Add managed blocking info for lock and monitor waits (#101192)

* Add managed blocking info for lock and monitor waits

- Added a managed `ThreadBlockingInfo` struct that is similar to CoreCLR's `DebugBlockingItem`
- Updated `Lock`, `Condition`, and `Monitor` to record the info
- The `LockOwnerOSThreadId` and `LockOwnerManagedThreadId` properties can be used by debuggers to determine which thread owns a lock that the current thread is waiting on
  - In CoreCLR, `Monitor` records the info using the `Monitor` object kinds. In NativeAOT, `Lock` and `Condition` are used for `Monitor` waits, so the object kinds would be `Lock/Condition`. For now, Mono's `Monitor` does not record this info.

Author: kouvel

src/coreclr/nativeaot/System.Private.CoreLib/src/System/Threading/Condition.cs

@@ -32,6 +32,8 @@ private static Waiter GetWaiterForCurrentThread()
         private Waiter? _waitersHead;
         private Waiter? _waitersTail;
 
+        internal Lock AssociatedLock => _lock;
+
         private unsafe void AssertIsInList(Waiter waiter)
         {
             Debug.Assert(_waitersHead != null && _waitersTail != null);
@@ -106,6 +108,8 @@ public unsafe bool Wait(int millisecondsTimeout, object? associatedObjectForMoni
             if (!_lock.IsHeldByCurrentThread)
                 throw new SynchronizationLockException();
 
+            using ThreadBlockingInfo.Scope threadBlockingScope = new(this, millisecondsTimeout);
+
             Waiter waiter = GetWaiterForCurrentThread();
             AddWaiter(waiter);
 

src/coreclr/nativeaot/System.Private.CoreLib/src/System/Threading/Lock.NativeAot.cs

@@ -24,6 +24,12 @@ public sealed partial class Lock
         /// </summary>
         public Lock() => _spinCount = SpinCountNotInitialized;
 
+#pragma warning disable CA1822 // can be marked as static - varies between runtimes
+        internal ulong OwningOSThreadId => 0;
+#pragma warning restore CA1822
+
+        internal int OwningManagedThreadId => (int)_owningThreadId;
+
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         internal bool TryEnterOneShot(int currentManagedThreadId)
         {

src/coreclr/vm/appdomain.cpp

@@ -1158,6 +1158,13 @@ void SystemDomain::Init()
 
         // Finish loading CoreLib now.
         m_pSystemAssembly->GetDomainAssembly()->EnsureActive();
+
+        // Set AwareLock's offset of the holding OS thread ID field into ThreadBlockingInfo's static field. That can be used
+        // when doing managed debugging to get the OS ID of the thread holding the lock. The offset is currently not zero, and
+        // zero is used in managed code to determine if the static variable has been initialized.
+        _ASSERTE(AwareLock::GetOffsetOfHoldingOSThreadId() != 0);
+        CoreLibBinder::GetField(FIELD__THREAD_BLOCKING_INFO__OFFSET_OF_LOCK_OWNER_OS_THREAD_ID)
+            ->SetStaticValue32(AwareLock::GetOffsetOfHoldingOSThreadId());
     }
 
 #ifdef _DEBUG

src/coreclr/vm/corelib.h

@@ -583,6 +583,10 @@ END_ILLINK_FEATURE_SWITCH()
 DEFINE_CLASS(MONITOR,               Threading,              Monitor)
 DEFINE_METHOD(MONITOR,              ENTER,                  Enter,                      SM_Obj_RetVoid)
 
+DEFINE_CLASS(THREAD_BLOCKING_INFO,  Threading,              ThreadBlockingInfo)
+DEFINE_FIELD(THREAD_BLOCKING_INFO,  OFFSET_OF_LOCK_OWNER_OS_THREAD_ID, s_monitorObjectOffsetOfLockOwnerOSThreadId)
+DEFINE_FIELD(THREAD_BLOCKING_INFO,  FIRST,                  t_first)
+
 DEFINE_CLASS(PARAMETER,             Reflection,             ParameterInfo)
 
 DEFINE_CLASS(PARAMETER_MODIFIER,    Reflection,             ParameterModifier)

src/coreclr/vm/syncblk.cpp

@@ -2851,22 +2851,23 @@ BOOL SyncBlock::Wait(INT32 timeOut)
 
