如何让UI线程等待信号量，但处理其他调度程序请求？ （就像MessageBox.Show本身一样）

通常，当UI线程调用MessageBox.Show()类的东西时，当前代码执行不会继续，直到用户单击OK，但程序将继续运行在UI线程上调度的其他代码。

在这个问题中 ，我遇到了一个问题，就是在一次调用UI线程上调度了太多的委托。 我想在继续执行之前暂停某些点。

在我的新error handling程序中，我使用信号量来确保一次只处理一个错误。 我发送一个MessageBox来提醒用户，当他们点击“确定”时，我释放信号量，允许处理下一个错误。

问题是它没有按预期运行。 如果同时发生两次对HandleError的调度调用，则第一次调用MessageBox.Show，第二次调用UI线程。 奇怪的是，对MessageBox.Show()的调度调用永远不会被执行 – 整个应用程序只是挂起 – 所以当用户单击“确定”时应该释放的信号量被永久锁定。 这个解决方案缺少什么？

 private static ConcurrentDictionary QueuedErrors = new ConcurrentDictionary(); private static Semaphore Lock_HandleError = new Semaphore(1, 1); //Only one Error can be processed at a time private static void ErrorHandled(Exception ex) { DateTime value; QueuedErrors.TryRemove(ex, out value); Lock_HandleError.Release(); } private static bool ExceptionHandlingTerminated = false; public static void HandleError(Exception ex, string extraInfo = "", bool showMsgBox = true, bool resetApplication = true) { if( ExceptionHandlingTerminated || App.Current == null) return; QueuedErrors.TryAdd(ex, DateTime.Now); //Thread safe tracking of how many simultaneous errors are being thrown Lock_HandleError.WaitOne(); //This will ensure only one error is processed at a time. if( ExceptionHandlingTerminated || App.Current == null ) { ErrorHandled(ex); return; } try { if( QueuedErrors.Count > 10 ) { ExceptionHandlingTerminated = true; throw new Exception("Too many simultaneous errors have been thrown in the background."); } if( Thread.CurrentThread != Dispatcher.CurrentDispatcher.Thread ) { //We're not on the UI thread, we must dispatch this call. ((App)App.Current).Dispatcher.BeginInvoke((Action) delegate(Exception _ex, string _extraInfo, bool _showMsgBox, bool _resetApplication) { ErrorHandled(_ex); //Release the semaphore taken by the spawning HandleError call HandleError(_ex, _extraInfo, _showMsgBox, _resetApplication); }, DispatcherPriority.Background, new object[] { ex, extraInfo, showMsgBox, resetApplication }); return; } if( showMsgBox ) { //IF the UI is processing a visual tree event (such as IsVisibleChanged), it throws an exception when showing a MessageBox as described here: http://social.msdn.microsoft.com/forums/en-US/wpf/thread/44962927-006e-4629-9aa3-100357861442 //The solution is to dispatch and queue the MessageBox. We must use BeginInvoke because dispatcher processing is suspended in such cases. Dispatcher.CurrentDispatcher.BeginInvoke((Action)delegate(Exception _ex, String _ErrMessage) { MessageBox.Show(_ErrMessage, "MUS Application Error", MessageBoxButton.OK, MessageBoxImage.Error); ErrorHandled(_ex); //Release the semaphore taken by the spawning HandleError call }, DispatcherPriority.Background, new object[]{ ex, extraInfo }); } else { ErrorHandled(ex); } } catch( Exception terminatingError ) { ExceptionHandlingTerminated = true; Dispatcher.CurrentDispatcher.BeginInvoke((Action)delegate(String _fatalMessage) { MessageBox.Show(_fatalMessage, "Fatal Error", MessageBoxButton.OK, MessageBoxImage.Stop); if( App.Current != null ) App.Current.Shutdown(1); }, DispatcherPriority.Background, new object[] { fatalMessage }); ErrorHandled(ex); //Release the semaphore taken by this HandleError call which will allow all other queued HandleError calls to continue and check the ExceptionHandlingTerminated flag. } } 

不要担心奇怪的丢失消息字符串，我剪掉了很多细节，使模式更清晰。

Answer 1

假设您要查找的行为是为了让每个消息框依次等待，直到前一个消息框被清除，您需要这样的模式：

1. 事件源将消息排入阻塞队列
2. 事件源在后台线程上调用委托以“处理队列”
3. “处理队列”委托获取锁定（如您所做），使消息出列，并调用（同步）UI线程以显示消息。 然后它循环，做同样的事情直到队列是emtpy。

所以这样的事情（未经测试的代码）：

 private static ConcurrentQueue> QueuedErrors = new ConcurrentQueue>(); private static Object Lock_HandleError = new Object(); public static void HandleError(Exception ex, string extraInfo = "", bool showMsgBox = true, bool resetApplication = true) { QueuedErrors.Enqueue(new Tuple(ex, DateTime.Now)); ThreadPool.QueueUserWorkItem(()=>((App)App.Current).Dispatcher.Invoke((Action) () => { lock (Lock_HandleError) Tuple currentEx; while (QueuedErrors.TryDequeue(out currentEx)) MessageBox.Show( currentEx.Item1, // The exception "MUS Application Error", MessageBoxButton.OK, MessageBoxImage.Error); })) ); 

