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  • How to avoid concurrent execution of a time-consuming task without blocking?

    - by Diego V
    I want to efficiently avoid concurrent execution of a time-consuming task in a heavily multi-threaded environment without making threads wait for a lock when another thread is already running the task. Instead, in that scenario, I want them to gracefully fail (i.e. skip its attempt to execute the task) as fast as possible. To illustrate the idea considerer this unsafe (has race condition!) code: private static boolean running = false; public void launchExpensiveTask() { if (running) return; // Do nothing running = true; try { runExpensiveTask(); } finally { running = false; } } I though about using a variation of Double-Checked Locking (consider that running is a primitive 32-bit field, hence atomic, it could work fine even for Java below 5 without the need of volatile). It could look like this: private static boolean running = false; public void launchExpensiveTask() { if (running) return; // Do nothing synchronized (ThisClass.class) { if (running) return; running = true; try { runExpensiveTask(); } finally { running = false; } } } Maybe I should also use a local copy of the field as well (not sure now, please tell me). But then I realized that anyway I will end with an inner synchronization block, that still could hold a thread with the right timing at monitor entrance until the original executor leaves the critical section (I know the odds usually are minimal but in this case we are thinking in several threads competing for this long-running resource). So, could you think in a better approach?

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  • Can I control object creation using MEF?

    - by Akash
    I need to add some extension points to our existing code, and I've been looking at MEF as a possible solution. We have an IRandomNumberGenerator interface, with a default implementation (ConcreteRNG) that we would like to be swappable. This sounds like an ideal scenario for MEF, but I've been having problems with the way we instantiate the random number generators. Our current code looks like: public class Consumer { private List<IRandomNumberGenerator> generators; private List<double> seeds; public Consumer() { generators = new List<IRandomNumberGenerator>(); seeds = new List<double>(new[] {1.0, 2.0, 3.0}); foreach(var seed in seeds) { generators.Add(new ConcreteRNG(seed); } } } In other words, the consumer is responsible for instantiating the RNGs it needs, including providing the seed that each instance requires. What I'd like to do is to have the concrete RNG implementation discovered and instantiated by MEF (using the DirectoryCatalog). I'm not sure how to achieve this. I could expose a Generators property and mark it as an [Import], but how do I provide the required seeds? Is there some other approach I am missing?

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  • WCF Authentication Error

    - by Timmy O' Tool
    I'm accessing a third party WCF service (I have no access to the service configuration) We're using SSL certificates for the authentication. I'm getting this error when trying to access to any of the provided methods The HTTP request is unauthorized with client authentication scheme 'Negotiate'. The authentication header received from the server was 'Negotiate,NTLM I checked many google links and no luck so far- No idea what else to check on my side.

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  • where to store temporary data in MVC 2.0 project

    - by StuffHappens
    Hello! I'm starting to learn MVC 2.0 and I'm trying to create a site with a quiz: user is asked a question and given several options of answer. If he chooses the right answer he gets some points, if he doesn't, he looses them. I tried to do this the following way public class HomeController : Controller { private ITaskGenerator taskGenerator = new TaskGenerator(); private string correctAnswer; public ActionResult Index() { var task = taskGenerator .GenerateTask(); ViewData["Task"] = task.Task; ViewData["Options"] = task.Options; correctAnswer= task.CorrectAnswer; return View(); } public ActionResult Answer(string id) { if (id == correctAnswer) return View("Correct") return View("Incorrect"); } } But I have a problem: when user answers the cotroller class is recreated and I loose correct answer. So what is the best place to store correct answer? Should I create a static class for this purpose? Thanks for your help!

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  • instantiate object with reflection using constructor arguments

    - by justin
    I'm trying to figure out how to instantiate a case class object with reflection. Is there any support for this? The closest I've come is looking at scala.reflect.Invocation, but this seems more for executing methods that are a part of an object. case class MyClass(id:Long, name:String) def instantiate[T](className:String)(args:Any*) : T = { //your code here } Is close to the API I'm looking for. Any help would be appreciated.

