Modern async (#955)

* Modernize C# code

Task.Run instead of TaskFactory.StartNew.
await instead of Wait()
String interpolation instead of concatenation

* Use modern async constructs

async/await and Task.Run

* Fix formatting

* Catch OperationCanceledException when using await

Author: ErlendLandro

snippets/csharp/VS_Snippets_Misc/tpl_cancellation/cs/cancel1.cs

@@ -6,53 +6,55 @@
 
 public class Example
 {
-   public static void Main()
-   {
-      var tokenSource = new CancellationTokenSource();
-      var token = tokenSource.Token;
+    public static async Task Main()
+    {
+        var tokenSource = new CancellationTokenSource();
+        var token = tokenSource.Token;
 
-      // Store references to the tasks so that we can wait on them and  
-      // observe their status after cancellation. 
-      Task t;
-      var tasks = new ConcurrentBag<Task>();
+        // Store references to the tasks so that we can wait on them and
+        // observe their status after cancellation.
+        Task t;
+        var tasks = new ConcurrentBag<Task>();
 
-      Console.WriteLine("Press any key to begin tasks...");
-      Console.ReadKey(true);
-      Console.WriteLine("To terminate the example, press 'c' to cancel and exit...");
-      Console.WriteLine();
-        
-      // Request cancellation of a single task when the token source is canceled. 
-      // Pass the token to the user delegate, and also to the task so it can  
-      // handle the exception correctly.
-      t = Task.Factory.StartNew( () => DoSomeWork(1, token), token);
-      Console.WriteLine("Task {0} executing", t.Id);
-      tasks.Add(t);
+        Console.WriteLine("Press any key to begin tasks...");
+        Console.ReadKey(true);
+        Console.WriteLine("To terminate the example, press 'c' to cancel and exit...");
+        Console.WriteLine();
+
+        // Request cancellation of a single task when the token source is canceled.
+        // Pass the token to the user delegate, and also to the task so it can
+        // handle the exception correctly.
+        t = Task.Run(() => DoSomeWork(1, token), token);
+        Console.WriteLine("Task {0} executing", t.Id);
+        tasks.Add(t);
+
+        // Request cancellation of a task and its children. Note the token is passed
+        // to (1) the user delegate and (2) as the second argument to Task.Run, so
+        // that the task instance can correctly handle the OperationCanceledException.
+        t = Task.Run(() =>
+        {
+            // Create some cancelable child tasks.
+            Task tc;
+            for (int i = 3; i <= 10; i++)
+            {
+                // For each child task, pass the same token
+                // to each user delegate and to Task.Run.
+                tc = Task.Run(() => DoSomeWork(i, token), token);
+                Console.WriteLine("Task {0} executing", tc.Id);
+                tasks.Add(tc);
+                // Pass the same token again to do work on the parent task.
+                // All will be signaled by the call to tokenSource.Cancel below.
+                DoSomeWork(2, token);
+            }
+        }, token);
 
-      // Request cancellation of a task and its children. Note the token is passed 
-      // to (1) the user delegate and (2) as the second argument to StartNew, so  
-      // that the task instance can correctly handle the OperationCanceledException.
-      t = Task.Factory.StartNew( () => {
-                                     // Create some cancelable child tasks.  
-                                     Task tc;
-                                     for (int i = 3; i <= 10; i++) {
-                                        // For each child task, pass the same token 
-                                        // to each user delegate and to StartNew.
-                                        tc = Task.Factory.StartNew( iteration => DoSomeWork((int)iteration, token), i, token);
-                                        Console.WriteLine("Task {0} executing", tc.Id);
-                                        tasks.Add(tc);
-                                        // Pass the same token again to do work on the parent task.  
-                                        // All will be signaled by the call to tokenSource.Cancel below.
-                                        DoSomeWork(2, token);
-                                     } 
-                                  }, 
-                                  token);
-                                           
         Console.WriteLine("Task {0} executing", t.Id);
         tasks.Add(t);
 
         // Request cancellation from the UI thread. 
         char ch = Console.ReadKey().KeyChar;
-        if (ch == 'c'|| ch == 'C' ) {
+        if (ch == 'c' || ch == 'C')
+        {
             tokenSource.Cancel();
             Console.WriteLine("\nTask cancellation requested.");
 
@@ -61,63 +63,59 @@ public static void Main()
             // if you do wait, you must enclose the call in a try-catch block to 
             // catch the TaskCanceledExceptions that are thrown. If you do  
             // not wait, no exception is thrown if the token that was passed to the  
-            // StartNew method is the same token that requested the cancellation. 
-        } 
+            // Task.Run method is the same token that requested the cancellation.
+        }
 
