Add task merging for graph updates

src/DynamoCore/Core/Threading/UpdateGraphAsyncTask.cs

@@ -18,7 +18,7 @@ class UpdateGraphAsyncTask : AsyncTask
 
         private GraphSyncData graphSyncData;
         private EngineController engineController;
-        private readonly bool verboseLogging;
+        private bool verboseLogging;
 
         internal override TaskPriority Priority
         {
@@ -31,13 +31,13 @@ internal override TaskPriority Priority
 
         #region Public Class Operational Methods
 
-        internal UpdateGraphAsyncTask(IScheduler scheduler, bool verboseLogging) : base(scheduler)
+        internal UpdateGraphAsyncTask(IScheduler scheduler, bool verboseLogging1) : base(scheduler)
         {
-            this.verboseLogging = verboseLogging;
+            this.verboseLogging = verboseLogging1;
         }
 
         /// <summary>
-        /// This method is called by codes that intent to start a graph update.
+        /// This method is called by code that intends to start a graph update.
         /// This method is called on the main thread where node collection in a 
         /// WorkspaceModel can be safely accessed.
         /// </summary>
@@ -62,8 +62,9 @@ internal bool Initialize(EngineController controller, WorkspaceModel workspace)
                 graphSyncData = engineController.ComputeSyncData(workspace.Nodes, ModifiedNodes, verboseLogging);
                 return graphSyncData != null;
             }
-            catch (Exception)
+            catch (Exception e)
             {
+                System.Diagnostics.Debug.WriteLine("UpgradeGraphAsyncTask saw: " + e.ToString());
                 return false;
             }
         }
@@ -102,6 +103,32 @@ protected override void HandleTaskCompletionCore()
             }
         }
 
+        protected override AsyncTask.TaskMergeInstruction CanMergeWithCore(AsyncTask otherTask)
+        {
+            var theOtherTask = otherTask as UpdateGraphAsyncTask;
+            if (theOtherTask == null)
+                return base.CanMergeWithCore(otherTask);
+
+
+            // Comparing to another UpdateGraphAsyncTask, verify that they are updating
+            // a similar set of nodes
+
+            // Other node is either equal or a superset of this task
+            if (ModifiedNodes.All(x => theOtherTask.ModifiedNodes.Contains(x)))
+            {
+                return TaskMergeInstruction.KeepOther;
+            }
+
+            // This node is a superset of the other
+            if (theOtherTask.ModifiedNodes.All(x => ModifiedNodes.Contains(x)))
+            {
+                return TaskMergeInstruction.KeepThis;
+            }
+
+            // They're different, keep both
+            return TaskMergeInstruction.KeepBoth;
+        }
+
         #endregion
 
         #region Public Class Properties