Answer 2

我决定按照建议将它们存储在一个集合中。 我只是按顺序处理错误，然后从堆栈中弹出一个新的错误（如果有的话）。 如果堆栈上出现太多错误，那么我假设我们处于级联错误状态，并且我在一条消息中将错误聚合在一起并关闭应用程序。

 private static ConcurrentStack> ErrorStack = new ConcurrentStack>(); private static bool ExceptionHandlingTerminated = false; private static bool ErrorBeingHandled = false; //Only one Error can be processed at a time public static void HandleError(Exception ex, bool showMsgBox) { HandleError(ex, "", showMsgBox, true); } public static void HandleError(Exception ex, string extraInfo, bool showMsgBox) { HandleError(ex, extraInfo, showMsgBox, true); } public static void HandleError(Exception ex, string extraInfo = "", bool showMsgBox = true, bool resetApplication = true) { if( ExceptionHandlingTerminated || App.Current == null) return; if( ErrorBeingHandled ) { //Queue up this error, it'll be handled later. Don't bother if we've already queued up more than 10 errors, we're just going to be terminating the application in that case anyway. if( ErrorStack.Count < 10 ) ErrorStack.Push(new Tuple(DateTime.Now, ex, extraInfo, showMsgBox, resetApplication)); //Thread safe tracking of how many simultaneous errors are being thrown return; } ErrorBeingHandled = true; try { if( Thread.CurrentThread != Dispatcher.CurrentDispatcher.Thread ) { ErrorBeingHandled = false; Invoke_HandleError( ex, extraInfo, showMsgBox, resetApplication ); return; } if( ErrorStack.Count >= 5 ) { ExceptionHandlingTerminated = true; Tuple errParams; String errQueue = String.Concat(DateTime.Now.ToString("hh:mm:ss.ff tt"), ": ", ex.Message, "\n"); while( ErrorStack.Count > 0 ) { if( ErrorStack.TryPop(out errParams) ) { errQueue += String.Concat(errParams.Item1.ToString("hh:mm:ss.ff tt"), ": ", errParams.Item2.Message, "\n"); } } extraInfo = "Too many simultaneous errors have been thrown in the background:"; throw new Exception(errQueue); } if( !((App)App.Current).AppStartupComplete ) { //We can't handle errors the normal way if the app hasn't started yet. extraInfo = "An error occurred before the application could start." + extraInfo; throw ex; } if( resetApplication ) { ((MUSUI.App)App.Current).ResetApplication(); } if( showMsgBox ) { //(removed)... Prepare Error message //IF the UI is processing a visual tree event (such as IsVisibleChanged), it throws an exception when showing a MessageBox as described here: http://social.msdn.microsoft.com/forums/en-US/wpf/thread/44962927-006e-4629-9aa3-100357861442 //The solution is to dispatch and queue the MessageBox. We must use BeginInvoke because dispatcher processing is suspended in such cases. Dispatcher.CurrentDispatcher.BeginInvoke((Action)delegate(Exception _ex, String _ErrMessage) { MessageBox.Show(App.Current.MainWindow, _ErrMessage, "MUS Application Error", MessageBoxButton.OK, MessageBoxImage.Error); ErrorHandled(_ex); //Release the block on the HandleError method and handle any additional queued errors. }, DispatcherPriority.Background, new object[]{ ex, ErrMessage }); } else { ErrorHandled(ex); } } catch( Exception terminatingError ) { ExceptionHandlingTerminated = true; //A very serious error has occurred, such as the application not loading, and we must shut down. Dispatcher.CurrentDispatcher.BeginInvoke((Action)delegate(String _fatalMessage) { MessageBox.Show(_fatalMessage, "Fatal Error", MessageBoxButton.OK, MessageBoxImage.Stop); if( App.Current != null ) App.Current.Shutdown(1); }, DispatcherPriority.Background, new object[] { fatalMessage + "\n" + terminatingError.Message }); } } //The set of actions to be performed when error handling is done. private static void ErrorHandled(Exception ex) { ErrorBeingHandled = false; //If other errors have gotten queued up since this one was being handled, or remain, process the next one if(ErrorStack.Count > 0) { if( ExceptionHandlingTerminated || App.Current == null) return; Tuple errParams; //Pop an error off the queue and deal with it: ErrorStack.TryPop(out errParams); HandleError(errParams.Item2, errParams.Item3, errParams.Item4, errParams.Item5); } } //Dispatches a call to HandleError on the UI thread. private static void Invoke_HandleError(Exception ex, string extraInfo, bool showMsgBox, bool resetApplication) { ((App)App.Current).Dispatcher.BeginInvoke((Action) delegate(Exception _ex, string _extraInfo, bool _showMsgBox, bool _resetApplication) { ErrorHandled(_ex); //Release the semaphore taken by the spawning HandleError call HandleError(_ex, _extraInfo, _showMsgBox, _resetApplication); }, DispatcherPriority.Background, new object[] { ex, extraInfo, showMsgBox, resetApplication }); }