6

我正在尝试使用 Fody 包装从具有通用异常格式的方法抛出的所有异常。

所以我添加了所需的接口声明和类实现，如下所示：

using System;
using System.Diagnostics;
using System.Reflection;
using System.Threading.Tasks;

[module: MethodDecorator]

public interface IMethodDecorator
{
  void Init(object instance, MethodBase method, object[] args);
  void OnEntry();
  void OnExit();
  void OnException(Exception exception);
  void OnTaskContinuation(Task t);
}


[AttributeUsage(
    AttributeTargets.Module |
    AttributeTargets.Method |
    AttributeTargets.Assembly |
    AttributeTargets.Constructor, AllowMultiple = true)]
public class MethodDecorator : Attribute, IMethodDecorator
{
  public virtual void Init(object instance, MethodBase method, object[] args) { }

  public void OnEntry()
  {
    Debug.WriteLine("base on entry");
  }

  public virtual void OnException(Exception exception)
  {
    Debug.WriteLine("base on exception");
  }

  public void OnExit()
  {
    Debug.WriteLine("base on exit");
  }

  public void OnTaskContinuation(Task t)
  {
    Debug.WriteLine("base on continue");
  }
}

看起来像这样的域实现

using System;
using System.Diagnostics;
using System.Linq;
using System.Reflection;
using System.Runtime.ExceptionServices;

namespace CC.Spikes.AOP.Fody
{
  public class FodyError : MethodDecorator
  {
    public string TranslationKey { get; set; }
    public Type ExceptionType { get; set; }

    public override void Init(object instance, MethodBase method, object[] args)
    {
      SetProperties(method);
    }

    private void SetProperties(MethodBase method)
    {
      var attribute = method.CustomAttributes.First(n => n.AttributeType.Name == nameof(FodyError));
      var translation = attribute
        .NamedArguments
        .First(n => n.MemberName == nameof(TranslationKey))
        .TypedValue
        .Value
          as string;

      var exceptionType = attribute
        .NamedArguments
        .First(n => n.MemberName == nameof(ExceptionType))
        .TypedValue
        .Value
          as Type;


      TranslationKey = translation;
      ExceptionType = exceptionType;
    }

    public override void OnException(Exception exception)
    {
      Debug.WriteLine("entering fody error exception");
      if (exception.GetType() != ExceptionType)
      {
        Debug.WriteLine("rethrowing fody error exception");
        //rethrow without losing stacktrace
        ExceptionDispatchInfo.Capture(exception).Throw();
      }

      Debug.WriteLine("creating new fody error exception");
      throw new FodyDangerException(TranslationKey, exception);

    }
  }

  public class FodyDangerException : Exception
  {
    public string CallState { get; set; }
    public FodyDangerException(string message, Exception error) : base(message, error)
    {

    }
  }
}

这适用于同步代码。但是对于异步代码，会跳过异常处理程序，即使所有其他 IMethodDecorator 都已执行（如OnExit、 和OnTaskContinuation）。

例如，查看以下测试类：

public class FodyTestStub
{ 

  [FodyError(ExceptionType = typeof(NullReferenceException), TranslationKey = "EN_WHATEVER")]
  public async Task ShouldGetErrorAsync()
  {
    await Task.Delay(200);
    throw new NullReferenceException();
  }

  public async Task ShouldGetErrorAsync2()
  {
    await Task.Delay(200);
    throw new NullReferenceException();
  }
}

