Throttle semantic analysis requests for better performance

src/PowerShellEditorServices.Transport.Stdio/Request/ErrorRequest.cs

@@ -6,13 +6,19 @@
 using Microsoft.PowerShell.EditorServices.Session;
 using Microsoft.PowerShell.EditorServices.Transport.Stdio.Event;
 using Microsoft.PowerShell.EditorServices.Transport.Stdio.Message;
+using Microsoft.PowerShell.EditorServices.Utility;
+using System;
 using System.Collections.Generic;
+using System.Threading;
+using System.Threading.Tasks;
 
 namespace Microsoft.PowerShell.EditorServices.Transport.Stdio.Request
 {
     [MessageTypeName("geterr")]
     public class ErrorRequest : RequestBase<ErrorRequestArguments>
     {
+        private static CancellationTokenSource existingRequestCancellation;
+
         public static ErrorRequest Create(params string[] filePaths)
         {
             return new ErrorRequest
@@ -30,8 +36,78 @@ public override void ProcessMessage(
         {
             List<ScriptFile> fileList = new List<ScriptFile>();
 
+            // If there's an existing task, attempt to cancel it
+            try
+            {
+                if (existingRequestCancellation != null)
+                {
+                    // Try to cancel the request
+                    existingRequestCancellation.Cancel();
+
+                    // If cancellation didn't throw an exception,
+                    // clean up the existing token
+                    existingRequestCancellation.Dispose();
+                    existingRequestCancellation = null;
+                }
+            }
+            catch (Exception e)
+            {
+                // TODO: Catch a more specific exception!
+                Logger.Write(
+                    LogLevel.Error,
+                    string.Format(
+                        "Exception while cancelling analysis task:\n\n{0}",
+                        e.ToString()));
+
+                return;
+            }
+
+            // Create a fresh cancellation token and then start the task.
+            // We create this on a different TaskScheduler so that we
+            // don't block the main message loop thread.
+            // TODO: Is there a better way to do this?
+            existingRequestCancellation = new CancellationTokenSource();
+            Task.Factory.StartNew(
+                () =>
+                    DelayThenInvokeDiagnostics(
+                        this.Arguments.Delay,
+                        this.Arguments.Files,
+                        editorSession,
+                        messageWriter,
+                        existingRequestCancellation.Token),
+                CancellationToken.None,
+                TaskCreationOptions.None,
+                TaskScheduler.Default);
+        }
+
+        private static async Task DelayThenInvokeDiagnostics(
+            int delayMilliseconds,
+            string[] filesToAnalyze,
+            EditorSession editorSession,
+            MessageWriter messageWriter,
+            CancellationToken cancellationToken)
+        {
+            // First of all, wait for the desired delay period before
+            // analyzing the provided list of files
+            try
+            {
+                await Task.Delay(delayMilliseconds, cancellationToken);
+            }
+            catch (TaskCanceledException)
+            {
+                // If the task is cancelled, exit directly
+                return;
+            }
+
+            // If we've made it past the delay period then we don't care
+            // about the cancellation token anymore.  This could happen
+            // when the user stops typing for long enough that the delay
+            // period ends but then starts typing while analysis is going
+            // on.  It makes sense to send back the results from the first
+            // delay period while the second one is ticking away.
+
             // Get the requested files
-            foreach (string filePath in this.Arguments.Files)
+            foreach (string filePath in filesToAnalyze)
             {
                 ScriptFile scriptFile = 
                     editorSession.Workspace.GetFile(

src/PowerShellEditorServices.Transport.Stdio/StdioHost.cs

@@ -142,7 +142,7 @@ async Task ListenForMessages()
             MessageReader messageReader = 
                 new MessageReader(
                     System.Console.In, 
-                    MessageFormat.WithoutContentLength,
+                    MessageFormat.WithContentLength,
                     messageTypeResolver);
 
             MessageWriter messageWriter = 

src/PowerShellEditorServices/Utility/Logger.cs

@@ -126,15 +126,16 @@ public LogWriter(LogLevel minimumLogLevel, string logFilePath, bool deleteExisti
                         logFilePath);
             }
 
-            // Open the log file for writing with UTF8 encoding
-            this.textWriter =
-                new StreamWriter(
-                    new FileStream(
-                        logFilePath,
-                        deleteExisting ?
-                            FileMode.Create :
-                            FileMode.Append),
-                    Encoding.UTF8);
+            if (!this.TryOpenLogFile(logFilePath, deleteExisting))
+            {
+                // If the log file couldn't be opened at this location,
+                // try opening it in a more reliable path
+                this.TryOpenLogFile(
+                    Path.Combine(
+                        Environment.GetFolderPath(Environment.SpecialFolder.LocalApplicationData),
+                        Path.GetFileName(logFilePath)),
+                    deleteExisting);
+            }
         }
 
         public void Write(
@@ -144,7 +145,8 @@ public void Write(
             string callerSourceFile = null,
             int callerLineNumber = 0)
         {
-            if (logLevel >= this.minimumLogLevel)
+            if (this.textWriter != null &&
+                logLevel >= this.minimumLogLevel)
             {
                 // Print the timestamp and log level
                 this.textWriter.WriteLine(
@@ -176,5 +178,39 @@ public void Dispose()
                 this.textWriter = null;
             }
         }
+
+        private bool TryOpenLogFile(
+            string logFilePath, 
+            bool deleteExisting)
+        {
+            try
+            {
+                // Open the log file for writing with UTF8 encoding
+                this.textWriter =
+                    new StreamWriter(
+                        new FileStream(
+                            logFilePath,
+                            deleteExisting ?
+                                FileMode.Create :
+                                FileMode.Append),
+                        Encoding.UTF8);
+
+                return true;
+            }
+            catch (Exception e)
+            {
+                if (e is UnauthorizedAccessException ||
+                    e is IOException)
+                {
+                    // This exception is thrown when we can't open the file
+                    // at the path in logFilePath.  Return false to indicate
+                    // that the log file couldn't be created.
+                    return false;
+                }
+
+                // Unexpected exception, rethrow it
+                throw;
+            }
+        }
     }
 }

test/PowerShellEditorServices.Test.Host/LanguageServiceManager.cs

@@ -73,7 +73,7 @@ public void Start()
             this.MessageWriter = 
                 new MessageWriter(
                     this.languageServiceProcess.StandardInput,
-                    MessageFormat.WithoutContentLength,
+                    MessageFormat.WithContentLength,
                     messageTypeResolver);
 
             // Wait for the 'started' event