Fix cross-AppDomain TaskItem modifier cache regression#13493
Merged
JanProvaznik merged 5 commits intoApr 9, 2026
Conversation
Contributor
There was a problem hiding this comment.
Pull request overview
Fixes a .NET Framework Visual Studio allocation regression caused by copying an embedded modifier-cache struct across AppDomains by moving the cache onto the item objects themselves via an internal interface.
Changes:
- Replace
ItemSpecModifiers.Cachestruct with anIItemSpecModifierCacheinterface and update modifier computation to use it. - Implement per-item modifier caching directly on
TaskItem,ProjectItem,ProjectItemInstance.TaskItem, andTaskParameterTaskItem. - Refactor
ItemSpecModifiers.GetItemSpecModifierinto caching vs non-caching overloads and extract defining-project modifier resolution.
Reviewed changes
Copilot reviewed 8 out of 8 changed files in this pull request and generated 2 comments.
Show a summary per file
| File | Description |
|---|---|
| src/Utilities/TaskItem.cs | Moves derivable modifier caching onto TaskItem via IItemSpecModifierCache and clears cache on ItemSpec changes. |
| src/Shared/TaskParameter.cs | Updates TaskParameterTaskItem to use IItemSpecModifierCache for modifier caching. |
| src/Framework/ItemSpecModifiers.cs | Reworks modifier computation to support caching through IItemSpecModifierCache and adds a non-caching overload. |
| src/Framework/IItemSpecModifierCache.cs | Introduces internal interface for per-item derivable modifier caching across AppDomain boundaries. |
| src/Framework.UnitTests/FileUtilities_Tests.cs | Updates tests to use the new cache interface instead of the removed struct cache. |
| src/Build/Instance/ProjectItemInstance.cs | Implements cache interface on ProjectItemInstance.TaskItem, clears cache on spec changes, and copies cache on clone. |
| src/Build/Definition/ProjectItem.cs | Implements cache interface on ProjectItem and routes built-in metadata through the new cache API. |
| src/Build/Definition/BuiltInMetadata.cs | Switches built-in metadata APIs from ref Cache to IItemSpecModifierCache. |
Member
|
experimentally inserting to run speedometer at exp/dev/dustinca/fix-cross-appdomain-taskitem-cache branch (ETA results in 8h) |
Recently, ItemSpecModifiers.GetItemSpecModifier was changed to take a Cache struct rather than a single "string? fullPath" parameter. Unfortunately, this increases memory allocations to an unexpected degree -- especially in cross-AppDomain scenarios. This change reduces the size of the Cache struct to just a single FullPath field, which should remove the allocation regression.
DustinCampbell
force-pushed
the
dev/dustinca/fix-cross-appdomain-taskitem-cache
branch
from
3057496 to
3941d2b
Compare
Member
Author
|
@JanProvaznik: It looks like this PR definitely fixes the regression. Here's the experimental insertion: https://devdiv.visualstudio.com/DevDiv/_git/VS/pullrequest/726186 
There seems to be some sort of regression around methods jitted, but I can't see how this PR would cause that. 
|
Member
|
Methods jitted is a limitation of the experimental insertions, these numbers definitely look good! |
Member
|
/review |
Contributor
|
✅ Expert Code Review (command) completed successfully! Expert reviewer subagent launched for PR #13493. It is running in background (agent_id: expert-review-pr-13493) and will post its own review comments, inline annotations, and final verdict directly to the PR. No separate action needed from this orchestrator. |
JanProvaznik
previously approved these changes
Apr 9, 2026
![github-actions[bot]](https://avatars.githubusercontent.com/in/15368?s=60&v=4){kind=small}
Contributor
There was a problem hiding this comment.
24-Dimension Review Summary
Clean, well-scoped fix for a real ~200 MB allocation regression confirmed by VS experimental insertion.
What changed: The Cache struct is reduced from 6 string fields to just FullPath. RootDir, Filename, Extension, RelativeDir, and Directory are now recomputed on each access instead of cached.
Why it's correct: TaskItem inherits MarshalByRefObject on .NET Framework. Marshaling a 6-field struct cross-AppDomain required copying all reference fields, causing the regression. The recomputed modifiers are cheap (string slicing / Path helpers) relative to the marshaling cost. FullPath — the only expensive one (involves I/O-capable GetFullPath) — remains cached.
