使用任务有条件延续 [英] Using Tasks with conditional continuations
问题描述
我如何使用任务有条件延续有点糊涂了。
I'm a little confused about how to use Tasks with conditional Continuations.
如果我有一个任务,然后我想继续进行任务处理成功和错误,然后等待这些完成。
If I have a task, and then I want to continue with a tasks that handle success and error, and then wait on those to complete.
void FunctionThrows() {throw new Exception("faulted");}
static void MyTest()
{
var taskThrows = Task.Factory.StartNew(() => FunctionThrows());
var onSuccess = taskThrows.ContinueWith(
prev => Console.WriteLine("success"),
TaskContinuationOptions.OnlyOnRanToCompleted);
var onError = taskThrows.ContinueWith(
prev => Console.WriteLine(prev.Exception),
TaskContinuationOptions.OnlyOnFaulted);
//so far, so good
//this throws because onSuccess was cancelled before it was started
Task.WaitAll(onSuccess, onError);
}
这是在做任务的成功/失败分支的preferred方式?此外,我怎么加入所有这些任务,假设我已经创建延续了很长的线,各有自己的错误处理。
Is this the preferred way of doing task success/failure branching? Also, how am I supposed to join all these tasks, suppose I've created a long line of continuations, each having their own error handling.
//for example
var task1 = Task.Factory.StartNew(() => ...)
var task1Error = task1.ContinueWith( //on faulted
var task2 = task1.ContinueWith( //on success
var task2Error = task2.ContinueWith( //on faulted
var task3 = task2.ContinueWith( //on success
//etc
调用为WaitAll
这些不约而同地抛出,因为有些延续会由于被取消的 TaskContinuationOptions
,和调用等待
上已取消的任务抛出。
如何加入这些没有得到任务已取消例外?
Calling WaitAll
on these invariably throws, because some of the continuations will be cancelled due to the TaskContinuationOptions
, and calling Wait
on a cancelled task throws.
How do I join these without getting the "A task was cancelled" exception"?
推荐答案
我觉得你的主要问题是,你是说这两个任务,以等待与您的来电
I think your main problem is that you're telling those two tasks to "Wait" with your call to
Task.WaitAll(onSuccess, onError);
在的onSuccess 和的onError 的延续是自动设置为你和将要执行的 的其先行任务完成后。
The onSuccess and onError continuations are automatically setup for you and will be executed after their antecedent task completes.
如果您只需更换你的 Task.WaitAll(...)
与 taskThrows.Start();
我相信你会得到所需的输出。
If you simply replace your Task.WaitAll(...)
with taskThrows.Start();
I believe you will get the desired output.
下面是一个有点一个例子,我放在一起的:
Here is a bit of an example I put together:
class Program
{
static int DivideBy(int divisor)
{
Thread.Sleep(2000);
return 10 / divisor;
}
static void Main(string[] args)
{
const int value = 0;
var exceptionTask = new Task<int>(() => DivideBy(value));
exceptionTask.ContinueWith(result => Console.WriteLine("Faulted ..."), TaskContinuationOptions.OnlyOnFaulted | TaskContinuationOptions.AttachedToParent);
exceptionTask.ContinueWith(result => Console.WriteLine("Success ..."), TaskContinuationOptions.OnlyOnRanToCompletion | TaskContinuationOptions.AttachedToParent);
exceptionTask.Start();
try
{
exceptionTask.Wait();
}
catch (AggregateException ex)
{
Console.WriteLine("Exception: {0}", ex.InnerException.Message);
}
Console.WriteLine("Press <Enter> to continue ...");
Console.ReadLine();
}
}
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