Cleanup on the finalizer thread when a thread is detached, not when the managed thread object is finalized.

Author: jkoritzinsky

src/coreclr/System.Private.CoreLib/src/System/Threading/Thread.CoreCLR.cs

@@ -178,13 +178,6 @@ private void Initialize()
         /// <summary>Clean up the thread when it goes away.</summary>
         ~Thread()
         {
-            // During the actual thread shutdown,
-            // it may not be practical for us to run enough managed code to clean up
-            // any managed code that needs to know when a thread exits.
-            // Instead, run that clean up here when the thread object is finalized
-            // (which is definitely after the thread has exited)
-            OnThreadExiting();
-
             // Do any additional finalization that's required on the unmanaged side.
             InternalFinalize();
         }

src/coreclr/vm/corelib.h

@@ -969,6 +969,7 @@ DEFINE_CLASS(DIRECTONTHREADLOCALDATA, Threading, Thread+DirectOnThreadLocalData)
 DEFINE_CLASS(THREAD,                Threading,              Thread)
 DEFINE_METHOD(THREAD,               START_CALLBACK,                          StartCallback,                               IM_RetVoid)
 DEFINE_METHOD(THREAD,               POLLGC,                                  PollGC,                               NoSig)
+DEFINE_METHOD(THREAD,               ON_THREAD_EXITING,                       OnThreadExiting,                      IM_RetVoid)
 
 #ifdef FEATURE_OBJCMARSHAL
 DEFINE_CLASS(AUTORELEASEPOOL,       Threading,              AutoreleasePool)

src/coreclr/vm/threads.cpp

@@ -2575,7 +2575,8 @@ void Thread::CoUninitialize()
 void Thread::CleanupDetachedThreads()
 {
     CONTRACTL {
-        NOTHROW;
+        THROWS;
+        MODE_COOPERATIVE;
         GC_TRIGGERS;
     }
     CONTRACTL_END;
@@ -2596,6 +2597,20 @@ void Thread::CleanupDetachedThreads()
         {
             STRESS_LOG1(LF_SYNC, LL_INFO1000, "T::CDT - detaching thread 0x%p\n", thread);
 
+            if (!thread->IsGCSpecial())
+            {
+                GCX_COOP();
+                // During the actual thread shutdown,
+                // it may not be practical for us to run enough managed code to clean up
+                // any managed code that needs to know when a thread exits.
+                // Instead, run that clean up here when the thread object is finalized
+                // (which is definitely after the thread has exited)
+                PREPARE_NONVIRTUAL_CALLSITE(METHOD__THREAD__ON_THREAD_EXITING);
+                DECLARE_ARGHOLDER_ARRAY(args, 1);
+                args[ARGNUM_0] = OBJECTREF_TO_ARGHOLDER(thread->GetExposedObject());
+                CALL_MANAGED_METHOD_NORET(args);
+            }
+
             // Unmark that the thread is detached while we have the
             // thread store lock. This will ensure that no other
             // thread will race in here and try to delete it, too.