任务和异常沉默 [英] Task and exception silence

问题描述

为什么在任务中抛出的异常是静默异常，你永远不知道是否抛出了一个异常。

Why exceptions thrown within a task are silent exception and you never know if a certain exception has been thrown

try
{

 Task task = new Task(
  () => {
          throw null;
        }
        );
  task.Start();
 }
 catch
 {
  Console.WriteLine("Exception");
 }  

该程序在一个完整的沉默中成功运行！
线程的行为不同

the program run successfully in a complete silence! where the behavior of threads is different

try
{

 Thread thread = new Thread(
  () => {
          throw null;
        }
        );
  thread .Start();
 }
 catch
 {
  Console.WriteLine("Exception");
 }

在这种情况下将抛出一个空指针异常。
有什么区别？

a null pointer exception will be thrown in this case. What is the difference?

推荐答案

这种情况的行为取决于你拥有的框架;在4.0中，您实际上需要注意 - 如果您不处理 TaskScheduler.UnobservedTaskException ，则在收集/确定后会错误 ，并且将杀死你的进程。

The behaviour of that scenario depends on what framework you have; in 4.0, you actually need to be careful - if you don't handle TaskScheduler.UnobservedTaskException, it will error later when it gets collected/finalized, and will kill your process.

TaskScheduler.UnobservedTaskException += (sender, args) =>
{
    Trace.WriteLine(args.Exception.Message); // somebody forgot to check!
    args.SetObserved();
};

这个变化在4.5，IIRC。

This changes in 4.5, IIRC.

要检查任务的结果，可能失败，您可以注册一个延续 - 即调用 ContinueWith 并检查结果的异常。或者，访问任务的 .Result （也将执行隐式 Wait（））将重新表达发生的例外。观察一个任务的结果是很好的，因为它清除了最终化标志，这意味着它可以更便宜地收集。

To check the outcome of a Task that might fail, you could register a continuation - i.e. call ContinueWith and check the result's exception. Alternatively, accessing the .Result of the task (which would also do an implicit Wait()) will re-surface the exception that happened. It is good to observe the result of a task, as that clears the finalization flag, meaning it can be collected more cheaply.

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