C#中的Promise等效项 [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#的替代方法.

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，并且希望它看起来与此类似:

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，但是即使模式有所不同，我也无法找到实现同一目标的合理方法.

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在这里无济于事，因为我没有要等待的任务！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<T>是未来(或Task是单位返回的未来).
• TaskCompletionSource<T>是一个承诺.

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

因此您的代码将这样翻译:

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很少见.对于单元测试，我只需要进行常规的异步等待:

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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