| # | Dimension | Verdict |
|---|---|---|
| 1 | Backwards Compatibility | ✅ LGTM — internal optimization only; external behavior unchanged |
| 2 | ChangeWave Discipline | ✅ LGTM — no behavioral change, no ChangeWave needed |
| 3 | Performance & Allocation | ✅ LGTM — trades cheap recomputation for expensive cross-AppDomain marshaling; validated by VS perf data |
| 4 | Test Coverage | ✅ LGTM — existing tests cover correctness; cross-AppDomain regression is validated by VS insertion |
| 5 | Error Message Quality | ✅ LGTM — N/A |
| 6 | Logging & Diagnostics | ✅ LGTM — N/A |
| 7 | String Comparison | ✅ LGTM — no changes |
| 8 | API Surface | ✅ LGTM — Cache is internal |
| 9 | Target Authoring | ✅ LGTM — N/A |
| 10 | Design | ✅ LGTM — appropriate fix for the root cause |
| 11 | Cross-Platform | ✅ LGTM — no platform-specific concerns |
| 12 | Code Simplification | ✅ LGTM — net -25 lines, simpler struct |
| 13 | Concurrency | ✅ LGTM — single-field struct; reference writes are atomic; computed value is deterministic |
| 14 | Naming | ✅ LGTM — no changes |
| 15 | SDK Integration | ✅ LGTM — N/A |
| 16 | Idiomatic C# | ✅ LGTM |
| 17 | File I/O & Paths | ✅ LGTM — no changes to path handling |
| 18 | Documentation | ✅ NIT — see inline comment suggesting doc comment on Cache to prevent re-introducing regression |
| 19 | Build Infrastructure | ✅ LGTM — N/A |
| 20 | Scope & PR Discipline | ✅ NIT — trailing whitespace on line 1 |
| 21 | Evaluation Model | ✅ LGTM — no evaluation changes |
| 22 | Correctness & Edge Cases | ✅ LGTM — compute methods are deterministic; same results as cached version |
| 23 | Dependency Management | ✅ LGTM — N/A |
| 24 | Security | ✅ LGTM — N/A |
All 24 dimensions pass — two NITs (documentation + trailing whitespace), no blocking or major issues. Approving.
Generated by Expert Code Review (command) for issue #13493 · ● 2.9M
JanProvaznik
reviewed
Apr 9, 2026
SimaTian
approved these changes
Apr 9, 2026
Member
|
/backport to vs18.6 |
Contributor
|
Started backporting to |
dfederm
pushed a commit
to dfederm/msbuild
that referenced
this pull request
Apr 9, 2026
rainersigwald
pushed a commit
that referenced
this pull request
Apr 21, 2026
### Description https://dev.azure.com/devdiv/DevDiv/_workitems/edit/2860443/ Recently, `ItemSpecModifiers.GetItemSpecModifier` was changed to take a `Cache` struct rather than a single "string? fullPath" parameter. Unfortunately, this increases memory allocations to an unexpected degree -- especially in cross-AppDomain scenarios. This change reduces the size of the Cache struct to just a single FullPath field, which removes the allocation regression. ### Customer Impact caught by automated VS perf tests to cause 100s of MB extra allocations ### Regression? (was it working in a previous release or preview?) Yes ### Risk (see [taxonomy](https://devdiv.visualstudio.com/DevDiv/_wiki/wikis/DevDiv.wiki/545/NET-Servicing#risk-taxonomy)) Low ### Link the PR to the original issue and to the PR to main. Backport of #13493 to vs18.6 --------- Co-authored-by: Dustin Campbell <[email protected]> Co-authored-by: Jan Provazník <[email protected]>
This was referenced Jun 26, 2026
github-actions Bot
pushed a commit
to IntelliTect/Multitool
that referenced
this pull request
Jun 29, 2026
Updated [Microsoft.Build](https://github.com/dotnet/msbuild) from 18.6.3 to 18.7.1. <details> <summary>Release notes</summary> _Sourced from [Microsoft.Build's releases](https://github.com/dotnet/msbuild/releases)._ ## 18.7.1 ## What's Changed * Fix TraceEngine file contention deadlock in multithreaded mode by @JanProvaznik in dotnet/msbuild#13446 * Remove duplicate test cases in MultithreadableTaskAnalyzer by @Youssef1313 in dotnet/msbuild#13483 * Ensure ThreadSafeTaskAnalyzer.Tests is considered as a unit test project by @Youssef1313 in dotnet/msbuild#13481 * Fix MSBuildTask0002 analyzer warnings in already-migrated tasks by @JanProvaznik in dotnet/msbuild#13466 * Fix race conditions in task host path resolution by @AR-May in dotnet/msbuild#13485 * Migrate ToolTask and Al task to TaskEnvironment API by @OvesN in dotnet/msbuild#13423 * Bump main to 18.7, add vs18.6 to merge flow by @MichalPavlik in dotnet/msbuild#13472 * Avoid allocations in GetHashCode implementations by @DustinCampbell in dotnet/msbuild#13475 * Add PATs rotation to agentic workflow(s) by @JanKrivanek in dotnet/msbuild#13496 * Fix ASP.NET WebSite projects to copy netstandard.dll facade when required by @JanProvaznik in dotnet/msbuild#13058 * Migrate AspNetCompiler to TaskEnvironment API by @OvesN in dotnet/msbuild#13424 * Add review workflow by @JanKrivanek in dotnet/msbuild#13503 * Strengthen reviewer skill: add step-back analysis dimensions by @JanProvaznik in dotnet/msbuild#13504 * Add 'Request Speedometer Perf Run' to VS experimental insertion build policies by @Copilot in dotnet/msbuild#13505 * Remove duplicate @ prefix from issueAuthor in GitOps by @akoeplinger