如何实现返回的任务和LT接口方法; T＆GT;？ [英] How to implement interface method that returns Task<T>?

问题描述

我有一个接口

interface IFoo
{
  Task<Bar> CreateBarAsync();
}

有两种方法来创建酒吧一异步和一个同步的。我想要提供一个接口实现为每个这两种方法的

There are two methods to create Bar, one asynchronous and one synchronous. I want to provide an interface implementation for each of these two methods.

有关异步方法，实施看起来是这样的：

For the asynchronous method, the implementation could look like this:

class Foo1 : IFoo
{
  async Task<Bar> CreateBarAsync()
  {
    return await AsynchronousBarCreatorAsync();
  }
}

不过，我应该如何实现类 foo2的，它使用的同步的方法来创建酒吧？

But HOW should I implement the class Foo2 that uses the synchronous method to create Bar?

我的可以的实施方法来同步运行：

I could implement the method to run synchronously:

  async Task<Bar> CreateBarAsync()
  {
    return SynchronousBarCreator();
  }

，编译器会发出警告，然后对方法签名使用异步：

这异步方法缺乏'等待'运营商，并会同步运行。请考虑使用'等待'操作，以等待非阻塞API调用，或等待Task.Run（......）做在后台线程CPU密集型的工作。

This async method lacks 'await' operators and will run synchronously. Consider using the 'await' operator to await non-blocking API calls, or 'await Task.Run(...)' to do CPU-bound work on a background thread.

或者说，我的可以的实施方法明确地返回任务＆LT;酒吧＆GT; 。在我看来，code将如下的可读性：

Or, I could implement the method to explicitly return Task<Bar>. In my opinion the code will then look less readable:

  Task<Bar> CreateBarAsync()
  {
    return Task.Run(() => SynchronousBarCreator());
  }

从性能的角度来看，我认为这两种方法都有大致相同的开销，还是？

From a performance point of view, I suppose both approaches have about the same overhead, or?

我应该选择哪一种方法;贯彻落实异步法同步或明确包裹同步方法调用在工作？

Which approach should I choose; implement the async method synchronously or explicitly wrap the synchronous method call in a Task?

修改

我工作的这个项目确实是一个.NET 4项目的异步 / 计谋的距离的微软异步的NuGet包。在.NET 4中， Task.Run 然后可以用 TaskEx.Run 取代。我有意识地用在这个例子中的.NET 4.5以上的方法在做的主要问题更加清晰的希望。

The project I am working on is really a .NET 4 project with async / await extensions from the Microsoft Async NuGet package. On .NET 4, Task.Run can then be replaced with TaskEx.Run. I consciously used the .NET 4.5 method in the example above in the hope of making the primary question more clear.

推荐答案

当你必须实现从接口异步方法，你的实现是同步的，你可以使用Ned的解决方案：

When you have to implement an async method from an interface and your implementation is synchronous, you can either use Ned's solution:

public Task<Bar> CreateBarAsync()
{
    return Task.FromResult<Bar>(SynchronousBarCreator());
}

使用此解决方案中，该方法看起来异步但是同步的。

With this solution, the method looks async but is synchronous.

或者你提出的解决方案：

Or the solution you proposed:

  Task<Bar> CreateBarAsync()
  {
    return Task.Run(() => SynchronousBarCreator());
  }

这样的方法确实是异步。

This way the method is truly async.

您还没有通用的解决方案，将匹配的如何实现，返回任务界面的方法的所有情况。这取决于上下文：是你的执行速度不够快，那么在另一个线程调用它是无用的？如何使用这个接口被此方法调用时（将其冻结的应用程序）？它甚至有可能调用您的实现在另一个线程？

You don't have a generic solution that will match all cases of "How to implement interface method that returns Task". It depends on the context: is your implementation fast enough so invoking it on another thread is useless? How is this interface used a when is this method invoked (will it freeze the app)? Is it even possible to invoke your implementation in another thread?

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