当 SQL 服务器关闭时，SqlConnection OpenAsync 阻塞 UI

Question

我有一个简单的 WPF 客户端应用程序 (.NET 4.6.2)，只需一个按钮。 SqlConnection.OpenAsync 方法在完成以下步骤后阻塞 UI 线程：

SQL 服务器已启动并可从客户端访问
启动客户端应用程序
单击按钮 => UI 未被阻止（如预期的那样）=> 消息框显示 'ok'
关闭SQL服务器
单击按钮 => UI 被阻止 - OpenAsync 块 UI => 消息框 'show' 错误
再次点击按钮=>UI不再被屏蔽=>消息框显示'error'

只有从点击->成功到点击->错误 OpenAsync 阻塞 UI 线程。我错过了什么？

private async void Button_Click(object sender, RoutedEventArgs e)
{
    try
    {
        using (var conn = new SqlConnection("...."))
        {
            await conn.OpenAsync();
        }
    }
    catch (System.Exception)
    {
        MessageBox.Show("err");
        return;
    }
    MessageBox.Show("ok");
}

编辑：

在挂起期间暂停调试器时调用堆栈：

System.Data.dll!SNINativeMethodWrapper.SNIOpenSyncEx(SNINativeMethodWrapper.ConsumerInfo consumerInfo, string constring, ref System.IntPtr pConn, byte[] spnBuffer, byte[] instanceName, bool fOverrideCache, bool fSync, int timeout, bool fParallel, int transparentNetworkResolutionStateNo, int totalTimeout, bool isAzureSqlServerEndpoint)    Unknown
    System.Data.dll!System.Data.SqlClient.SNIHandle.SNIHandle(SNINativeMethodWrapper.ConsumerInfo myInfo, string serverName, byte[] spnBuffer, bool ignoreSniOpenTimeout, int timeout, out byte[] instanceName, bool flushCache, bool fSync, bool fParallel, System.Data.SqlClient.TransparentNetworkResolutionState transparentNetworkResolutionState, int totalTimeout)   Unknown
    System.Data.dll!System.Data.SqlClient.TdsParserStateObject.CreatePhysicalSNIHandle(string serverName, bool ignoreSniOpenTimeout, long timerExpire, out byte[] instanceName, byte[] spnBuffer, bool flushCache, bool async, bool fParallel, System.Data.SqlClient.TransparentNetworkResolutionState transparentNetworkResolutionState, int totalTimeout) Unknown
    System.Data.dll!System.Data.SqlClient.TdsParser.Connect(System.Data.SqlClient.ServerInfo serverInfo, System.Data.SqlClient.SqlInternalConnectionTds connHandler, bool ignoreSniOpenTimeout, long timerExpire, bool encrypt, bool trustServerCert, bool integratedSecurity, bool withFailover, bool isFirstTransparentAttempt, System.Data.SqlClient.SqlAuthenticationMethod authType, bool disableTnir, System.Data.SqlClient.SqlAuthenticationProviderManager sqlAuthProviderManager)  Unknown
    System.Data.dll!System.Data.SqlClient.SqlInternalConnectionTds.AttemptOneLogin(System.Data.SqlClient.ServerInfo serverInfo, string newPassword, System.Security.SecureString newSecurePassword, bool ignoreSniOpenTimeout, System.Data.ProviderBase.TimeoutTimer timeout, bool withFailover, bool isFirstTransparentAttempt, bool disableTnir)  Unknown
    System.Data.dll!System.Data.SqlClient.SqlInternalConnectionTds.LoginNoFailover(System.Data.SqlClient.ServerInfo serverInfo, string newPassword, System.Security.SecureString newSecurePassword, bool redirectedUserInstance, System.Data.SqlClient.SqlConnectionString connectionOptions, System.Data.SqlClient.SqlCredential credential, System.Data.ProviderBase.TimeoutTimer timeout)    Unknown
    System.Data.dll!System.Data.SqlClient.SqlInternalConnectionTds.OpenLoginEnlist(System.Data.ProviderBase.TimeoutTimer timeout, System.Data.SqlClient.SqlConnectionString connectionOptions, System.Data.SqlClient.SqlCredential credential, string newPassword, System.Security.SecureString newSecurePassword, bool redirectedUserInstance) Unknown
    System.Data.dll!System.Data.SqlClient.SqlInternalConnectionTds.SqlInternalConnectionTds(System.Data.ProviderBase.DbConnectionPoolIdentity identity, System.Data.SqlClient.SqlConnectionString connectionOptions, System.Data.SqlClient.SqlCredential credential, object providerInfo, string newPassword, System.Security.SecureString newSecurePassword, bool redirectedUserInstance, System.Data.SqlClient.SqlConnectionString userConnectionOptions, System.Data.SqlClient.SessionData reconnectSessionData, System.Data.ProviderBase.DbConnectionPool pool, string accessToken, bool applyTransientFaultHandling, System.Data.SqlClient.SqlAuthenticationProviderManager sqlAuthProviderManager)    Unknown
    System.Data.dll!System.Data.SqlClient.SqlConnectionFactory.CreateConnection(System.Data.Common.DbConnectionOptions options, System.Data.Common.DbConnectionPoolKey poolKey, object poolGroupProviderInfo, System.Data.ProviderBase.DbConnectionPool pool, System.Data.Common.DbConnection owningConnection, System.Data.Common.DbConnectionOptions userOptions) Unknown
    System.Data.dll!System.Data.ProviderBase.DbConnectionFactory.CreatePooledConnection(System.Data.ProviderBase.DbConnectionPool pool, System.Data.Common.DbConnection owningObject, System.Data.Common.DbConnectionOptions options, System.Data.Common.DbConnectionPoolKey poolKey, System.Data.Common.DbConnectionOptions userOptions)   Unknown
    System.Data.dll!System.Data.ProviderBase.DbConnectionPool.CreateObject(System.Data.Common.DbConnection owningObject, System.Data.Common.DbConnectionOptions userOptions, System.Data.ProviderBase.DbConnectionInternal oldConnection)   Unknown
    System.Data.dll!System.Data.ProviderBase.DbConnectionPool.UserCreateRequest(System.Data.Common.DbConnection owningObject, System.Data.Common.DbConnectionOptions userOptions, System.Data.ProviderBase.DbConnectionInternal oldConnection)  Unknown
    System.Data.dll!System.Data.ProviderBase.DbConnectionPool.TryGetConnection(System.Data.Common.DbConnection owningObject, uint waitForMultipleObjectsTimeout, bool allowCreate, bool onlyOneCheckConnection, System.Data.Common.DbConnectionOptions userOptions, out System.Data.ProviderBase.DbConnectionInternal connection)   Unknown
    System.Data.dll!System.Data.ProviderBase.DbConnectionPool.TryGetConnection(System.Data.Common.DbConnection owningObject, System.Threading.Tasks.TaskCompletionSource<System.Data.ProviderBase.DbConnectionInternal> retry, System.Data.Common.DbConnectionOptions userOptions, out System.Data.ProviderBase.DbConnectionInternal connection)    Unknown
    System.Data.dll!System.Data.ProviderBase.DbConnectionFactory.TryGetConnection(System.Data.Common.DbConnection owningConnection, System.Threading.Tasks.TaskCompletionSource<System.Data.ProviderBase.DbConnectionInternal> retry, System.Data.Common.DbConnectionOptions userOptions, System.Data.ProviderBase.DbConnectionInternal oldConnection, out System.Data.ProviderBase.DbConnectionInternal connection)    Unknown
    System.Data.dll!System.Data.ProviderBase.DbConnectionInternal.TryOpenConnectionInternal(System.Data.Common.DbConnection outerConnection, System.Data.ProviderBase.DbConnectionFactory connectionFactory, System.Threading.Tasks.TaskCompletionSource<System.Data.ProviderBase.DbConnectionInternal> retry, System.Data.Common.DbConnectionOptions userOptions)  Unknown
    System.Data.dll!System.Data.ProviderBase.DbConnectionClosed.TryOpenConnection(System.Data.Common.DbConnection outerConnection, System.Data.ProviderBase.DbConnectionFactory connectionFactory, System.Threading.Tasks.TaskCompletionSource<System.Data.ProviderBase.DbConnectionInternal> retry, System.Data.Common.DbConnectionOptions userOptions)    Unknown
    System.Data.dll!System.Data.SqlClient.SqlConnection.TryOpenInner(System.Threading.Tasks.TaskCompletionSource<System.Data.ProviderBase.DbConnectionInternal> retry)  Unknown
    System.Data.dll!System.Data.SqlClient.SqlConnection.TryOpen(System.Threading.Tasks.TaskCompletionSource<System.Data.ProviderBase.DbConnectionInternal> retry)   Unknown
    System.Data.dll!System.Data.SqlClient.SqlConnection.OpenAsync(System.Threading.CancellationToken cancellationToken) Unknown
    System.Data.dll!System.Data.Common.DbConnection.OpenAsync() Unknown
>   TestWpf.exe!TestWpf.UndoManagerTest.UndoManagerTestView.Button_Click(object sender, System.Windows.RoutedEventArgs e) Line 35   C#
    PresentationCore.dll!System.Windows.RoutedEventHandlerInfo.InvokeHandler(object target, System.Windows.RoutedEventArgs routedEventArgs) Unknown
    PresentationCore.dll!System.Windows.EventRoute.InvokeHandlersImpl(object source, System.Windows.RoutedEventArgs args, bool reRaised)    Unknown
    PresentationCore.dll!System.Windows.UIElement.RaiseEventImpl(System.Windows.DependencyObject sender, System.Windows.RoutedEventArgs args)   Unknown
    PresentationCore.dll!System.Windows.UIElement.RaiseEvent(System.Windows.RoutedEventArgs e)  Unknown
    PresentationFramework.dll!System.Windows.Controls.Primitives.ButtonBase.OnClick()   Unknown
    PresentationFramework.dll!System.Windows.Controls.Button.OnClick()  Unknown
    PresentationFramework.dll!System.Windows.Controls.Primitives.ButtonBase.OnMouseLeftButtonUp(System.Windows.Input.MouseButtonEventArgs e)    Unknown
    PresentationCore.dll!System.Windows.UIElement.OnMouseLeftButtonUpThunk(object sender, System.Windows.Input.MouseButtonEventArgs e)  Unknown
