C# 中的 Promise 等价物 [英] Promise equivalent in C#

问题描述

在 Scala 中有一个 Promise 类可用于手动完成 Future.我正在寻找 C# 中的替代品.

In Scala there is a Promise class that could be used to complete a Future manually. I am looking for an alternative in C#.

我正在编写一个测试，我希望它看起来像这样:

I am writing a test and I want it to look it similar to this:

// var MyResult has a field `Header`
var promise = new Promise<MyResult>;

handlerMyEventsWithHandler( msg =>
    promise.Complete(msg);
);

// Wait for 2 seconds
var myResult = promise.Future.Await(2000);

Assert.Equals("my header", myResult.Header);

我知道这可能不是 C# 的正确模式，但我无法找到一种合理的方法来实现相同的目标，即使模式略有不同.

I understand that this is probably not the right pattern for C#, but I couldn't figure out a reasonable way to achieve the same thing even with somewhat different pattern.

请注意，async/await 在这里没有帮助，因为我没有等待的任务！我只能访问将在另一个线程上运行的处理程序.

please note, that async/await doesn't help here, as I don't have a Task to await! I just have an access to a handler that will be run on another thread.

推荐答案

在 C# 中:

• Task 是未来(或 Task 是返回单位的未来).
• TaskCompletionSource 是一个承诺.

• Task<T> is a future (or Task for a unit-returning future).
• TaskCompletionSource<T> is a promise.

所以你的代码会翻译成这样:

So your code would translate as such:

// var promise = new Promise<MyResult>;
var promise = new TaskCompletionSource<MyResult>();

// handlerMyEventsWithHandler(msg => promise.Complete(msg););
handlerMyEventsWithHandler(msg => promise.TrySetResult(msg));

// var myResult = promise.Future.Await(2000);
var completed = await Task.WhenAny(promise.Task, Task.Delay(2000));
if (completed == promise.Task)
  ; // Do something on timeout
var myResult = await completed;

Assert.Equals("my header", myResult.Header);

定时异步等待"有点尴尬，但在现实世界的代码中也相对不常见.对于单元测试，我只会做一个常规的异步等待:

The "timed asynchronous wait" is a bit awkward, but it's also relatively uncommon in real-world code. For unit tests, I would just do a regular asynchronous wait:

var promise = new TaskCompletionSource<MyResult>();

handlerMyEventsWithHandler(msg => promise.TrySetResult(msg));

var myResult = await promise.Task;

Assert.Equals("my header", myResult.Header);

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