C＃启动任务运行异步方法

Question

我试图创建将运行异步方法的任务，问题是，我不能await的Action参数在任务的构造函数，或Task.Factory.StartNew的参数。

根据我如何实例化我的任务，我有不同的问题。我已经提供了七个例子，并对各自在下面创建的问题发表了评论

示例代码：（任务创建的7个例子）

private ConcurrentDictionary<int, Task> Tasks { get; set; } 
    private bool active = true; 

    private async Task StartTasks() 
    { 
     int numTasks = 5; 

     for(int i = 0; i < numTasks; i++) 
     { 
      //Task status is almost instantly "RanTocompletion" while work is still being done 
      Task task = new Task<Task>(DoWork, "someinfo", TaskCreationOptions.LongRunning); 
      task.Start(); 

      //Cannot await method group 
      Task task = new Task(await DoWork, "someinfo", TaskCreationOptions.LongRunning); 
      task.Start(); 

      //Task status is almost instantly "RanTocompletion" while work is still being done 
      Task task = new Task(async (object state) => await DoWork(state), "someinfo", TaskCreationOptions.LongRunning); 
      task.Start(); 

      //Throws a "Start may not be called on a promise-style task." Exception 
      Task task = new Task<Task>(DoWork, "someinfo", TaskCreationOptions.LongRunning).Unwrap(); 
      task.Start(); 

      //Task starts doing work after Start() is called, then throws a "Start may not be called on a promise-style task." Exception 
      Task task = new Task(DoWork, "someinfo", TaskCreationOptions.LongRunning); 
      task.Start(); 

      //Task starts doing work, but status is "WaitingForActivation 
      Task task = Task.Factory.StartNew(DoWork, "someinfo", TaskCreationOptions.LongRunning); 

      //Throws a "Start may not be called on a promise-style task." Exception 
      Task task = Task.Factory.StartNew(DoWork, "someinfo", TaskCreationOptions.LongRunning).Unwrap(); 

      //For checking up on tasks as work is done 
      Tasks.TryAdd(task.Id, Task); 
     } 
    } 

    private async Task DoWork(object state) 
    { 
     while (active) 
     { 
      await MakeHttpRequest(); 
      await DoSomethingCpuBound(); 
      //..etc 
     } 
     //do any cleanup and return 
    } 

我不能使用Task.Run()，因为不提供TaskCreationOptions。这些任务将在字面上运行。

如何启动任务以等待异步操作？

Answer 1

如何启动任务以等待异步操作？

在TAP中，tasks are returned "hot"。所以你从字面上只需要调用该方法，并保持它的任务返回：

private ConcurrentDictionary<int, Task> Tasks { get; set; } 
private async Task StartTasks() 
{ 
    for(int i = 0; i < 5; i++) 
    { 
    Task task = DoWork(null); 
    Tasks.TryAdd(task.Id, task); 
    } 
} 

我不能使用Task.Run（），因为不提供TaskCreationOptions。这些任务将在字面上运行。

你不需要TaskCreationOptions。 The LongRunning flag is just a hint, and the thread pool will recover within a couple of seconds even if you don't specify that hint。但这并不重要，因为你的工作是异步的，所以它不需要首先在线程池上运行。