Implement CloseAsync. Fixes #467

src/MySqlConnector/MySql.Data.MySqlClient/MySqlConnection.cs

@@ -100,7 +100,7 @@ public override void EnlistTransaction(System.Transactions.Transaction transacti
 				if (existingConnection != null)
 				{
 					// can reuse the existing connection
-					DoClose(changeState: false);
+					CloseAsync(changeState: false, IOBehavior.Synchronous, CancellationToken.None).GetAwaiter().GetResult();
 					TakeSessionFrom(existingConnection);
 					return;
 				}
@@ -225,7 +225,8 @@ private void TakeSessionFrom(MySqlConnection other)
 		EnlistedTransactionBase m_enlistedTransaction;
 #endif
 
-		public override void Close() => DoClose(changeState: true);
+		public override void Close() => CloseAsync(changeState: true, IOBehavior.Synchronous, CancellationToken.None).GetAwaiter().GetResult();
+		public Task CloseAsync(CancellationToken cancellationToken = default) => CloseAsync(changeState: true, IOBehavior.Asynchronous, cancellationToken);
 
 		public override void ChangeDatabase(string databaseName) => ChangeDatabaseAsync(IOBehavior.Synchronous, databaseName, CancellationToken.None).GetAwaiter().GetResult();
 		public Task ChangeDatabaseAsync(string databaseName) => ChangeDatabaseAsync(IOBehavior.Asynchronous, databaseName, CancellationToken.None);
@@ -411,7 +412,7 @@ protected override void Dispose(bool disposing)
 			try
 			{
 				if (disposing)
-					DoClose(changeState: true);
+					CloseAsync(changeState: true, IOBehavior.Synchronous, CancellationToken.None).GetAwaiter().GetResult();
 			}
 			finally
 			{
@@ -645,12 +646,40 @@ private void VerifyNotDisposed()
 				throw new ObjectDisposedException(GetType().Name);
 		}
 
-		private void DoClose(bool changeState)
+		private Task CloseAsync(bool changeState, IOBehavior ioBehavior, CancellationToken cancellationToken)
+		{
+			if (m_connectionState == ConnectionState.Closed)
+				return Utility.CompletedTask;
+
+			// check fast path
+			if (m_activeReader is null &&
+				CurrentTransaction is null &&
+#if !NETSTANDARD1_3
+				m_enlistedTransaction is null &&
+#endif
+				m_connectionSettings.Pooling)
+			{
+				m_cachedProcedures = null;
+				if (m_session is object)
+				{
+					m_session.ReturnToPool();
+					m_session = null;
+				}
+				if (changeState)
+					SetState(ConnectionState.Closed);
+
+				return Utility.CompletedTask;
+			}
+
+			return DoCloseAsync(changeState, ioBehavior, cancellationToken);
+		}
+
+		private async Task DoCloseAsync(bool changeState, IOBehavior ioBehavior, CancellationToken cancellationToken)
 		{
 #if !NETSTANDARD1_3
 			// If participating in a distributed transaction, keep the connection open so we can commit or rollback.
 			// This handles the common pattern of disposing a connection before disposing a TransactionScope (e.g., nested using blocks)
-			if (!(m_enlistedTransaction is null))
+			if (m_enlistedTransaction is object)
 			{
 				// make sure all DB work is done
 				m_activeReader?.Dispose();
@@ -701,7 +730,7 @@ private void DoClose(bool changeState)
 						if (m_connectionSettings.Pooling)
 							m_session.ReturnToPool();
 						else
-							m_session.DisposeAsync(IOBehavior.Synchronous, CancellationToken.None).GetAwaiter().GetResult();
+							await m_session.DisposeAsync(ioBehavior, cancellationToken).ConfigureAwait(false);
 						m_session = null;
 					}
 

tests/MySqlConnector.Tests/ConnectionTests.cs

@@ -46,6 +46,25 @@ public void PooledConnectionIsReturnedToPool()
 			Assert.Equal(1, m_server.ActiveConnections);
 		}
 
+		[Fact]
+		public async Task PooledConnectionIsReturnedToPoolAsync()
+		{
+			Assert.Equal(0, m_server.ActiveConnections);
+
+			m_csb.Pooling = true;
+			using (var connection = new MySqlConnection(m_csb.ConnectionString))
+			{
+				await connection.OpenAsync();
+				Assert.Equal(1, m_server.ActiveConnections);
+
+				Assert.Equal(m_server.ServerVersion, connection.ServerVersion);
+				await connection.CloseAsync();
+				Assert.Equal(1, m_server.ActiveConnections);
+			}
+
+			Assert.Equal(1, m_server.ActiveConnections);
+		}
+
 		[Fact]
 		public async Task UnpooledConnectionIsClosed()
 		{

tests/SideBySide/ConnectAsync.cs

@@ -79,6 +79,8 @@ public async Task State()
 				Assert.Equal(ConnectionState.Closed, connection.State);
 				await connection.OpenAsync();
 				Assert.Equal(ConnectionState.Open, connection.State);
+				await connection.CloseAsync();
+				Assert.Equal(ConnectionState.Closed, connection.State);
 			}
 		}