Task Parallel Library (TPL)

I did the following and it solved my problem. The UI is not blocked anymore. I know it is not the best solution but at least it works. Thanks again a lot for your help.

private void InserClient(int ClientId)
        {
           Task tsk;
            tsk = Task.Factory.StartNew(() =>
            {
                AddClient(ClientId)
            });
        }

private void AddClient(ClientId)
{
            try
            {
                  some database code .......
            }
            catch (Exception ex)
            {
                this.BeginInvoke((System.Action)delegate
                {
                        EnableButtons(true);
                        throw ex;
                });
            }
}

You can avoid explicit marshaling with tsk.ContinueWith() but only if you use the 'synchronization context scheduler' rather than the default TaskScheduler.

If you declare this field in your Form class:

private TaskScheduler uiScheduler;

then in the constructor initialize it as follows:

public Form1()
{
    InitializeComponent();
    uiScheduler = TaskScheduler.FromCurrentSynchronizationContext();
}

and then change InserClient as follows:

        private void InserClient(int ClientId)
        {
           Task tsk;
            tsk = Task.Factory.StartNew(() =>
            {
                AddClient(ClientId)
            });

            try
            {
                tsk.ContinueWith(x =>
                    {
                        LoadClients();
                        EnableButtons(true); 
                   }, uiScheduler);

                tsk.Wait();
            }
            catch (AggregateException ex)
            {
                EnableButtons(true);
                throw ex.Flatten();
            }
        } 

it should avoid the need to use Invoke or BeginInvoke within the Task. However, I'm not sure whether that will cover the EnableButtons(true) statement in the 'catch' clause as that isn't really part of the Task.

when you start the Task, from a Button_Click handler or wherever, to start it on a new threadpool thread, you'll now need to do:

Task.Factory.StartNew(() => InserClient(ClientId));

Could you give some code for the solution you just suggested?

Thanks

I wanted to avoid Invoke or BeginInvoke. I thought tsk.ContinueWith was supposed to do that or I'm mistaken?

If I remove Task.Wait() exception is not thrown but UI is fine (no blocking). If I add Task.Wait() I get exception but UI is blocked.

This thing started to confuse me. TPL was supposed to be much easier to use that traditional Threading yet is so unclear and confusing.

If I call the Task.Wait() the task is executed syncrhonously and not asynchronously. I noticed that because the main thread (UI) os blocked until the Task is completed.

What we were missing here is that you have to call the Task's Wait() method for the unhandled exceptions to be wrapped in an AggregateException and rethrown on the calling thread. So if you insert the highlighted line, then it should work:

 private void InserClient(int ClientId)
        {
           Task tsk;
            tsk = Task.Factory.StartNew(() =>
            {
                AddClient(ClientId)
            });

            try
            {
                tsk.ContinueWith(x =>
                    {
                        LoadClients();
                        EnableButtons(true); 
                   });

                tsk.Wait();
            }
            catch (AggregateException ex)
            {
                EnableButtons(true);
                throw ex.Flatten();
            }
        }

thank a lot for your assistance.

if you mean try something like this after first catch block I already tried it and it does not work.

catch (Exception ex)
            {
                EnableButtons(true);
                throw ex.Flatten();
            }

I know I marked it as answered but I m still experiencing problems.   I create an exception in AddClient(Convert.toInt32("S")) but the exception is not thrown.
Can you help me please     

        private void InserClient(int ClientId)
        {
           Task tsk;
            tsk = Task.Factory.StartNew(() =>
            {
                AddClient(ClientId)
            });

            try
            {
                tsk.ContinueWith(x =>
                    {
                        LoadClients();
                        EnableButtons(true);
                   });
            }
            catch (AggregateException ex)
            {
                EnableButtons(true);
                throw ex.Flatten();
            }
        }

        private void AddClient(int ClientId)
        {
            using (CLIENTSDataContext dataContext = new CLIENTSDataContext(MyConnectionString))
            {
                Convert.ToInt32("S");
                dataContext.INSERT_Client(ClientName, ClientAddress);
            }
        }

Thanks a lot.

I enclosed the result of the Task into Try/Catch which catches AggregateException and Flattens it.