取消等待任务而无需显式检查 [英] Canceling await tasks without explicit checks

问题描述

我正在开发使用C#的NPC脚本的在线游戏服务器.为了获得无状态的NPC，我使用了枚举器，在必须等待客户端响应时屈服，并在获得响应后调用MoveNext.

I'm developing an online game server that uses C# for its NPC scripts. To get stateless NPCs I'm using enumerators, yielding when I have to wait for a response from the client, and calling MoveNext once I got it.

Talk()
    Msg("test");
    Select("Yes", "No");
    yield return true;
    Msg(Response);

(简化的例子，实际的收益率要复杂一些.)

(Simplified example, the yielding is a little more complex in reality.)

这工作正常，但是异步/等待会使它更整洁，更轻松，更灵活.

This is working fine, but async/wait would make make it cleaner, easier, and more flexible.

Talk()
    Msg("test");
    Msg(await Select("Yes", "No"));

玩异步/等待，我发现我唯一的问题是脚本不像发送一些消息那样简单.从主要Talk函数调用其他函数时，我必须等待它们，否则执行将不会停止.其他功能还可以调用更多功能，从而产生未知数量的等待.

Playing around with async/wait I've found my only problem to be that the scripts aren't as simple as sending some messages. When calling other functions from the main Talk function I have to await them, since the execution wouldn't stop otherwise. The other functions could also call even more, creating an unknown amount of awaits.

Talk()
    Msg("test");
    await OtherTalk();
    Msg("end"); // would be called right away

OtherTalk()
    Msg("test2");
    Msg(await Select("Yes", "No"));

如果我用这样的副谈话"方法关闭NPC，我可能会悬空很多任务，因为我不会回到链上. NPC已关闭，没有更多响应，任务一直在等待.

If I close the NPC inside such a "sub talk" method I'd potentially leave quite a few tasks hanging in the air, because I wouldn't return up the chain. NPC closed, no more responses, tasks keep waiting.

解决此问题的方法是重新建立链，并在等待该函数后进行显式检查，以检查NPC是否已关闭.但是我希望它们尽可能简单明了，坦率地说，在每次调用函数后都添加if是否太单调乏味.该服务器软件还将由新手使用，他们可能会忘记这种检查，这可能会导致问题，具体取决于脚本的作用.

The solution to this problem would be going the chain back up, with explicit checks after the await of such a function, to check if the NPC was closed somewhere down the line. But I want them to be as simple and straight forward as possible, and frankly, having an if after each call of a function would be too tedious for my taste. The server software will also be used by newbies, who might forget such a check, which could lead to problems, depending on what the script does.

我现在的实际问题是，是否有人可以想到一种取消任务的方法，而无需对脚本本身进行显式检查.

My actual question now is if someone can think of a way to cancel the Tasks, without explicit checks in the scripts themselves.

推荐答案

TPL具有内置的取消功能.

The TPL has built-in cancellation features.

使所有函数都接受CanellationToken，并在调用每个异步函数时传递令牌.

Make all of your functions accept a CanellationToken, and pass the token along when calling every async function.

不时地在函数内部调用token.ThrowIfCancellationRequested()，整个异步调用链将中止，直到您处理取消为止.

Every now and then, inside the functions, call token.ThrowIfCancellationRequested(), and the entire async callchain will abort, until you handle the cancellation.

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