[bgen] Cache attribute lookups to reduce memory allocations by rolfbjarne · Pull Request #25782 · dotnet/macios

rolfbjarne · 2026-06-23T13:14:23Z

Cache various attribute query results in bgen to avoid repeated reflection and attribute conversion work. This reduces total memory allocations by ~22% and GC pressure by ~25-39% when generating bindings.

Changes:

Cache GetCustomAttributes<T> results per (provider, type) pair
Cache HasAttribute<T> results to avoid repeated GetCustomAttributesData() calls
Cache common platform attributes as singletons in AttributeFactory
Cache GetAllParentAttributes results per MemberInfo
Cache ConstructorInfo lookups per (type, argTypes) to avoid repeated reflection
Cache static Type[] arrays for attribute constructors
Cache getter/setter ExportAttribute results per PropertyInfo

Performance (tvOS bindings, 3-run averages):

Metric	Before	After	Diff
Time	23.9s	20.9s	-12.5%
Allocs	7003MB	5439MB	-22.3%
Gen0	1268	951	-25.0%
Gen1	414	254	-38.6%

GetCustomAttributes<T> was being called repeatedly on the same providers. Each call would re-invoke GetCustomAttributesData, iterate all attributes, and re-instantiate matching ones. Cache results in a Dictionary<(ICustomAttributeProvider, Type), object> so subsequent queries for the same provider+type return instantly. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Add a Dictionary<(ICustomAttributeProvider, Type), bool> cache for HasAttribute<T> queries. This method is called thousands of times per platform with the same arguments. Caching the boolean result avoids repeated GetCustomAttributesData() + type comparison work. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

…tory Cache no-version/no-message IntroducedAttribute and UnavailableAttribute instances as static singletons (one per platform). Return cached instances from CreateNoVersionSupportedAttribute, CreateUnsupportedAttribute, and CloneFromOtherPlatform when applicable, avoiding repeated heap allocations for identical platform attributes. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Cache GetAllParentAttributes results per MemberInfo context. Since callers only read from the returned list (never mutate it), the cached list can be safely shared across multiple callers with the same context. This avoids re-walking the parent chain and re-querying attributes for the same member on repeated calls. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

…in AttributeFactory - Cache Type[] arrays for attribute constructors to avoid repeated allocations - Cache ConstructorInfo lookups per (type, argTypes) to avoid repeated reflection - Cache Version objects in AvailabilityBaseAttribute to avoid creating new instances for the same version values Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Cache the ExportAttribute lookups for property getters and setters to avoid repeated attribute queries on the same PropertyInfo. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Copilot

Pull request overview

This PR improves bgen performance by adding several reflection/attribute-related caches to reduce repeated allocations and GC pressure during binding generation.

Changes:

Cache ExportAttribute lookups for property getters/setters and cache parent availability attribute traversal in Generator.
Cache GetCustomAttributes<T> and HasAttribute<T> results in AttributeManager to avoid repeated reflection and attribute conversion.
Add constructor/argument caching in AttributeFactory/AttributeFactory.ConstructorArguments and reuse singleton availability attributes for common no-version cases.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
src/bgen/Generator.cs	Adds caches for getter/setter `ExportAttribute` lookups and parent availability attribute collection.
src/bgen/AttributeManager.cs	Adds per-(provider,type) caches for `GetCustomAttributes<T>` and `HasAttribute<T>`.
src/bgen/AttributeFactory.cs	Caches attribute constructor lookups and reuses singleton no-version availability attributes.
src/bgen/AttributeFactory.ConstructorArguments.cs	Reuses static `Type[]` constructor signature arrays to avoid repeated allocations.

Move the constructorCache dictionary from the static AttributeFactory class to the instance-based AttributeManager class. This eliminates the static mutable state that could be problematic when tests run in parallel. The cache is passed through to AttributeFactory and AttributeConversionManager methods as a parameter. Convenience overloads without the parameter are kept for test compatibility (they use a static fallback cache). Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

…caching

Remove the two convenience CreateNewAttribute overloads (that didn't take an AttributeManager parameter) and the static defaultConstructorCache they used. Remove the corresponding tests that called those overloads. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Copilot

Pull request overview

Copilot reviewed 6 out of 6 changed files in this pull request and generated 3 comments.

