如何在C ++/Cli中使用等待 [英] How to consume an awaitable in C++/Cli

问题描述

async/await在C#世界中广受欢迎.异步功能还倾向于在应用程序中迅速传播:需要等待，因此调用函数必须是异步的，因此也是需要等待的等待方式，等等.

async/await gained a lot of popularity in the C# world the past few years. Async functions also tend to spread rapidly within an application: Awaitables need to be awaited, therefore the calling function must be async and is therefore also an awaitable which needs to be awaited,... and so forth.

我正在C ++/Cli项目中使用C#库.该库公开了异步API. Visual C ++编译器不支持async/await.因此，我无法等待该库提供给我的任何API.

I'm using a C# library in a C++/Cli project. The library exposes async APIs. The Visual C++ compiler does not support async/await. Hence I have no way to await any of the APIs the library gives me.

我有以下选择:

• 调用异步函数并放开它":这不是一个选择，因为我经常需要返回值才能继续.
• 调用Wait()或访问Task/Task<T>对象的Result属性，异步函数返回:

• Call the async function and "letting it go": Not an option since I often need the return values to proceed.
• Calling Wait() or accessing the Result property of the Task/Task<T> objects the async function returns: Causes the infamous dead-lock of the UI thread.

有什么办法可以使这项工作成功吗?如果需要的话，我不介意同步执行异步API.

Is there any way to make this work? I wouldn't mind executing the async APIs synchronously if I have to.

推荐答案

在我看来，您的问题更多是更大问题的征兆.我个人尽量避免将业务逻辑放在C ++-CLI模块中.具体来说，我尝试将ref class功能限制在3个主要区域:

To me, it sounds like your problem is more of a symptom of a bigger issue. I personally try to avoid as much as I can putting business logic in a C++-CLI module. Specifically, I try to limit a ref class functionality to 3 main areas:

• 将托管方法调用转换为本地方法调用(必要时包括转换参数).
• 将本机返回值转换为托管返回值.甚至可以将接收回调的异步函数转换为返回Task的方法.
• 将本机事件(回调)转换为托管事件.

• Translating managed method calls to native method calls (that includes transforming parameters if necessary).
• Translating native return values to managed return values. This can even be translating an asynchronous function receiving a callback to a method returning Task.
• Translating native events (callbacks) to managed events.

我可能是错的，但是在您的情况下，听起来您的C ++代码没有很好地解耦，您最终将其不同部分连接到了C ++-CLI模块中.

I Might be wrong, but in your situation it sounds like your C++ code is not well decoupled and you end up wiring different parts of it inside a C++-CLI module.

关于您的问题，我将使用Task.ContinueWith系列方法而不是async / await来执行异步延续.但是，如果希望在特定的SynchronizationContext(例如UI线程)上调用延续，则必须特别注意提供正确的TaskScheduler.

As for your question, I would use Task.ContinueWith family of methods to perform the asynchronous continuation instead of async / await. Yet, If you want the continuation to be invoked on a specific SynchronizationContext (such as UI thread) then special care must be taken to supply the right TaskScheduler.

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