Question

我正在尝试使用Fody来包装从具有常见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");
  }
}

以及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，即使执行了所有其他IMethodDecorator（例如OnExit和OnTaskContinuation），也会跳过异常处理程序。

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ShouldGetErrorAsync生成以下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;
}

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;
}

如果我打电话给ShouldGetErrorAsync，Fody会拦截电话，并将方法主体包裹在try catch中。但是如果该方法是异步的，即使仍然调用fodyError.OnTaskContinuation(task)和fodyError.OnExit()，它也永远不会遇到catch语句。

另一方面，即使IL中没有错误处理块，ShouldGetErrorAsync也会正确处理错误。

我的问题是，Fody应该如何生成IL以正确注入错误块并使其截获异步错误？

Here is a repo with tests that reproduces the issue

Answer 1

您只是将“试听”放在“开球”内容的周围。方法，这只会保护你到第一次需要重新安排的时间点（当异步方法首先需要重新安排时，＆＃39;启动＆＃39;方法将结束，所以当它不会在堆栈上时异步方法恢复）。

您应该考虑修改状态机上实现IAsyncStateMachine.MoveNext()的方法。特别是，在异步方法构建器（SetException(Exception)，AsyncVoidMethodBuilder或AsyncTaskMethodBuilder）上查找对AsyncTaskMethodBuilder<TResult>的调用，并在传递异常之前将其包装。

Answer 2

await确保异步方法看起来很简单，不是吗？ :)您刚刚在该抽象中发现了泄漏 - 该方法通常在找到第一个await后立即返回，并且您的异常帮助程序无法拦截任何后续异常。

您需要做的是同时实现OnException，并处理方法的返回值。当方法返回并且任务未完成时，您需要结束任务上的错误延续，这需要按照您希望的方式处理异常。 Fody家伙想到了 - 这就是OnTaskContinuation的用途。您需要检查Task.Exception以查看潜在任务中是否存在异常，并根据需要进行处理。

我认为这只有在你想要在执行日志记录时重新抛出异常时才会起作用 - 它不允许你用不同的东西替换异常。你应该测试：）

Fody Async MethodDecorator处理异常

2 个答案: