Autofac拦截异步执行顺序

Question

所以我有这门课:

public class MappingBootstrap : IMappingBootstrap
{
    public virtual async Task Map()
    {
        // Order is very important

        await this.mapper1.Map();

        await this.mapper2.Map();

        await this.mapper3.Map();

        await this.mapper4.Map();
    }
}

我有Autofac拦截器:

public class LoggingInterceptor : IInterceptor
{
    public void Intercept(IInvocation invocation)
    {
        var methodReference = Guid.NewGuid();
        Console.WriteLine($"Calling {invocation?.Method?.DeclaringType?.Name}.{invocation?.Method?.Name} : {methodReference}");

        var startNew = Stopwatch.StartNew();

        invocation?.Proceed();

        startNew.Stop();

        Console.WriteLine($"{methodReference} : Done, time taken: {startNew.ElapsedMilliseconds}ms");
    }
}

这会产生输出:

调用IMapperBootstrap.Map:54425559-71fe-4f23-ab47-d0f3371ec819
调用IMapper1.Map:51babb34-fa83-42ed-84e7-a1e979528116
51babb34-fa83-42ed-84e7-a1e979528116:完成,所用时间:219ms
54425559-71fe-4f23- ab47-d0f3371ec819:完成,所用时间:221ms
呼叫IMapper2.Map:41c812a2-d82d-48f6-9b8d-139b52eb28e3
41c812a2-d82d-48f6-9b8d-139b52eb28e3:完成,所用时间:9ms
呼叫IMapper3.Map:c91bed04-8f86-47d3 -a35a-417e354c2c5f
c91bed04-8f86-47d3-a35a-417e354c2c5f:完成,所需时间:994ms
调用IMapper4.Map:035cad27-1ba8-4bd1-b85f-396f64998d97
035cad27-1ba8-4bd1-b85f-396f64998d97:完成,所用时间:18ms

正如您所看到的,MappingBoostrap.Map完成后的第一个Mapper1.Map而不是我期望的所有功能完成后的结束.为什么？

---

Autofac配置:

builder.Register(context => new LoggingInterceptor());

builder
    .RegisterAssemblyTypes(typeof(Bootstrapper).Assembly)
    .Where(x => x.Namespace.Contains("Mapping"))
    .AsImplementedInterfaces()
    .EnableInterfaceInterceptors()
    .InterceptedBy(typeof(LoggingInterceptor));

Answer 1

为什么？

当您调用这样的异步方法时:

mapping.Map();

它只启动方法.这就是异步方法的工作方式(正如我在博客中解释的那样).如果await异步方法返回任务,则当前方法将暂停,直到异步方法完成:

await mapping.Map();

在拦截的情况下,理想的解决方案是使Proceed和Intercept方法异步:

public async Task InterceptAsync(IInvocation invocation)
{
  ...
  await invocation?.ProceedAsync();
  ...
}

不幸的是,Autofac没有内置的异步方法理解,所以这是不可能的.相反,你必须调用Proceed,它只是启动异步方法.异步方法返回一个Task,表示该方法的执行.要挂钩完成该方法,您应该用Task自己的方法替换它.

对于一个简单的Task返回方法,你可以使用这样的东西:

public void Intercept(IInvocation invocation)
{
  var methodReference = Guid.NewGuid();
  Console.WriteLine($"Calling {invocation?.Method?.DeclaringType?.Name}.{invocation?.Method?.Name} : {methodReference}");

  var startNew = Stopwatch.StartNew();

  invocation.Proceed();
  invocation.ReturnValue = WatchAsync(methodReference, startNew, (Task)invocation.ReturnValue);
}

private static async Task WatchAsync(Guid methodReference,
    Stopwatch stopwatch, Task methodExecution)
{
  try
  {
    await methodExecution.ConfigureAwait(false);
  }
  finally
  {
    stopwatch.Stop();
    Console.WriteLine($"{methodReference} : Done, time taken: {stopwatch.ElapsedMilliseconds}ms");
  }
}