-        try {
-            Task.WaitAll(tasks.ToArray());
+        try
+        {
+            await Task.WhenAll(tasks.ToArray());
         }
-        catch (AggregateException e) {
-           Console.WriteLine("\nAggregateException thrown with the following inner exceptions:");
-           // Display information about each exception. 
-           foreach (var v in e.InnerExceptions) {
-              if (v is TaskCanceledException)
-                 Console.WriteLine("   TaskCanceledException: Task {0}", 
-                                   ((TaskCanceledException) v).Task.Id);
-              else
-                 Console.WriteLine("   Exception: {0}", v.GetType().Name);
-           } 
-           Console.WriteLine();
+        catch (OperationCanceledException)
+        {
+            Console.WriteLine($"\n{nameof(OperationCanceledException)} thrown\n");
         }
         finally
         {
-           tokenSource.Dispose();
+            tokenSource.Dispose();
         }
 
         // Display status of all tasks. 
         foreach (var task in tasks)
             Console.WriteLine("Task {0} status is now {1}", task.Id, task.Status);
-   }
+    }
 
-   static void DoSomeWork(int taskNum, CancellationToken ct)
-   {
-      // Was cancellation already requested? 
-      if (ct.IsCancellationRequested == true) {
-         Console.WriteLine("Task {0} was cancelled before it got started.",
-                           taskNum);
-         ct.ThrowIfCancellationRequested();
-      } 
+    static void DoSomeWork(int taskNum, CancellationToken ct)
+    {
+        // Was cancellation already requested?
+        if (ct.IsCancellationRequested)
+        {
+            Console.WriteLine("Task {0} was cancelled before it got started.",
+                              taskNum);
+            ct.ThrowIfCancellationRequested();
+        }
 
-      int maxIterations = 100;
+        int maxIterations = 100;
 
-      // NOTE!!! A "TaskCanceledException was unhandled 
-      // by user code" error will be raised here if "Just My Code" 
-      // is enabled on your computer. On Express editions JMC is 
-      // enabled and cannot be disabled. The exception is benign. 
-      // Just press F5 to continue executing your code. 
-      for (int i = 0; i <= maxIterations; i++) {
-         // Do a bit of work. Not too much. 
-         var sw = new SpinWait();
-         for (int j = 0; j <= 100; j++)
-            sw.SpinOnce();
+        // NOTE!!! A "TaskCanceledException was unhandled
+        // by user code" error will be raised here if "Just My Code"
+        // is enabled on your computer. On Express editions JMC is
+        // enabled and cannot be disabled. The exception is benign.
+        // Just press F5 to continue executing your code.
+        for (int i = 0; i <= maxIterations; i++)
+        {
+            // Do a bit of work. Not too much.
+            var sw = new SpinWait();
+            for (int j = 0; j <= 100; j++)
+                sw.SpinOnce();
 
-         if (ct.IsCancellationRequested) {
-            Console.WriteLine("Task {0} cancelled", taskNum);
-            ct.ThrowIfCancellationRequested();
-         } 
-      } 
-   } 
-}  
+            if (ct.IsCancellationRequested)
+            {
+                Console.WriteLine("Task {0} cancelled", taskNum);
+                ct.ThrowIfCancellationRequested();
+            }
+        }
+    }
+}
 // The example displays output like the following:
 //       Press any key to begin tasks...
 //    To terminate the example, press 'c' to cancel and exit...
@@ -135,10 +133,7 @@ static void DoSomeWork(int taskNum, CancellationToken ct)
 //    Task 2 cancelled
 //    Task 7 cancelled
 //    
-//    AggregateException thrown with the following inner exceptions:
-//       TaskCanceledException: Task 2
-//       TaskCanceledException: Task 8
-//       TaskCanceledException: Task 7
+//    OperationCanceledException thrown
 //    
 //    Task 2 status is now Canceled
 //    Task 1 status is now RanToCompletion

snippets/csharp/VS_Snippets_Misc/tpl_cancellation/cs/snippet02.cs

@@ -2,16 +2,16 @@
 using System;
 using System.Threading;
 using System.Threading.Tasks;
+
 class Program
 {
-    static void Main()
+    static async Task Main()
     {
         var tokenSource2 = new CancellationTokenSource();
         CancellationToken ct = tokenSource2.Token;
 
-        var task = Task.Factory.StartNew(() =>
+        var task = Task.Run(() =>
         {
-
             // Were we already canceled?
             ct.ThrowIfCancellationRequested();
 
@@ -27,19 +27,18 @@ static void Main()
                 }
 
             }
-        }, tokenSource2.Token); // Pass same token to StartNew.
+        }, tokenSource2.Token); // Pass same token to Task.Run.
 
         tokenSource2.Cancel();
 
-        // Just continue on this thread, or Wait/WaitAll with try-catch:
+        // Just continue on this thread, or await with try-catch:
         try
         {
-            task.Wait();
+            await task;
         }
-        catch (AggregateException e)
+        catch (OperationCanceledException e)
         {
-            foreach (var v in e.InnerExceptions)
-                Console.WriteLine(e.Message + " " + v.Message);
+            Console.WriteLine($"{nameof(OperationCanceledException)} thrown with message: {e.Message}");
         }
         finally
         {