Fix ctypes assignment conversion and backing-buffer retention by 1ndahous3 · Pull Request #9251 · RustPython/RustPython

1ndahous3 · 2026-10-20T14:27:18Z

Follow-up to #9229 and its private-holder review.

Summary

Share typed conversion across array, pointer and field assignments: fix float-pointer writes and integer wrapping, reject incompatible ctypes values, and propagate conversion errors before changing storage.
Return writable typed views for scalar-subclass fields and the retained Python object for py_object fields.
Flatten and deduplicate private backing-buffer references to prevent nested holder growth on repeated self-copy. Preserve existing string owners when assigning raw addresses.
Keep tuple-created temporary objects alive until bytes and owners are installed, so finalizers observe the new value and can safely reenter assignment.
Avoid temporary byte-buffer allocation for integer assignments.
Keep scalar assignment converters fixed at type initialization so later _type_ changes cannot alter the write width or reinterpret values.
Preserve full-width Windows X address and null assignments.

Performance

Median ns/operation, release builds.

Windows 11 x64

Operation	Before, ns	After, ns	Before / after
Unchanged string-structure self-copy	2,054	1,007	2.04×
Structure assignment to an array	1,624	613	2.65×
Integer array write	477	375	1.27×
Integer pointer write	639	378	1.69×
Integer structure-field write	535	425	1.26×

Debian 13 amd64

Operation	Before, ns	After, ns	Before / after
Unchanged string-structure self-copy	1,952	900	2.17×
Structure assignment to an array	1,539	567	2.71×
Integer array write	404	326	1.24×
Integer pointer write	554	325	1.70×
Integer structure-field write	464	359	1.29×

Known limitations

Root-wide ownership snapshots still duplicate owner IDs across copied slots; narrowing them by field path would lose raw aliases. Native BSTR string allocation and ownership remain incomplete.

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

Summary by CodeRabbit

Bug Fixes
- Improved ctypes assignments for arrays, pointers, structures, scalar values, characters, floating-point values, integers, and Python objects.
- Added more consistent type conversion, byte-order handling, and validation for incompatible values.
- Preserved referenced buffers and temporary objects correctly, reducing unexpected invalid or dangling pointer views.
- Improved handling of null pointers, pointer-backed values, repeated self-copy assignments, and pointer-sized storage.
- Conversion errors now propagate reliably without corrupting existing record bytes.
Tests
- Added regression coverage for conversions, error handling, object lifetime, pointer buffers, and temporary values.

Assisted-by: Codex:GPT-6

chatgpt-codex-connector · 2026-10-20T14:27:34Z

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📝 Code Review	✅ Completed 2026-10-20T19:00:36.618415Z	`8850198`	New commits

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coderabbitai · 2026-10-20T14:28:05Z

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Reviewing files that changed from the base of the PR and between eb6ff46 and e9178dd.

📒 Files selected for processing: 4

crates/host_env/src/ctypes.rs
crates/vm/src/stdlib/_ctypes/base.rs
crates/vm/src/stdlib/_ctypes/simple.rs
extra_tests/snippets/stdlib_ctypes.py

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📝 Walkthrough

The change centralizes ctypes assignment conversion in CDataValue, adds deduplicated owner retention, and routes array, pointer, and field writes through the shared flow. It updates simple-type serialization, pointer-width "X" storage, and regression coverage.

Changes: ctypes assignment conversion and ownership

Layer / File(s)	Summary
Owner retention and simple-type conversion `crates/vm/src/stdlib/_ctypes/base.rs`, `crates/vm/src/stdlib/_ctypes/simple.rs`, `crates/host_env/src/ctypes.rs`	`PyCData` now tracks deduplicated private owners. Simple-type assignment serializes supported values, applies endian handling, and returns owner metadata. `"X"` uses pointer-sized storage.
Shared assignment preparation `crates/vm/src/stdlib/_ctypes/base.rs`	`CDataValue` prepares assignment bytes and ownership metadata. Field assignment uses this conversion, scalar object-pointer fields resolve referenced Python objects, and simple ctypes types support views.
Array and pointer assignment integration `crates/vm/src/stdlib/_ctypes/array.rs`, `crates/vm/src/stdlib/_ctypes/pointer.rs`, `extra_tests/snippets/stdlib_ctypes.py`	Array and pointer item assignments use `CDataValue`. Tests cover conversion errors, unchanged destination data, temporary finalization, backing-owner retention, fixed-width writes, and BSTR null storage.

Priority: ⬇️ Low

Estimated code review effort: 4 (Complex) | ~45 minutes

Change: Bug fix

Sequence Diagram(s)

sequenceDiagram
  participant Assignment as Array or pointer assignment
  participant CDataValue
  participant Storage as CData storage
  participant PyCData as Owner retention
  Assignment->>CDataValue: Prepare converted bytes and owner references
  CDataValue->>Storage: Write prepared bytes
  CDataValue->>PyCData: Retain required owners

Suggested reviewers: youknowone

Merge Risk: 🔵 Low · up to e9178

The assignment changes do not appear to introduce a material regression. Large ctypes owner graphs retain an existing scaling limitation, so merging is reasonable with owner awareness of that limitation.

