add a flag to make message processing parallel (#1482)

* add a flag to make message processing parallel

* use discard

* add comment

src/Microsoft.SqlTools.Hosting/Hosting/Protocol/MessageDispatcher.cs

@@ -57,6 +57,12 @@ namespace Microsoft.SqlTools.Hosting.Protocol
         protected MessageWriter MessageWriter { get; private set; }
 
 
+        /// <summary>
+        /// Whether the message should be handled without blocking the main thread.
+        /// </summary>
+        public bool ParallelMessageProcessing { get; set; }
+
+
         #endregion
 
         #region Constructors
@@ -305,22 +311,39 @@ namespace Microsoft.SqlTools.Hosting.Protocol
 
             if (handlerToAwait != null)
             {
-                try
+                if (this.ParallelMessageProcessing)
                 {
-                    await handlerToAwait;
-                }
-                catch (TaskCanceledException)
-                {
-                    // Some tasks may be cancelled due to legitimate
-                    // timeouts so don't let those exceptions go higher.
-                }
-                catch (Exception e)
-                {
-                    if (!(e is AggregateException && ((AggregateException)e).InnerExceptions[0] is TaskCanceledException))
+                    // Run the task in a separate thread so that the main
+                    // thread is not blocked.
+                    _ = Task.Run(() =>
                     {
-                        // Log the error but don't rethrow it to prevent any errors in the handler from crashing the service
-                        Logger.Write(TraceEventType.Error, string.Format("An unexpected error occured in the request handler: {0}", e.ToString()));
-                    }
+                        _ = RunTask(handlerToAwait);
+                    });
+                }
+                else
+                {
+                    await RunTask(handlerToAwait);
+                }
+            }
+        }
+
+        private async Task RunTask(Task task)
+        {
+            try
+            {
+                await task;
+            }
+            catch (TaskCanceledException)
+            {
+                // Some tasks may be cancelled due to legitimate
+                // timeouts so don't let those exceptions go higher.
+            }
+            catch (Exception e)
+            {
+                if (!(e is AggregateException && ((AggregateException)e).InnerExceptions[0] is TaskCanceledException))
+                {
+                    // Log the error but don't rethrow it to prevent any errors in the handler from crashing the service
+                    Logger.Write(TraceEventType.Error, string.Format("An unexpected error occured in the request handler: {0}", e.ToString()));
                 }
             }
         }

src/Microsoft.SqlTools.Hosting/Hosting/Protocol/ProtocolEndpoint.cs

@@ -44,7 +44,7 @@ namespace Microsoft.SqlTools.Hosting.Protocol
         /// handlers for requests, responses, and events that are
         /// transmitted through the channel.
         /// </summary>
-        protected MessageDispatcher MessageDispatcher { get; set; }
+        internal MessageDispatcher MessageDispatcher { get; set; }
 
         /// <summary>
         /// Initializes an instance of the protocol server using the

src/Microsoft.SqlTools.Hosting/Utility/CommandOptions.cs

@@ -63,6 +63,9 @@ namespace Microsoft.SqlTools.Hosting.Utility
                             case "-service-name":
                                 ServiceName = args[++i];
                                 break;
+                            case "-parallel-message-processing":
+                                ParallelMessageProcessing = true;
+                                break;
                             default:
                                 ErrorMessage += string.Format("Unknown argument \"{0}\"" + Environment.NewLine, argName);
                                 break;
@@ -131,6 +134,12 @@ namespace Microsoft.SqlTools.Hosting.Utility
 
         public bool AutoFlushLog { get; private set; } = false;
 
+        /// <summary>
+        /// A temporary flag to decide whether the message handling should block the main thread.
+        /// Eventually we will fix the issues and make this the default behavior.
+        /// </summary>
+        public bool ParallelMessageProcessing { get; private set; } = false;
+
         public virtual void SetLocale(string locale)
         {
             try
@@ -155,7 +164,7 @@ namespace Microsoft.SqlTools.Hosting.Utility
             // Creating cultureInfo from our given locale
             CultureInfo language = new CultureInfo(locale);
             Locale = locale;
-            
+
             // Allow the system set Number Format and Date Format to be preserved when changing the locale.
             NumberFormatInfo NumberFormat = CultureInfo.CurrentCulture.NumberFormat;
             DateTimeFormatInfo DateTimeFormat = CultureInfo.CurrentCulture.DateTimeFormat;

src/Microsoft.SqlTools.ServiceLayer/Program.cs

@@ -45,6 +45,7 @@ namespace Microsoft.SqlTools.ServiceLayer
 
                 SqlToolsContext sqlToolsContext = new SqlToolsContext(hostDetails);
                 ServiceHost serviceHost = HostLoader.CreateAndStartServiceHost(sqlToolsContext);
+                serviceHost.MessageDispatcher.ParallelMessageProcessing = commandOptions.ParallelMessageProcessing;
 
                 // If this service was started by another process, then it should shutdown when that parent process does.
                 if (commandOptions.ParentProcessId != null)
@@ -58,9 +59,9 @@ namespace Microsoft.SqlTools.ServiceLayer
             }
             catch (Exception ex)
             {
-                try 
+                try
                 {
-                    Logger.WriteWithCallstack(TraceEventType.Critical, $"An unhandled exception occurred: {ex}");                    
+                    Logger.WriteWithCallstack(TraceEventType.Critical, $"An unhandled exception occurred: {ex}");
                 }
                 catch (Exception loggerEx)
                 {