Fix CancellationTokenRegistration usage

The code was only disposing/unregistering cancellation token registrations if an exception happened, but not if everything completed successfully.  This leaks registrations into the cancellation token for as long as the token is alive.

The code was also allocating a new delegate for CancelIgnoreFailure on every registration.  This can be avoided by passing 'this' through as the object state to the registration, letting the compiler cache the delegate for the lambda.

Author: stephentoub

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

@@ -157,7 +157,7 @@ public virtual Task<int> ExecuteNonQueryAsync(CancellationToken cancellationToke
                 CancellationTokenRegistration registration = new CancellationTokenRegistration();
                 if (cancellationToken.CanBeCanceled)
                 {
-                    registration = cancellationToken.Register(CancelIgnoreFailure);
+                    registration = cancellationToken.Register(s => ((DbCommand)s).CancelIgnoreFailure(), this);
                 }
 
                 try
@@ -166,9 +166,12 @@ public virtual Task<int> ExecuteNonQueryAsync(CancellationToken cancellationToke
                 }
                 catch (Exception e)
                 {
-                    registration.Dispose();
                     return Task.FromException<int>(e);
                 }
+                finally
+                {
+                    registration.Dispose();
+                }
             }
         }
 
@@ -203,7 +206,7 @@ protected virtual Task<DbDataReader> ExecuteDbDataReaderAsync(CommandBehavior be
                 CancellationTokenRegistration registration = new CancellationTokenRegistration();
                 if (cancellationToken.CanBeCanceled)
                 {
-                    registration = cancellationToken.Register(CancelIgnoreFailure);
+                    registration = cancellationToken.Register(s => ((DbCommand)s).CancelIgnoreFailure(), this);
                 }
 
                 try
@@ -212,9 +215,12 @@ protected virtual Task<DbDataReader> ExecuteDbDataReaderAsync(CommandBehavior be
                 }
                 catch (Exception e)
                 {
-                    registration.Dispose();
                     return Task.FromException<DbDataReader>(e);
                 }
+                finally
+                {
+                    registration.Dispose();
+                }
             }
         }
 
@@ -234,7 +240,7 @@ public virtual Task<object> ExecuteScalarAsync(CancellationToken cancellationTok
                 CancellationTokenRegistration registration = new CancellationTokenRegistration();
                 if (cancellationToken.CanBeCanceled)
                 {
-                    registration = cancellationToken.Register(CancelIgnoreFailure);
+                    registration = cancellationToken.Register(s => ((DbCommand)s).CancelIgnoreFailure(), this);
                 }
 
                 try
@@ -243,9 +249,12 @@ public virtual Task<object> ExecuteScalarAsync(CancellationToken cancellationTok
                 }
                 catch (Exception e)
                 {
-                    registration.Dispose();
                     return Task.FromException<object>(e);
                 }
+                finally
+                {
+                    registration.Dispose();
+                }
             }
         }