.net - MS 考试 70-536 - 如何从线程中抛出和处理异常？

Question

在MS Exam 70-536 .Net Foundation ，第1课Creating Threads中的Chapter 7“Threading”有一段文字:

Be aware that because the WorkWithParameter method takes an object, Thread.Start could be called with any object instead of the string it expects. Being careful in choosing your starting method for a thread to deal with unknown types is crucial to good threading code. Instead of blindly casting the method parameter into our string, it is a better practice to test the type of the object, as shown in the following example:

' VB
Dim info As String = o as String
If info Is Nothing Then
    Throw InvalidProgramException("Parameter for thread must be a string")
End If
// C#
string info = o as string;
if (info == null)
{
    throw InvalidProgramException("Parameter for thread must be a string");
} 

所以，我试过了，但是异常处理不当(没有控制台异常条目，程序终止)，我的代码有什么问题(如下)？

class Program
    {
        static void Main(string[] args)
        {
            Thread thread = new Thread(SomeWork);
            try
            {
                thread.Start(null);
                thread.Join();
            }
            catch (InvalidProgramException ex)
            {
                Console.WriteLine(ex.Message);
            }
            finally
            {

                Console.ReadKey();
            }
        }

        private static void SomeWork(Object o)
        {
            String value = (String)o;
            if (value == null)
            {
                throw new InvalidProgramException("Parameter for "+
                    "thread must be a string");
            }
        }
    }

感谢您的宝贵时间!

Answer 1

Main 方法中的异常处理程序运行在与抛出异常不同的线程中。因此，thread 中的异常无法在Main 中捕获。检查here讨论为什么你不想跨线程抛出/捕获异常。你应该做的是使用一个对象来包装你的线程逻辑但支持异常。例如:

class Program
{
    static void Main(string[] args)
    {
        ExceptionHandlingThreadWrapper wrapper = new ExceptionHandlingThreadWrapper();
        Thread thread = new Thread(wrapper.Run);
        try
        {
            thread.Start(null);
            thread.Join();
            if (wrapper.Exception != null)
                throw new Exception("Caught exception", wrapper.Exception);
        }
        catch (Exception ex)
        {
            Console.WriteLine(ex.ToString());
        }
        finally { Console.ReadKey(); }
    }
}

public class ExceptionHandlingThreadWrapper
{
    public ExceptionHandlingThreadWrapper()
    {
        this.Exception = null;
    }

    public Exception Exception { get; set; }

    public void Run(Object obj)
    {
        try
        {
            String value = obj as String;
            if (value == null)
                throw new Exception("Argument must be string");
        }
        catch (Exception ex)
        {
            this.Exception = ex;
        }
    }
}