Task.wait和continueWIth [英] Task.wait and continueWIth

问题描述

  var task = Task< string> .Factory.StartNew（（）= > longrunningmethod（）
 .ContinueWith（a => 
 longrunningmethodcompleted（（Task< string>）a，
 TaskScheduler.FromCurrentSynchronizationContext（））））） 
 
 task.Wait（）; 
  

我的任务将调用longrunning方法，完成后将调用completed方法。
在我的longrunning方法我延迟 Thread.Sleep（30000）。当我使用Task.wait系统挂起，它不调用longrunningmethodcompleted方法。如果我不使用Task.wait，一切都很好。

解决方案

我强烈怀疑你的上下文是一个UI上下文。 p>

在这种情况下，你会导致死锁，因为你告诉 longrunningmethodcompleted 在当前 SynchronizationContext 。

然后你通过调用 Wait 中。继续将永远不会完成，因为它需要在 Wait 中阻塞的线程上执行。

修复此问题，则不能对在该上下文中运行的延续使用 Wait 。我假设 longrunningmethodcompleted 必须在UI线程上运行，所以解决方案是替换调用 Wait 调用 ContinueWith ：

  var ui = TaskScheduler.FromCurrentSynchronizationContext（）; 
 var task = Task> .Factory.StartNew（（）=> longrunningmethod（）
 .ContinueWith（a => 
 longrunningmethodcompleted（（Task< string>）a，
 ui）; 
 task.ContinueWith（...，ui）; 
  

或者，您可以升级到VS2012并使用 async / await ，这样可以编写更清晰的代码， / p>

  var task = Task.Run（（）=> longrunningmethod（））; 
 await task; 
 longrunningmethodcompleted（task）; 
  

I am having a task like below.

var task = Task<string>.Factory.StartNew(() => longrunningmethod()
    .ContinueWith(a =>
             longrunningmethodcompleted((Task<string>)a,
                  TaskScheduler.FromCurrentSynchronizationContext())));

task.Wait();

My task will call the longrunningmethod and after completing it will call completed method. Inside my longrunningmethod I am delaying by Thread.Sleep(30000). When I use Task.wait system hangs and it's not calling longrunningmethodcompleted method. If I don't use Task.wait everything flows good.

解决方案

I strongly suspect your context is a UI context.

In that case, you're causing the deadlock because you're telling longrunningmethodcompleted to execute on the current SynchronizationContext.

Then you're blocking that context by calling Wait. The continuation will never complete because it needs to execute on the thread that is blocked in Wait.

To fix this, you can't use Wait on a continuation running in that context. I'm assuming that longrunningmethodcompleted must run on the UI thread, so the solution is to replace the call to Wait with a call to ContinueWith:

var ui = TaskScheduler.FromCurrentSynchronizationContext();
var task = Task<string>.Factory.StartNew(() => longrunningmethod()
    .ContinueWith(a =>
         longrunningmethodcompleted((Task<string>)a,
         ui);
task.ContinueWith(..., ui);

Or, you can upgrade to VS2012 and use async/await, which lets you write much cleaner code like this:

var task = Task.Run(() => longrunningmethod());
await task;
longrunningmethodcompleted(task);

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