From 2885b4b13804511a76836f63fc5bdf732ab800dc Mon Sep 17 00:00:00 2001
From: "N. Taylor Mullen" <nimullen@microsoft.com>
Date: Fri, 27 Apr 2018 11:47:34 -0700
Subject: [PATCH] Make document tracker resilient to multiple subscribes.

- Added tests to verify new functionality.

#2314
---
 .../DefaultVisualStudioDocumentTracker.cs     | 12 ++++
 .../DefaultVisualStudioDocumentTrackerTest.cs | 66 +++++++++++++++++++
 2 files changed, 78 insertions(+)

diff --git a/src/Microsoft.VisualStudio.Editor.Razor/DefaultVisualStudioDocumentTracker.cs b/src/Microsoft.VisualStudio.Editor.Razor/DefaultVisualStudioDocumentTracker.cs
index bc31eba667..b9c976bdb9 100644
--- a/src/Microsoft.VisualStudio.Editor.Razor/DefaultVisualStudioDocumentTracker.cs
+++ b/src/Microsoft.VisualStudio.Editor.Razor/DefaultVisualStudioDocumentTracker.cs
@@ -29,6 +29,7 @@ namespace Microsoft.VisualStudio.Editor.Razor
         private readonly Workspace _workspace;
         private bool _isSupportedProject;
         private ProjectSnapshot _projectSnapshot;
+        private int _subscribeCount;
 
         // Only allow a single tag helper computation task at a time.
         private (ProjectSnapshot project, Task task) _computingTagHelpers;
@@ -177,12 +178,18 @@ namespace Microsoft.VisualStudio.Editor.Razor
         {
             _foregroundDispatcher.AssertForegroundThread();
 
+            if (_subscribeCount++ > 0)
+            {
+                return;
+            }
+
             _projectSnapshot = _projectManager.GetOrCreateProject(_projectPath);
             _isSupportedProject = true;
 
             _projectManager.Changed += ProjectManager_Changed;
             _workspaceEditorSettings.Changed += EditorSettingsManager_Changed;
             _importDocumentManager.Changed += Import_Changed;
+
             _importDocumentManager.OnSubscribed(this);
 
             OnContextChanged(ContextChangeKind.ProjectChanged);
@@ -192,6 +199,11 @@ namespace Microsoft.VisualStudio.Editor.Razor
         {
             _foregroundDispatcher.AssertForegroundThread();
 
+            if (_subscribeCount == 0 || _subscribeCount-- > 1)
+            {
+                return;
+            }
+
             _importDocumentManager.OnUnsubscribed(this);
 
             _projectManager.Changed -= ProjectManager_Changed;
diff --git a/test/Microsoft.VisualStudio.Editor.Razor.Test/DefaultVisualStudioDocumentTrackerTest.cs b/test/Microsoft.VisualStudio.Editor.Razor.Test/DefaultVisualStudioDocumentTrackerTest.cs
index 0e47ecfe9c..f14f8bbfd8 100644
--- a/test/Microsoft.VisualStudio.Editor.Razor.Test/DefaultVisualStudioDocumentTrackerTest.cs
+++ b/test/Microsoft.VisualStudio.Editor.Razor.Test/DefaultVisualStudioDocumentTrackerTest.cs
@@ -98,6 +98,72 @@ namespace Microsoft.VisualStudio.Editor.Razor
 
         private DefaultVisualStudioDocumentTracker DocumentTracker { get; }
 
+        [ForegroundFact]
+        public void Subscribe_NoopsIfAlreadySubscribed()
+        {
+            // Arrange
+            var callCount = 0;
+            DocumentTracker.ContextChanged += (sender, args) =>
+            {
+                callCount++;
+            };
+            DocumentTracker.Subscribe();
+
+            // Call count is 2 right now:
+            // 1 trigger for initial subscribe context changed.
+            // 1 trigger for TagHelpers being changed (computed).
+
+            // Act
+            DocumentTracker.Subscribe();
+
+            // Assert
+            Assert.Equal(2, callCount);
+        }
+
+        [ForegroundFact]
+        public void Unsubscribe_NoopsIfAlreadyUnsubscribed()
+        {
+            // Arrange
+            var callCount = 0;
+            DocumentTracker.Subscribe();
+            DocumentTracker.ContextChanged += (sender, args) =>
+            {
+                callCount++;
+            };
+            DocumentTracker.Unsubscribe();
+
+            // Act
+            DocumentTracker.Unsubscribe();
+
+            // Assert
+            Assert.Equal(1, callCount);
+        }
+
+        [ForegroundFact]
+        public void Unsubscribe_NoopsIfSubscribeHasBeenCalledMultipleTimes()
+        {
+            // Arrange
+            var callCount = 0;
+            DocumentTracker.Subscribe();
+            DocumentTracker.Subscribe();
+            DocumentTracker.ContextChanged += (sender, args) =>
+            {
+                callCount++;
+            };
+
+            // Act - 1
+            DocumentTracker.Unsubscribe();
+
+            // Assert - 1
+            Assert.Equal(0, callCount);
+
+            // Act - 2
+            DocumentTracker.Unsubscribe();
+
+            // Assert - 2
+            Assert.Equal(1, callCount);
+        }
+
         [ForegroundFact]
         public void EditorSettingsManager_Changed_TriggersContextChanged()
         {