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• Confused about my future. Doubt about .Net or Java way.

  - by dotNET

  I'm very confused about choosing the programming langage to follow in the next step of my life. I'm right now so familiar with C++, VB.NET and PHP, but to jump to a higher level I must choose between JEE(JSP, Servlets, JSF, Spring, EJB, Struts, Hibernate,...) and .NET(ASP.NET, C#). Because I cant learn them at the same time. And you realize that, when I mentioned JEE a lot of things comes to the head. In my personnal experience I prefere the .NET, but Java seems to be a better choice. believe me, i'm not writing a subjective topic. I just want to know what must I follow to get succes in my life. The question here is : Is there any things that can be done with Java, and cannot be done with .NET. Is there any chances that I can follow the uncounted number of frameworks that are always in developpement. ... (also something not said) ?

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• using static methods and classes

  - by vedant1811

  I know that static methods/variables are associated with the class and not the objects of the class and are useful in situations when we need to keep count of, say the number of objects of the class that were created. Non-static members on the other hand may need to work on the specific object (i.e. to use the variables initialized by the constructor) My question what should we do when we need neither of the functionalities? Say I just need a utility function that accepts value(s) and returns a value besed solely on the values passed. I want to know whether such methods should be static or not. How is programming efficiency affected and which is a better coding practice/convention and why. PS: I don't want to spark off a debate, I just want a subjective answer and/or references.

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• How compilers know about other classes and their properties?

  - by OnResolve

  I'm writing my first programming language that is object orientated and so far so good with create a single 'class'. But, let's say I want to have to classes, say ClassA and ClassB. Provided these two have nothing to do with each other then all is good. However, say ClassA creates a ClassB--this poses 2 related questions: -How would the compiler know when compiling ClassA that ClassB even exists, and, if it does, how does it know it's properties? My thoughts thus far had been: instead of compiling each class at a time (i.e scan, parse and generate code) each "file (not really file, per se, but a "class") do I need to scan + parse each first, then generate code for all?

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• How to begin serious game development (in C++) [closed]

  - by Rondogiannis Aristophanes

  I would like to start developing games. I have tried before Game Maker 8, which was a very easy way to start creating games, if you were new in game development. Then, I tried Unity 3D, which was a much more serious and complete tool to create computer-games, and required some experience. And now, I would like to start creating games, and don't use any special environment or developer, but just code (in C++ preferably). So, here is my question: from where should I begin, if I would like to start programming games? Thanks in advance. Note: I work in ubuntu 10.04, I can also use windows 7, but I prefer ubuntu.

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• What is the difference from the push and pull development models?

  - by michelpm

  I was reading Extreme Programming Explained, Second Edition and in the chapter 11 "The Theory of Constraints" the authors talk about the old and obsolete "push" development model and the XP way, the "pull" development model. It looks like a quite important concept, but it takes only a very small paragraph and two images that are mere illustrations of the "waterfall" and iterative process, nothing specific about these models except by the image caption. I searched and it doesn't go any further about it in the rest of the book. I couldn't find any further explanations or discussions about it in the Internet either. If the only difference about those is that one is "waterfall" and the other is iterative, them why push and why pull? Does anyone understand what is really the difference between those two and give some good examples?

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• Need to organize words based on their components, any other way aside from brute force?

  - by Lathan

  I'm not sure if this process has a name. I have some words (about 9,000). They are in Japanese, but I'll try to explain this using English words. I want to categorize the words by the components (in English, letters). A B C act bar play This should create: A: play B: bar C: act Now, 'a' appears in all 3 words, but I want to make sure that each category (letter) has at least word. Now, it would make sense to delete a word after it's used, but there are a few cases where 2 letters make up one word and that's each letter's only word--so I'd like to account for that somehow. Is there an approach for solving this aside from brute force? Dynamic programming perhaps? Even a name for this process (if it exists) would be great.

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• Starting With Desktop Apps [closed]

  - by perl.j

  I've been programming for a while now. It is a great hobby for me! Actually, It's my only hobby! But I haven't really programmed in a specific area i.e. desktop, web, etc.. After a long while of research, I've decided to jump into making Desktop Applications. But how should I go about doing this? Are there languages that are used to do this, or is it possible to use Python, Perl, C, etc. to make vivid, "amazing-quality", "highly functional" Desktop Apps? Also, what are some good resources to begin learning this? Thanks!

