Question

我尝试创建将运行异步方法的任务，问题是我无法await任务构造函数中的Action参数，或者参数Task.Factory.StartNew。

根据我实例化任务的方式，我有不同的问题。我已经提供了七个例子，其中包含对每个问题的评论。

示例代码:(创建任务的七个示例）

    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
    }

我无法使用Task.Run()，因为它不提供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"。所以你只需要调用方法并保持它返回的任务：

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);
  }
}

我无法使用Task.Run（），因为它不提供TaskCreationOptions。这些任务将在字面上运行。

您不需要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所以它不需要首先在线程池上运行。

C＃启动任务来运行异步方法

1 个答案: