Only allow the rundown thread to write events during rundown to avoid corruption of the trace file. (#17358)

Author: brianrob

src/vm/eventpipe.cpp

@@ -594,6 +594,15 @@ void EventPipe::WriteEventInternal(EventPipeEvent &event, EventPipeEventPayload
     }
     else if(s_pConfig->RundownEnabled())
     {
+        // It is possible that some events that are enabled on rundown can be emitted from other threads.
+        // We're not interested in these events and they can cause corrupted trace files because rundown
+        // events are written synchronously and not under lock.
+        // If we encounter an event that did not originate on the thread that is doing rundown, ignore it.
+        if(!s_pConfig->IsRundownThread(pThread))
+        {
+            return;
+        }
+
         BYTE *pData = payload.GetFlatData();
         if (pData != NULL)
         {

src/vm/eventpipeconfiguration.cpp

@@ -19,6 +19,7 @@ EventPipeConfiguration::EventPipeConfiguration()
 
     m_enabled = false;
     m_rundownEnabled = false;
+    m_pRundownThread = NULL;
     m_pConfigProvider = NULL;
     m_pSession = NULL;
     m_pProviderList = new SList<SListElem<EventPipeProvider*>>();
@@ -409,6 +410,7 @@ void EventPipeConfiguration::Disable(EventPipeSession *pSession)
 
     m_enabled = false;
     m_rundownEnabled = false;
+    m_pRundownThread = NULL;
     m_pSession = NULL;
 }
 
@@ -440,8 +442,10 @@ void EventPipeConfiguration::EnableRundown(EventPipeSession *pSession)
     // Build the rundown configuration.
     _ASSERTE(m_pSession == NULL);
 
-    // Enable rundown.
+    // Enable rundown and keep track of the rundown thread.
     // TODO: Move this into EventPipeSession once Enable takes an EventPipeSession object.
+    m_pRundownThread = GetThread();
+    _ASSERTE(m_pRundownThread != NULL);
     m_rundownEnabled = true;
 
     // Enable tracing.

src/vm/eventpipeconfiguration.h

@@ -82,6 +82,15 @@ class EventPipeConfiguration
     // Delete deferred providers.
     void DeleteDeferredProviders();
 
+    // Determine if the specified thread is the rundown thread.
+    // Used during rundown to ignore events from all other threads so that we don't corrupt the trace file.
+    inline bool IsRundownThread(Thread *pThread)
+    {
+        LIMITED_METHOD_CONTRACT;
+
+        return (pThread == m_pRundownThread);
+    }
+
 private:
 
     // Get the provider without taking the lock.
@@ -111,6 +120,9 @@ class EventPipeConfiguration
 
     // True if rundown is enabled.
     Volatile<bool> m_rundownEnabled;
+
+    // The rundown thread.  If rundown is not enabled, this is NULL.
+    Thread *m_pRundownThread;
 };
 
 #endif // FEATURE_PERFTRACING