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• What do you need to master a language and its technology? [closed]

  - by LongTTH

  Possible Duplicate: how to really master a programming language Let say about Java(just a sample, you can talk about C#, PHP, C++ ... it's just similar) and 10 (ten) levels, 1 is newbie and 10 is master. How can you identify someone at which level based on his knowledge? I do not tend to compare languages, I do tend to know what indicate a master or a newbie in a language and its (language's) based technology. Yeah, I know there aren't on earth a language stand alone, it always come with a technology with it. Let say in Java, you can memorize all of its keyword and syntax in just few days, but to know it (I mean do something with it effectively), you must read the Oracle (Sun) javadoc many many times (I'm not mention the 3rd party product yet).

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• Would you use (a dialect of) LISP for a real-world application? Where and why?

  - by Anto

  LISP (and dialects such as Scheme, Common LISP and Clojure) haven't gained much industry support even though they are quite decent programming languages. (At the moment though it seems like they are gaining some traction). Now, this is not directly related to the question, which is would you use a LISP dialect for a production program? What kind of program and why? Usages of the kind of being integrated into some other code (e.g. C) are included as well, but note that it is what you mean in your answer. Broad concepts are preferred but specific applications are okey as well.

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• Why are my labels not updating in my update panel in ASP.NET?

  - by CowKingDeluxe

  I have a label in my update panel that I want to update its text on after a successful asynchronus file upload. Here's my markup: <asp:UpdatePanel ID="UpdatePanel1" runat="server"><ContentTemplate> Step 1 (<asp:Label ID="label_fileupload" runat="server" />): <br /> <ajaxToolkit:AsyncFileUpload ID="AsyncFileUpload1" Width="200px" runat="server" CompleteBackColor="Lime" UploaderStyle="Modern" ErrorBackColor="Red" ThrobberID="Throbber" UploadingBackColor="#66CCFF" OnClientUploadStarted="StartUpload" /> <asp:Label ID="Throbber" runat="server" Style="display: none"><img src="/images/indicator.gif" alt="loading" /></asp:Label> <br /> <asp:Label ID="statuslabel" runat="server" Text="Label"></asp:Label> </ContentTemplate></asp:UpdatePanel> Here is my code-behind: Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load If (IsPostBack) Then Else label_fileupload.Text = "Incomplete" label_fileupload.CssClass = "uploadincomplete" statuslabel.Text = "NOT DONE" End If End Sub Public Sub AsyncFileUpload1_UploadedComplete1(ByVal sender As Object, ByVal e As AjaxControlToolkit.AsyncFileUploadEventArgs) Handles AsyncFileUpload1.UploadedComplete System.Threading.Thread.Sleep(1000) If (AsyncFileUpload1.HasFile) Then Dim strPath As String = MapPath("/images/White.png") AsyncFileUpload1.SaveAs(strPath) End If label_fileupload.Text = "Complete" label_fileupload.CssClass = "uploadcomplete" statuslabel.Text = "DONE" End Sub When I set the labels to update via a button click, they work. But when I set them to update via the Upload complete event, they don't work. Is there some way around this to get the labels to update their text / css class from the UploadedComplete event of an asynchronous file upload control?

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• Sync Vs. Async Sockets Performance in C#

  - by Michael Covelli

  Everything that I read about sockets in .NET says that the asynchronous pattern gives better performance (especially with the new SocketAsyncEventArgs which saves on the allocation). I think this makes sense if we're talking about a server with many client connections where its not possible to allocate one thread per connection. Then I can see the advantage of using the ThreadPool threads and getting async callbacks on them. But in my app, I'm the client and I just need to listen to one server sending market tick data over one tcp connection. Right now, I create a single thread, set the priority to Highest, and call Socket.Receive() with it. My thread blocks on this call and wakes up once new data arrives. If I were to switch this to an async pattern so that I get a callback when there's new data, I see two issues The threadpool threads will have default priority so it seems they will be strictly worse than my own thread which has Highest priority. I'll still have to send everything through a single thread at some point. Say that I get N callbacks at almost the same time on N different threadpool threads notifying me that there's new data. The N byte arrays that they deliver can't be processed on the threadpool threads because there's no guarantee that they represent N unique market data messages because TCP is stream based. I'll have to lock and put the bytes into an array anyway and signal some other thread that can process what's in the array. So I'm not sure what having N threadpool threads is buying me. Am I thinking about this wrong? Is there a reason to use the Async patter in my specific case of one client connected to one server?

