 µs 1.14 µs 2.17×
1 MiB bytes 25.04 µs 1.12 µs 22.33×

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Written with Codex (GPT-6), reviewed by a human before submission.

Summary by CodeRabbit

  • Performance
    • Reduced copying when writing byte-string data to the operating system, while preserving retry behavior for interrupted writes.
  • Reliability
    • Data from writable or externally managed buffers is copied before use, so changes to the underlying storage do not alter the copied data.

@1ndahous3
Reuse unlocked buffers in os.write
fb9ada1 
Assisted-by: Codex:gpt-6
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Codex Review Summary

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Review Status Commit Review trigger
📝 Code Review ✅ Completed 2026-10-14T12:40:23.237465Z 64343fa New commits
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Review in Change Stack →

Important

Review skipped

Review was skipped as selected files did not have any reviewable changes.

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📥 Commits

Reviewing files that changed from the base of the PR and between fb9ada1 and 29338d7.

📒 Files selected for processing: 3
  • crates/common/src/borrow.rs
  • crates/vm/src/function/buffer.rs
  • crates/vm/src/stdlib/_ctypes/function.rs

Included review availability: This review used your included allowance. Your plan provides up to 10 included reviews per hour; 4 remain after this review.

📝 Walkthrough

borrow_buf_unlocked now borrows only unlocked buffers sourced from PyBytes; it copies buffers from other exporters. _os::write uses the borrowed buffer, with its existing EINTR signal-check and retry behavior unchanged.

Changes: OS write buffer

Layer / File(s) Summary
Restrict unlocked buffer borrowing
crates/vm/src/function/buffer.rs, crates/common/src/borrow.rs, crates/vm/src/stdlib/_ctypes/function.rs		 Unlocked buffers are borrowed only when sourced from PyBytes; other buffers are copied. Documentation describes the borrowing limits, and tests check snapshots of raw-memory views and borrowing of bytes storage.
Borrow argument buffer
crates/vm/src/stdlib/os.rs		 write uses an unlocked borrowed buffer instead of first creating an owned copy. Its existing interruption handling remains in place.

Priority: ➖ Normal

Estimated code review effort: 2 (Simple) | ~10 minutes

Change: Refactor

Suggested reviewers: youknowone

Merge Risk: ⚪ Minimal · up to 29338

The write optimization preserves stable buffer contents during writes and retries. No merge-blocking issue was found.

Pre-merge checks: Passed 5
Passed Passed checks: 5 passed
Check name Status Explanation
Docstring Coverage Passed Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 5 functions across 4 files.
Linked Issues check Passed Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check Passed Check skipped because no linked issues were found for this pull request.
Description Check Passed Check skipped - CodeRabbit’s high-level summary is enabled.
Title check Passed The title clearly and concisely describes the primary change: reusing unlocked buffers in os.write to avoid unnecessary copying.
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💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit: fb9ada1053

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Comment thread crates/vm/src/stdlib/os.rs
@1ndahous3
Snapshot buffers without immutable storage
29338d7 
Assisted-by: Codex:gpt-6
@1ndahous3
Merge upstream main
64343fa 
Assisted-by: Codex:gpt-6
@codspeed

codspeed Bot commented Oct 14, 2026

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Merging this PR will not alter performance

✅ 62 untouched benchmarks
⏩ 4 skipped benchmarks1

Comparing 1ndahous3:os_write_borrow_bytes (64343fa) with main (0816af6)

Open in CodSpeed

Footnotes

  1. 4 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

@youknowone
youknowone merged commit c85829b into RustPython:main Oct 14, 2026
30 checks passed
@youknowdot youknowdot mentioned this pull request Oct 14, 2026
Merged
1 task done
@1ndahous3
1ndahous3 deleted the os_write_borrow_bytes branch October 15, 2026 09:58
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@1ndahous3 @youknowone