Speed up pasting from console

Pasting from the console was slow for 2 primary reasons:

* StringBuilder is pathologically slow if you "Insert" at the end
* Rendering requires parsing, this was happening for every character

The first issue is trival to fix - call Append when truly appending.

To address the second issue, I'm queueing up characters when we
want to read a character.  If enough characters are queued up, we
ignore requests to render if we've rendered recently.  This is
fine because we know we'll render soon because queued characters
will come along that will force us to render again.

Author: lzybkr

PSReadLine/ReadLine.cs

@@ -7,6 +7,7 @@
 using System.Management.Automation;
 using System.Management.Automation.Language;
 using System.Text;
+using System.Threading;
 
 namespace PSConsoleUtilities
 {
@@ -134,6 +135,8 @@ static KeyHandler MakeKeyHandler(Action<ConsoleKeyInfo?, object> action, string
         private ConsoleColor _initialBackgroundColor;
         private ConsoleColor _initialForegroundColor;
         private CHAR_INFO _space;
+        private readonly Queue<ConsoleKeyInfo> _queuedKeys;
+        private DateTime _lastRenderTime;
 
         // History state
         private HistoryQueue<HistoryItem> _history;
@@ -184,7 +187,20 @@ public PSConsoleReadlineOptions Options
         [ExcludeFromCodeCoverage]
         private static ConsoleKeyInfo ReadKey()
         {
-            var key = Console.ReadKey(true);
+            var start = DateTime.Now;
+            while (Console.KeyAvailable)
+            {
+                _singleton._queuedKeys.Enqueue(Console.ReadKey(true));
+                if ((DateTime.Now - start).Milliseconds > 2)
+                {
+                    // Don't spend too long in this loop if there are lots of queued keys
+                    break;
+                }
+            }
+
+            var key = _singleton._queuedKeys.Count > 0
+                ? _singleton._queuedKeys.Dequeue()
+                : Console.ReadKey(true);
             _singleton._log.Key(key.KeyChar, key.Key, key.Modifiers);
             return key;
         }
@@ -426,8 +442,9 @@ private PSConsoleReadLine()
             _dispatchTable = new Dictionary<ConsoleKeyInfo, KeyHandler>(_cmdKeyMap);
             _chordDispatchTable = new Dictionary<ConsoleKeyInfo, Dictionary<ConsoleKeyInfo, KeyHandler>>();
 
-            _buffer = new StringBuilder();
+            _buffer = new StringBuilder(8 * 1024);
             _savedCurrentLine = new HistoryItem();
+            _queuedKeys = new Queue<ConsoleKeyInfo>();
 
             _pushedEditGroupCount = new Stack<int>();
 
@@ -468,6 +485,7 @@ private void Initialize()
             _tabCommandCount = 0;
 
             _consoleBuffer = ReadBufferLines(_initialY, 1 + Options.ExtraPromptLineCount);
+            _lastRenderTime = DateTime.Now;
         }
 
         private static void Chord(ConsoleKeyInfo? key = null, object arg = null)
@@ -1394,7 +1412,16 @@ private void MoveCursor(int offset)
         public static void Insert(char c)
         {
             _singleton.SaveEditItem(EditItemInsertChar.Create(c, _singleton._current));
-            _singleton._buffer.Insert(_singleton._current, c);
+
+            // Use Append if possible because Insert at end makes StringBuilder quite slow.
+            if (_singleton._current == _singleton._buffer.Length)
+            {
+                _singleton._buffer.Append(c);
+            }
+            else
+            {
+                _singleton._buffer.Insert(_singleton._current, c);
+            }
             _singleton._current += 1;
             _singleton.Render();
         }
@@ -1406,7 +1433,16 @@ public static void Insert(char c)
         public static void Insert(string s)
         {
             _singleton.SaveEditItem(EditItemInsertString.Create(s, _singleton._current));
-            _singleton._buffer.Insert(_singleton._current, s);
+
+            // Use Append if possible because Insert at end makes StringBuilder quite slow.
+            if (_singleton._current == _singleton._buffer.Length)
+            {
+                _singleton._buffer.Append(s);
+            }
+            else
+            {
+                _singleton._buffer.Insert(_singleton._current, s);
+            }
             _singleton._current += s.Length;
             _singleton.Render();
         }
@@ -1650,8 +1686,12 @@ private string ParseInput()
 
         private void Render()
         {
-            // This function is not very effecient when pasting large chunks of text
-            // into the console.
+            // If there are a bunch of keys queued up, skip rendering if we've rendered
+            // recently.
+            if (_queuedKeys.Count > 10 && (DateTime.Now - _lastRenderTime).Milliseconds < 50)
+            {
+                return;
+            }
 
             _renderForDemoNeeded = false;
 
@@ -1805,6 +1845,8 @@ private void Render()
             {
                 Console.WindowTop = _initialY + bufferLineCount + 1 - Console.WindowHeight;
             }
+
+            _lastRenderTime = DateTime.Now;
         }
 
         private static void WriteBufferLines(CHAR_INFO[] buffer, ref int top)
@@ -1968,16 +2010,18 @@ private COORD ConvertOffsetToCoordinates(int offset)
             int y = _initialY + Options.ExtraPromptLineCount;
 
             int bufferWidth = Console.BufferWidth;
+            var continuationPromptLength = Options.ContinuationPrompt.Length;
             for (int i = 0; i < offset; i++)
             {
-                if (_buffer[i] == '\n')
+                char c = _buffer[i];
+                if (c == '\n')
                 {
                     y += 1;
-                    x = Options.ContinuationPrompt.Length;
+                    x = continuationPromptLength;
                 }
                 else
                 {
-                    x += char.IsControl(_buffer[i]) ? 2 : 1;
+                    x += char.IsControl(c) ? 2 : 1;
                     // Wrap?  No prompt when wrapping
                     if (x >= bufferWidth)
                     {