     _ASSERTE ((SyncBlock*)((DWORD_PTR)walk->m_Next->m_WaitSB & ~1)== this);
 
-    PendingSync   syncState(walk);
-
-    OBJECTREF     obj = m_Monitor.GetOwningObject();
-    syncState.m_Object = OBJECTREFToObject(obj);
-
-    m_Monitor.IncrementTransientPrecious();
-
     // While we are in this frame the thread is considered blocked on the
-    // event of the monitor lock according to the debugger
+    // event of the monitor lock according to the debugger. DebugBlockingItemHolder
+    // can trigger a GC, so set it up before accessing the owning object.
     DebugBlockingItem blockingMonitorInfo;
     blockingMonitorInfo.dwTimeout = timeOut;
     blockingMonitorInfo.pMonitor = &m_Monitor;
     blockingMonitorInfo.pAppDomain = SystemDomain::GetCurrentDomain();
     blockingMonitorInfo.type = DebugBlock_MonitorEvent;
     DebugBlockingItemHolder holder(pCurThread, &blockingMonitorInfo);
 
+    PendingSync   syncState(walk);
+
+    OBJECTREF     obj = m_Monitor.GetOwningObject();
+    syncState.m_Object = OBJECTREFToObject(obj);
+
+    m_Monitor.IncrementTransientPrecious();
+
     GCPROTECT_BEGIN(obj);
     {
         GCX_PREEMP();

src/coreclr/vm/syncblk.h

@@ -602,6 +602,12 @@ class AwareLock
         LIMITED_METHOD_CONTRACT;
         return m_HoldingThread;
     }
+
+    static int GetOffsetOfHoldingOSThreadId()
+    {
+        LIMITED_METHOD_CONTRACT;
+        return (int)offsetof(AwareLock, m_HoldingOSThreadId);
+    }
 };
 
 #ifdef FEATURE_COMINTEROP

src/coreclr/vm/threaddebugblockinginfo.cpp

@@ -72,9 +72,37 @@ VOID ThreadDebugBlockingInfo::VisitBlockingItems(DebugBlockingItemVisitor visito
 // Holder constructor pushes a blocking item on the blocking info stack
 #ifndef DACCESS_COMPILE
 DebugBlockingItemHolder::DebugBlockingItemHolder(Thread *pThread, DebugBlockingItem *pItem) :
-m_pThread(pThread)
+    m_pThread(pThread), m_ppFirstBlockingInfo(nullptr)
 {
-    LIMITED_METHOD_CONTRACT;
+    CONTRACTL
+    {
+        THROWS;
+        GC_TRIGGERS;
+        MODE_COOPERATIVE;
+    }
+    CONTRACTL_END;
+
+    // Try to get the address of the thread-local slot for the managed ThreadBlockingInfo.t_first
+    EX_TRY
+    {
+        FieldDesc *pFD = CoreLibBinder::GetField(FIELD__THREAD_BLOCKING_INFO__FIRST);
+        m_ppFirstBlockingInfo = (ThreadBlockingInfo **)Thread::GetStaticFieldAddress(pFD);
+    }
+    EX_CATCH
+    {
+    }
+    EX_END_CATCH(RethrowTerminalExceptions);
+
+    if (m_ppFirstBlockingInfo != nullptr)
+    {
+        // Push info for the managed ThreadBlockingInfo
+        m_blockingInfo.objectPtr = pItem->pMonitor;
+        m_blockingInfo.objectKind = (ThreadBlockingInfo::ObjectKind)pItem->type;
+        m_blockingInfo.timeoutMs = (INT32)pItem->dwTimeout;
+        m_blockingInfo.next = *m_ppFirstBlockingInfo;
+        *m_ppFirstBlockingInfo = &m_blockingInfo;
+    }
+
     pThread->DebugBlockingInfo.PushBlockingItem(pItem);
 }
 #endif //DACCESS_COMPILE
@@ -84,6 +112,17 @@ m_pThread(pThread)
 DebugBlockingItemHolder::~DebugBlockingItemHolder()
 {
     LIMITED_METHOD_CONTRACT;
+
     m_pThread->DebugBlockingInfo.PopBlockingItem();
+
+    if (m_ppFirstBlockingInfo != nullptr)
+    {
+        // Pop info for the managed ThreadBlockingInfo
+        _ASSERTE(
+            m_ppFirstBlockingInfo ==
+            (void *)m_pThread->GetStaticFieldAddrNoCreate(CoreLibBinder::GetField(FIELD__THREAD_BLOCKING_INFO__FIRST)));
+        _ASSERTE(*m_ppFirstBlockingInfo == &m_blockingInfo);
+        *m_ppFirstBlockingInfo = m_blockingInfo.next;
+    }
 }
 #endif //DACCESS_COMPILE

