真正的异步WCF服务

我正在实现一个异步服务。在评估了微软的例子之后，我想知道他们的方法是否真的是异步的。我很确定是这样的，但是我在网上看到的一些样本和AsyncCallback参数让我很好奇。

public IAsyncResult BeginGetAcmeAnvil(AsyncCallback callback, object state)
{
  // Starts synchronous task
  var acmeAsyncResult = new AcmeAsyncResult<Anvil>
  {
     Data = new Anvil()
  };      
  return acmeAsyncResult;
}
public Anvil EndGetAcmeAnvil(IAsyncResult result)
{
  var acmeAsyncResult = result as AcmeAsyncResult<Anvil>;
  return acmeAsyncResult != null
    ? acmeAsyncResult.Data
    : new Anvil();
}

非常简单，但是为什么我们有一个AsyncCallback参数呢?我们不应该调用callback，这将反过来触发End方法吗?

我是这么想的:

public delegate void AsyncMethodCaller(AcmeAsyncResult<Anvil> acmeAsyncResult, 
                                       AsyncCallback callback);
public IAsyncResult BeginGetAcmeAnvil(AsyncCallback callback, object state)
{
  var acmeAsyncResult = new AcmeAsyncResult<Anvil>();
  var asyncMethodCaller = new AsyncMethodCaller(GetAnvilAsync);
  // Starts asynchronous task
  asyncMethodCaller.BeginInvoke(acmeAsyncResult, callback, null, null);
  return acmeAsyncResult;
}
private void GetAcmeAnvilAsync(AcmeAsyncResult<Anvil> acmeAsyncResult,
                               AsyncCallback callback)
{
  acmeAsyncResult.Data = new Anvil();
  callback(acmeAsyncResult);  // Triggers EndGetAcmeAnvil
}
public Anvil EndGetAcmeAnvil(IAsyncResult result)
{
  var acmeAsyncResult = result as AcmeAsyncResult<Anvil>;
  return acmeAsyncResult != null
    ? acmeAsyncResult.Data
    : new Anvil();
}

我使用loadUI做了一些负载测试，但是没有明显的性能变化。