Microsoft.Bcl.Async 中是否有 ExceptionDispatchInfo 的类似物？

Question

Microsoft.Bcl.Async 中有 ExceptionDispatchInfo 的类似物吗？我找不到类似的东西。

这个问题是由我的another question 触发的。当异常的父级task 可用时，我可以使用task.GetAwaiter().GetResult() 重新抛出，正如@StephenCleary 所建议的那样。

当它不可用时我有什么选择？

Answer 1

这里是ExceptionDispatchInfofrom Mono的实现。据我测试，它似乎与 Microsoft .NET 4.0 兼容。

public sealed class ExceptionDispatchInfo
{
    readonly Exception _exception;
    readonly object _source;
    readonly string _stackTrace;

    const BindingFlags PrivateInstance = BindingFlags.Instance | BindingFlags.NonPublic;
    static readonly FieldInfo RemoteStackTrace = typeof(Exception).GetField("_remoteStackTraceString", PrivateInstance);
    static readonly FieldInfo Source = typeof(Exception).GetField("_source", PrivateInstance);
    static readonly MethodInfo InternalPreserveStackTrace = typeof(Exception).GetMethod("InternalPreserveStackTrace", PrivateInstance);

    private ExceptionDispatchInfo(Exception source)
    {
        _exception = source;
        _stackTrace = _exception.StackTrace + Environment.NewLine;
        _source = Source.GetValue(_exception);
    }

    public Exception SourceException { get { return _exception; } }

    public static ExceptionDispatchInfo Capture(Exception source)
    {
        if (source == null)
            throw new ArgumentNullException("source");

        return new ExceptionDispatchInfo(source);
    }

    public void Throw()
    {
        try
        {
            throw _exception;
        }
        catch
        {
            InternalPreserveStackTrace.Invoke(_exception, new object[0]);
            RemoteStackTrace.SetValue(_exception, _stackTrace);
            Source.SetValue(_exception, _source);
            throw;
        }
    }
}

Answer 2

我已经对implementation provided by avo 进行了试验——但它并没有通过所有测试。我的意思是它提供了基本行为，但在更复杂的情况下会失败（例如多次投掷、重新捕获等......）。

作为Theraot.Core 的一部分，我对这个类做了一个反向移植，它可以在现代 Mono、旧 Mono（2.6 之前*）和任何 Microsoft .NET 从 2.0 到 4.0 中工作。

*：来自 Miguel de Icaza 的小提示 :)

下面的代码目前仅在 Feature 分支上，它最终将移至 master 分支（连同 Task for .NET 2.0 :)，此时它将通过 Theraot.Core nuget 提供。我把它留在这里以防有人需要它。

如果您发现任何问题，欢迎在项目 github（上面链接）的问题跟踪器上报告错误。

#if NET20 || NET30 || NET35 || NET40

using System.Reflection;

namespace System.Runtime.ExceptionServices
{
    /// <summary>
    /// The ExceptionDispatchInfo object stores the stack trace information and Watson information that the exception contains at the point where it is captured. The exception can be thrown at another time and possibly on another thread by calling the ExceptionDispatchInfo.Throw method. The exception is thrown as if it had flowed from the point where it was captured to the point where the Throw method is called.
    /// </summary>
    public sealed class ExceptionDispatchInfo
    {
        private static FieldInfo _remoteStackTraceString;

        private Exception _exception;
        private object _stackTraceOriginal;
        private object _stackTrace;

        private ExceptionDispatchInfo(Exception exception)
        {
            _exception = exception;
            _stackTraceOriginal = _exception.StackTrace;
            _stackTrace = _exception.StackTrace;
            if (_stackTrace != null)
            {
                _stackTrace += Environment.NewLine + "---End of stack trace from previous location where exception was thrown ---" + Environment.NewLine;
            }
            else
            {
                _stackTrace = string.Empty;
            }
        }

        /// <summary>
        /// Creates an ExceptionDispatchInfo object that represents the specified exception at the current point in code.
        /// </summary>
        /// <param name="source">The exception whose state is captured, and which is represented by the returned object.</param>
        /// <returns>An object that represents the specified exception at the current point in code. </returns>
        public static ExceptionDispatchInfo Capture(Exception source)
        {
            if (source == null)
            {
                throw new ArgumentNullException("source");
            }
            return new ExceptionDispatchInfo(source);
        }

        /// <summary>
        /// Gets the exception that is represented by the current instance.
        /// </summary>
        public Exception SourceException
        {
            get
            {
                return _exception;
            }
        }

        private static FieldInfo GetFieldInfo()
        {
            if (_remoteStackTraceString == null)
            {
                // ---
                // Code by Miguel de Icaza

                FieldInfo remoteStackTraceString =
                    typeof(Exception).GetField("_remoteStackTraceString",
                    BindingFlags.Instance | BindingFlags.NonPublic); // MS.Net

                if (remoteStackTraceString == null)
                    remoteStackTraceString = typeof(Exception).GetField("remote_stack_trace",
                        BindingFlags.Instance | BindingFlags.NonPublic); // Mono pre-2.6

                // ---
                _remoteStackTraceString = remoteStackTraceString;
            }
            return _remoteStackTraceString;
        }

        private static void SetStackTrace(Exception exception, object value)
        {
            FieldInfo remoteStackTraceString = GetFieldInfo();
            remoteStackTraceString.SetValue(exception, value);
        }

        /// <summary>
        /// Throws the exception that is represented by the current ExceptionDispatchInfo object, after restoring the state that was saved when the exception was captured.
        /// </summary>
        public void Throw()
        {
            try
            {
                throw _exception;
            }
            catch (Exception exception)
            {
                GC.KeepAlive(exception);
                var newStackTrace = _stackTrace + BuildStackTrace(Environment.StackTrace);
                SetStackTrace(_exception, newStackTrace);
                throw;
            }
        }

        private string BuildStackTrace(string trace)
        {
            var items = trace.Split(new[] { Environment.NewLine }, StringSplitOptions.RemoveEmptyEntries);
            var newStackTrace = new Text.StringBuilder();
            var found = false;
            foreach (var item in items)
            {
                // Only include lines that has files in the source code
                if (item.Contains(":"))
                {
                    if (item.Contains("System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()"))
                    {
                        // Stacktrace from here on will be added by the CLR
                        break;
                    }
                    if (found)
                    {
                        newStackTrace.Append(Environment.NewLine);
                    }
                    found = true;
                    newStackTrace.Append(item);
                }
                else if (found)
                {
                    break;
                }
            }
            var result = newStackTrace.ToString();
            return result;
        }
    }
}

#endif