我目前正在尝试在必须以.Net 4.0为目标的程序中实现.Net 4.5的Task.Delay()方法的替代品.我在
this blog找到了以下代码.
/* You can write Task-based asynchronous methods by utilizing a TaskCompletionSource.
A TaskCompletionSource gives you a 'slave' Task that you can manually signal.
Calling SetResult() signals the task as complete,and any continuations kick off. */
void Main()
{
for (int i = 0; i < 10000; i++)
{
Task task = Delay (2000);
task.ContinueWith (_ => "Done".Dump());
}
}
Task Delay (int milliseconds) // Asynchronous NON-BLOCKING method
{
var tcs = new TaskCompletionSource<object>();
new Timer (_ => tcs.SetResult (null)).Change (milliseconds,-1);
return tcs.Task;
}
任务对我来说都是新手. System.Threading.Timer和TaskCompletionSource对我来说是全新的(截至今天),我正在与他们挣扎.除此之外,我想知道如何在此代码中添加CancellationToken功能.我假设我可以像这样在Delay()方法中添加一个参数：
Task Delay (int milliseconds,CancellationToken token) // Asynchronous NON-BLOCKING method
{
var tcs = new TaskCompletionSource<object>();
new Timer (_ => tcs.SetResult (null)).Change (milliseconds,-1);
return tcs.Task;
}
解决方法
我试图尽可能少地更改你的代码,但这是一个工作示例,其行为与Task.Delay相同.
重要的是要注意我使用TrySetCanceled和TrySetResult,因为Timer可以在任务取消后完成.理想情况下,您想要停止计时器.
另请注意,取消的任务将抛出TaskCanceledException
static void Main(string[] args)
{
// A cancellation source that will cancel itself after 1 second
var cancellationTokenSource = new CancellationTokenSource(TimeSpan.FromSeconds(1));
try
{
// This will only wait 1 second because as it will be cancelled.
Task t = Delay(5000,cancellationTokenSource.Token);
t.Wait();
Console.WriteLine("The task completed");
}
catch (AggregateException exception)
{
// Expecting a TaskCanceledException
foreach (Exception ex in exception.InnerExceptions)
Console.WriteLine("Exception: {0}",ex.Message);
}
Console.WriteLine("Done");
Console.ReadLine();
}
private static Task Delay(int milliseconds,CancellationToken token)
{
var tcs = new TaskCompletionSource<object>();
token.Register(() => tcs.TrySetCanceled());
Timer timer = new Timer(_ => tcs.TrySetResult(null));
timer.Change(milliseconds,-1);
return tcs.Task;
}
再读一下你的问题.如果您需要Task.Delay并且您的目标是.NET 4.0,那么您应该使用http://www.nuget.org/packages/Microsoft.Bcl.Async/中的Microsoft Async nuget包它包含方法TaskEx.Delay