    PresentationCore.dll!System.Windows.Input.MouseButtonEventArgs.InvokeEventHandler(System.Delegate genericHandler, object genericTarget) Unknown
    PresentationCore.dll!System.Windows.RoutedEventArgs.InvokeHandler(System.Delegate handler, object target)   Unknown
    PresentationCore.dll!System.Windows.RoutedEventHandlerInfo.InvokeHandler(object target, System.Windows.RoutedEventArgs routedEventArgs) Unknown
    PresentationCore.dll!System.Windows.EventRoute.InvokeHandlersImpl(object source, System.Windows.RoutedEventArgs args, bool reRaised)    Unknown
    PresentationCore.dll!System.Windows.UIElement.ReRaiseEventAs(System.Windows.DependencyObject sender, System.Windows.RoutedEventArgs args, System.Windows.RoutedEvent newEvent)  Unknown
    PresentationCore.dll!System.Windows.UIElement.OnMouseUpThunk(object sender, System.Windows.Input.MouseButtonEventArgs e)    Unknown
    PresentationCore.dll!System.Windows.Input.MouseButtonEventArgs.InvokeEventHandler(System.Delegate genericHandler, object genericTarget) Unknown
    PresentationCore.dll!System.Windows.RoutedEventArgs.InvokeHandler(System.Delegate handler, object target)   Unknown
    PresentationCore.dll!System.Windows.RoutedEventHandlerInfo.InvokeHandler(object target, System.Windows.RoutedEventArgs routedEventArgs) Unknown
    PresentationCore.dll!System.Windows.EventRoute.InvokeHandlersImpl(object source, System.Windows.RoutedEventArgs args, bool reRaised)    Unknown
    PresentationCore.dll!System.Windows.UIElement.RaiseEventImpl(System.Windows.DependencyObject sender, System.Windows.RoutedEventArgs args)   Unknown
    PresentationCore.dll!System.Windows.UIElement.RaiseTrustedEvent(System.Windows.RoutedEventArgs args)    Unknown
    PresentationCore.dll!System.Windows.UIElement.RaiseEvent(System.Windows.RoutedEventArgs args, bool trusted) Unknown
    PresentationCore.dll!System.Windows.Input.InputManager.ProcessStagingArea() Unknown
    PresentationCore.dll!System.Windows.Input.InputManager.ProcessInput(System.Windows.Input.InputEventArgs input)  Unknown
    PresentationCore.dll!System.Windows.Input.InputProviderSite.ReportInput(System.Windows.Input.InputReport inputReport)   Unknown
    PresentationCore.dll!System.Windows.Interop.HwndMouseInputProvider.ReportInput(System.IntPtr hwnd, System.Windows.Input.InputMode mode, int timestamp, System.Windows.Input.RawMouseActions actions, int x, int y, int wheel)   Unknown
    PresentationCore.dll!System.Windows.Interop.HwndMouseInputProvider.FilterMessage(System.IntPtr hwnd, MS.Internal.Interop.WindowMessage msg, System.IntPtr wParam, System.IntPtr lParam, ref bool handled)   Unknown
    PresentationCore.dll!System.Windows.Interop.HwndSource.InputFilterMessage(System.IntPtr hwnd, int msg, System.IntPtr wParam, System.IntPtr lParam, ref bool handled)    Unknown
    WindowsBase.dll!MS.Win32.HwndWrapper.WndProc(System.IntPtr hwnd, int msg, System.IntPtr wParam, System.IntPtr lParam, ref bool handled) Unknown
    WindowsBase.dll!MS.Win32.HwndSubclass.DispatcherCallbackOperation(object o) Unknown
    WindowsBase.dll!System.Windows.Threading.ExceptionWrapper.InternalRealCall(System.Delegate callback, object args, int numArgs)  Unknown
    WindowsBase.dll!System.Windows.Threading.ExceptionWrapper.TryCatchWhen(object source, System.Delegate callback, object args, int numArgs, System.Delegate catchHandler) Unknown
    WindowsBase.dll!System.Windows.Threading.Dispatcher.LegacyInvokeImpl(System.Windows.Threading.DispatcherPriority priority, System.TimeSpan timeout, System.Delegate method, object args, int numArgs)   Unknown
    WindowsBase.dll!MS.Win32.HwndSubclass.SubclassWndProc(System.IntPtr hwnd, int msg, System.IntPtr wParam, System.IntPtr lParam)  Unknown
    [Native to Managed Transition]  
    [Managed to Native Transition]  
    WindowsBase.dll!System.Windows.Threading.Dispatcher.PushFrameImpl(System.Windows.Threading.DispatcherFrame frame)   Unknown
    WindowsBase.dll!System.Windows.Threading.Dispatcher.PushFrame(System.Windows.Threading.DispatcherFrame frame)   Unknown
    PresentationFramework.dll!System.Windows.Application.RunDispatcher(object ignore)   Unknown
    PresentationFramework.dll!System.Windows.Application.RunInternal(System.Windows.Window window)  Unknown
    PresentationFramework.dll!System.Windows.Application.Run(System.Windows.Window window)  Unknown
    PresentationFramework.dll!System.Windows.Application.Run()  Unknown
    TestWpf.exe!TestWpf.App.Main() Line 53  C#

