Implement ISOSDacInterface::GetThreadAllocData in cDAC SOSDacImpl by Copilot · Pull Request #124817 · dotnet/runtime

Copilot · 2026-02-24T20:23:27Z

Description

Implements GetThreadAllocData in the cDAC SOSDacImpl, based on ClrDataAccess::GetThreadAllocData in request.cpp. This exposes per-thread GC allocation byte counts (alloc_bytes and alloc_bytes_uoh from gc_alloc_context) through the cDAC diagnostic interface.

Data descriptor & contract changes:

Add AllocBytes and AllocBytesLoh fields to GCAllocContext in datadescriptor.inc, mapped from gc_alloc_context::alloc_bytes and gc_alloc_context::alloc_bytes_uoh
Extend managed GCAllocContext data class with corresponding long properties
Add GetThreadAllocContext with out long allocBytes, out long allocBytesLoh parameters to IThread contract; implement in Thread_1

SOSDacImpl changes:

Define managed DacpAllocData struct (matches native layout: two ClrDataAddress fields)
Replace delegating stub with full implementation following existing patterns (parameter validation inside try/catch, throw new ArgumentException() for invalid address, throw new NullReferenceException() for null data pointer to produce E_POINTER, contract call, #if DEBUG legacy comparison)

Tests:

Unit tests: GetThreadAllocContext (non-zero values) and GetThreadAllocContext_ZeroValues across all 4 mock architectures
Dump test: walks all threads validating GetThreadAllocContext returns non-negative values
Extended MockDescriptors.Thread to set up RuntimeThreadLocals/EEAllocContext/GCAllocContext type hierarchy

Documentation:

Updated Thread.md and GC.md with new GCAllocContext field descriptors

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dotnet-policy-service · 2026-02-24T20:40:47Z

Tagging subscribers to this area: @agocke, @VSadov
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- Add AllocBytes and AllocBytesLoh fields to GCAllocContext data descriptor - Add ThreadAllocData record struct and GetThreadAllocData to IThread contract - Implement GetThreadAllocData in Thread_1.cs contract - Define DacpAllocData managed struct in ISOSDacInterface.cs - Implement GetThreadAllocData in SOSDacImpl.cs with DEBUG comparison - Add unit tests for GetThreadAllocData with non-zero and zero values - Add dump test for GetThreadAllocData - Update Thread.md and GC.md documentation Co-authored-by: max-charlamb <44248479+max-charlamb@users.noreply.github.com>

Co-authored-by: max-charlamb <44248479+max-charlamb@users.noreply.github.com>

max-charlamb

@copilot , address feedback

src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Legacy/SOSDacImpl.cs

...tive/managed/cdac/Microsoft.Diagnostics.DataContractReader.Abstractions/Contracts/IThread.cs

…eption for E_POINTER, rename to GetThreadAllocContext Co-authored-by: max-charlamb <44248479+max-charlamb@users.noreply.github.com>

Copilot · 2026-02-24T21:45:34Z

@copilot , address feedback

All three review comments addressed in 9fbc6c9. All 840 tests pass.

max-charlamb

@copilot , address feedback

...native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Contracts/Contracts/Thread_1.cs

Co-authored-by: max-charlamb <44248479+max-charlamb@users.noreply.github.com>

Copilot

Pull request overview

Implements ISOSDacInterface::GetThreadAllocData in the cDAC-based SOSDacImpl by exposing per-thread GC allocation byte counters from gc_alloc_context through the managed contracts and data descriptors.

Changes:

Added AllocBytes / AllocBytesLoh fields to the GCAllocContext data descriptor and managed data model.
Extended the IThread contract with GetThreadAllocContext returning a new ThreadAllocData record, and wired it into SOSDacImpl.GetThreadAllocData.
Added unit + dump tests and updated mock descriptors and design docs to cover/describe the new fields.

Reviewed changes

Copilot reviewed 11 out of 11 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
src/native/managed/cdac/tests/ThreadTests.cs	Adds unit tests for `GetThreadAllocContext`.
src/native/managed/cdac/tests/MockDescriptors/MockDescriptors.Thread.cs	Extends mock type layouts and thread creation to include alloc-context hierarchy and alloc byte values.
src/native/managed/cdac/tests/DumpTests/ThreadDumpTests.cs	Adds dump test to validate alloc context can be read across all threads.
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Legacy/SOSDacImpl.cs	Implements `GetThreadAllocData` using the `IThread` contract and follows existing try/catch + DEBUG-compare patterns.
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Legacy/ISOSDacInterface.cs	Introduces `DacpAllocData` and updates the interface signature to use it.
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Contracts/Data/GCAllocContext.cs	Reads new alloc-byte fields from the target in managed data representation.
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Contracts/Contracts/Thread_1.cs	Implements `IThread.GetThreadAllocContext`.
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Abstractions/Contracts/IThread.cs	Adds `ThreadAllocData` record and the new contract method.
src/coreclr/vm/datadescriptor/datadescriptor.inc	Adds `GCAllocContext` field descriptors for alloc byte counts.
docs/design/datacontracts/Thread.md	Documents new `GCAllocContext` field dependencies for the Thread contract.
docs/design/datacontracts/GC.md	Documents new `GCAllocContext` field descriptors used by GC-related contracts.

