监控任务完成

Question

我运行几个任务并将它们保存在一个列表中以检查它们是否已经完成。

我发现来自 async 方法的任务总是显示为 RanToCompletion，尽管任务本身仍然是运行ning。

有没有办法在这两种情况下从 Task 对象获取 "is complete" 信息？

这是一个显示此行为的简单测试用例。我运行两个任务，with/without 一个 async 方法，并在完成期间和之后检查状态。

private void test()
{

    ;
    Action actionAsync = funcAsync;
    Task taskAsync = Task.Run(actionAsync);
    Action action = func;
    Task task = Task.Run(action);

    var statusAsync = taskAsync.Status;
    var status = task.Status;

    // stati are either WaitingToRun or Running

    Thread.Sleep(TimeSpan.FromSeconds(2));

    // Now it's quite certain, that both have started

    var statusAsync2 = taskAsync.Status;
    var status2 = task.Status;

    Debug.Assert(statusAsync2 == TaskStatus.RanToCompletion);
    Debug.Assert(status2 == TaskStatus.Running);

    ;

    Thread.Sleep(TimeSpan.FromSeconds(12));

    // Now it's quite certain, that both have finished

    var statusAsync3 = taskAsync.Status;
    var status3 = task.Status;
    ;

    Debug.Assert(statusAsync3 == TaskStatus.RanToCompletion);
    Debug.Assert(status3 == TaskStatus.RanToCompletion);

}



private async void funcAsync()
{
    await Task.Delay(TimeSpan.FromSeconds(10));
}
private  void func()
{
    Thread.Sleep(TimeSpan.FromSeconds(10));
}

Answer 1

I discovered that tasks that come from an async method are always shown as RanToCompletion although the task itself was still running.

是的，因为您的 void 方法已经完成，这就是 Task.Run 调用的全部内容。如果您改为使用：

private async Task FuncAsync()
{
    await Task.Delay(TimeSpan.FromSeconds(10));
}

并使用 Func<Task> 代替 Action，然后您将调用 Task.Run(Func<Task>)，一切都会好起来的。

简短但完整的示例：

using System;
using System.Threading;
using System.Threading.Tasks;

class Test
{
    static void Main()
    {
        Func<Task> func = FuncAsync;
        Task task = Task.Run(func);
        for (int i = 0; i < 7; i++)
        {
            Console.WriteLine(task.Status);
            Thread.Sleep(1000);
        }        
    }

    private static async Task FuncAsync()
    {
        await Task.Delay(TimeSpan.FromSeconds(5));
    }
}

输出：

WaitingForActivation
WaitingForActivation
WaitingForActivation
WaitingForActivation
WaitingForActivation
RanToCompletion
RanToCompletion

尽可能避免编写 void 异步方法。它们基本上应该只用于事件处理程序。

监控任务完成

Monitoring Task completion

c#

task