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  • net c# lock statement in data access layer

    - by Pedro Rivera
    I saw a code where they have the data access layer like this: public class CustomerDA{ private static readonly object _sync = new object(); private static readonly CustomerDA _mutex = new CustomerDA(); private CustomerDA(){ } public CustomerDA GetInstance(){ lock(_sync){ return _mutex; } } public DataSet GetCustomers(){ //database SELECT //return a DataSet } public int UpdateCustomer(some parameters){ //update some user } } public class CustomerBO{ public DataSet GetCustomers(){ //some bussiness logic return CustomerDA.GetInstance().GetCustomers(); } } I was using it, but start thinking... "and what if had to build a facebook like application where there are hundreds of thousands of concurrent users? would I be blocking each user from doing his things until the previous user ends his database stuff? and for the Update method, is it useful to LOCK THREADS in the app when database engines already manage concurrency at database server level?" Then I started to think about moving the lock to the GetCustomers and UpdateCustomer methods, but think again: "is it useful at all?"

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  • Redirecting the response from a filter throws an IllegalStateException

    - by Ritesh M Nayak
    I am writing a filter that will handle all authentication related tasks. My filter is a standard servlet filter as shown below @Override public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain) throws IOException, ServletException { UserSession attribute = (UserSession)request.getSession().getAttribute("user_session_key"); if(attribute!=null && attribute.isValid()) { //proceed as usual, chain.doFilter(req, res); return; } else { //means the user is not authenticated, so we must redirect him/her to the login page ((HttpServletResponse)res).sendRedirect("loginpage"); return; } } But when I do this, I get an IllegalStateException thrown by Tomcat's ResponseFacade. How do I acheive this in a filter. I read in other SO threads that in TOmcat this is a problem as the response object is already commited. How do I get past this ?

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  • "Circuit breaker" for net.msmq?

    - by Alex
    Hi, The Circuit Breaker pattern, from the book Release It!, protects a service from requests while it is failing (or recovering). The net.msmq binding used with transactions give us nice retry and poison message capabilities. But I am missing the implementation of such a "Circuit breaker" pattern. A service is put under even heavier load by retries while it is already in a failure condition (like DB connectivity issues causing loads of blocked threads etc.). Anyone knows about a behavior extension or similar that explicitly closes the service host when defined failure thresholds have been exceeded? Cheers, Alex

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  • python threading and performace?

    - by kumar
    I had to do heavy I/o bound operation, i.e Parsing large files and converting from one format to other format. Initially I used to do it serially, i.e parsing one after another..! Performance was very poor ( it used take 90+ seconds). So I decided to use threading to improve the performance. I created one thread for each file. ( 4 threads) for file in file_list: t=threading.Thread(target = self.convertfile,args = file) t.start() ts.append(t) for t in ts: t.join() But for my astonishment, there is no performance improvement whatsoever. Now also it takes around 90+ seconds to complete the task. As this is I/o bound operation , I had expected to improve the performance. What am I doing wrong?

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  • Java: is Exception class thread-safe?

    - by Vilius Normantas
    As I understand, Java's Exception class is certainly not immutable (methods like initCause and setStackTrace give some clues about that). So is it at least thread-safe? Suppose one of my classes has a field like this: private final Exception myException; Can I safely expose this field to multiple threads? I'm not willing to discuss concrete cases where and why this situation could occur. My question is more about the principle: can I tell that a class which exposes field of Exception type is thread-safe? Another example: class CustomException extends Exception { ... } Is this class thread-safe?

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  • Close resources before exiting JFrame and TCP communication in Java

    - by Oz Molaim
    1. I'm writing a chat based application on TCP communication. I'm using NetBeans and I want to add functionality to the default EXIT_ON_CLOSE when exiting JFrame. The reason of course is because I want to clean resources and end threads safely. How can I call a method that clear resources and only then close the JFrame safely and end the process. 2. I need to implement the server side. The server has List/HashMap/Queue of 'Socket' with their chat nick-names. Is there any simple design pattern to do it correctly because I don't want to re-invent the wheel. thanks.

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  • For Loop help In a Hash Cracker Homework.