Pre-merge checks: 4 · 1

Failed checks: 1 warning

Check name	Status	Explanation	Resolution
Docstring Coverage		Docstring coverage is 44.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 50 functions across 6 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

Passed checks: 4 passed

Check name	Status	Explanation
Description Check		Check skipped - CodeRabbit’s high-level summary is enabled.
Title check		The title clearly and concisely identifies the primary changes: ctypes assignment conversion and backing-buffer retention.
Linked Issues check		Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check		Check skipped because no linked issues were found for this pull request.

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Inline comments:
Review comments at @crates/vm/src/stdlib/_ctypes/base.rs:
- Around line 1134-1138: Update hidden_refs to snapshot only private owners
whose keys belong to the source view’s unique_key subtree, including the view
key itself, rather than all owners from the root object; preserve the full
snapshot behavior for root objects without a base and retain the self-copy
guarantee without nesting holders.

Review comments at @crates/vm/src/stdlib/_ctypes/simple.rs:
- Around line 756-788: Update assignment_value’s pointer arm to include the
Windows BSTR type code "X", accepting PyStr values through the same string
conversion path as "Z". Also include "X" in
simple_storage_value_to_bytes_endian’s pointer-type handling so assignments
serialize across the full pointer-sized width.

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📒 Files selected for processing: 5

crates/vm/src/stdlib/_ctypes/array.rs
crates/vm/src/stdlib/_ctypes/base.rs
crates/vm/src/stdlib/_ctypes/pointer.rs
crates/vm/src/stdlib/_ctypes/simple.rs
extra_tests/snippets/stdlib_ctypes.py

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github-actions · 2026-10-20T19:00:56Z

📦 Library Dependencies

The following Lib/ modules were modified. Here are their dependencies:

:4: SyntaxWarning: invalid decimal literal
:7: SyntaxWarning: "\z" is an invalid escape sequence. Such sequences will not work in the future. Did you mean "\z"? A raw string is also an option.
:10: SyntaxWarning: "\400" is an invalid octal escape sequence. Such sequences will not work in the future. Did you mean "\400"? A raw string is also an option.
:4: SyntaxWarning: invalid decimal literal
:7: SyntaxWarning: "\z" is an invalid escape sequence. Such sequences will not work in the future. Did you mean "\z"? A raw string is also an option.
:10: SyntaxWarning: "\400" is an invalid octal escape sequence. Such sequences will not work in the future. Did you mean "\400"? A raw string is also an option.
:4: SyntaxWarning: invalid decimal literal
:7: SyntaxWarning: "\z" is an invalid escape sequence. Such sequences will not work in the future. Did you mean "\z"? A raw string is also an option.
:10: SyntaxWarning: "\400" is an invalid octal escape sequence. Such sequences will not work in the future. Did you mean "\400"? A raw string is also an option.
[ ] test: cpython/Lib/test/test_pyrepl (TODO: 8)
[x] test: cpython/Lib/test/test_repl.py (TODO: 3)

dependencies:

dependent tests: (no tests depend on pyrepl)

Legend:

[+] path exists in CPython
[x] up-to-date, [ ] outdated

fanninpm · 2026-10-20T20:03:23Z

cc @bschoenmaeckers

youknowone

Thanks!

Fix ctypes assignment conversion and backing-buffer retention

eb6ff46

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coderabbitai Bot reviewed Oct 20, 2026

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Comment thread crates/vm/src/stdlib/_ctypes/base.rs

Comment thread crates/vm/src/stdlib/_ctypes/simple.rs Outdated

chatgpt-codex-connector Bot reviewed Oct 20, 2026

View reviewed changes

Comment thread extra_tests/snippets/stdlib_ctypes.py

Comment thread crates/vm/src/stdlib/_ctypes/simple.rs Outdated

Comment thread crates/vm/src/stdlib/_ctypes/base.rs Outdated

Preserve ctypes assignment metadata and pointer-width writes

e9178dd

Assisted-by: Codex:GPT-6

chatgpt-codex-connector Bot reviewed Oct 20, 2026

View reviewed changes

Comment thread crates/host_env/src/ctypes.rs

Enable passing Windows console tests

8850198

Assisted-by: Codex:GPT-6

fanninpm requested a review from youknowone October 20, 2026 20:03

youknowone approved these changes Oct 21, 2026

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youknowone merged commit 11a6455 into RustPython:main Oct 21, 2026
30 checks passed

1ndahous3 deleted the ctypes_value_ownership branch October 25, 2026 09:34

This was referenced Oct 26, 2026

Fix ctypes scalar access, bitfields, and cyclic collection #9390

Merged

Preserve ctypes py_object provenance across casts and pointer writes #9391

Merged

Share ctypes backing-owner snapshots between aggregate copies #9392

Merged

coderabbitai Bot mentioned this pull request Oct 26, 2026

Fix ctypes subclass bitfields and native type metadata #9395

Merged

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Fix ctypes assignment conversion and backing-buffer retention - #9251

Fix ctypes assignment conversion and backing-buffer retention#9251
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Summary

Performance

Windows 11 x64

Debian 13 amd64

Known limitations

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