Answer 1

短版：

连接代码似乎在 OpenAsync 的同步部分。

在这种情况下，似乎只有一个选项——将 OpenAsync 视为基本同步方法并使用 Task.Run 执行它，以便在线程池线程上发生延迟

Task.Run(async () => ... await connection.OpenAsync() ...);

TLDR:

问题很可能源于 OpenAsync - https://github.com/microsoft/referencesource/blob/master/System.Data/System/Data/SqlClient/SqlConnection.cs#L1383

的当前实施

乍一看无法确定，但到目前为止，OpenAsync 及其调用的其他方法中似乎太少了。

这意味着搜索数据库主机并重试连接到已关闭服务的代码可能只是在当前 (GUI) 线程上执行，实际上并没有像人们期望的那样 "async voidness"。

而当您第二次调用它时，缓存的工作方式几乎 returns 瞬间。

因此，我建议您尝试在事件处理程序中添加 ConfigureAwait(false)。

using (var conn = new SqlConnection("...."))   
{
    await conn.OpenAsync().ConfigureAwait(false);
}

As ConfigureAwait ，那么大概意思是原来的连接代码在OpenAsync[=的同步部分52=].

在这种情况下，似乎只有一个选项 - 将 OpenAsync 视为基本同步方法并使用 Task.Run 执行它，以便在线程池线程上发生延迟：

private async void Button_Click(object sender, RoutedEventArgs e) { await Task.Run(async () => { try { using (var conn = new SqlConnection("....")) { await conn.OpenAsync(); } } catch (System.Exception) { MessageBox.Show("err"); return; } MessageBox.Show("ok"); } ); }

Answer 2

堆栈跟踪表明 ADO.NET 正在执行同步 IO，尽管您已请求异步 IO。这是 ADO.NET 中的一个错误，它可能发生在一些相当不常见的代码路径中，因此没有被注意到。

ADO.NET 最近进行了增量升级，以更好地支持异步 IO。在 .NET 的早期，异步数据库访问并不常见。

您可以尝试升级到更新的 .NET 版本。

在 GitHub 的 corefx 存储库中报告此错误。

您可以通过运行非 UI 线程上的阻塞操作来解决此问题：

await Task.Run(async () => await conn.OpenAsync());

当 SQL 服务器关闭时，SqlConnection OpenAsync 阻塞 UI

SqlConnection OpenAsync blocks UI when SQL Server is shutdown

c#

sqlconnection