By splitting observation removal lock and further adding lock, there was broken atomicity of the update.

As a result, a simultaneously running current query could not return any value for removed observation.
And this observation, once restored, was not returned as sample. After all it was an update of existing observation.
To mitigate the problem made update atomic.

Author: SergeyGulik

libraries/MTConnect.NET-Common/Buffers/MTConnectObservationBuffer.cs

@@ -589,40 +589,40 @@ protected void AddCurrentObservation(BufferObservation observation)
                 {
                     _currentObservations.TryGetValue(observation._key, out existingObservation);
                     _currentObservations.Remove(observation._key);
-                }
-
-                if (existingObservation.IsValid && !isUnavailable)
-                {
-                    if (resetTriggered == ResetTriggered.NOT_SPECIFIED)
+                
+                    if (existingObservation.IsValid && !isUnavailable)
                     {
-                        // Update Observations based on Representation
-                        switch (observation.Representation)
+                        if (resetTriggered == ResetTriggered.NOT_SPECIFIED)
                         {
-                            case DataItemRepresentation.DATA_SET:
+                            // Update Observations based on Representation
+                            switch (observation.Representation)
+                            {
+                                case DataItemRepresentation.DATA_SET:
 
-                                // Update DataSet Values
-                                var existingDataSetValues = GetDataSetValues(ref existingObservation);
-                                if (!existingDataSetValues.IsNullOrEmpty())
-                                {
-                                    observation.Values = CombineDataSetValues(observation.Values, ref existingDataSetValues);
-                                }
+                                    // Update DataSet Values
+                                    var existingDataSetValues = GetDataSetValues(ref existingObservation);
+                                    if (!existingDataSetValues.IsNullOrEmpty())
+                                    {
+                                        observation.Values = CombineDataSetValues(observation.Values, ref existingDataSetValues);
+                                    }
 
-                                break;
+                                    break;
 
-                            case DataItemRepresentation.TABLE:
+                                case DataItemRepresentation.TABLE:
 
-                                // Update Table Values
-                                var existingTableValues = GetTableValues(ref existingObservation);
-                                if (!existingTableValues.IsNullOrEmpty())
-                                {
-                                    observation.Values = CombineTableValues(observation.Values, ref existingTableValues);
-                                }
-                                break;
+                                    // Update Table Values
+                                    var existingTableValues = GetTableValues(ref existingObservation);
+                                    if (!existingTableValues.IsNullOrEmpty())
+                                    {
+                                        observation.Values = CombineTableValues(observation.Values, ref existingTableValues);
+                                    }
+                                    break;
+                            }
                         }
                     }
-                }
 
-                lock (_lock) _currentObservations.Add(observation._key, observation);
+                    _currentObservations.Add(observation._key, observation);
+                }
 
                 // Call Overridable Methods
                 OnCurrentObservationAdd(ref observation);
@@ -642,49 +642,53 @@ protected void AddCurrentCondition(BufferObservation observation)
                 var bufferObservations = new List<BufferObservation>();
 
                 IEnumerable<BufferObservation> existingObservations;
+                IEnumerable<BufferObservation> iBufferObservations;
                 lock (_lock)
                 {
                     _currentConditions.TryGetValue(observation._key, out existingObservations);
                     _currentConditions.Remove(observation._key);
-                }          
-
-                if (!existingObservations.IsNullOrEmpty())
-                {
-                    var conditionLevel = observation.GetValue(ValueKeys.Level);
-                    var nativeCode = observation.GetValue(ValueKeys.NativeCode);
 
-                    if (!(conditionLevel == ConditionLevel.NORMAL.ToString() && string.IsNullOrEmpty(nativeCode)) &&
-                        conditionLevel != ConditionLevel.UNAVAILABLE.ToString())
+                    if (!existingObservations.IsNullOrEmpty())
                     {
-                        foreach (var existingObservation in existingObservations)
-                        {
-                            var existingLevel = existingObservation.GetValue(ValueKeys.Level);
-                            var existingNativeCode = existingObservation.GetValue(ValueKeys.NativeCode);
+                        var conditionLevel = observation.GetValue(ValueKeys.Level);
+                        var nativeCode = observation.GetValue(ValueKeys.NativeCode);
 
-                            if (existingNativeCode != nativeCode && 
-                                existingLevel != ConditionLevel.UNAVAILABLE.ToString() &&
-                                existingObservation.Sequence != observation.Sequence)
+                        if (!(conditionLevel == ConditionLevel.NORMAL.ToString() && string.IsNullOrEmpty(nativeCode)) &&
+                            conditionLevel != ConditionLevel.UNAVAILABLE.ToString())
+                        {
+                            foreach (var existingObservation in existingObservations)
                             {
-                                bufferObservations.Add(existingObservation);
+                                var existingLevel = existingObservation.GetValue(ValueKeys.Level);
+                                var existingNativeCode = existingObservation.GetValue(ValueKeys.NativeCode);
+
+                                if (existingNativeCode != nativeCode &&
+                                    existingLevel != ConditionLevel.UNAVAILABLE.ToString() &&
+                                    existingObservation.Sequence != observation.Sequence)
+                                {
+                                    bufferObservations.Add(existingObservation);
+                                }
                             }
                         }
                     }
-                }
 
-                // Add the new Observation
-                bufferObservations.Add(observation);
+                    // Add the new Observation
+                    bufferObservations.Add(observation);
 
-                // If any WARNING or FAULT states present, then remove any NORMAL states
-                // Current should only show the active states
-                if (bufferObservations.Any(o => o.GetValue(ValueKeys.Level) == ConditionLevel.WARNING.ToString() || o.GetValue(ValueKeys.Level) == ConditionLevel.FAULT.ToString()))
-                {
-                    bufferObservations.RemoveAll(o => o.GetValue(ValueKeys.Level) == ConditionLevel.NORMAL.ToString());
-                }
+                    // If any WARNING or FAULT states present, then remove any NORMAL states
+                    // Current should only show the active states
+                    if (bufferObservations.Any(o =>
+                            o.GetValue(ValueKeys.Level) == ConditionLevel.WARNING.ToString() ||
+                            o.GetValue(ValueKeys.Level) == ConditionLevel.FAULT.ToString()))
+                    {
+                        bufferObservations.RemoveAll(o =>
+                            o.GetValue(ValueKeys.Level) == ConditionLevel.NORMAL.ToString());
+                    }
 
-                IEnumerable<BufferObservation> iBufferObservations = bufferObservations;
+                    iBufferObservations = bufferObservations;
 
-                // Add to stored List
-                lock (_lock) _currentConditions.Add(observation._key, iBufferObservations);
+                    // Add to stored List
+                    _currentConditions.Add(observation._key, iBufferObservations);
+                }
 
                 // Call Overridable Method
                 OnCurrentConditionChange(GetCurrentConditions());