diff --git a/vsintegration/src/FSharp.ProjectSystem.Base/Project/UIThread.cs b/vsintegration/src/FSharp.ProjectSystem.Base/Project/UIThread.cs
new file mode 100644
index 00000000000..1a0bb06e4ec
--- /dev/null
+++ b/vsintegration/src/FSharp.ProjectSystem.Base/Project/UIThread.cs
@@ -0,0 +1,232 @@
+// Copyright (c) Microsoft Corporation.  All Rights Reserved.  See License.txt in the project root for license information.
+
+using System;
+using System.Runtime.InteropServices;
+using System.Xml;
+using System.Collections;
+using System.Collections.Generic;
+using System.Threading;
+using System.IO;
+using System.Text;
+using System.Drawing;
+using System.Windows.Forms;
+using System.Diagnostics;
+using Microsoft.VisualStudio.Shell.Interop;
+using Microsoft.VisualStudio.OLE.Interop;
+using Microsoft.VisualStudio.TextManager.Interop;
+using Microsoft.VisualStudio.Threading;
+using Microsoft.VisualStudio.Shell;
+using IOleServiceProvider = Microsoft.VisualStudio.OLE.Interop.IServiceProvider;
+using IServiceProvider = System.IServiceProvider;
+using VsShell = Microsoft.VisualStudio.Shell.VsShellUtilities;
+using System.Diagnostics.CodeAnalysis;
+
+namespace Microsoft.VisualStudio.FSharp.LanguageService
+{
+    internal static class UIThread
+    {
+        static SynchronizationContext ctxt;
+        static bool isUnitTestingMode = false;
+#if DEBUG
+        static StackTrace captureStackTrace; // stack trace when ctxt was captured
+        static Thread uithread;
+#endif
+        public static SynchronizationContext TheSynchronizationContext
+        {
+            get
+            {
+                Debug.Assert(ctxt != null, "Tried to get TheSynchronizationContext before it was captured");
+                return ctxt;
+            }
+        }
+
+        public static void InitUnitTestingMode()
+        {
+            Debug.Assert(ctxt == null, "Context has already been captured; too late to InitUnitTestingMode");
+            isUnitTestingMode = true;
+        }
+
+        [Conditional("DEBUG")]
+        public static void MustBeCalledFromUIThread()
+        {
+#if DEBUG
+            Debug.Assert(uithread == System.Threading.Thread.CurrentThread || isUnitTestingMode, "This must be called from the GUI thread");
+#endif
+        }
+        public static void CaptureSynchronizationContext()
+        {
+            if (isUnitTestingMode) return;
+#if DEBUG
+            uithread = System.Threading.Thread.CurrentThread;
+#endif
+
+            if (ctxt == null)
+            {
+#if DEBUG
+                // This is a handy place to do this, since the product and all interesting unit tests
+                // must go through this code path.
+                AppDomain.CurrentDomain.UnhandledException += new UnhandledExceptionEventHandler(delegate (object sender, UnhandledExceptionEventArgs args)
+                {
+                    if (args.IsTerminating)
+                    {
+                        string s = String.Format("An unhandled exception is about to terminate the process.  Exception info:\n{0}", args.ExceptionObject.ToString());
+                        Debug.Assert(false, s);
+                    }
+                });
+                captureStackTrace = new StackTrace(true);
+#endif
+                ctxt = new WindowsFormsSynchronizationContext();
+            }
+            else
+            {
+#if DEBUG
+                // Make sure we are always capturing the same thread.
+                Debug.Assert(uithread == Thread.CurrentThread);
+#endif
+            }
+        }
+        private static readonly Queue<Action> ourUIQueue = new Queue<Action>();
+        private static bool ourIsReentrancy;
+
+        // Runs the action on UI thread. Prevents from reentracy.
+        public static void Run(Action action)
+        {
+            if (isUnitTestingMode)
+            {
+                action();
+                return;
+            }
+            Debug.Assert(ctxt != null, "The SynchronizationContext must be captured before calling this method");
+#if DEBUG
+            StackTrace stackTrace = new StackTrace(true);
+#endif
+            ctxt.Post(delegate (object ignore)
+            {
+                UIThread.MustBeCalledFromUIThread();
+                ourUIQueue.Enqueue(action);
+                if (ourIsReentrancy) return;
+                ourIsReentrancy = true;
+                try
+                {
+                    while (ourUIQueue.Count > 0)
+                    {
+                        try
+                        {
+                            var a = ourUIQueue.Dequeue();
+                            a();
+                        }
+#if DEBUG
+                        catch (Exception e)
+                        {
+                            // swallow, random exceptions should not kill process
+                            Debug.Assert(false, string.Format("UIThread.Run caught and swallowed exception: {0}\n\noriginally invoked from stack:\n{1}", e.ToString(), stackTrace.ToString()));
+                        }
+#else
+                        catch (Exception) {
+                            // swallow, random exceptions should not kill process
+                        }
+#endif
+
+                    }
+                }
+                finally
+                {
+                    ourIsReentrancy = false;
+                }
+            }, null);
+
+        }
+
+        /// <summary>
+        /// RunSync puts orignal exception stacktrace to Exception.Data by this key if action throws on UI thread
+        /// </summary>
+        /// WrappedStacktraceKey is a string to keep exception serializable.