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• Asynchronuos callback saves value but prints FAILED

  - by sprasad12

  Hi, I am using nested Asynchronous callbacks to save my front-end data to the back-end database. The data is being save into the tables the way i want them to, but it is printing that it failed. Here is the code: oksave.addClickHandler(new ClickHandler(){ public void onClick(ClickEvent event) { if(erasync == null) erasync = GWT.create(EntityRelationService.class); AsyncCallback<Void> callback = new AsyncCallback<Void>(){ public void onFailure(Throwable caught) { String msg = caught.getLocalizedMessage(); if (caught instanceof NotFoundException) { msg = ((NotFoundException) caught).getType() + ((NotFoundException) caught).getMessage(); } System.out.println("Failed" + msg); } public void onSuccess(Void result) { Label success = new Label("Name : " + pname.getText() + " was successfully saved"); Button close = new Button("close"); VerticalPanel sp = new VerticalPanel(); d1 = new DialogBox(); sp.add(success); sp.add(close); close.addClickHandler(new ClickHandler(){ @Override public void onClick(ClickEvent event) { if(erasync == null) erasync = GWT.create(EntityRelationService.class); AsyncCallback<Void> callbackOthers = new AsyncCallback<Void>(){ @Override public void onFailure(Throwable caught) { String msg = caught.getLocalizedMessage(); if (caught instanceof NotFoundException) { msg = ((NotFoundException) caught).getType() + ((NotFoundException) caught).getMessage(); } System.out.println("Failed" + msg); } @Override public void onSuccess(Void result) { System.out.println("Success"); } }; erasync.setEntityType(name, top, left, pname, callbackOthers); }); }; erasync.setProject(name, callback); }); Here it prints successful for the first callback, but for the nested one it says failed though it saves the value. Am i missing something? Any input will be of great help. Thank you.

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• Getting web page after calling DownloadStringAsync()?

  - by OverTheRainbow

  Hello I don't know enough about VB.Net yet to use the richer HttpWebRequest class, so I figured I'd use the simpler WebClient class to download web pages asynchronously (to avoid freezing the UI). However, how can the asynchronous event handler actually return the web page to the calling routine? Imports System.Net Public Class Form1 Private Shared Sub DownloadStringCallback2(ByVal sender As Object, ByVal e As DownloadStringCompletedEventArgs) If e.Cancelled = False AndAlso e.Error Is Nothing Then Dim textString As String = CStr(e.Result) 'HERE : How to return textString to the calling routine? End If End Sub Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click Dim client As WebClient = New WebClient() AddHandler client.DownloadStringCompleted, AddressOf DownloadStringCallback2 Dim uri As Uri = New Uri("http://www.google.com") client.DownloadStringAsync(uri) 'HERE : how to get web page back from callback function? End Sub End Class Thank you. Edit: I added a global, shared variable and a While/DoEvents/EndWhile, but there's got to be a cleaner way to do this :-/ Public Class Form1 Shared page As String Public Shared Sub AlertStringDownloaded(ByVal sender As Object, ByVal e As DownloadStringCompletedEventArgs) ' If the string request went as planned and wasn't cancelled: If e.Cancelled = False AndAlso e.Error Is Nothing Then page = CStr(e.Result) End If End Sub Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click Dim wc As New WebClient AddHandler wc.DownloadStringCompleted, AddressOf AlertStringDownloaded page = Nothing wc.DownloadStringAsync(New Uri("http://www.google.com")) 'Better way to wait until page has been filled? While page Is Nothing Application.DoEvents() End While RichTextBox1.Text = page End Sub End Class

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• Asynchronously populate datagridview in Windows Forms application

