cDAC: implement GetSyncBlockCleanupData

[Copilot]

Implements GetSyncBlockCleanupData and GetSyncBlockData in the cDAC. COM data is read directly from the sync block pointer (not via the object header) since objects on the cleanup list may not be valid managed objects.

Changes

• SyncBlock_1 — adds GetSyncBlockFromCleanupList(), GetNextSyncBlock(TargetPointer), and GetBuiltInComData(TargetPointer, ...) for cleanup-list traversal and COM data reads directly from a sync block
• SOSDacImpl.GetSyncBlockCleanupData — addr==0 walks from cleanup list head; addr!=0 reads the block at that pointer; both paths use SyncBlock.GetBuiltInComData directly
• SOSDacImpl.GetSyncBlockData — uses SyncBlock contract methods directly instead of going through the object header
• GetAdditionalThreadCount — returns 0 (conditional weak table traversal is a TODO)
• SLink — removed from the managed type system (DataType.SLink, Data/SLink.cs); LinkNext encodes the field offset directly in SyncBlockFactory, eliminating the need for a separate SLink type
• Tests — SyncBlockTests covering cleanup-list traversal (single/multi-item, last-item-returns-null) and GetBuiltInComData with/without interop info

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[rcj1]

@copilot please apply the following patch.
patch.patch

[Copilot]

@copilot please apply the following patch.
patch.patch

Applied in b2c0797. Key changes from the patch:

• Removed the hardcoded SyncBlockValue nested class from Object_1; the bit constants (SyncBlockIsHashOrSyncBlockIndex, SyncBlockIsHashCode, SyncBlockIndexMask) are now runtime globals read via ReadGlobal<uint>, backed by datadescriptor.inc macros (BIT_SBLK_IS_HASH_OR_SYNCBLKINDEX, BIT_SBLK_IS_HASHCODE, MASK_SYNCBLOCKINDEX)
• Moved syncBlockLinkOffset computation from SyncBlock_1's constructor into SyncBlockFactory
• Simplified SyncBlockCache.CleanupBlockList to direct field access (removed optional TryGetValue pattern)
• Moved the data == null check inside the try block in GetSyncBlockCleanupData; removed the addr != 0 guard on the DEBUG assertion
• Fixed request.cpp to allow syncBlock == 0

[Copilot]

Pull request overview

This PR implements the GetSyncBlockCleanupData API in the cDAC (Contracts Data for Diagnostics). It also fixes a pre-existing behavior discrepancy: the legacy C++ implementation incorrectly returned E_INVALIDARG for addr=0, while the API contract specifies that addr=0 should start cleanup list traversal from SyncBlockCache.m_pCleanupBlockList. Additionally, it refactors GetBuiltInComData to work directly from a sync block pointer, enabling safe access during cleanup when the associated managed object may not be valid.

Changes:

• Adds GetSyncBlockFromCleanupList(), GetNextSyncBlock(), and GetBuiltInComData(TargetPointer syncBlock, ...) to the ISyncBlock interface and SyncBlock_1 implementation
• Refactors Object_1.GetBuiltInComData to delegate to the SyncBlock contract, and moves the sync block bit constants (SyncBlockIsHashOrSyncBlockIndex, SyncBlockIsHashCode, SyncBlockIndexMask) to runtime globals exposed via the data descriptor
• Adds GetSyncBlockCleanupData implementation in SOSDacImpl using the new SyncBlock contract APIs, and updates GetSyncBlockData to use syncBlock.GetBuiltInComData directly

Reviewed changes

Copilot reviewed 18 out of 18 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
ISyncBlock.cs	Adds three new cleanup-list and COM-data interface methods
SyncBlock_1.cs	Implements new methods; receives syncBlockLinkOffset for list pointer arithmetic
SyncBlockFactory.cs	Computes and passes syncBlockLinkOffset to SyncBlock_1
Object_1.cs	Removes SyncBlockValue nested class; reads bit constants from runtime globals; delegates GetBuiltInComData to ISyncBlock
SOSDacImpl.cs	Implements GetSyncBlockCleanupData; updates GetSyncBlockData to use SyncBlock contract
ISOSDacInterface.cs	Adds DacpSyncBlockCleanupData struct; updates GetSyncBlockCleanupData signature
Constants.cs	Adds three new SyncBlock* global name constants
SyncBlockCache.cs	Adds CleanupBlockList field
datadescriptor.inc	Exposes SyncBlockCache.CleanupBlockList and three bit constants as globals
syncblk.h	Adds CleanupBlockList to cdac_data<SyncBlockCache>
request.cpp	Removes syncBlock == 0 from E_INVALIDARG guard
SyncBlockTests.cs	New unit tests for cleanup list traversal and COM data
MockDescriptors.SyncBlock.cs	New test descriptor for SyncBlock cleanup list
MockDescriptors.Object.cs	Adds three new globals to Object mock
MockDescriptors.cs	Adds CleanupBlockList to SyncBlockCacheFields
SyncBlock.md	Documents new APIs, data descriptors
Object.md	Documents new globals and delegation pattern

[rcj1]

@copilot do you know why the build and test is stalling https://dev.azure.com/dnceng-public/public/_build/results?buildId=1316850

[Copilot]

@copilot do you know why the build and test is stalling https://dev.azure.com/dnceng-public/public/_build/results?buildId=1316850

The build isn't stalled — it spent about 7+ hours in the queue (queued at 21:44 UTC, started running at ~04:58 UTC) and has been executing normally since then. As of now, 5 of 7 jobs have completed successfully; the remaining 2 (cDAC_windows_x64_release/DAC_windows_x64_release and Build / Test) are still in progress. No failures yet. The long delay was queue wait time, not a stuck build.

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[rcj1]

/ba-g unrelated fails