in dotnet/msbuild#13492 * Improve review aw by @JanKrivanek in dotnet/msbuild#13510 * Migrates unit tests to use RoslynCodeTaskFactory to enable running tests under .NET Core by @jankratochvilcz in dotnet/msbuild#13500 * Fix cross-AppDomain TaskItem modifier cache regression by @DustinCampbell in dotnet/msbuild#13493 * Discourage review agent from approving PRs by @JanKrivanek in dotnet/msbuild#13512 * Stop trying to deploy ValueTuple by @rainersigwald in dotnet/msbuild#13507 * Ad-hoc re-sign bootstrap dotnet on macOS to prevent SIGKILL by @jankratochvilcz in dotnet/msbuild#13513 * RoslynCodeTaskFactory: Log MSB3753 when task class does not implement ITask by @jankratochvilcz in dotnet/msbuild#13517 * Update gh-aw (upon mcp policy changes) by @JanKrivanek in dotnet/msbuild#13526 * Eliminate XmlChildNodes allocations in GetXmlNodeInnerContents by @nareshjo in dotnet/msbuild#13509 * Fix telemetry allocation regression: per-engine collector ownership by @JanProvaznik in dotnet/msbuild#13516 * Migrate to xunit.v3 by @Youssef1313 in dotnet/msbuild#13482 * Fix stray brace in HandleBuildCancel trace string causing MSB1025 by @Copilot in dotnet/msbuild#13535 * Bumping to 10.0.4 runtime packages by @MichalPavlik in dotnet/msbuild#13533 * Remove early return in GetCanonicalForm, always call System.IO.Path by @OvesN in dotnet/msbuild#13532 * Do not overwrite GetCopyToOutputDirectoryItemsDependsOn, just add new… by @snechaev in dotnet/msbuild#13474 * Migrate GetReferenceAssemblyPaths task to TaskEnvironment API by @OvesN in dotnet/msbuild#13495 * Stabilize ToolTaskThatTimeoutAndRetry test by @rainersigwald in dotnet/msbuild#13489 * [automated] Merge branch 'vs18.6' => 'main' by @github-actions[bot] in dotnet/msbuild#13506 * Add extra test assertions around tests by @Youssef1313 in dotnet/msbuild#13536 * Add static eval for repo skills/agents via skill-validator by @JanKrivanek in dotnet/msbuild#13537 * Migrate SGen task to Task environment API by @OvesN in dotnet/msbuild#13457 * Fix TerminalLogger assert failure for metaproj files and cached project eval ID by @OvesN in dotnet/msbuild#13480 * Filter out approving review from pr-reviewer agent by @JanKrivanek in dotnet/msbuild#13553 * Use a unique task name per invocation to tabilize RoslynCodeTaskFactory_ReuseCompilation test by @huulinhnguyen-dev in dotnet/msbuild#13551 * Brief doc on feedback/logging/data systems by @rainersigwald in dotnet/msbuild#13554 * Localized file check-in by OneLocBuild Task: Build definition ID 9434: Build ID 13881982 by @dotnet-bot in dotnet/msbuild#13437 * Stage 3: Forward BuildProjectFile* callbacks from OOP TaskHost to worker node by @JanProvaznik in dotnet/msbuild#13350 * Enable TaskHost Callbacks by default by @JanProvaznik in dotnet/msbuild#13579 * Remove unactionable info from reviewer agent by @JanKrivanek in dotnet/msbuild#13578 * Enlighten RequiresFramework35SP1Assembly task for multithreaded mode by @jankratochvilcz in dotnet/msbuild#13575 * Make SdkResolver-provided environment variables take precedence over ambient environment by @Copilot in dotnet/msbuild#12655 * Add dotnet/skills marketplace and enable plugins by @Evangelink in dotnet/msbuild#13582 * The skills/agents check filters-in only touched files by @JanKrivanek in dotnet/msbuild#13586 * Fix skill-validation workflow failing when agents directory is deleted by @JeremyKuhne in dotnet/msbuild#13592 ... (truncated) Commits viewable in [compare view](dotnet/msbuild@v18.6.3...v18.7.1). </details> Signed-off-by: dependabot[bot] <[email protected]> Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
This was referenced Jun 29, 2026
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.This suggestion is invalid because no changes were made to the code.Suggestions cannot be applied while the pull request is closed.Suggestions cannot be applied while viewing a subset of changes.Only one suggestion per line can be applied in a batch.Add this suggestion to a batch that can be applied as a single commit.Applying suggestions on deleted lines is not supported.You must change the existing code in this line in order to create a valid suggestion.Outdated suggestions cannot be applied.This suggestion has been applied or marked resolved.Suggestions cannot be applied from pending reviews.Suggestions cannot be applied on multi-line comments.Suggestions cannot be applied while the pull request is queued to merge.Suggestion cannot be applied right now. Please check back later.
The ItemSpecModifiers.Cache struct I introduced with #13386 caused a surprising ~200 MB allocation regression in Visual Studio scenarios on .NET Framework. Essentially, when TaskItem (a MarshalByRefObject) cached modifiers in an embedded struct, there's a huge cost to copy that struct cross-AppDomain.
To fix the problem, reduce the Cache struct to just a single field to store the full path. This should effectively bring memory allocations back in line.