终止任务的正确方法是什么？

Question

有一个关于立即终止任务的正确方法的问题。例如，我有以下代码：

public async Task<string> DoAsync()
{
    var result = await Task.Run(() =>
    {
        //Some heavy request here in a row (5 seconds per request)
        DoHeavyRequest(); // 1
        DoHeavyRequest(); // 2
        DoHeavyRequest(); // 3
        DoHeavyRequest(); // 4

        return "success";
    });

    return results;
}

我怎么能在一分钟内取消这项任务？例如，我运行了7秒的任务，我期望只调用第一次，可能是第二次“重请求”，3-4将根本不会被调用。

提前谢谢。

Answer 1

我建议取消

public async Task<string> DoAsync(CancellationToken token) {
  var result = await Task.Run(() =>  {
    //TODO: you may want to pass token to DoHeavyRequest() and cancel there as well
    token.ThrowIfCancellationRequested();
    DoHeavyRequest(); // 1

    token.ThrowIfCancellationRequested();
    DoHeavyRequest(); // 2

    token.ThrowIfCancellationRequested();
    DoHeavyRequest(); // 3

    token.ThrowIfCancellationRequested();
    DoHeavyRequest(); // 4

    return "success";
  });

  return "results";
}

// Let's preserve the current interface - call without cancellation
public async Task<string> DoAsync() {
  return await DoAsync(CancellationToken.None);
}

..。

// Run, wait up to 7 seconds then cancel 
try {
  using (CancellationTokenSource cts = new CancellationTokenSource(7000)) {
    // Task completed, its result is in the result
    string result = await DoAsync(cts.Token);

    //TODO: Put relevant code here 
  }  
catch (TaskCanceledException) { 
  // Task has been cancelled (in this case by timeout)

  //TODO: Put relevant code here  
}