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Asked: 2026-05-11T15:43:01+00:00

I have an idea why but I’d like to ask if someone has a

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I have an idea why but I’d like to ask if someone has a good grasp on why the exception raised inside a thread is never caught by the code that started it. Here’s some very simple code to demonstrate what I mean:

using System; using System.Collections.Generic; using System.Threading;  namespace TestCrash {     class Program     {         private static void Crash(object control)         {             AutoResetEvent are = (AutoResetEvent)(((object[])control)[0]);             are.Set();             throw new Exception('Burn baby burn');         }         static void Main(string[] args)         {             try             {                 List<WaitHandle> waitHandles = new List<WaitHandle>();                 for (int i = 0; i < 100; i++)                 {                     AutoResetEvent are = new AutoResetEvent(false);                     waitHandles.Add(are);                     object[] procControl = new object[] { are };                     ThreadPool.QueueUserWorkItem(Crash, procControl);                     WaitHandle.WaitAll(waitHandles.ToArray());                 }             }             catch (Exception ex)             {                 Console.WriteLine(ex.Message);             }         }     } }

I naively thought that by having the try/catch I would be safe, but I found out the hard way that it is not the case (it is crashing one of my services).

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1 Answer

  1. Well in general, you’ve no idea where the originating thread will be by the time the exception is thrown in the new thread – why would it be waiting around for the thread to throw an exception?

    Think of the stacks involved – when an exception is thrown, it goes up the stack until it reaches an appropriate catch block. The new thread has a completely separate stack to the creating thread, so it’ll never reach the catch block in the creating thread’s stack.

    EDIT: Of course, you could design your system so that the creating thread did wait for other things to happen – a bit like the message loop in a Windows Forms application. The new thread could then catch the exception and send a message to the creating thread, which could then deal with the exception. That isn’t the normal setup though – you have to do it all explicitly.

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