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  • where store event handler method in WPF - MVVM

    - by netmajor
    Hey, Where should I store event methods for button Click event ?Normally it's store in code behind of wpf page, <Button Name="myButton" Click="myButton_Click">Click Me</Button> but in MVVM it should be store in other view-model class and bind to click property of button like that?? <Button Name="myButton" Click="{Binding StaticResouces myButton_Click}">Click Me</Button>

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  • Click at specified client area

    - by VixinG
    Click doesn't work - I don't know why and can't find a solution :( ie. Click(150,215) should move mouse to the client area and click there. [DllImport("user32.dll")] private static extern bool ScreenToClient(IntPtr hWnd, ref Point lpPoint); [DllImport("user32", SetLastError = true)] private static extern int SetCursorPos(int x, int y); static void MouseMove(int x, int y) { Point p = new Point(x * -1, y * -1); ScreenToClient(hWnd, ref p); p = new Point(p.X * -1, p.Y * -1); SetCursorPos(p.X, p.Y); } static void Click(int x, int y) { MouseMove(x, y); SendMessage(hWnd, WM_LBUTTONDOWN, (IntPtr)0x1, new IntPtr(y * 0x10000 + x)); SendMessage(hWnd, WM_LBUTTONUP, (IntPtr)0x1, new IntPtr(y * 0x10000 + x)); } Edit: Of course I can use mouse_event for that, but I would like to see a solution for SendMessage()... [DllImport("user32.dll")] static extern void mouse_event(int dwFlags, int dx, int dy, int dwData, int dwExtraInfo); const int LEFTDOWN = 0x00000002; const int LEFTUP = 0x00000004; static void Click(int x, int y) { MouseMove(x, y); mouse_event((int)(LEFTDOWN), 0, 0, 0, 0); mouse_event((int)(LEFTUP), 0, 0, 0, 0); }

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  • Method parameters confusion

    - by elec
    Often time methods take more than 3 parameters which are all of the same type, eg. void mymethod (String param1, String param2, String param3) then it's very easy for the client to mix up the parameters orders, for instance inverting param1 and param2: mymethod (param2, param1, param3); ...which can be the cause of much time spent debugging what should be a trivial matter. Any tips on how to avoid this sort of mistake (apart from unit tests) ?

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  • good c++ documentation design example?

    - by Eye of Hell
    Hello. I'm tuning documentation generator for internal purpose that generates HTML documentation for C++ classes and methods. Is it any example available of good HTML documentation design? MSDN ( like this ) looks kinda outdated, same is doxygen / javadoc / sphinx results. Anyone ever see an documentation that looks REALLY good?

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  • can I have an abstract base class with the key attribute being generic

    - by Greg
    Hi, I want to create a re-usable library. I was going to use extension methods however I run into some issues in some cases for the client to have to specify in the calling method the types. QUESTION - If I use an abstract base class as the basis, can I specify an attribute/property in the class to be generic (e.g. the key property might be an 'int' in one case, or a 'string' in another)?

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  • How to model and handle presentation DTO's to abstract from complicated domain model?

    - by arrages
    Hi I am developing an application that needs to work with a complex domain model using Hibernate. This application uses Spring MVC and using the domain objects in the presentation layer is very messy so I think I should use DTO's that go to and from my service layer so that these match what I need in my views. Now lets assume I have a CarLease entity whose properties are not simple java primitives but it's composed with other entities like Make, Model, etc public class CarLease { private Make make; Private Model model; . . . } most properties are in this fashion and they are selectable using drop down selects on the jsp view, each will post back an ID to the controller. Now considering some standard use cases: create, edit, display How would you go about modeling the presentation DTO's to be used as form backing objects and communication between presentation and service layers?? Would you create a different DTO for each case (create, edit, display), would you make DTO's for the complex attributes? if so where would you translate the ID to entity? how and where would you handle validation, DTO/Domain assembly, what would you return from service layer methods? (create, edit, get) As you can see, I now I will benefit by separating my view from the domain objects (very complex with lots of stuff I don't need.) but I am having a hard time finding any real world examples and best practices for this. I need some architecture guidance from top to bottom, please keep in mind I will use Spring MVC in case that may leverage on your anwser. thanks in advance.

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  • Performance - FunctionCall vs Event vs Action vs Delegate

