如何链接独立的 C# 任务? [英] How to chain independent C# tasks?

问题描述

假设我有两个独立的异步函数(我无法控制)来创建 Task 对象:

Let's say I have two independent async functions (that I don't control) that create Task objects:

Task A();
Task B();

和其他一些非异步函数

void X();

如何构建一个单独的 Task 链来依次执行所有这些任务并允许附加更多的延续(将在 X 之后执行)?

How do I construct a single Task chain that executes all of these in sequence and allows further continuations (that will execute after X) to be appended?

如果我这样做:

Task Sequential()
{
   return A()
     .ContinueWith(t => { B(); })
     .ContinueWith(t => { X(); });
}

这不起作用，因为 B 将启动一个新的任务链.如果 B 需要很长时间才能完成，X 将首先执行(以及 Sequential 的调用者可能在返回的任务上继续执行的其他任何内容).我需要 X 作为单个任务链中的最后一个元素，并以 B 任务作为其先例.

that does not work, because B will start a new Task chain. If B takes a long time to complete, X will be executed first (along with whatever else the caller of Sequential might ContinueWith on the returned Task). I need X to be the last element in a single Task chain, with the B Task as its precedent.

如果我这样做:

Task Sequential()
{
   return A()
     .ContinueWith(t => { B().ContinueWith(t => { X(); }); });
}

这只能部分解决问题，因为即使 A、B 和 X 现在按顺序执行，如果调用者执行 Sequential().ContinueWith，则该继续将与 B 和 X 并行执行，而不是在 X 之后执行.

that only partially solves the problem, because even though A, B and X will now execute in sequential order, if the caller does Sequential().ContinueWith, that continuation will execute in parallel to B and X, not after X.

推荐答案

有什么理由不使用 await?例如，

Is there any reason not to use await? For example,

async Task Sequential()
{
    await A();
    await B();
    X();
}

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