src/coreclr/vm/threaddebugblockinginfo.h

@@ -14,8 +14,8 @@
 // Different ways thread can block that the debugger will expose
 enum DebugBlockingItemType
 {
-    DebugBlock_MonitorCriticalSection,
-    DebugBlock_MonitorEvent,
+    DebugBlock_MonitorCriticalSection, // maps to ThreadBlockingInfo.ObjectKind.MonitorLock below and in managed code
+    DebugBlock_MonitorEvent, // maps to ThreadBlockingInfo.ObjectKind.MonitorWait below and in managed code
 };
 
 typedef DPTR(struct DebugBlockingItem) PTR_DebugBlockingItem;
@@ -65,15 +65,35 @@ class ThreadDebugBlockingInfo
 };
 
 #ifndef DACCESS_COMPILE
+
+// This is the equivalent of the managed ThreadBlockingInfo (see ThreadBlockingInfo.cs), which is used for tracking blocking
+// info from the managed side, similarly to DebugBlockingItem
+struct ThreadBlockingInfo
+{
+    enum class ObjectKind : INT32
+    {
+        MonitorLock, // maps to DebugBlockingItemType::DebugBlock_MonitorCriticalSection
+        MonitorWait  // maps to DebugBlockingItemType::DebugBlock_MonitorEvent
+    };
+
+    void *objectPtr;
+    ObjectKind objectKind;
+    INT32 timeoutMs;
+    ThreadBlockingInfo *next;
+};
+
 class DebugBlockingItemHolder
 {
 private:
     Thread *m_pThread;
+    ThreadBlockingInfo **m_ppFirstBlockingInfo;
+    ThreadBlockingInfo m_blockingInfo;
 
 public:
     DebugBlockingItemHolder(Thread *pThread, DebugBlockingItem *pItem);
     ~DebugBlockingItemHolder();
 };
+
 #endif //!DACCESS_COMPILE
 
 #endif // __ThreadBlockingInfo__

src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems

@@ -1265,6 +1265,7 @@
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\Thread.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\ProcessorIdCache.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\ThreadAbortException.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)System\Threading\ThreadBlockingInfo.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\ThreadExceptionEventArgs.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\ThreadInt64PersistentCounter.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\ThreadInterruptedException.cs" />
@@ -2786,4 +2787,4 @@
     <Compile Include="$(MSBuildThisFileDirectory)System\Numerics\IUnaryPlusOperators.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Numerics\IUnsignedNumber.cs" />
   </ItemGroup>
-</Project>
+</Project>

src/libraries/System.Private.CoreLib/src/System/Threading/Lock.NonNativeAot.cs

@@ -16,6 +16,12 @@ public sealed partial class Lock
         /// </summary>
         public Lock() => _spinCount = s_maxSpinCount;
 
+        internal ulong OwningOSThreadId => _owningThreadId;
+
+#pragma warning disable CA1822 // can be marked as static - varies between runtimes
+        internal int OwningManagedThreadId => 0;
+#pragma warning restore CA1822
+
         private static TryLockResult LazyInitializeOrEnter() => TryLockResult.Spin;
         private static bool IsSingleProcessor => Environment.IsSingleProcessor;
 

src/libraries/System.Private.CoreLib/src/System/Threading/Lock.cs

@@ -477,6 +477,8 @@ private ThreadId TryEnterSlow(int timeoutMs, ThreadId currentThreadId)
                     waitStartTimeTicks = Stopwatch.GetTimestamp();
                 }
 
+                using ThreadBlockingInfo.Scope threadBlockingScope = new(this, timeoutMs);
+
                 bool acquiredLock = false;
                 int waitStartTimeMs = timeoutMs < 0 ? 0 : Environment.TickCount;
                 int remainingTimeoutMs = timeoutMs;