  - by dcryptd

  howzit! I'm a web developer that has been recently requested to develop a Windows forms application, so please bear with me (or dont laugh!) if my question is a bit elementary. After many sessions with my client, we eventually decided on an interface that contains a tabcontrol with 5 tabs. Each tab has a datagridview that may eventually hold up to 25,000 rows of data (with about 6 columns each). I have successfully managed to bind the grids when the tab page is loaded and it works fine for a few records, but the UI freezes when I bound the grid with 20,000 dummy records. The "freeze" occurs when I click on the tab itself, and the UI only frees up (and the tab page is rendered) once the bind is complete. I communicated this to the client and mentioned the option of paging for each grid, but she is adament w.r.t. NOT wanting this. My only option then is to look for some asynchronous method of doing this in the background. I don't know much about threading in windows forms, but I know that I can use the BackgroundWorker control to achieve this. My only issue after reading up a bit on it is that it is ideally used for "long-running" tasks and I/O operations. My questions: How does one determine a long-running task? How does one NOT MISUSE the BackgroundWorker control, ie. is there a general guideline to follow when using this? (I understand that opening/spawning multiple threads may be undesirable in certain instances) Most importantly: How can I achieve (asychronously) binding of the datagridview after the tab page - and all its child controls - loads. Thank you for reading this (ahem) lengthy query, and I highly appreciate any responses/thoughts/directions on this matter! Cheers!

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• C# TCP Async EndReceive() throws InvalidOperationException ONLY on Windows XP 32-bit

  - by James Farmer

  I have a simple C# Async Client using a .NET socket that waits for timed messages from a local Java server used for automating commands. The messages come in asynchronously and is written to a ring buffer. This implementation seems to work fine on Windows Vista/7/8 and OSX, but will randomly throw this exception while it's receiving a message from the local Java server: Unhandled Exception: System.InvalidOperationException: EndReceive can only be called once for each asynchronous operation.     at System.Net.Sockets.Socket.EndReceive(IAsyncResult asyncResult, SocketError& errorCode)     at System.Net.Sockets.Socket.EndReceive(IAsyncResult asyncResult)     at SocketTest.Controller.RecvAsyncCallback(IAsyncResult ar)     at System.Net.LazyAsyncResult.Complete(IntPtr userToken)     ... I've looked online for this error, but have found nothing really helpful. This is the code where it seems to break: /// <summary> /// Callback to receive socket data /// </summary> /// <param name="ar">AsyncResult to pass to End</param> private void RecvAsyncCallback(IAsyncResult ar) { // The exception will randomly happen on this call int bytes = _socket.EndReceive(_recvAsyncResult); // check for connection closed if (bytes == 0) { return; } _ringBuffer.Write(_buffer, 0, bytes); // Checks buffer CheckBuffer(); _recvAsyncResult = _sock.BeginReceive(_buffer, 0, _buffer.Length, SocketFlags.None, RecvAsyncCallback, null); } The error doesn't happen on any particular moment except in the middle of receiving a message. The message itself can be any length for this to happen, and the exception can happen right away, or sometimes even up to a minute of perfect communication. I'm pretty new with sockets and network communication, and I feel I might be missing something here. I've tested on at least 8 different computers, and the only similarity with the computers that throw this exception is that their OS is Windows XP 32-bit.

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• Sync Vs. Async Sockets Performance in .NET

  - by Michael Covelli

  Everything that I read about sockets in .NET says that the asynchronous pattern gives better performance (especially with the new SocketAsyncEventArgs which saves on the allocation). I think this makes sense if we're talking about a server with many client connections where its not possible to allocate one thread per connection. Then I can see the advantage of using the ThreadPool threads and getting async callbacks on them. But in my app, I'm the client and I just need to listen to one server sending market tick data over one tcp connection. Right now, I create a single thread, set the priority to Highest, and call Socket.Receive() with it. My thread blocks on this call and wakes up once new data arrives. If I were to switch this to an async pattern so that I get a callback when there's new data, I see two issues The threadpool threads will have default priority so it seems they will be strictly worse than my own thread which has Highest priority. I'll still have to send everything through a single thread at some point. Say that I get N callbacks at almost the same time on N different threadpool threads notifying me that there's new data. The N byte arrays that they deliver can't be processed on the threadpool threads because there's no guarantee that they represent N unique market data messages because TCP is stream based. I'll have to lock and put the bytes into an array anyway and signal some other thread that can process what's in the array. So I'm not sure what having N threadpool threads is buying me. Am I thinking about this wrong? Is there a reason to use the Async patter in my specific case of one client connected to one server?

