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reject SemLock reduce - #6738

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youknowone merged 1 commit into
RustPython:mainfrom
youknowone:semlock-pickle
Jan 16, 2026
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reject SemLock reduce#6738
youknowone merged 1 commit into
RustPython:mainfrom
youknowone:semlock-pickle

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@youknowone youknowone commented Jan 15, 2026 •
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Summary by CodeRabbit

  • Bug Fixes
    • Fixed pickling behavior for SemLock objects. Attempting to serialize a SemLock instance directly now properly raises an error. Users must utilize the multiprocessing.SemLock wrapper to enable serialization support for these objects.

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coderabbitai Bot commented Jan 15, 2026 •
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πŸ“ Walkthrough

Walkthrough

A new __reduce__ method is added to the SemLock class in the multiprocessing module. This method raises a TypeError to prevent direct pickling of SemLock objects, requiring users to use the appropriate multiprocessing.SemLock wrapper for serialization support instead.

Changes

Cohort / File(s) Summary
SemLock pickling restriction
crates/stdlib/src/multiprocessing.rs		 Added __reduce__ method to SemLock class that raises TypeError with message "cannot pickle 'SemLock' object" to block direct serialization

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~2 minutes

Possibly related PRs

  • RustPython/RustPython#6542: Modifies the core SemLock implementation in multiprocessing module; this PR complements it by adding pickle prevention via the __reduce__ method.

Poem

🐰 A lock that cannot be pickled sweet,
No brines nor jars shall make it neat,
For SemLock stays locked away,
Wrap it well, the proper way! πŸ”’

πŸš₯ Pre-merge checks | βœ… 3
βœ… Passed checks (3 passed)
Check name Status Explanation
Description Check βœ… Passed Check skipped - CodeRabbit’s high-level summary is enabled.
Title check βœ… Passed The title 'reject SemLock reduce' directly and specifically describes the main change: preventing SemLock objects from being pickled by implementing a reduce method that rejects serialization.
Docstring Coverage βœ… Passed Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.

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✨ Finishing touches
  • πŸ“ Generate docstrings
πŸ“œ Recent review details

Configuration used: Path: .coderabbit.yml

Review profile: CHILL

Plan: Pro

πŸ“₯ Commits

Reviewing files that changed from the base of the PR and between 609dbb1 and 5697ab3.

β›” Files ignored due to path filters (1)
  • Lib/test/test_concurrent_futures/test_process_pool.py is excluded by !Lib/**
πŸ“’ Files selected for processing (1)
  • crates/stdlib/src/multiprocessing.rs
🧰 Additional context used
πŸ““ Path-based instructions (1)
**/*.rs

πŸ“„ CodeRabbit inference engine (.github/copilot-instructions.md)

**/*.rs: Follow the default rustfmt code style using cargo fmt to format Rust code
Always run clippy to lint code (cargo clippy) before completing tasks and fix any warnings or lints introduced by changes
Follow Rust best practices for error handling and memory management
Use the macro system (pyclass, pymodule, pyfunction, etc.) when implementing Python functionality in Rust

Files:

  • crates/stdlib/src/multiprocessing.rs
πŸ”‡ Additional comments (1)
crates/stdlib/src/multiprocessing.rs (1)

550-555: LGTM!

The __reduce__ method correctly prevents direct pickling of SemLock objects by raising a TypeError. This is consistent with CPython's behavior and the existing _rebuild classmethod design patternβ€”the higher-level multiprocessing.synchronize.SemLock wrapper is expected to handle serialization while using _rebuild for reconstruction.

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@youknowone
youknowone marked this pull request as ready for review January 16, 2026 01:14
@youknowone

youknowone commented Jan 16, 2026

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ran 10 times, no problem

@youknowone
youknowone merged commit 746e71a into RustPython:main Jan 16, 2026
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@youknowone
youknowone deleted the semlock-pickle branch January 16, 2026 01:18
@coderabbitai coderabbitai Bot mentioned this pull request Feb 23, 2026
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