Exception not thrown/shown on different thread

Unity Engine
1

Hello.
I am using multiple threads in Unity ( mainly for networking, not using UNET ).
When an exception occurs in one of the threads, that aren’t the main unity thread, then I doesn’t get any information/hint about it. It is not showing anything in the editor’s console.
To replicate the problem one could just call the following line of code in your unity application:

This throws an exception in a new Thread. Debug.logs work fine inside different threads, but throwing an exception doesn’t show anything.
I even tried to use try/catch around this line of code, but still doesn’t show anything.
Any ideas?

Accessing a VisualElement in any way, from an event, throws exception
Task.Run doesn't output any error information.
Script stops execution without any errors or warnings
2

Try/Catch should work fine. This code works for me:

public void RunThread()
{
    try
   {
      DoThings();
   }
   catch (Exception e)
   {
      Debug.Log(e);
   }
}
3

I never said try/catch doesn’t work. It works within the main thread. But try putting it around the line of code I mentioned in the opening post. Just put “new Thread(()=>{throw new Exception();}).Start();” anywhere in your unity app, so it gets called at some point, you won’t see an exception and that is my problem.
If I put this line of code in a try/catch block then it still does not show an exception.

4

Okay, to match your syntax EXACTLY with a delegate rather than a full method, this should show an exception:

new Thread(()=>
{
   try
   {
      throw new Exception();
   }
   catch (Exception e)
   {
      Debug.LogError(e);
   }
}).Start();
1 Like
5

Depending on how you want to handle the exception maybe one of the solutions mentioned in the answer of this thread might help out: c# - catch exception that is thrown in different thread - Stack Overflow

Notice that you don’t have access the Task though, so you’ll have to do with the two option in the .net 3.5 section of the answer.

1 Like
6

Ah, yes, that’s actually showing me that an exception was thrown. But why won’t it show something without the try/catch ? Also when I just put throw new Exception(); it shows the exception, even without try/catch. But if an exception occurs on a different thread, then I have to use try/catch? Why?
Also: Thanks for your answer!

1 Like
7

because the Console only listens to exceptions on its own thread, as it was designed for. Non-unity threads are outside the scope of its responsibility.

1 Like
8

That makes sense and Debug.Log is always linked to the main thread somehow so if I place try/catch around my code in a different thread, then it will be shown in the console?

9

If you place the try/catch in a different thread it will only show up in that thread. Check the link I posted yesterday, as in that thread you will see a way you can get the exception to show up in the log by manually pushing it to the calling thread.

10

I also encountered the same issue and I found a solution which uses AppDomain class in .NET.
You can check below sample codes which explains all by itself:

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using System.Threading;
using System;

public class Test : MonoBehaviour {

    Thread t1;
    List<int> a = null;

    void Start ()
    {
        AppDomain app1 = AppDomain.CurrentDomain
        app1.UnhandledException += App1_UnhandledException;
        try
        {

            t1 = new Thread(new ThreadStart(Main1));
            t1.Start();
        }
        catch(Exception e)
        {

        }
      
      
    }

    private void App1_UnhandledException(object sender, UnhandledExceptionEventArgs e)
    {


        Debug.Log(e.ExceptionObject.ToString());

    }

    void Main1()
    {
        a.Add(1); // this should cause an expection.
     
    }
  

    private void OnDestroy()
    {
        try
        {
            t1.Abort();
        }
        catch
        {

        }
    }
}
2 Likes