-Async write performance

Src/Newtonsoft.Json/JsonTextWriter.Async.cs

@@ -314,9 +314,26 @@ namespace Newtonsoft.Json
             return _safeAsync ? DoWritePropertyNameAsync(name, cancellationToken) : base.WritePropertyNameAsync(name, cancellationToken);
         }
 
-        internal async Task DoWritePropertyNameAsync(string name, CancellationToken cancellationToken)
+        internal Task DoWritePropertyNameAsync(string name, CancellationToken cancellationToken)
         {
-            await InternalWritePropertyNameAsync(name, cancellationToken).ConfigureAwait(false);
+            Task task = InternalWritePropertyNameAsync(name, cancellationToken);
+            if (!task.IsCompleted)
+            {
+                return DoWritePropertyNameAsync(task, name, cancellationToken);
+            }
+
+            task = WriteEscapedStringAsync(name, _quoteName, cancellationToken);
+            if (!task.IsCompleted)
+            {
+                return JavaScriptUtils.WriteCharAsync(task, _writer, ':', cancellationToken);
+            }
+
+            return _writer.WriteAsync(':', cancellationToken);
+        }
+
+        private async Task DoWritePropertyNameAsync(Task task, string name, CancellationToken cancellationToken)
+        {
+            await task.ConfigureAwait(false);
 
             await WriteEscapedStringAsync(name, _quoteName, cancellationToken).ConfigureAwait(false);
 

Src/Newtonsoft.Json/Linq/JProperty.Async.cs

@@ -41,9 +41,28 @@ namespace Newtonsoft.Json.Linq
         /// <param name="cancellationToken">The token to monitor for cancellation requests.</param>
         /// <param name="converters">A collection of <see cref="JsonConverter"/> which will be used when writing the token.</param>
         /// <returns>A <see cref="Task"/> that represents the asynchronous write operation.</returns>
-        public override async Task WriteToAsync(JsonWriter writer, CancellationToken cancellationToken, params JsonConverter[] converters)
+        public override Task WriteToAsync(JsonWriter writer, CancellationToken cancellationToken, params JsonConverter[] converters)
         {
-            await writer.WritePropertyNameAsync(_name, cancellationToken).ConfigureAwait(false);
+            Task task = writer.WritePropertyNameAsync(_name, cancellationToken);
+            if (!task.IsCompleted)
+            {
+                return WriteToAsync(task, writer, cancellationToken, converters);
+            }
+
+            JToken value = Value;
+            if (value != null)
+            {
+                return value.WriteToAsync(writer, cancellationToken, converters);
+            }
+            else
+            {
+                return writer.WriteNullAsync(cancellationToken);
+            }
+        }
+
+        private async Task WriteToAsync(Task task, JsonWriter writer, CancellationToken cancellationToken, params JsonConverter[] converters)
+        {
+            await task.ConfigureAwait(false);
 
             JToken value = Value;
             if (value != null)

Src/Newtonsoft.Json/Utilities/JavaScriptUtils.cs

@@ -359,6 +359,11 @@ namespace Newtonsoft.Json.Utilities
 #if !(NET20 || NET35 || NET40 || PORTABLE40)
         public static Task WriteEscapedJavaScriptStringAsync(TextWriter writer, string s, char delimiter, bool appendDelimiters, bool[] charEscapeFlags, StringEscapeHandling stringEscapeHandling, JsonTextWriter client, char[] writeBuffer, CancellationToken cancellationToken = default(CancellationToken))
         {
+            if (cancellationToken.IsCancellationRequested)
+            {
+                return cancellationToken.FromCanceled();
+            }
+
             if (appendDelimiters)
             {
                 return WriteEscapedJavaScriptStringWithDelimitersAsync(writer, s, delimiter, charEscapeFlags, stringEscapeHandling, client, writeBuffer, cancellationToken);
@@ -372,10 +377,31 @@ namespace Newtonsoft.Json.Utilities
             return WriteEscapedJavaScriptStringWithoutDelimitersAsync(writer, s, charEscapeFlags, stringEscapeHandling, client, writeBuffer, cancellationToken);
         }
 
-        private static async Task WriteEscapedJavaScriptStringWithDelimitersAsync(TextWriter writer, string s, char delimiter,
+        private static Task WriteEscapedJavaScriptStringWithDelimitersAsync(TextWriter writer, string s, char delimiter,
             bool[] charEscapeFlags, StringEscapeHandling stringEscapeHandling, JsonTextWriter client, char[] writeBuffer, CancellationToken cancellationToken)
         {
-            await writer.WriteAsync(delimiter).ConfigureAwait(false);
+            Task task = writer.WriteAsync(delimiter, cancellationToken);
+            if (!task.IsCompleted)
+            {
+                return WriteEscapedJavaScriptStringWithDelimitersAsync(task, writer, s, delimiter, charEscapeFlags, stringEscapeHandling, client, writeBuffer, cancellationToken);
+            }
+
+            if (!string.IsNullOrEmpty(s))
+            {
+                task = WriteEscapedJavaScriptStringWithoutDelimitersAsync(writer, s, charEscapeFlags, stringEscapeHandling, client, writeBuffer, cancellationToken);
+                if (!task.IsCompleted)
+                {
+                    return WriteCharAsync(task, writer, delimiter, cancellationToken);
+                }
+            }
+
+            return writer.WriteAsync(delimiter, cancellationToken);
+        }
+
+        private static async Task WriteEscapedJavaScriptStringWithDelimitersAsync(Task task, TextWriter writer, string s, char delimiter,
+            bool[] charEscapeFlags, StringEscapeHandling stringEscapeHandling, JsonTextWriter client, char[] writeBuffer, CancellationToken cancellationToken)
+        {
+            await task.ConfigureAwait(false);
 
             if (!string.IsNullOrEmpty(s))
             {
@@ -385,6 +411,12 @@ namespace Newtonsoft.Json.Utilities
             await writer.WriteAsync(delimiter).ConfigureAwait(false);
         }
 
+        public static async Task WriteCharAsync(Task task, TextWriter writer, char c, CancellationToken cancellationToken)
+        {
+            await task.ConfigureAwait(false);
+            await writer.WriteAsync(c, cancellationToken).ConfigureAwait(false);
+        }
+
         private static Task WriteEscapedJavaScriptStringWithoutDelimitersAsync(
             TextWriter writer, string s, bool[] charEscapeFlags, StringEscapeHandling stringEscapeHandling,
             JsonTextWriter client, char[] writeBuffer, CancellationToken cancellationToken)