    - by hwcverwe
    Currently I am using Microsoft Sync Framework to synchronize databases. I need to gather information per record which is inserted/updated/deleted by Microsoft Sync Framework and do something with this information. The sync speed can go over 50.000 records per minute. So that means my additional code need to be very lightweight otherwise it will be a huge performance penalty. Microsoft Sync Framework raises an SyncProgress event for each record. I am subscribed to that code like this: // Assembly1 SyncProvider.SyncProgress += OnSyncProgress; // .... private void OnSyncProgress(object sender, DbSyncProgressEventArgs e) { switch (args.Stage) { case DbSyncStage.ApplyingInserts: // MethodCall/Delegate/Action<>/EventHandler<> => HandleInsertedRecordInformation // Do something with inserted record info break; case DbSyncStage.ApplyingUpdates: // MethodCall/Delegate/Action<>/EventHandler<> => HandleUpdatedRecordInformation // Do something with updated record info break; case DbSyncStage.ApplyingDeletes: // MethodCall/Delegate/Action<>/EventHandler<> => HandleDeletedRecordInformation // Do something with deleted record info break; } } Somewhere else in another assembly I have three methods: // Assembly2 public class SyncInformation { public void HandleInsertedRecordInformation(...) {...} public void HandleUpdatedRecordInformation(...) {...} public void HandleInsertedRecordInformation(...) {...} } Assembly2 has a reference to Assembly1. So Assembly1 does not know anything about the existence of the SyncInformation class which need to handle the gathered information. So I have the following options to trigger this code: use events and subscribe on it in Assembly2 1.1. EventHandler< 1.2. Action< 1.3. Delegates using dependency injection: public class Assembly2.SyncInformation : Assembly1.ISyncInformation Other? I know the performance depends on: OnSyncProgress switch using a method call, delegate, Action< or EventHandler< Implementation of SyncInformation class I currently don't care about the implementation of the SyncInformation class. I am mainly focused on the OnSyncProgress method and how to call the SyncInformation methods. So my questions are: What is the most efficient approach? What is the most in-efficient approach? Is there a better way than using a switch in OnSyncProgress?

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  • ThreadExceptionEventHandler and invoking delegates

    - by QmunkE
    If I assign a ThreadExceptionEventHandler to Application.ThreadException, why when I invoke a delegate method using a control on the main application thread are any exceptions thrown by that delegate not triggering the event handler? i.e. static void Main() { ... Application.ThreadException += new System.Threading.ThreadExceptionEventHandler(Application_ThreadException); Application.Run(new Form1()); } static void Application_ThreadException(object sender, System.Threading.ThreadExceptionEventArgs e) { Console.Error.Write("A thread exception occurred!"); } ... private void Form1_Load(object sender, EventArgs e) { Thread syncThread = new Thread(new ThreadStart(this.ThrowException)); syncThread.Start(); } private void ThrowException() { button1.Invoke(new MethodInvoker(delegate { // Not handled by ThreadExceptionEventHandler? throw new Exception(); })); } The context on this is that I have a background thread started from a form which is throwing an unhandled exception which terminates the application. I know this thread is going to be unreliable since it is network connectivity reliant and so subject to being terminated at any point, but I'm just interested as to why this scenario doesn't play out as I expect?

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  • How do I fix my Unit Test to have global access to everything?

    - by SLC
    Usually when you add one (in Visual Basic), it pops up a message asking if you want to enable an option that lets the test access things like private methods etc. However, I am editing a solution that does not have this enabled. I'd like to enable it so my unit tests will work, but I can't find the setting. Can anyone tell me how to enable it after the project has been created?

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  • c++/boost: use tuple ctors when subclassing

    - by bbb
    Hi there, is there some way to use a boost tuple's ctors as an addition to the subclass methods (and ctors) like here? // typedef boost::tuple<int, SomeId, SomeStatus> Conn; // Conn(1); // works and initializes using default ctors of Some* struct Conn : boost::tuple<int, AsynchId, AccDevRetStatus> {}; Conn(1); // "no matching function call" (but i want it so much) T.H.X.

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  • Using a Hash table

    - by Maria Attard
    I have 2 lists in my program one that store objects of type student and another one which stores objects of type marks. I have 3 methods one that inputs the details of the students, one that inputs the marks and one to view student details and their marks. My question is how I can use a hash table to get the Id of a student and then use it to input the marks and then how to retrieve both the student details and their marks altogether. Please help me if you can.

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  • Perl Regular Expression [] for <>

    - by bmucklow
    So I am trying to read an XML file into a string in Perl and send it as part of a SOAP message. I know this is not ideal as there are methods for SOAP sending files, however, I am limited to having to use the SOAP that is set up, and it is not set up for sending with file support. Therefore I need to parse out the markup tags < and replace them with []. What is the best way to do this?

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  • Documentation tool for .net applications

    - by jovialwhispers
    I have an ASP.NET 2.0 application, developed in the early days of 2.0. There are almost no comment tags in the application. Is there any tool which can grab all the classes from that application generate a report [in chm or html or pdf] with all the classes and belonging methods, hierarchy of the classes and any kind of visual presentation of the over all flow/relationship/architecture? Thanks

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  • C# why unit test has this strange behaviour?

