c# - 为什么 Task.WhenAny() 没有按预期工作
问题描述
我正在尝试为可等待的任务实现超时模式,如下所述:https ://stackoverflow.com/a/11191070
但是,我得到了意想不到的结果。我编写了一个小型控制台应用程序来演示(这篇文章的底部)。这些是我得到的场景和结果:
Scenario 1
DelayTask Thread.Sleep(10000);
ActualTask Thread.Sleep(100);
Invoked with await Task.WhenAny(...
Result: THEN clause invoked CORRECT
Scenario 2
DelayTask Thread.Sleep(100);
ActualTask Thread.Sleep(10000);
Invoked with await Task.WhenAny(...
Result: THEN clause invoked INCORRECT
Scenario 3
DelayTask Thread.Sleep(10000);
ActualTask Thread.Sleep(100);
Invoked WITHOUT await: Task.WhenAny(...
Result: ELSE clause invoked INCORRECT
Scenario 4
DelayTask Thread.Sleep(100);
ActualTask Thread.Sleep(10000);
Invoked WITHOUT await: Task.WhenAny(...
Result: ELSE clause invoked CORRECT
任何人都可以解释为什么它没有按预期运行。蒂亚!
class Program
{
static void Main(string[] args)
{
Run();
}
private static async void Run()
{
var _cancelWorkTokenSource = new CancellationTokenSource();
var task = ActualTask(_cancelWorkTokenSource.Token);
var delayTask = DelayTask(_cancelWorkTokenSource.Token);
if (await Task.WhenAny(task, delayTask) == task)
{
Console.WriteLine("Task Succeeded in time.");
}
else
{
Console.WriteLine("Task exceeded time limit");
};
Console.ReadLine();
}
private static async Task DelayTask(CancellationToken cancelToken)
{
Thread.Sleep(10000);
}
private static async Task ActualTask(CancellationToken cancelToken)
{
Thread.Sleep(100);
}
}
解决方案
因为您的虚拟方法实施不正确。更改Thread.Sleep
为await Task.Delay
:
private static async Task DelayTask(CancellationToken cancelToken)
{
await Task.Delay(10000);
}
private static async Task ActualTask(CancellationToken cancelToken)
{
await Task.Delay(100);
}
您的代码中现在发生了什么:
var task = ActualTask(_cancelWorkTokenSource.Token)
阻塞当前线程 10000 毫秒并返回完成的任务- 之后
var delayTask = DelayTask(_cancelWorkTokenSource.Token);
阻塞当前线程 100 毫秒并返回已完成的任务 await Task.WhenAny(task, delayTask)
选择其中的第一个,因为两者都已完成
添加到您的代码Console.WriteLine(task.IsCompleted);
并Console.WriteLine(delayTask.IsCompleted);
在相应的变量初始化后进行检查。