When cloning an attribute to another platform, if the version is at or below the target platform's minimum, create a no-version attribute instead of clamping to the minimum version. For Introduced attributes this means no version at all (since GenerateSupported would have stripped it anyway). For Deprecated/Obsoleted, use the minimum version. This avoids creating attributes whose version would later need to be stripped, and together with the earlier change to not mutate Version in GenerateSupported, makes attribute caching fully safe. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

…caching

vs-mobiletools-engineering-service2 · 2026-06-25T18:16:24Z

✅ [PR Build #d2b76df] Build passed (Detect API changes) ✅

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vs-mobiletools-engineering-service2 · 2026-06-25T18:21:42Z

✅ [PR Build #d2b76df] Build passed (Build packages) ✅

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Hash: d2b76df21fcedd0ea5058dce8f628970e0756a28 [PR build]

vs-mobiletools-engineering-service2 · 2026-06-25T18:32:59Z

✅ API diff for current PR / commit

NET (empty diffs)

iOS: vsdrops gist ( No breaking changes )
tvOS: vsdrops gist ( No breaking changes )
MacCatalyst: vsdrops gist ( No breaking changes )
macOS: vsdrops gist ( No breaking changes )

✅ API diff vs stable

NET (empty diffs)

iOS: vsdrops gist ( No breaking changes )
tvOS: vsdrops gist ( No breaking changes )
MacCatalyst: vsdrops gist ( No breaking changes )
macOS: vsdrops gist ( No breaking changes )

ℹ️ Generator diff

Generator Diff: vsdrops (html) vsdrops (raw diff) gist (raw diff) - Please review changes)

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Hash: d2b76df21fcedd0ea5058dce8f628970e0756a28 [PR build]

vs-mobiletools-engineering-service2 · 2026-06-26T12:08:46Z

✅ [PR Build #d2b76df] Build passed (Build macOS tests) ✅

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Hash: d2b76df21fcedd0ea5058dce8f628970e0756a28 [PR build]

rolfbjarne · 2026-06-26T15:05:09Z

/review

github-actions · 2026-06-26T15:06:25Z

✅ .NET for Apple Platforms PR Reviewer completed successfully!

github-actions

Review Summary

This is a well-executed performance optimization that adds strategic caching to bgen's attribute processing pipeline. The changes deliver significant improvements (12.5% faster, 22.3% fewer allocations, 25-38% less GC pressure) through careful caching of reflection operations and attribute instances.

✅ Strengths

Smart caching strategy: Targets the hot paths (reflection, attribute construction, attribute queries)
Correct cache keys: All dictionaries use appropriate composite keys (provider + type, type + constructor args)
Thread-safe design: All caches are instance fields on AttributeManager, avoiding shared mutable state
Preserved semantics: No behavior changes, only performance improvements
Good test coverage: Unit tests verify the singleton caching behavior

📊 Performance Impact

The PR description shows compelling results:

Build time: 23.9s → 20.9s (-12.5%)
Allocations: 7003MB → 5439MB (-22.3%)
Gen0 GC: 1268 → 951 (-25.0%)
Gen1 GC: 414 → 254 (-38.6%)

Code Quality

Clean separation of concerns
Minimal surface area changes (all internal/private)
No breaking changes
Existing tests pass

This is a solid performance improvement with low risk. The caching is well-designed and correctly implemented.

Generated by .NET for Apple Platforms PR Reviewer for issue #25782 · 64.4 AIC · ⌖ 8.59 AIC · ⊞ 5K
_{Comment /review to run again}

vs-mobiletools-engineering-service2 · 2026-06-26T15:21:42Z

🚀 [CI Build #d2b76df] Test results 🚀

Test results

✅ All tests passed on VSTS: test results.

