Exceptions in multithreaded application.

Question

I have heard from a very discerning person that an exception being thrown (and not caught) in a thread is being propagated to the parent thread. Is that true? I have tried some

Answer 1

There is a very simple solution for the special case when the main thread waits for the completion of the other thread (see https://msdn.microsoft.com/en-us/library/58195swd(v=vs.110).aspx#Examples). It requires only a class exception variable.

The modified code sample completed by an exception handler may look like this.

using System;
using System.Threading;

class WaitOne
{
    static AutoResetEvent autoEvent = new AutoResetEvent(false);
    static Exception SavedException = null;

    static void Main()
    {
        Console.WriteLine("Main starting.");

        ThreadPool.QueueUserWorkItem(
            new WaitCallback(WorkMethod), autoEvent);

        // Wait for work method to signal.
        autoEvent.WaitOne();
        if (SavedException != null)
        {
           // handle this exception as you want
        }

        Console.WriteLine("Work method signaled.\nMain ending.");
    }

    static void WorkMethod(object stateInfo) 
    {
        Console.WriteLine("Work starting.");

        // Simulate time spent working.
        try
        {
          Thread.Sleep(new Random().Next(100, 2000));
          throw new Exception("Test exception");
        }
        catch (Exception ex)
        {
            SavedException = ex;
        }            

        // Signal that work is finished.
        Console.WriteLine("Work ending.");
        ((AutoResetEvent)stateInfo).Set();
    }
}