BeginInvoke 和类数组

Question

我有一个如图所示的类设置 - 我知道长时间运行的任务会更好，但这是非常精简的原始状态。我已经删除了任何似乎对问题没有必要的内容。

TLDR：

1. 代码循环运行，列出的条件（1/2/3）可以独立执行
2. 日志显示condition3 仅在currentParentRun.ChildRuns.Count > 0 时才会执行
3. 错误被抛出并被捕获，表明（连同其他日志）在 BeginInvoke 的调用函数中，计数 >0 的 currentParentRun.ChildRuns[currentParentRun.ChildRuns.Count - 1] 以某种方式超出了范围。

    // Class created and owned by UI
    public class DataProcessor
    {
        private BackgroundWorker worker = new BackgroundWorker();

        private ParentRun currentParentRun = null;

        public DataProcessor()
        {
            // register background worker events
            worker.WorkerSupportsCancellation = false;
            worker.WorkerReportsProgress = false;
            worker.DoWork += worker_DoWork;
            worker.RunWorkerCompleted += worker_RunWorkerCompleted;

            worker.RunWorkerAsync();
        }

        private void worker_DoWork(object sender, DoWorkEventArgs e)
        {
            while (process)
            {
                try
                {
                    // Create a new parent
                    if (condition1)
                    {
                        currentParentRun = new ParentRun();
                    }

                    // Create a new child (parent will always be not null here)
                    if (condition2)
                    {
                        ChildRun childRun = new ChildRun();

                        currentParentRun.ChildRuns.Add(childRun);
                    }
                    
                    // Call the UI and update
                    if (condition3)
                    {
                        ShowFinishedChildUI();
                    }
                    
                    System.Threading.Thread.Sleep(loopDelayProcessor);
                }
                catch (Exception ex)
                {
                }
            }
        }
        
        public void ShowFinishedChildUI()
        {
            System.Windows.Application.Current.Dispatcher.BeginInvoke((Action)(() => ShowFinishedChildUIDelegate()));
        }

        public void ShowFinishedChildUIDelegate()
        {
            // Parent is the UI being updated
            parent.ShowFinishedChild(currentParentRun.ParentRunID, 
                currentParentRun.ChildRuns[currentParentRun.ChildRuns.Count - 1].ChildRunID);

            resetParentDisplay = false;
        }
    }

这里，“父”是拥有的 UI 控件，我们使用 BeginInvoke 发送调用 UI 函数来更新。

每 20-30k 个新的“父”创建偶尔会发生什么，而在处理过程中，Index was out of range. Must be non-negative and less than the size of the collection. 的 ShowFinishedChildUIDelegate 函数出现错误据我所知，它是 总是至少非零，这让我认为在同一行代码之间的某个地方，孩子的数量在之间变化

currentParentRun.ChildRuns[...]

和

currentParentRun.ChildRuns.Count - 1

是否有可能如果在委托处理时主代码块中的condition2 得到满足，那么同一行代码可以有不同的值，其中子代的数量大于类的数量列表？这是我的最佳猜测，但我不确定如何验证。

谢谢。

更详细的错误：

2021-03-19 12:00:12.8174|ERROR|GeneralLogger|UnhandledException StackTrace :    at System.ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument argument, ExceptionResource resource)
   at System.Collections.Generic.List`1.get_Item(Int32 index)
   at QASystem.Classes.DataProcessor.ShowFinishedChildUIDelegate() in D:\..\QASystem\QASystem\Classes\DataProcessor.cs:line 756
   at QASystem.Classes.DataProcessor.<ShowFinishedChildUI>b__76_0() in D:\..\QASystem\QASystem\Classes\DataProcessor.cs:line 751
   at System.Windows.Threading.ExceptionWrapper.InternalRealCall(Delegate callback, Object args, Int32 numArgs)
   at System.Windows.Threading.ExceptionWrapper.TryCatchWhen(Object source, Delegate callback, Object args, Int32 numArgs, Delegate catchHandler)
   at System.Windows.Threading.DispatcherOperation.InvokeImpl()
   at System.Windows.Threading.DispatcherOperation.InvokeInSecurityContext(Object state)
   at MS.Internal.CulturePreservingExecutionContext.CallbackWrapper(Object obj)
   at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
   at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
   at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
   at MS.Internal.CulturePreservingExecutionContext.Run(CulturePreservingExecutionContext executionContext, ContextCallback callback, Object state)
   at System.Windows.Threading.DispatcherOperation.Invoke()
   at System.Windows.Threading.Dispatcher.ProcessQueue()
   at System.Windows.Threading.Dispatcher.WndProcHook(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam, Boolean& handled)
   at MS.Win32.HwndWrapper.WndProc(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam, Boolean& handled)
   at MS.Win32.HwndSubclass.DispatcherCallbackOperation(Object o)
   at System.Windows.Threading.ExceptionWrapper.InternalRealCall(Delegate callback, Object args, Int32 numArgs)
   at System.Windows.Threading.ExceptionWrapper.TryCatchWhen(Object source, Delegate callback, Object args, Int32 numArgs, Delegate catchHandler)
   at System.Windows.Threading.Dispatcher.LegacyInvokeImpl(DispatcherPriority priority, TimeSpan timeout, Delegate method, Object args, Int32 numArgs)
   at MS.Win32.HwndSubclass.SubclassWndProc(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam)
   at MS.Win32.UnsafeNativeMethods.DispatchMessage(MSG& msg)
   at System.Windows.Threading.Dispatcher.PushFrameImpl(DispatcherFrame frame)
   at System.Windows.Threading.Dispatcher.PushFrame(DispatcherFrame frame)
   at System.Windows.Application.RunDispatcher(Object ignore)
   at System.Windows.Application.RunInternal(Window window)
   at System.Windows.Application.Run(Window window)
   at System.Windows.Application.Run()
   at QASystem.App.Main()

Answer 1

一个可能的猜测是代码不是线程安全的。该示例根本不包含同步。例如，代码可以按以下顺序运行：

1. 线程A：var count = currentParentRun.ChildRuns.Count - 1;
2. 线程 B：currentParentRun = new ParentRun();
3. 线程A：currentParentRun.ChildRuns[count];

如您所见，这可能会导致错误的、线程不安全的行为。

解决此问题的一种方法是在 UI 更新时插入锁以防止修改。另一种方法是创建数据的副本并将此副本提供给 UI，从而防止多个线程访问相同数据的风险。即

 var parentId = currentParentRun.ParentRunID; 
 var childId = currentParentRun.ChildRuns[currentParentRun.ChildRuns.Count - 1].ChildRunID;
 Dispatcher.BeginInvoke((Action)(() => ShowFinishedChildUIDelegate(parentId, childId)));