🎉 All 199 tests passed 🎉

Tests counts

✅ assembly-processing: All 1 tests passed. Html Report (VSDrops) Download
✅ cecil: All 1 tests passed. Html Report (VSDrops) Download
✅ dotnettests (iOS): All 1 tests passed. Html Report (VSDrops) Download
✅ dotnettests (MacCatalyst): All 1 tests passed. Html Report (VSDrops) Download
✅ dotnettests (macOS): All 1 tests passed. Html Report (VSDrops) Download
✅ dotnettests (Multiple platforms): All 1 tests passed. Html Report (VSDrops) Download
✅ dotnettests (tvOS): All 1 tests passed. Html Report (VSDrops) Download
✅ framework: All 2 tests passed. Html Report (VSDrops) Download
✅ fsharp: All 4 tests passed. Html Report (VSDrops) Download
✅ generator: All 5 tests passed. Html Report (VSDrops) Download
✅ interdependent-binding-projects: All 4 tests passed. Html Report (VSDrops) Download
✅ introspection: All 4 tests passed. Html Report (VSDrops) Download
✅ linker (iOS): All 15 tests passed. Html Report (VSDrops) Download
✅ linker (MacCatalyst): All 15 tests passed. Html Report (VSDrops) Download
✅ linker (macOS): All 21 tests passed. Html Report (VSDrops) Download
✅ linker (tvOS): All 15 tests passed. Html Report (VSDrops) Download
✅ monotouch (iOS): All 18 tests passed. Html Report (VSDrops) Download
✅ monotouch (MacCatalyst): All 17 tests passed. Html Report (VSDrops) Download
✅ monotouch (macOS): All 18 tests passed. Html Report (VSDrops) Download
✅ monotouch (tvOS): All 18 tests passed. Html Report (VSDrops) Download
✅ msbuild: All 2 tests passed. Html Report (VSDrops) Download
✅ sharpie: All 1 tests passed. Html Report (VSDrops) Download
✅ windows: All 3 tests passed. Html Report (VSDrops) Download
✅ xcframework: All 4 tests passed. Html Report (VSDrops) Download
✅ xtro: All 1 tests passed. Html Report (VSDrops) Download

macOS tests

✅ Tests on macOS Monterey (12): All 5 tests passed. [attempt 2] Html Report (VSDrops) Download
✅ Tests on macOS Ventura (13): All 5 tests passed. [attempt 3] Html Report (VSDrops) Download
✅ Tests on macOS Sonoma (14): All 5 tests passed. [attempt 2] Html Report (VSDrops) Download
✅ Tests on macOS Sequoia (15): All 5 tests passed. [attempt 3] Html Report (VSDrops) Download
✅ Tests on macOS Tahoe (26): All 5 tests passed. [attempt 2] Html Report (VSDrops) Download

Linux Build Verification

✅ Linux build succeeded

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Hash: d2b76df21fcedd0ea5058dce8f628970e0756a28 [PR build]

rolfbjarne and others added 7 commits June 23, 2026 15:09

[bgen] Cache getter/setter ExportAttribute results per PropertyInfo

2836ece

Cache the ExportAttribute lookups for property getters and setters to avoid repeated attribute queries on the same PropertyInfo. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Remove Version caching from AvailabilityBaseAttribute

f9fa2c0

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

rolfbjarne added the copilot label Jun 23, 2026

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rolfbjarne and others added 2 commits June 23, 2026 19:25

Merge remote-tracking branch 'origin/main' into dev/rolf/bgen-attrib-…

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…caching

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Comment thread tests/bgen/AttributeFactoryTests.cs

Comment thread src/bgen/AttributeManager.cs

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rolfbjarne and others added 2 commits June 25, 2026 09:52

Merge remote-tracking branch 'origin/main' into dev/rolf/bgen-attrib-…

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…caching

rolfbjarne dismissed dalexsoto’s stale review via 7a6519f June 25, 2026 07:52

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dalexsoto approved these changes Jun 25, 2026

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Merge branch 'main' into dev/rolf/bgen-attrib-caching

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github-actions Bot reviewed Jun 26, 2026

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rolfbjarne merged commit d357e92 into main Jun 29, 2026
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rolfbjarne deleted the dev/rolf/bgen-attrib-caching branch June 29, 2026 11:42

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vs-mobiletools-engineering-service2 commented Jun 25, 2026

✅ [PR Build #d2b76df] Build passed (Detect API changes) ✅

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✅ [PR Build #d2b76df] Build passed (Build packages) ✅

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vs-mobiletools-engineering-service2 commented Jun 25, 2026

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vs-mobiletools-engineering-service2 commented Jun 26, 2026

✅ [PR Build #d2b76df] Build passed (Build macOS tests) ✅

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Review Summary

✅ Strengths

📊 Performance Impact

Code Quality

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vs-mobiletools-engineering-service2 commented Jun 26, 2026

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rolfbjarne commented Jun 23, 2026 •

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