通过任务调用异步操作

Question

I have Duplex and Sessionfull service and an operation as:

public FindStudies_DTO_OUT FindStudies(FindStudies_DTO_IN findStudies_DTO_IN)
    {
        var token = Token;
        List<Study_C> ret = new List<Study_C>();
        _dispatcherCallBack = OperationContext.Current.GetCallbackChannel<IDispatcherCallBack>();
        AnnuncedFindStudies += DispatcherService_AnnuncedFindStudies;
        AnnuncedSPError += DispatcherService_AnnuncedSPError;
        Parallel.ForEach(Cluster, sp =>
        {
            //Blah blah
            OnAnnuncedSPError(new SPError_DTO()
            {
                ServicePointName = sp.Name,
                ErrorMessage = "Ping failed for " + sp.Name
            });
            var result = new List<Study_C>();//Filled
            lock (ret)
            {
                OnAnnounceFindStudies(new FindStudies_DTO()
                {
                    ServicePointName = sp.Name,
                    Studies = result
                });
                ret.AddRange(result);
            }
            //blah blah
        });
        return new FindStudies_DTO_OUT(ret.Sort(findStudies_DTO_IN.SortColumnName, findStudies_DTO_IN.SortOrderBy));
    }

and In consumer side (Web application in generic handler):

var findTask = Task.Factory.StartNew(() =>
                    {
                        DispatcherClient dispatcherClient = new DispatcherClient(new DispatcherCallBack(), "dispatcherEndPoint", Token, Global.Cluster);
                        dispatcherClient.AnnuncedSPError += DispatcherClient_AnnuncedSPError;
                        dispatcherClient.AnnuncedFindStudies += DispatcherClient_AnnuncedFindStudies;
                        var res = dispatcherClient.FindStudies(new FindStudies_DTO_IN(startIndex, numberOfRows, col.FromText(sortColumnName), sort.FromText(sortOrder), criteria, searchMatching));
                        studies = Studies;
                    });
                    findTask .Wait();

in client-side when I set break-point on var findTask everything works perfectly but when I remove break-point it works just in the first go but after that I have get the below exception:

InvalidOperationException: An asynchronous operation cannot be started at this time. Asynchronous operations may only be started within an asynchronous handler or module or during certain events in the Page lifecycle. If this exception occurred while executing a Page, ensure that the Page is marked <%@ Page Async="true" %>. This exception may also indicate an attempt to call an "async void" method, which is generally unsupported within ASP.NET request processing. Instead, the asynchronous method should return a Task, and the caller should await it.

does anybody know how the client-side should be implemented?

Thanks in advance.

Answer 1

I don't know why I can't use infinite wait in client side, but from what I have read here it is recommended don't do that asyc over sync and vice versa.

Anyway I have resolved this problem by below solution:

In server side a task be run and some event are handled in that:

public FindStudies_DTO_OUT FindStudies(FindStudies_DTO_IN findStudies_DTO_IN)
    {
        var token = Token;
        List<Study_C> ret = new List<Study_C>();
        _dispatcherCallBack = OperationContext.Current.GetCallbackChannel<IDispatcherCallBack>();
        AnnuncedFindStudies += (s, e) =>
        {
            _dispatcherCallBack.OnAnnounceFindStudies(e);
        };
        AnnuncedSPError += (s, e) =>
        {
            _dispatcherCallBack.OnAnnunceSPError(e);
        };
        AnnuncedComplete += (s, e) =>
        {
            _dispatcherCallBack.OnAnnunceComplete();
        };
        Task.Run(() =>
        {
            //Blah blah
            if (proxyGetError)
                OnAnnuncedSPError(new SPError_DTO()
                {
                    ServicePointName = sp.Name,
                    ErrorMessage = "Ping failed for " + sp.Name
                });
            var result = new List<Study_C>();//Filled
            lock (ret)
            {
                OnAnnounceFindStudies(new FindStudies_DTO()
                {
                    ServicePointName = sp.Name,
                    Studies = result
                }); 
            }
            //blah blah
            OnAnnounceComplete();
        });
        return new FindStudies_DTO_OUT();
    }

and in consumer side a task be run also with a timeout and it be completed when AnnuncedComplete get raised:

 DispatcherClient dispatcherClient = new DispatcherClient(new DispatcherCallBack(), "dispatcherEndPoint", Token, Global.Cluster);
                    Task.Run(() =>
                    {
                        studies = new List<Study_C>();
                        try
                        {
                            ManualResetEvent ev = new ManualResetEvent(false);
                            dispatcherClient.AnnuncedSPError += (s, e) =>
                            {
                                spErrorMessage += e.ServicePointName + "<br/>";
                            };
                            dispatcherClient.AnnuncedFindStudies += (s, e) =>
                            { 
                                lock (studies)
                                {
                                    studies.AddRange(e.Studies);
                                }
                            };
                            dispatcherClient.AnnuncedComplete += (s, e) =>
                            {
                                ev.Set();
                            };
                            var rrr = dispatcherClient.FindStudies(new FindStudies_DTO_IN(startIndex, numberOfRows, col.FromText(sortColumnName), sort.FromText(sortOrder), criteria, searchMatching)).Studies;
                            ev.WaitOne();
                        }
                        catch (Exception exp)
                        {
                            Logging.Log(LoggingMode.Error, "Failed to Find Studies by Dispatcher, EXP:{0}", exp);
                        }
                    }).Wait(dispatcherClient.Endpoint.Binding.ReceiveTimeout);

The main problem was findTask.Wait() with no milliseconds timeout but by setting milliseconds timeout for task everything works nice.

I think in ASP.Net pipeline an infinite task is not acceptable for this reason engine should know a task will be ended finally by timeout....