Remove stale gauges from dotnet-counters UI

src/Tools/dotnet-counters/CounterMonitor.cs

@@ -169,6 +169,7 @@ private void HandleCounterRate(TraceEvent obj)
                 CounterPayload payload = new RatePayload(meterName, instrumentName, null, unit, tags, rate, _interval, obj.TimeStamp);
                 _renderer.CounterPayloadReceived(payload, _pauseCmdSet);
             }
+
         }
 
         private void HandleGauge(TraceEvent obj)
@@ -192,6 +193,12 @@ private void HandleGauge(TraceEvent obj)
                 CounterPayload payload = new GaugePayload(meterName, instrumentName, null, unit, tags, lastValue, obj.TimeStamp);
                 _renderer.CounterPayloadReceived(payload, _pauseCmdSet);
             }
+            else
+            {
+                // for observable instruments we assume the lack of data is meaningful and remove it from the UI
+                CounterPayload payload = new RatePayload(meterName, instrumentName, null, unit, tags, 0, _interval, obj.TimeStamp);
+                _renderer.CounterStopped(payload);
+            }
         }
 
         private void HandleHistogram(TraceEvent obj)

src/Tools/dotnet-counters/Exporters/CSVExporter.cs

@@ -83,6 +83,8 @@ public void CounterPayloadReceived(CounterPayload payload, bool _)
             }
         }
 
+        public void CounterStopped(CounterPayload payload) { }
+
         public void Stop()
         {
             string outputString;

src/Tools/dotnet-counters/Exporters/ConsoleWriter.cs

@@ -233,6 +233,48 @@ public void CounterPayloadReceived(CounterPayload payload, bool pauseCmdSet)
             }
         }
 
+        public void CounterStopped(CounterPayload payload)
+        {
+            lock (_lock)
+            {
+                string providerName = payload.ProviderName;
+                string counterName = payload.Name;
+                string tags = payload.Tags;
+
+                if (!providers.TryGetValue(providerName, out ObservedProvider provider))
+                {
+                    return;
+                }
+
+                if (!provider.Counters.TryGetValue(counterName, out ObservedCounter counter))
+                {
+                    return;
+                }
+
+                ObservedTagSet tagSet = null;
+                if (tags != null)
+                {
+                    if (!counter.TagSets.TryGetValue(tags, out tagSet))
+                    {
+                        return;
+                    }
+                    else
+                    {
+                        counter.TagSets.Remove(tags);
+                        if(counter.TagSets.Count == 0)
+                        {
+                            provider.Counters.Remove(counterName);
+                        }
+                    }
+                }
+                else
+                {
+                    provider.Counters.Remove(counterName);
+                }
+                AssignRowsAndInitializeDisplay();
+            }
+        }
+
         private static int GetLineWrappedLines(string text)
         {
             string[] lines = text.Split(Environment.NewLine);

src/Tools/dotnet-counters/Exporters/ICounterRenderer.cs

@@ -10,6 +10,7 @@ public interface ICounterRenderer
         void EventPipeSourceConnected();
         void ToggleStatus(bool paused);
         void CounterPayloadReceived(CounterPayload payload, bool paused);
+        void CounterStopped(CounterPayload payload);
         void SetErrorText(string errorText);
         void Stop();
     }

src/Tools/dotnet-counters/Exporters/JSONExporter.cs

@@ -81,6 +81,8 @@ public void CounterPayloadReceived(CounterPayload payload, bool _)
             }
         }
 
+        public void CounterStopped(CounterPayload payload) { }
+
         public void Stop()
         {
             lock (_lock)