Catching Exceptions in a .NET Thread

Question

How could you find out that an Exception occurred in a Thread in a MultiThreaded Application ? and consecutively clean the resources ?

Because otherwise the Thread can be still remaining in memory and running.

Answer 1

As Sean has said, you have to do all exception handling and cleanup inside the thread method, you can't do it in the Thread initialization. For example:

public void Run()
{
    try
    {
        Thread thread1 = new Thread(ThreadEntry1);
        thread1.Start();

        Thread thread2 = new Thread(ThreadEntry2);
        thread2.Start();
    }
    catch (NotImplementedException)
    {
        // Neither are caught here
        Console.WriteLine("Caught you");
    }
}

private void ThreadEntry1()
{
    throw new NotImplementedException("Oops");
}

private void ThreadEntry2()
{
    throw new NotImplementedException("Oops2");
}

Instead, this approach is more self-contained and obviously also works:

public void Run()
{
    Thread thread1 = new Thread(ThreadEntry1);
    thread1.Start();
}

private void ThreadEntry1()
{
    try
    {
        throw new NotImplementedException("Oops");
    }
    catch (NotImplementedException)
    {
        Console.WriteLine("Ha! Caught you");
    }
}

If you want to know if the Thread has failed, then you should consider an array of WaitHandles, and signal back to your calling method. An alternative and simpler approach is to simply increment a counter each time a thread's operation finishes:

Interlocked.Increment(ref _mycounter);

Answer 2

If you're worried about this sort of thing then you should wrap your threads entry point in a try/catch block and do the cleanup explicitly. Any exception passing out of the thread entry point will cause your app to shut down.