Copilot · 2026-02-24T21:57:57Z

src/native/managed/cdac/tests/ThreadTests.cs

+    [Theory]
+    [ClassData(typeof(MockTarget.StdArch))]  
+    public void GetThreadAllocContext(MockTarget.Architecture arch)
+    {
+        long allocBytes = 1024;
+        long allocBytesLoh = 4096;
+
+        TargetPointer addr = thread.AddThread(1, new TargetNUInt(1234), allocBytes, allocBytesLoh);
+
+        Target target = CreateTarget(thread);
+        IThread contract = target.Contracts.Thread;


GetThreadAllocContext test references a thread variable that isn't declared in the method scope (unlike the other tests that create TargetTestHelpers/MockMemorySpace.Builder/MockDescriptors.Thread). This will not compile and also means the arch parameter isn't used to build the target. Create a local MockDescriptors.Thread using the provided arch before calling AddThread/CreateTarget.

...ative/managed/cdac/Microsoft.Diagnostics.DataContractReader.Contracts/Data/GCAllocContext.cs

max-charlamb · 2026-02-24T22:36:48Z

@copilot, please fix build break

…dAllocContext test and fix trailing whitespace Co-authored-by: max-charlamb <44248479+max-charlamb@users.noreply.github.com>

Copilot · 2026-02-24T22:41:38Z

@copilot, please fix build break

Fixed in 0e5922e — the GetThreadAllocContext test was missing TargetTestHelpers/MockMemorySpace.Builder/MockDescriptors.Thread setup. Also cleaned up remaining trailing whitespace in Thread_1.cs. All 24 thread tests pass.

rcj1 · 2026-02-24T22:44:26Z

...tive/managed/cdac/Microsoft.Diagnostics.DataContractReader.Abstractions/Contracts/IThread.cs

    TargetPointer LastThrownObjectHandle,
    TargetPointer NextThread);

+public record struct ThreadAllocData(


Use out variables

@copilot use out variables instead of this struct

Done in fa4b867 — replaced ThreadAllocData record struct with out long allocBytes, out long allocBytesLoh parameters on GetThreadAllocContext, matching the pattern used by GetStackLimitData. Updated Thread_1 implementation, SOSDacImpl caller, and all tests.

…ontext Co-authored-by: rcj1 <77995559+rcj1@users.noreply.github.com>

Initial plan

31fae06

Copilot AI assigned Copilot and max-charlamb Feb 24, 2026

Copilot started work on behalf of max-charlamb February 24, 2026 20:23 View session

github-actions bot added the area-System.Threading label Feb 24, 2026

Copilot AI and others added 2 commits February 24, 2026 21:02

Fix documentation: align field descriptions with native comments

764358c

Co-authored-by: max-charlamb <44248479+max-charlamb@users.noreply.github.com>

Copilot AI changed the title ~~[WIP] Implement GetThreadAllocData in SOSDacImpl~~ Implement ISOSDacInterface::GetThreadAllocData in cDAC SOSDacImpl Feb 24, 2026

Copilot finished work on behalf of max-charlamb February 24, 2026 21:09

max-charlamb reviewed Feb 24, 2026

View reviewed changes

Copilot started work on behalf of max-charlamb February 24, 2026 21:38 View session

Address review feedback: move checks inside try, use NullReferenceExc…

9fbc6c9

…eption for E_POINTER, rename to GetThreadAllocContext Co-authored-by: max-charlamb <44248479+max-charlamb@users.noreply.github.com>

Copilot finished work on behalf of max-charlamb February 24, 2026 21:46

Merge branch 'main' into copilot/implement-get-thread-alloc-data

a4ca9e9

max-charlamb reviewed Feb 24, 2026

View reviewed changes

...native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Contracts/Contracts/Thread_1.cs Outdated Show resolved Hide resolved

max-charlamb marked this pull request as ready for review February 24, 2026 21:52

Copilot AI review requested due to automatic review settings February 24, 2026 21:52

Copilot started work on behalf of max-charlamb February 24, 2026 21:52 View session

Copilot started reviewing on behalf of max-charlamb February 24, 2026 21:53 View session

Remove extra trailing whitespace in Thread_1.cs

0abc066

Co-authored-by: max-charlamb <44248479+max-charlamb@users.noreply.github.com>

Copilot finished work on behalf of max-charlamb February 24, 2026 21:56

Copilot AI reviewed Feb 24, 2026

View reviewed changes

max-charlamb requested a review from rcj1 February 24, 2026 22:36

Copilot started work on behalf of max-charlamb February 24, 2026 22:36 View session

Fix build break: add missing MockDescriptors.Thread setup in GetThrea…

0e5922e

…dAllocContext test and fix trailing whitespace Co-authored-by: max-charlamb <44248479+max-charlamb@users.noreply.github.com>

Copilot finished work on behalf of max-charlamb February 24, 2026 22:42

rcj1 reviewed Feb 24, 2026

View reviewed changes

Copilot started work on behalf of rcj1 February 24, 2026 22:45 View session

Replace ThreadAllocData struct with out parameters on GetThreadAllocC…

fa4b867

…ontext Co-authored-by: rcj1 <77995559+rcj1@users.noreply.github.com>

Copilot finished work on behalf of rcj1 February 24, 2026 22:54

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Copilot AI commented Feb 24, 2026 •

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