    - by 5YrsLaterDBA
    I have a class to encrypt the connectionString. public class SKM { private string connStrName = "AndeDBEntities"; internal void encryptConnStr() { if(isConnStrEncrypted()) return; ... } private bool isConnStrEncrypted() { bool status = false; // Open app.config of executable. System.Configuration.Configuration config = ConfigurationManager.OpenExeConfiguration(ConfigurationUserLevel.None); // Get the connection string from the app.config file. string connStr = config.ConnectionStrings.ConnectionStrings[connStrName].ConnectionString; status = !(connStr.Contains("provider")); Log.logItem(LogType.DebugDevelopment, "isConnStrEncrypted", "SKM::isConnStrEncrypted()", "isConnStrEncrypted=" + status); return status; } } Above code works fine in my application. But not in my unit test project. In my unit test project, I test the encryptConnStr() method. it will call isConnStrEncrypted() method. Then exception (null pointer) will be thrown at this line: string connStr = config.ConnectionStrings.ConnectionStrings[connStrName].ConnectionString; I have to use index like this to pass the unit test: string connStr = config.ConnectionStrings.ConnectionStrings[0].ConnectionString; I remember it worked several days ago at the time I added above unit test. But now it give me an error. The unit test is not integrated with our daily auto build yet. We only have ONE connectionStr. It works with product but not in unit test. Don't know why. Anybody can explain to me?

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  • Objective C: Include class and call method

    - by Nic Hubbard
    I have built a class which has a few methods in it, once of which returns an array, lets call this class A. I have a second class, class B, which I would like to use to call the method from class A. But, now how do I call that method from class A and store what is returned in a var in class B? Do I have to initiate the class? I have made sure to include the .h file from class A into class B. Thanks for helping a newbie.

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  • Linking two pages using JSP

    - by jamesatha
    So, I am trying to use JSP to create a set of webpages. I want to link two pages so that if the user clicks a button in one page, it will trigger an event in the other page. Is there an efficient way to do this? I was taking a look at creating cookies and/or sessions. Any suggestions on these two methods? Thanks

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  • JLabel transparency problem

    - by Rendicahya
    I have a dark-gray JPanel with a JLabel on it. I set new Color(0, 0, 0, .5f) (tranparent) as the background of the JLabel and I change the text several times using a button. The problem is, everytime the text is changed, the previous text still remains behind the new text. I change the text from "123456789" to "1234567", "12345" and "123". Here is the screenshot: How do I get rid of this "shadow"? Here's the code: public class TransparentJLabel extends JFrame { private int i = 0; private String[] value = {"123456789", "1234567", "12345", "123", "1"}; public TransparentJLabel() { setSize(300, 160); setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE); setLayout(null); JPanel panel = new JPanel(); panel.setBackground(new Color(102, 102, 102)); panel.setLayout(null); panel.setBounds(0, 0, 300, 160); final JLabel label = new JLabel(); label.setText(value[0]); label.setFont(new Font("Times New Roman", 1, 36)); label.setForeground(new Color(255, 255, 255)); label.setBackground(new Color(0, 0, 0, .5f)); label.setHorizontalAlignment(SwingConstants.CENTER); label.setOpaque(true); label.setBounds(10, 10, 270, 70); JButton button = new JButton(); button.setText("Change"); button.setBounds(100, 90, 90, 25); button.addActionListener(new ActionListener() { public void actionPerformed(ActionEvent e) { label.setText(value[++i]); } }); panel.add(label); panel.add(button); add(panel); } public static void main(String[] args) { EventQueue.invokeLater(new Runnable() { public void run() { new TransparentJLabel().setVisible(true); } }); } }

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  • Optimization of a c++ matrix/bitmap class

    - by Andrew
    I am searching a 2D matrix (or bitmap) class which is flexible but also fast element access. The contents A flexible class should allow you to choose dimensions during runtime, and would look something like this (simplified): class Matrix { public: Matrix(int w, int h) : data(new int[x*y]), width(w) {} void SetElement(int x, int y, int val) { data[x+y*width] = val; } // ... private: // symbols int width; int* data; }; A faster often proposed solution using templates is (simplified): template <int W, int H> class TMatrix { TMatrix() data(new int[W*H]) {} void SetElement(int x, int y, int val) { data[x+y*W] = val; } private: int* data; }; This is faster as the width can be "inlined" in the code. The first solution does not do this. However this is not very flexible anymore, as you can't change the size anymore at runtime. So my question is: Is there a possibility to tell the compiler to generate faster code (like when using the template solution), when the size in the code is fixed and generate flexible code when its runtime dependend? I tried to achieve this by writing "const" where ever possible. I tried it with gcc and VS2005, but no success. This kind of optimization would be useful for many other similar cases.

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