如何取消异步调用？ [英] How to cancel an asynchronous call?

问题描述

如何取消异步调用？在.NET APM似乎并不支持此操作。

How to cancel an asynchronous call? The .NET APM doesn't seem to support this operation.

我有以下的环在我的code的派生多个线程的线程池。当我点击我的用户界面的一个按钮，我想这些线程（或异步调用）结束。

I have the following loop in my code which spawns multiple threads on the ThreadPool. When I click a button on my UI, I would like these threads (or asynchronous calls) to end.

foreach (var sku in skus)
{
    loadSku.BeginInvoke(...
}

有没有优雅的解决方案不是创建一个全球性的取消标记，并具有异步方法来寻找它的其他？

Is there any elegant solution other than creating a global "Cancel flag" and having the asynchronous methods to look for it?

推荐答案

取消标记，就是要做到这一点，虽然不是全球性的，不一定。不可避免的一点是，你需要的一些的方式发信号给线程，它应该停止它在做什么。

A "cancel flag" is the way to do it, though not a global one, necessarily. The unavoidable point is that you need some way to signal to the thread that it should stop what it's doing.

在的BeginInvoke 的情况下，这是很难做什么，但一个全球性的标志，因为工作开展的线程池，而你不知道哪个线程。你有几个选项（在顺序preference）：

In the case of BeginInvoke, this is hard to do with anything but a global flag, because the work is carried out on the threadpool, and you don't know which thread. You have a couple of options (in order of preference):

1. 使用的BackgroundWorker ，而不是的BeginInvoke 的。这有<一个href="http://msdn.microsoft.com/en-us/library/system.componentmodel.backgroundworker.cancelasync.aspx">cancellation功能烤入。这有其他好处，如<一href="http://msdn.microsoft.com/en-us/library/system.componentmodel.backgroundworker.progresschanged.aspx">progress监测和<一href="http://msdn.microsoft.com/en-us/library/system.componentmodel.backgroundworker.runworkercompleted.aspx">"Work完整的回调，也很好处理异常的。
2. 使用 ThreadPool.QueueUserWorkItem ，传递一个对象具有状态的取消（）方法，设置一个取消标志，正在执行的code可以检查。当然，你需要保持一个参考状态对象，所以你可以调用取消（）就可以了（这是后话了的BackgroundWorker 为你做 - 你有一个组件的形式（感谢弗雷德里克提醒一下。这一点）。
3. 创建你自己的的ThreadStart 委托，传递一个状态对象与选项2。

1. Use the BackgroundWorker instead of BeginInvoke. This has cancellation functionality baked-in. This has other benefits, like progress monitoring, and "Work complete" callbacks. It also nicely handles exceptions.
2. Use ThreadPool.QueueUserWorkItem, passing in an object as the state that has a Cancel() method that sets a Cancelled flag that the executing code can check. Of course you'll need to keep a reference to the state object so you can call Cancel() on it (which is something the BackgroundWorker does for you - you have a component on your form. (Thanks to Fredrik for reminding about this).
3. Create your own ThreadStart delegate, passing in a state object as with option 2.

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