move waiting on threads to finish writing outside of the lock

src/coreclr/src/vm/eventpipesession.cpp

@@ -542,25 +542,37 @@ void EventPipeSession::SuspendWriteEvent()
     }
     CONTRACTL_END;
 
+    // Collect all threads that are currently active so we don't have to 
+    // wait for events to finish writing under the lock.
+    CQuickArrayList<EventPipeThread *> threadList;
     {
         SpinLockHolder holder(EventPipeThread::GetGlobalThreadLock());
 
         EventPipeThreadIterator eventPipeThreads = EventPipeThread::GetThreads();
         EventPipeThread *pThread = nullptr;
         while (eventPipeThreads.Next(&pThread))
         {
-            // Wait for the thread to finish any writes to this session
-            YIELD_WHILE(pThread->GetSessionWriteInProgress() == GetIndex());
-
-            // Since we've already disabled the session, the thread won't call back in to this
-            // session once its done with the current write
+            // Add ref so the thread doesn't disappear when we release the lock
+            pThread->AddRef();
+            threadList.Push(pThread);
         }
     }
 
+    for (size_t i = 0; i < threadList.Size(); i++)
+    {
+        EventPipeThread *pThread = threadList[i];
+        // Wait for the thread to finish any writes to this session
+        YIELD_WHILE(pThread->GetSessionWriteInProgress() == GetIndex());
+
+        // Since we've already disabled the session, the thread won't call back in to this
+        // session once its done with the current write
+
+        pThread->Release();
+    }
+
     if (m_pBufferManager != nullptr)
     {
-        // Force all in-progress writes to either finish or cancel
-        // This is required to ensure we can safely flush and delete the buffers
+        // Convert all buffers to read only to ensure they get flushed
         m_pBufferManager->SuspendWriteEvent(GetIndex());
     }
 }