TPL如何执行“回访” [英] TPL How to Perform a 'Call-Back'

问题描述

我有一个小的应用程序，需要测试SQL连接字符串的连接数（每完成一处，一时间）。要做到这一点，我将 ConnectionTimeout = 5 暂时避免了漫长的等待，如果连接无效， ConnectionTimeout = 0 （永远等待）说。

要避免UI挂，而我们试图打开（）坏连接（甚至与 ConnectionTimeout = 5 的等待的SQLException 可长达二十秒为单位），我要运行使用任务并行库（TPL）一个单独的线程测试。所以我剥离我的新主题，如：

 任务<布尔> asyncTestConn = Task.Factory.StartNew<布尔> 
（（）=> TestConnection（康涅狄格州，bShowErrMsg））; 
返回asyncTestConn.Result; 
  

的问题是，这仍然是锁定的用户界面（明确），因为它正在等待结果之前返回到调用者。如何允许代码同时从异步工作？

$得到最终的结果控制返回到UI（释放的GUI） b $ b

此外，从内工作我能做到合法 MessageBox.Show（一些信息）？这不适用于 BackgroundWorkers 工作和汇集线程是默认后台线程;但它似乎并不成为一个问题。感谢您的时间

解决方案

您是对的，这是在等待发生的：

 收益asyncTestConn.Result; 
  

您可以简单地建立在TestConnection（尾部的精达代码）或使用继续：

  //未经检验的
 //任务<布尔> asyncTestConn = Task.Factory.Create<布尔> （
任务<布尔> asyncTestConn =新任务<布尔>（
（）=> TestConnection（康涅狄格州，bShowErrMsg））; 
 asyncTestConn.ContinueWith（MyFinishCode）; 
 asyncTestConn 。开始（）
  

我可以做合法 MessageBox.Show（一些信息）？

其实是，在MessageBox是线程安全的。应尽可能从BGW为好。

但你用了很多延长工作寿命，这不是一个好主意。

I have a small application that needs to test SQL connection strings for a number of connections (each done one-at-a-time). To do this I set the ConnectionTimeout = 5 temporarily to avoid a long wait if the connection is not valid and ConnectionTimeout = 0 (wait forever), say.

To avoid the UI hanging whilst we attempt to Open() a bad connection (even with ConnectionTimeout = 5 the wait for the SqlException can be up to twenty seconds), I want to run the test on a separate thread using Task Parallel Library (TPL). So I spin-off my new thread like:

Task<bool> asyncTestConn = Task.Factory.StartNew<bool>
    (() => TestConnection(conn, bShowErrMsg));
return asyncTestConn.Result;

The problem is that this is still locking the UI (clearly), as it is waiting for the result before returning to the caller. How do I allow the code to return control to the UI (freeing up the GUI) whilst getting the eventual result from the asynchronous Task?

Also, from within a Task can I legitimately do MessageBox.Show("Some message")? This does not work for BackgroundWorkers and this pooled-thread is a background thread by default; yet it does not seem to be a problem. Thanks for your time.

解决方案

You are right, this is where the waiting happens:

 return asyncTestConn.Result;

You could simply build the finish-up code in the tail of TestConnection() or use a Continuation:

// untested
//Task<bool> asyncTestConn = Task.Factory.Create<bool> (
Task<bool> asyncTestConn = new Task<bool> (
    () => TestConnection(conn, bShowErrMsg));
asyncTestConn.ContinueWith(MyFinishCode);
asyncTestConn.Start()

can I legitimately do MessageBox.Show("Some message")?

Actually Yes, the MessageBox is thread-safe. Should be possible from a Bgw as well.

But you are prolonging the life of the Task by a lot, it's not a good idea.

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