我看到这ShouldGetErrorAsync会产生以下 IL 代码：

// CC.Spikes.AOP.Fody.FodyTestStub
[FodyError(ExceptionType = typeof(NullReferenceException), TranslationKey = "EN_WHATEVER"), DebuggerStepThrough, AsyncStateMachine(typeof(FodyTestStub.<ShouldGetErrorAsync>d__3))]
public Task ShouldGetErrorAsync()
{
    MethodBase methodFromHandle = MethodBase.GetMethodFromHandle(methodof(FodyTestStub.ShouldGetErrorAsync()).MethodHandle, typeof(FodyTestStub).TypeHandle);
    FodyError fodyError = (FodyError)Activator.CreateInstance(typeof(FodyError));
    object[] args = new object[0];
    fodyError.Init(this, methodFromHandle, args);
    fodyError.OnEntry();
    Task task;
    try
    {
        FodyTestStub.<ShouldGetErrorAsync>d__3 <ShouldGetErrorAsync>d__ = new FodyTestStub.<ShouldGetErrorAsync>d__3();
        <ShouldGetErrorAsync>d__.<>4__this = this;
        <ShouldGetErrorAsync>d__.<>t__builder = AsyncTaskMethodBuilder.Create();
        <ShouldGetErrorAsync>d__.<>1__state = -1;
        AsyncTaskMethodBuilder <>t__builder = <ShouldGetErrorAsync>d__.<>t__builder;
        <>t__builder.Start<FodyTestStub.<ShouldGetErrorAsync>d__3>(ref <ShouldGetErrorAsync>d__);
        task = <ShouldGetErrorAsync>d__.<>t__builder.Task;
        fodyError.OnExit();
    }
    catch (Exception exception)
    {
        fodyError.OnException(exception);
        throw;
    }
    return task;
}

并ShouldGetErrorAsync2生成：

    // CC.Spikes.AOP.Fody.FodyTestStub
[DebuggerStepThrough, AsyncStateMachine(typeof(FodyTestStub.<ShouldGetErrorAsync2>d__4))]
public Task ShouldGetErrorAsync2()
{
    FodyTestStub.<ShouldGetErrorAsync2>d__4 <ShouldGetErrorAsync2>d__ = new FodyTestStub.<ShouldGetErrorAsync2>d__4();
    <ShouldGetErrorAsync2>d__.<>4__this = this;
    <ShouldGetErrorAsync2>d__.<>t__builder = AsyncTaskMethodBuilder.Create();
    <ShouldGetErrorAsync2>d__.<>1__state = -1;
    AsyncTaskMethodBuilder <>t__builder = <ShouldGetErrorAsync2>d__.<>t__builder;
    <>t__builder.Start<FodyTestStub.<ShouldGetErrorAsync2>d__4>(ref <ShouldGetErrorAsync2>d__);
    return <ShouldGetErrorAsync2>d__.<>t__builder.Task;
}

如果我调用ShouldGetErrorAsync，Fody 将拦截调用，并将方法体包装在 try catch 中。但是，如果该方法是异步的，即使fodyError.OnTaskContinuation(task)andfodyError.OnExit()仍然被调用，它也永远不会命中 catch 语句。

另一方面，ShouldGetErrorAsync即使在 IL 中没有错误处理块，也会很好地处理错误。

我的问题是，Fody 应该如何生成 IL 以正确注入错误块并使其拦截异步错误？

这是一个带有重现问题的测试的 repo

4

2 回答 2

1

await确实使异步方法看起来很简单，不是吗？:) 您刚刚在该抽象中发现了一个泄漏-该方法通常在await找到第一个后立即返回，并且您的异常助手无法拦截任何以后的异常。

您需要做的是实现OnException, 并处理方法的返回值。当方法返回并且任务未完成时，您需要结束任务的错误延续，这需要以您希望的方式处理异常。Fody 的人想到了这一点——这就是它的OnTaskContinuation用途。您需要检查Task.Exception以查看任务中是否存在异常，并根据需要进行处理。

我认为这只有在您想在进行日志记录或其他操作时重新抛出异常时才有效 - 它不允许您用不同的东西替换异常。你应该测试一下:)

于 2016-02-01T11:37:33.993 回答
1

您只是将 try-catch 放在“启动”方法的内容周围，这只会保护您直到它首先需要重新安排时间（“启动”方法将在异步方法首先结束时结束需要重新调度，因此当异步方法恢复时不会在堆栈上）。

您应该考虑修改在IAsyncStateMachine.MoveNext()状态机上实现的方法。特别是，查找对SetException(Exception)异步方法构建器（或）的调用AsyncVoidMethodBuilder，并在将异常传入之前将其包装起来。AsyncTaskMethodBuilderAsyncTaskMethodBuilder<TResult>

于 2016-02-01T08:53:09.257 回答