[Debugger] Fix regression introduced when optimizing handlers

https://github.com/mono/monodevelop/commit/ef5ea322347547cb6d971b6097b41965312178e6 introduced a regression where we would load the children on a background thread.

That seems to race with debugger suspending/resuming. Go back to running on the UI thread. Also, fix up usage of the token source.

1 files changed, 9 insertions, 4 deletions

diff --git a/main/src/addins/MonoDevelop.Debugger/MonoDevelop.Debugger/ObjectValueTreeView.cs b/main/src/addins/MonoDevelop.Debugger/MonoDevelop.Debugger/ObjectValueTreeView.cs
index afceba6802..1a54b30564 100644
--- a/main/src/addins/MonoDevelop.Debugger/MonoDevelop.Debugger/ObjectValueTreeView.cs
+++ b/main/src/addins/MonoDevelop.Debugger/MonoDevelop.Debugger/ObjectValueTreeView.cs
@@ -947,15 +947,20 @@ namespace MonoDevelop.Debugger
 			}
 
 			int numberOfChildren = store.IterNChildren (iter);
-			Task.Run (() => {
+
+			var token = cancellationTokenSource.Token;
+			Runtime.RunInMainThread (() => {
+				if (token.IsCancellationRequested)
+					return Array.Empty<ObjectValue> ();
+
 				try {
 					return value.GetRangeOfChildren (numberOfChildren - 1, 20);
 				} catch (Exception ex) {
 					// Note: this should only happen if someone breaks ObjectValue.GetAllChildren()
 					LoggingService.LogError ("Failed to get ObjectValue children.", ex);
-					return new ObjectValue[0];
+					return Array.Empty<ObjectValue> ();
 				}
-			}, cancellationTokenSource.Token).ContinueWith (t => {
+			}).ContinueWith (t => {
 				TreeIter it;
 				if (disposed)
 					return;
@@ -975,7 +980,7 @@ namespace MonoDevelop.Debugger
 				if (compact)
 					RecalculateWidth ();
 				enumerableLoading.Remove (value);
-			}, cancellationTokenSource.Token, TaskContinuationOptions.NotOnCanceled, Runtime.MainTaskScheduler).Ignore ();
+			}, token, TaskContinuationOptions.OnlyOnRanToCompletion, Runtime.MainTaskScheduler).Ignore ();
 		}
 
 		void RefreshRow (TreeIter iter, ObjectValue val)