Waiting for counter group reset

src/libraries/System.Private.CoreLib/src/System/Diagnostics/Tracing/CounterGroup.cs

@@ -162,8 +162,8 @@ private void EnableTimer(float pollingIntervalInSeconds)
                 if (s_pollingThread == null)
                 {
                     s_pollingThreadSleepEvent = new AutoResetEvent(false);
+                    s_needsResetCounterGroupEvent = new AutoResetEvent(false);
                     s_counterGroupEnabledList = new List<CounterGroup>();
-                    s_needsResetCounterGroup = [];
                     s_pollingThread = new Thread(PollForValues)
                     {
                         IsBackground = true,
@@ -172,19 +172,18 @@ private void EnableTimer(float pollingIntervalInSeconds)
                     s_pollingThread.InternalUnsafeStart();
                 }
 
+                s_needsResetCounterGroup = this;
                 if (!s_counterGroupEnabledList!.Contains(this))
                 {
                     s_counterGroupEnabledList.Add(this);
                 }
 
-                if (!s_needsResetCounterGroup!.Contains(this))
-                {
-                    s_needsResetCounterGroup.Add(this);
-                }
-
                 // notify the polling thread that the polling interval may have changed and the sleep should
                 // be recomputed
                 s_pollingThreadSleepEvent!.Set();
+
+                // reset counters before leaving this method to prevent them from being overwritten
+                s_needsResetCounterGroupEvent!.WaitOne();
             }
         }
 
@@ -193,7 +192,8 @@ private void DisableTimer()
             Debug.Assert(Monitor.IsEntered(s_counterGroupLock));
             _pollingIntervalInMilliseconds = 0;
             s_counterGroupEnabledList?.Remove(this);
-            s_needsResetCounterGroup?.Remove(this);
+            if (s_needsResetCounterGroup == this)
+                s_needsResetCounterGroup = null;
         }
 
         private void OnTimer()
@@ -247,7 +247,9 @@ private void OnTimer()
         private static AutoResetEvent? s_pollingThreadSleepEvent;
 
         private static List<CounterGroup>? s_counterGroupEnabledList;
-        private static List<CounterGroup>? s_needsResetCounterGroup;
+        private static CounterGroup? s_needsResetCounterGroup;
+        private static AutoResetEvent? s_needsResetCounterGroupEvent;
+
         private static void PollForValues()
         {
             AutoResetEvent? sleepEvent = null;
@@ -257,18 +259,13 @@ private static void PollForValues()
             // calling into the callbacks can cause a re-entrancy into CounterGroup.Enable()
             // and result in a deadlock. (See https://github.com/dotnet/runtime/issues/40190 for details)
             var onTimers = new List<CounterGroup>();
-            var countersToReset = new List<DiagnosticCounter>();
             while (true)
             {
+                ResetCounterGroupIfNeeded();
+
                 int sleepDurationInMilliseconds = int.MaxValue;
                 lock (s_counterGroupLock)
                 {
-                    foreach (CounterGroup counterGroup in s_needsResetCounterGroup!)
-                    {
-                        countersToReset.AddRange(counterGroup._counters);
-                    }
-                    s_needsResetCounterGroup.Clear();
-
                     sleepEvent = s_pollingThreadSleepEvent;
                     foreach (CounterGroup counterGroup in s_counterGroupEnabledList!)
                     {
@@ -284,23 +281,6 @@ private static void PollForValues()
                     }
                 }
 
-                foreach (DiagnosticCounter counter in countersToReset)
-                {
-                    if (counter is IncrementingEventCounter ieCounter)
-                    {
-                        ieCounter.UpdateMetric();
-                    }
-                    else if (counter is IncrementingPollingCounter ipCounter)
-                    {
-                        ipCounter.UpdateMetric();
-                    }
-                    else if (counter is EventCounter eCounter)
-                    {
-                        eCounter.ResetStatistics();
-                    }
-                }
-                countersToReset.Clear();
-
                 foreach (CounterGroup onTimer in onTimers)
                 {
                     onTimer.OnTimer();
@@ -314,6 +294,36 @@ private static void PollForValues()
             }
         }
 
+        private static void ResetCounterGroupIfNeeded()
+        {
+            if (s_needsResetCounterGroup == null)
+            {
+                return;
+            }
+
+            // we can access _counters without s_counterGroupLock here, because the lock is held by a thread waiting on s_needsResetCounterGroupEvent,
+            // so the counters can't be changed until s_needsResetCounterGroupEvent is fired
+            foreach (DiagnosticCounter counter in s_needsResetCounterGroup._counters)
+            {
+                if (counter is IncrementingEventCounter ieCounter)
+                {
+                    ieCounter.UpdateMetric();
+                }
+                else if (counter is IncrementingPollingCounter ipCounter)
+                {
+                    ipCounter.UpdateMetric();
+                }
+                else if (counter is EventCounter eCounter)
+                {
+                    eCounter.ResetStatistics();
+                }
+            }
+
+            s_needsResetCounterGroup = null;
+            s_needsResetCounterGroupEvent!.Set();
+        }
+
+
 #endregion // Timer Processing
 
     }