+        public static readonly string WrappedStacktraceKey = "$$Microsoft.VisualStudio.Package.UIThread.WrappedStacktraceKey$$";
+
+        public static void RunSync(Action a)
+        {
+            if (isUnitTestingMode)
+            {
+                a();
+                return;
+            }
+            Exception exn = null;
+            Debug.Assert(ctxt != null, "The SynchronizationContext must be captured before calling this method");
+            // Send on UI thread will execute immediately.
+            ctxt.Send(ignore =>
+            {
+                try
+                {
+                    UIThread.MustBeCalledFromUIThread();
+                    a();
+                }
+                catch (Exception e)
+                {
+                    exn = e;
+                }
+            }, null
+            );
+            if (exn != null)
+            {
+                // throw exception on calling thread, preserve stacktrace
+                if (!exn.Data.Contains(WrappedStacktraceKey)) exn.Data[WrappedStacktraceKey] = exn.StackTrace;
+                throw exn;
+            }
+        }
+
+        /// <summary>
+        /// Local JoinableTaskContext
+        /// ensuring non-reentrancy.
+        /// </summary>
+        private static JoinableTaskContext jtc = null;
+        private static JoinableTaskFactory JTF
+        {
+            get
+            {
+                if (jtc == null)
+                {
+                    JoinableTaskContext j = null;
+                    if (VsTaskLibraryHelper.ServiceInstance == null)
+                    {
+                        j = new JoinableTaskContext();
+                    }
+                    else
+                    {
+                        j = ThreadHelper.JoinableTaskContext;
+                    }
+                    Interlocked.CompareExchange(ref jtc, j, null);
+                }
+
+                return jtc.Factory;
+            }
+        }
+
+        /// <summary>
+        /// Performs a callback on the UI thread and blocks until it is done, using the VS mechanism for
+        /// ensuring non-reentrancy.
+        /// </summary>
+        [SuppressMessage("Microsoft.Design", "CA1031:DoNotCatchGeneralExceptionTypes")]
+        internal static T DoOnUIThread<T>(Func<T> callback)
+        {
+            return JTF.Run<T>(async delegate
+            {
+                await JTF.SwitchToMainThreadAsync();
+                return callback();
+            });
+        }
+
+        /// <summary>
+        /// Performs a callback on the UI thread and blocks until it is done, using the VS mechanism for
+        /// ensuring non-reentrancy.
+        /// </summary>
+        [SuppressMessage("Microsoft.Design", "CA1031:DoNotCatchGeneralExceptionTypes")]
+        internal static void DoOnUIThread(Action callback)
+        {
+            JTF.Run(async delegate
+            {
+                await JTF.SwitchToMainThreadAsync();
+                callback();
+            });
+        }
+    }
+}
\ No newline at end of file
diff --git a/vsintegration/src/FSharp.ProjectSystem.FSharp/ProjectSystem.fsproj b/vsintegration/src/FSharp.ProjectSystem.FSharp/ProjectSystem.fsproj
index 47bcceed324..7af3d3e0bee 100644
--- a/vsintegration/src/FSharp.ProjectSystem.FSharp/ProjectSystem.fsproj
+++ b/vsintegration/src/FSharp.ProjectSystem.FSharp/ProjectSystem.fsproj
@@ -40,7 +40,6 @@
   <ItemGroup>
     <ProjectReference Include="$(FSharpSourcesRoot)\fsharp\FSharp.Core\FSharp.Core.fsproj" />
     <ProjectReference Include="$(FSharpSourcesRoot)\fsharp\FSharp.Compiler.Private\FSharp.Compiler.Private.fsproj" />
-    <ProjectReference Include="..\FSharp.LanguageService\FSharp.LanguageService.fsproj" />
     <ProjectReference Include="..\FSharp.VS.FSI\FSharp.VS.FSI.fsproj" />
     <ProjectReference Include="..\FSharp.ProjectSystem.Base\Project\ProjectSystem.Base.csproj" />
     <ProjectReference Include="..\FSharp.ProjectSystem.PropertyPages\FSharp.PropertiesPages.vbproj" />