This is probably one of the most frequent questions in the Stackoverflow, however I couldn't find the exact answer to my question:
I would like to design a pattern, which allows to start thread B from thread A and under specific condition (for example when exception occurs) call the method in thread A. In case of exception the correct thread matters a lot because the exception must call a catch method in the main thread A. If a thread A is an UI thread then everything is simple (call .Invoke() or .BeginInvoke() and that's it). The UI thread has some mechanism how it is done and I would like to get some insights how it would be possible to write my own mechanism for the non-UI thread. The commonly suggested method to achieve this is using the message pumping
http://www.codeproject.com/Articles/32113/Understanding-SynchronizationContext-Part-II
but the while loop would block the thread A and this is not what I need and not the way how UI thread handles this issue. There are multiple ways to work around this issue but I would like to get a deeper understanding of the issue and write my own generic utility independently of the chosen methods like using System.Threading.Thread or System.Threading.Tasks.Task or BackgroundWorker or anything else and independently if there is a UI thread or not (e.g. Console application).
Below is the example code, which I try to use for testing the catching of the exception (which clearly indicates the wrong thread an exception is thrown to). I will use it as an utility with all the locking features, checking if a thread is running, etc. that is why I create an instance of a class.
class Program
{
static void Main(string[] args)
{
CustomThreads t = new CustomThreads();
try
{
// finally is called after the first action
t.RunCustomTask(ForceException, ThrowException); // Runs the ForceException and in a catch calls the ThrowException
// finally is never reached due to the unhandled Exception
t.RunCustomThread(ForceException, ThrowException);
}
catch (Exception ex)
{
Console.WriteLine(ex.Message);
}
// well, this is a lie but it is just an indication that thread B was called
Console.WriteLine("DONE, press any key");
Console.ReadKey();
}
private static void ThrowException(Exception ex)
{
throw new Exception(ex.Message, ex);
}
static void ForceException()
{
throw new Exception("Exception thrown");
}
}
public class CustomThreads
{
public void RunCustomTask(Action action, Action<Exception> action_on_exception)
{
Task.Factory.StartNew(() => PerformAction(action, action_on_exception));
}
public void RunCustomThread(Action action, Action<Exception> action_on_exception)
{
new Thread(() => PerformAction(action, action_on_exception)).Start();
}
private void PerformAction(Action action, Action<Exception> action_on_exception)
{
try
{
action();
}
catch (Exception ex)
{
action_on_exception.Invoke(ex);
}
finally
{
Console.WriteLine("Finally is called");
}
}
}
One more interesting feature that I've found is that new Thread() throws unhandled Exception and finally is never called whereas new Task() does not, and finally is called. Maybe someone could comment on the reason of this difference.
