Update code with Task.FromCanceled/FromException/CompletedTask

The codebase was using TaskCompletionSource to create already canceled/faulted tasks.  With Task.FromCanceled/FromException, this is no longer necessary.  It was also using TaskCompletionSource to create an already completed task; with FromResult that wasn't necessary previously anyway, but we can improve upon it regardless with CompletedTask.

Author: stephentoub

src/System.Data.Common/src/System/Data/Common/AdapterUtil.cs

@@ -16,21 +16,6 @@ internal static class ADP
         // location so that the catcher of the exception will have the appropriate call stack.
         // This class is used so that there will be compile time checking of error messages.
 
-        static internal Task<T> CreatedTaskWithException<T>(Exception ex)
-        {
-            TaskCompletionSource<T> completion = new TaskCompletionSource<T>();
-            completion.SetException(ex);
-            return completion.Task;
-        }
-
-        static internal Task<T> CreatedTaskWithCancellation<T>()
-        {
-            TaskCompletionSource<T> completion = new TaskCompletionSource<T>();
-            completion.SetCanceled();
-            return completion.Task;
-        }
-
-
         // NOTE: Initializing a Task in SQL CLR requires the "UNSAFE" permission set (http://msdn.microsoft.com/en-us/library/ms172338.aspx)
         // Therefore we are lazily initializing these Tasks to avoid forcing customers to use the "UNSAFE" set when they are actually using no Async features
         static private Task<bool> s_trueTask = null;

src/System.Data.Common/src/System/Data/Common/DbCommand.cs

@@ -150,7 +150,7 @@ public virtual Task<int> ExecuteNonQueryAsync(CancellationToken cancellationToke
         {
             if (cancellationToken.IsCancellationRequested)
             {
-                return ADP.CreatedTaskWithCancellation<int>();
+                return Task.FromCanceled<int>(cancellationToken);
             }
             else
             {
@@ -167,7 +167,7 @@ public virtual Task<int> ExecuteNonQueryAsync(CancellationToken cancellationToke
                 catch (Exception e)
                 {
                     registration.Dispose();
-                    return ADP.CreatedTaskWithException<int>(e);
+                    return Task.FromException<int>(e);
                 }
             }
         }
@@ -196,7 +196,7 @@ protected virtual Task<DbDataReader> ExecuteDbDataReaderAsync(CommandBehavior be
         {
             if (cancellationToken.IsCancellationRequested)
             {
-                return ADP.CreatedTaskWithCancellation<DbDataReader>();
+                return Task.FromCanceled<DbDataReader>(cancellationToken);
             }
             else
             {
@@ -213,7 +213,7 @@ protected virtual Task<DbDataReader> ExecuteDbDataReaderAsync(CommandBehavior be
                 catch (Exception e)
                 {
                     registration.Dispose();
-                    return ADP.CreatedTaskWithException<DbDataReader>(e);
+                    return Task.FromException<DbDataReader>(e);
                 }
             }
         }
@@ -227,7 +227,7 @@ public virtual Task<object> ExecuteScalarAsync(CancellationToken cancellationTok
         {
             if (cancellationToken.IsCancellationRequested)
             {
-                return ADP.CreatedTaskWithCancellation<object>();
+                return Task.FromCanceled<object>(cancellationToken);
             }
             else
             {
@@ -244,7 +244,7 @@ public virtual Task<object> ExecuteScalarAsync(CancellationToken cancellationTok
                 catch (Exception e)
                 {
                     registration.Dispose();
-                    return ADP.CreatedTaskWithException<object>(e);
+                    return Task.FromException<object>(e);
                 }
             }
         }

src/System.Data.Common/src/System/Data/Common/DbConnection.cs

@@ -115,26 +115,22 @@ public Task OpenAsync()
 
         public virtual Task OpenAsync(CancellationToken cancellationToken)
         {
-            TaskCompletionSource<object> taskCompletionSource = new TaskCompletionSource<object>();
-
             if (cancellationToken.IsCancellationRequested)
             {
-                taskCompletionSource.SetCanceled();
+                return Task.FromCanceled(cancellationToken);
             }
             else
             {
                 try
                 {
                     Open();
-                    taskCompletionSource.SetResult(null);
+                    return Task.CompletedTask;
                 }
                 catch (Exception e)
                 {
-                    taskCompletionSource.SetException(e);
+                    return Task.FromException(e);
                 }
             }
-
-            return taskCompletionSource.Task;
         }
 
         public void Dispose()

src/System.Data.Common/src/System/Data/Common/DbDataReader.cs

@@ -188,7 +188,7 @@ virtual public Task<T> GetFieldValueAsync<T>(int ordinal, CancellationToken canc
         {
             if (cancellationToken.IsCancellationRequested)
             {
-                return ADP.CreatedTaskWithCancellation<T>();
+                return Task.FromCanceled<T>(cancellationToken);
             }
             else
             {
@@ -198,7 +198,7 @@ virtual public Task<T> GetFieldValueAsync<T>(int ordinal, CancellationToken canc
                 }
                 catch (Exception e)
                 {
-                    return ADP.CreatedTaskWithException<T>(e);
+                    return Task.FromException<T>(e);
                 }
             }
         }
@@ -216,7 +216,7 @@ virtual public Task<bool> IsDBNullAsync(int ordinal, CancellationToken cancellat
         {
             if (cancellationToken.IsCancellationRequested)
             {
-                return ADP.CreatedTaskWithCancellation<bool>();
+                return Task.FromCanceled<bool>(cancellationToken);
             }
             else
             {
@@ -226,7 +226,7 @@ virtual public Task<bool> IsDBNullAsync(int ordinal, CancellationToken cancellat
                 }
                 catch (Exception e)
                 {
-                    return ADP.CreatedTaskWithException<bool>(e);
+                    return Task.FromException<bool>(e);
                 }
             }
         }
@@ -244,7 +244,7 @@ virtual public Task<bool> ReadAsync(CancellationToken cancellationToken)
         {
             if (cancellationToken.IsCancellationRequested)
             {
-                return ADP.CreatedTaskWithCancellation<bool>();
+                return Task.FromCanceled<bool>(cancellationToken);
             }
             else
             {
@@ -254,7 +254,7 @@ virtual public Task<bool> ReadAsync(CancellationToken cancellationToken)
                 }
                 catch (Exception e)
                 {
-                    return ADP.CreatedTaskWithException<bool>(e);
+                    return Task.FromException<bool>(e);
                 }
             }
         }
@@ -268,7 +268,7 @@ virtual public Task<bool> NextResultAsync(CancellationToken cancellationToken)
         {
             if (cancellationToken.IsCancellationRequested)
             {
-                return ADP.CreatedTaskWithCancellation<bool>();
+                return Task.FromCanceled<bool>(cancellationToken);
             }
             else
             {
@@ -278,7 +278,7 @@ virtual public Task<bool> NextResultAsync(CancellationToken cancellationToken)
                 }
                 catch (Exception e)
                 {
-                    return ADP.CreatedTaskWithException<bool>(e);
+                    return Task.FromException<bool>(e);
                 }
             }
         }