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• SmtpClient.SendAsync - How to ensure my application doesn't finish before callback?

  - by James

  Hi, I need to send emails asychronously through a console application. I need to do some DB updates on the callback but my application is exiting before the callback code gets run! How can I stop this from happening in a nice manner rather than simply guessing how long to wait before exiting. I would imagine the Async calls get placed in some form of thread? Is it possible to check if any are waiting to be called? Sample Code private static void SendCompletedCallback(object sender, AsyncCompletedEventArgs e) { // Get the unique identifier for this asynchronous operation. String token = (string) e.UserState; if (e.Cancelled) { Console.WriteLine("[{0}] Send canceled.", token); } if (e.Error != null) { Console.WriteLine("[{0}] {1}", token, e.Error.ToString()); } else { // update DB Console.WriteLine("Message sent."); } } public static void Main(string[] args) { var users = Repository.GetUsers(); SmtpClient client = new SmtpClient("Host"); client.SendCompleted += new SendCompletedEventHandler(SendCompletedCallback); MailAddress from = new MailAddress("[email protected]", "System", Encoding.UTF8); foreach (var user in users) { MailAddress to = new MailAddress(user.Email); MailMessage message = new MailMessage(from, to); message.Body = "This is a test"; message.BodyEncoding = System.Text.Encoding.UTF8; message.Subject = "test message 1" + someArrows; message.SubjectEncoding = System.Text.Encoding.UTF8; string userState = String.Format("Message for user id {0}", user.ID); client.SendAsync(message, userState); message.Dispose(); } // need to wait here until I have received a callback for each message // otherwise the application will exit }

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• WCF Service timeout in Callback

  - by Muckers Mate

  I'm trying to get to grips with WCF, in particular writing a WCF Service application with callback. I've setup the service, together with the callback contract but when the callback is called, the app is timing out. Essentially, from a client I'm setting a property within the service class. The Setter of this property, if it fails validation fires a callback and, well, this is timing out. I realise that this is probably to it not being an Asynchronous calback, but can someone please show me how to resolve this? Thanks // The call back (client-side) interface public interface ISAPUploadServiceReply { [OperationContract(IsOneWay = true)] void Reply(int stateCode); } // The Upload Service interface [ServiceContract(CallbackContract = typeof(ISAPUploadServiceReply))] public interface ISAPUploadService { int ServerState { [OperationContract] get; [OperationContract(IsOneWay=true)] set; And the implementation... public int ServerState { get { return serverState; } set { if (InvalidState(Value)) { var to = OperationContext.Current.GetCallbackChannel<ISAPUploadServiceReply>(); to.Reply(eInvalidState); } else serverState = value; } }

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• WCF Callback Contract InvalidOperationException: Collection has been modified

  - by mrlane

  We are using a WCF service with a Callback contract. Communication is Asynchronous. The service contract is defined as: [ServiceContract(Namespace = "Silverlight", CallbackContract = typeof(ISessionClient),SessionMode = SessionMode.Allowed)] public interface ISessionService With a method: [OperationContract(IsOneWay = true)] void Send(Message message); The callback contract is defined as [ServiceContract] public interface ISessionClient With methods: [OperationContract(IsOneWay = true, AsyncPattern = true)] IAsyncResult BeginSend(Message message, AsyncCallback callback, object state); void EndSend(IAsyncResult result); The implementation of BeginSend and EndSend in the callback channel are as follows: public void Send(ActionMessage actionMessage) { Message message = Message.CreateMessage(_messageVersion, CommsSettings.SOAPActionReceive, actionMessage, _messageSerializer); lock (LO_backChannel) { try { _backChannel.BeginSend(message, OnSendComplete, null); } catch (Exception ex) { _hasFaulted = true; } } } private void OnSendComplete(IAsyncResult asyncResult) { lock (LO_backChannel) { try { _backChannel.EndSend(asyncResult); } catch (Exception ex) { _hasFaulted = true; } } } We are getting an InvalidOperationException: "Collection has been modified" on _backChannel.EndSend(asyncResult) seemingly randomly, and we are really out of ideas about what is causing this. I understand what the exception means, and that concurrency issues are a common cause of such exceptions (hence the locks), but it really doesn't make any sense to me in this situation. The clients of our service are Silverlight 3.0 clients using PollingDuplexHttpBinding which is the only binding available for Silverlight. We have been running fine for ages, but recently have been doing a lot of data binding, and this is when the issues started. Any help with this is appreciated as I am personally stumped at this time.

