为什么原来的任务取消，当它ContinueWith别的东西吗？ [英] Why is the original task canceled when it ContinueWith something else?

问题描述

这是连续4周了我一头扎进C＃编程。这真的很有趣，但我得到了一个痛苦的屁股：

It's been 4 weeks since I dived into C# programming. It's really fun, however, I got a pain in the ass:

当我开始与 HttpClient.PostAsync（）任务孤单，它工作正常。但是，如果我继续用别的东西，在原单任务将被取消，而不是我。 。貌似任务不高兴被继续

When I start a Task with HttpClient.PostAsync() alone, it works fine. But if I continue with something else, the orginal Task will be canceled, not by me. Looks like the Task is not happy about being continued.

Task<HttpResponseMessage> task0;
Task task1;

using (var client = new HttpClient())
{
    HttpContent content = new ByteArrayContent(new byte[]{});

    task0 = client.PostAsync("<valid http address>", content);

    task1 = task0.ContinueWith((t) =>
    {
         // Do nothing
    });
}

task1.Wait();

// I got task0.IsCanceled == true here

我试过

I tried:

1，添加 task0.wait（）后，立即 PostAsync（）将解决这个问题，但它不是我想要的。因为我需要异步的性能优势，做这将使它完全同步。

1, Add task0.wait() immediately after PostAsync() will solve the issue but it's not what I want. Because I need the performance benefit from async and doing that will make it totally sync.

2，添加 task0.wait（） task1.wait（）将导致 TaskCanceledExcpetion 。

3，删除任务1 并等待 task0 都会好的。

3, Remove task1 and wait on task0 will be OK.

4，呼叫 task0.start（）将得到开始可能不会被要求承诺式的任务。

4, Call task0.start() will got "Start may not be called on a promise-style task."

所以，PLZ有人告诉我，我做错了。

So, plz someone tell me what am I doing wrong?

PS：

在我问这个问题，我GOOGLE了它好几天。而从StackOverflow的一些问题可能​​看起来培训相关，但事实证明他们是不一样的我的。

Before I asked this question, I had googled it for days. And some questions from StackOverflow might look relevent, but it turned out they were not the same to mine.

的谁取消了我的任务是什么？她/他问为什么不执行后续任务。

Who canceled my Task? She/He was asking why the continuation task wasn't executed.

为什么TaskCanceledException发生？她/他被搞乱与其中的CancellationToken我从来没和得到意想不到的结果。

Why does TaskCanceledException occur? She/He was messing up with the CancellationToken which I never did and got unexpected result.

我也看到这个的任务取消并仍然得到任何线索。

I've also read this Task Cancellation and still got no clue.

推荐答案

您的HttpClient 最有可能得到处理 PostAsync之前的结束。删除使用语句用于测试目的，并如预期一切都将正常工作。你应该在不同的点配置客户端，当请求完成。

Your HttpClient most likely get's disposed before PostAsync is finished. Remove using statement for test purposes, and everything will work as expected. You should dispose your client at a different point, when request is finished.

此外，许多建议的HttpClient 的重用单个实例尽可能多的，如果你的应用程序逻辑允许它。

Also, many would recommend reuse single instance of HttpClient as much as possible, if your application logic allows it.

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