[release/6.0] Ensure that tls_destructionMonitor is initialized if a thread is attached to the runtime. (#65406)

* Ensure that tls_destructionMonitor is initialized if a thread is attached to the runtime.

* relax the assert

* no call to `EnsureTlsDestructionMonitor` on unsetting a thread.

* remove obsolete comment

Co-authored-by: vsadov <8218165+VSadov@users.noreply.github.com>

3 files changed, 38 insertions, 20 deletions

diff --git a/src/coreclr/vm/ceemain.cpp b/src/coreclr/vm/ceemain.cpp
index 87106bbff4b..bce2d8ae807 100644
--- a/src/coreclr/vm/ceemain.cpp
+++ b/src/coreclr/vm/ceemain.cpp
@@ -1878,35 +1878,42 @@ BOOL STDMETHODCALLTYPE EEDllMain( // TRUE on success, FALSE on error.
 
 struct TlsDestructionMonitor
 {
-    ~TlsDestructionMonitor()
+    bool m_activated = false;
+
+    void Activate()
     {
-        // Don't destroy threads here if we're in shutdown (shutdown will
-        // clean up for us instead).
+        m_activated = true;
+    }
 
-        Thread* thread = GetThreadNULLOk();
-        if (thread)
+    ~TlsDestructionMonitor()
+    {
+        if (m_activated)
         {
+            Thread* thread = GetThreadNULLOk();
+            if (thread)
+            {
 #ifdef FEATURE_COMINTEROP
-            // reset the CoInitialize state
-            // so we don't call CoUninitialize during thread detach
-            thread->ResetCoInitialized();
+                // reset the CoInitialize state
+                // so we don't call CoUninitialize during thread detach
+                thread->ResetCoInitialized();
 #endif // FEATURE_COMINTEROP
-            // For case where thread calls ExitThread directly, we need to reset the
-            // frame pointer. Otherwise stackwalk would AV. We need to do it in cooperative mode.
-            // We need to set m_GCOnTransitionsOK so this thread won't trigger GC when toggle GC mode
-            if (thread->m_pFrame != FRAME_TOP)
-            {
+                // For case where thread calls ExitThread directly, we need to reset the
+                // frame pointer. Otherwise stackwalk would AV. We need to do it in cooperative mode.
+                // We need to set m_GCOnTransitionsOK so this thread won't trigger GC when toggle GC mode
+                if (thread->m_pFrame != FRAME_TOP)
+                {
 #ifdef _DEBUG
-                thread->m_GCOnTransitionsOK = FALSE;
+                    thread->m_GCOnTransitionsOK = FALSE;
 #endif
-                GCX_COOP_NO_DTOR();
-                thread->m_pFrame = FRAME_TOP;
-                GCX_COOP_NO_DTOR_END();
+                    GCX_COOP_NO_DTOR();
+                    thread->m_pFrame = FRAME_TOP;
+                    GCX_COOP_NO_DTOR_END();
+                }
+                thread->DetachThread(TRUE);
             }
-            thread->DetachThread(TRUE);
-        }
 
-        ThreadDetaching();
+            ThreadDetaching();
+        }
     }
 };
 
@@ -1914,6 +1921,11 @@ struct TlsDestructionMonitor
 // is called when a thread is being shut down.
 thread_local TlsDestructionMonitor tls_destructionMonitor;
 
+void EnsureTlsDestructionMonitor()
+{
+    tls_destructionMonitor.Activate();
+}
+
 #ifdef DEBUGGING_SUPPORTED
 //
 // InitializeDebugger initialized the Runtime-side COM+ Debugging Services
diff --git a/src/coreclr/vm/ceemain.h b/src/coreclr/vm/ceemain.h
index 1f96cdea85f..688f41c6deb 100644
--- a/src/coreclr/vm/ceemain.h
+++ b/src/coreclr/vm/ceemain.h
@@ -45,6 +45,8 @@ void ForceEEShutdown(ShutdownCompleteAction sca = SCA_ExitProcessWhenShutdownCom
 // Notification of a DLL_THREAD_DETACH or a Thread Terminate.
 void ThreadDetaching();
 
+void EnsureTlsDestructionMonitor();
+
 void SetLatchedExitCode (INT32 code);
 INT32 GetLatchedExitCode (void);
 
diff --git a/src/coreclr/vm/threads.cpp b/src/coreclr/vm/threads.cpp
index e454953181f..28446a25fc3 100644
--- a/src/coreclr/vm/threads.cpp
+++ b/src/coreclr/vm/threads.cpp
@@ -376,6 +376,10 @@ void SetThread(Thread* t)
     LIMITED_METHOD_CONTRACT
 
     gCurrentThreadInfo.m_pThread = t;
+    if (t != NULL)
+    {
+        EnsureTlsDestructionMonitor();
+    }
 }
 
 void SetAppDomain(AppDomain* ad)