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• What issues to consider when rolling your own data-backend for Silverlight / AJAX on non-ASP.NET ser

  - by Edward Tanguay

  I have read-only Silverlight and AJAX apps which read static text and XML files from a PHP/Apache server, which works very nicely with features such as asynchronous loading, lazy-loading only what I need for each page, loading in the background, developed a little query language to get a PHP script to create custom XML files etc. it's pragmatic read-only REST, and all works fast and fine for read-only sites. Now I want to also add the ability to write data from these apps to a database on the same PHP/Apache server. For those of you who have built similar data-access layers, what do I need to consider while building this, especially regarding security so that not just any client can write and alter my database, e.g.: check HTTP_USER_AGENT for security check REMOTE_ADDR for security require a special code for security, perhaps a list of TAN codes (such as banks use for online transactions) each which can only be used once, both the client and server have these I wonder if there is some kind of standard REST query I should lean on for e.g. building SQL-like statements in the URL parameters, e.g. http://www.thedatalayersite.com/query?insertinto=customers&... Any thoughts, notes from experience, ideas, gotchas, especially ideas on tightening down security in this endeavor would be helpful.

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• Adding a ServiceReference programmatically during async postback

  - by Oliver

  Is it possible to add a new ServiceReference instance to the ScriptManager on the Page during an asynchronous postback so that subsequently I can use the referenced web service through client side script? I'm trying to do this inside a UserControl that sits inside a Repeater, that's why adding the ScriptReference programmatically during Page_Load does not work here. EDIT 2: This is the code I call from my UserControl which does not do what I expect (adding the ServiceReference to the ScriptManager during the async postback): private void RegisterWebservice(Type webserviceType) { var scm = ScriptManager.GetCurrent(Page); if (scm == null) throw new InvalidOperationException("ScriptManager needed on the Page!"); scm.Services.Add(new ServiceReference("~/" + webserviceType.Name + ".asmx")); } My goal is for my my UserControl to be as unobtrusive to the surrounding application as possible; otherwise I would have to statically define the ServiceReference in a ScriptManagerProxy on the containing Page, which is not what I want. EDIT: I must have been tired when I wrote this post... because I meant to write ServiceReference not ScriptReference. Updated the text above accordingly. Now I have: <asp:ScriptManagerProxy runat="server" ID="scmProxy"> <Services> <asp:ServiceReference Path="~/UsefulnessWebService.asmx" /> </Services> </asp:ScriptManagerProxy> but I want to register the webservice in the CodeBehind.

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• boost::asio::async_resolve Problem

  - by Moo-Juice

  Hi All, I'm in the process of constructing a Socket class that uses boost::asio. To start with, I made a connect method that took a host and a port and resolved it to an IP address. This worked well, so I decided to look in to async_resolve. However, my callback always gets an error code of 995 (using the same destination host/port as when it worked synchronously). code: Function that starts the resolution: // resolve a host asynchronously template<typename ResolveHandler> void resolveHost(const String& _host, Port _port, ResolveHandler _handler) const { boost::asio::ip::tcp::endpoint ret; boost::asio::ip::tcp::resolver::query query(_host, boost::lexical_cast<std::string>(_port)); boost::asio::ip::tcp::resolver r(m_IOService); r.async_resolve(query, _handler); }; // eo resolveHost Code that calls this function: void Socket::connect(const String& _host, Port _port) { // Anon function for resolution of the host-name and asynchronous calling of the above auto anonResolve = [this](const boost::system::error_code& _errorCode, boost::asio::ip::tcp::resolver_iterator _epIt) { // raise event onResolve.raise(SocketResolveEventArgs(*this, !_errorCode ? (*_epIt).host_name() : String(""), _errorCode)); // perform connect, calling back to anonymous function if(!_errorCode) connect(*_epIt); }; // Resolve the host calling back to anonymous function Root::instance().resolveHost(_host, _port, anonResolve); }; // eo connect The message() function of the error_code is: The I/O operation has been aborted because of either a thread exit or an application request And my main.cpp looks like this: int _tmain(int argc, _TCHAR* argv[]) { morse::Root root; TextSocket s; s.connect("somehost.com", 1234); while(true) { root.performIO(); // calls io_service::run_one() } return 0; } Thanks in advance!

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• WCF Async callback setup for polled device

  - by Mark Pim

  I have a WCF service setup to control a USB fingerprint reader from our .Net applications. This works fine and I can ask it to enroll users and so on. The reader allows identification (it tells you that a particular user has presented their finger, as opposed to asking it to verify that a particular user's finger is present), but the device must be constantly polled while in identification mode for its status - when a user is detected the status changes. What I want is for an interested application to notify the service that it wants to know when a user is identified, and provide a callback that gets triggered when this happens. The WCF service will return immediately and spawn a thread in the background to continuously poll the device. This polling could go on for hours at a time if no one tries to log in. What's the best way to acheive this? My service contract is currently defined as follows: [ServiceContract (CallbackContract=typeof(IBiometricCallback))] public interface IBiometricWcfService { ... [OperationContract (IsOneWay = true)] void BeginIdentification(); ... } public interface IBiometricCallback { ... [OperationContract(IsOneWay = true)] void IdentificationFinished(int aUserId, string aMessage, bool aSuccess); ... } In my BeginIdentification() method can I easily spawn a worker thread to poll the device, or is it easier to make the WCF service asynchronous?

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• InvalidOperationException: The Undo operation encountered a context that is different from what was

  - by McN

  I got the following exception: Exception Type: System.InvalidOperationException Exception Message: The Undo operation encountered a context that is different from what was applied in the corresponding Set operation. The possible cause is that a context was Set on the thread and not reverted(undone). Exception Stack: at System.Threading.SynchronizationContextSwitcher.Undo() at System.Threading.ExecutionContextSwitcher.Undo() at System.Threading.ExecutionContext.runFinallyCode(Object userData, Boolean exceptionThrown) at System.Runtime.CompilerServices.RuntimeHelpers.ExecuteBackoutCodeHelper(Object backoutCode, Object userData, Boolean exceptionThrown) at System.Runtime.CompilerServices.RuntimeHelpers.ExecuteCodeWithGuaranteedCleanup(TryCode code, CleanupCode backoutCode, Object userData) at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state) at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state) at System.Net.ContextAwareResult.Complete(IntPtr userToken) at System.Net.LazyAsyncResult.ProtectedInvokeCallback(Object result, IntPtr userToken) at System.Net.Sockets.BaseOverlappedAsyncResult.CompletionPortCallback(UInt32 errorCode, UInt32 numBytes, NativeOverlapped* nativeOverlapped) at System.Threading._IOCompletionCallback.PerformIOCompletionCallback(UInt32 errorCode, UInt32 numBytes, NativeOverlapped* pOVERLAP) Exception Source: mscorlib Exception TargetSite.Name: Undo Exception HelpLink: The application is a Visual Studio 2005 (.Net 2.0) console application. It is a server for multiple TCP/IP connections, doing asynchronous socket reads and synchronous socket writes. In searching for an answer I came across this post which talks about a call to Application.Doevents() which I don't use in my code. I also found this post which has a resolution involved with Component which I also don't use in my code. The application does reference a library that I created that contains custom user controls and components, but they are not being used by the application. Question: What caused this to happen and how do I prevent this from happening again? Or a more realistic question: What does this exception actually mean? How is "context" defined in this situation? Anything that can help me understand what is going on would be very much appreciated.

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• Two pass JSP page rendering

  - by dotsid

  Suppose an example. I have following interface: public interface DataSource<T> { Future<T> fetch(); } This datasource can do asynchronous data fetching. And we have following tag for using datasource in JSP: <html> <d:fetch from="${orderDS}" var="orders"> <c:foreach in="${orders}" var="order"> <div class="order"> <c:out value="${order.title}" /> </div> </c:foreach> </d:fetch> </html> So, what I want? I want JSP rendering engine to call my custom tag (FetchTag in this example) twice. On first call FetchTag will do DataSource.fetch() call and save Future locally as a object field. On second call FetchTag do Future.get() call and will be blocked until data becomes available. Is there any way to do such a thing?

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