    - by aaron burns
    On the homework I am working on we are making a hash cracker. I am implementing it so as to have my cracker. java call worker.java. Worker.java implements Runnable. Worker is to take the start and end of a list of char, the hash it is to crack, and the max length of the password that made the hash. I know I want to do a loop in run() BUT I cannot think of how I would do it so it would go to the given max pasword length. I have posted the code I have so far. Any directions or areas I should look into.... I thought there was a way to do this with a certain way to write the loop but I don't know or can't find the correct syntax. Oh.. also. In main I divide up so x amount of threads can be chosen and I know that as of write now it only works for an even number of the 40 possible char given. package HashCracker; import java.util.*; import java.security.MessageDigest; import java.security.NoSuchAlgorithmException; public class Cracker { // Array of chars used to produce strings public static final char[] CHARS = "abcdefghijklmnopqrstuvwxyz0123456789.,-!".toCharArray(); public static final int numOfChar=40; /* Given a byte[] array, produces a hex String, such as "234a6f". with 2 chars for each byte in the array. (provided code) */ public static String hexToString(byte[] bytes) { StringBuffer buff = new StringBuffer(); for (int i=0; i<bytes.length; i++) { int val = bytes[i]; val = val & 0xff; // remove higher bits, sign if (val<16) buff.append('0'); // leading 0 buff.append(Integer.toString(val, 16)); } return buff.toString(); } /* Given a string of hex byte values such as "24a26f", creates a byte[] array of those values, one byte value -128..127 for each 2 chars. (provided code) */ public static byte[] hexToArray(String hex) { byte[] result = new byte[hex.length()/2]; for (int i=0; i<hex.length(); i+=2) { result[i/2] = (byte) Integer.parseInt(hex.substring(i, i+2), 16); } return result; } public static void main(String args[]) throws NoSuchAlgorithmException { if(args.length==1)//Hash Maker { //create a byte array , meassage digestand put password into it //and get out a hash value printed to the screen using provided methods. byte[] myByteArray=args[0].getBytes(); MessageDigest hasher=MessageDigest.getInstance("SHA-1"); hasher.update(myByteArray); byte[] digestedByte=hasher.digest(); String hashValue=Cracker.hexToString(digestedByte); System.out.println(hashValue); } else//Hash Cracker { ArrayList<Thread> myRunnables=new ArrayList<Thread>(); int numOfThreads = Integer.parseInt(args[2]); int charPerThread=Cracker.numOfChar/numOfThreads; int start=0; int end=charPerThread-1; for(int i=0; i<numOfThreads; i++) { //creates, stores and starts threads. Runnable tempWorker=new Worker(start, end, args[1], Integer.parseInt(args[1])); Thread temp=new Thread(tempWorker); myRunnables.add(temp); temp.start(); start=end+1; end=end+charPerThread; } } } import java.util.*; public class Worker implements Runnable{ private int charStart; private int charEnd; private String Hash2Crack; private int maxLength; public Worker(int start, int end, String hashValue, int maxPWlength) { charStart=start; charEnd=end; Hash2Crack=hashValue; maxLength=maxPWlength; } public void run() { byte[] myHash2Crack_=Cracker.hexToArray(Hash2Crack); for(int i=charStart; i<charEnd+1; i++) { Cracker.numOfChar[i]////// this is where I am stuck. } } }

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  • Using static mutex in a class

    - by Dmitry Yudakov
    I have a class that I can have many instances of. Inside it creates and initializes some members from a 3rd party library (that use some global variables) and is not thread-safe. I thought about using static boost::mutex, that would be locked in my class constructor and destructor. Thus creating and destroying instances among my threads would be safe for the 3rd party members. class MyClass { static boost::mutex mx; // 3rd party library members public: MyClass(); ~MyClass(); }; MyClass::MyClass() { boost::mutex::scoped_lock scoped_lock(mx); // create and init 3rd party library stuff } MyClass::~MyClass() { boost::mutex::scoped_lock scoped_lock(mx); // destroy 3rd party library stuff } I cannot link because I receive error: undefined reference to `MyClass::mx` Do I need some special initialization of such static member? Is the whole conception of static mutex wrong?

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  • Running junit tests in parallel ?

    - by krosenvold
    I'm using junit 4.4 and maven and I have a large number of long-running integration tests. When it comes to parallellizing test suites there are a few solutions that allow me to run each test method in a single test-class in parallel. But all of these require that I change the tests in one way or another. I really think it would be a much cleaner solution to run X different test classes in X threads in parallel. I have hundreds of tests so I don't really care about threading individual test-classes. Is there any way to do this ?

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  • Are there any nasty side affects if i lock the HttpContext.Current.Cache.Insert method

    - by Ekk
    Apart from blocking other threads reading from the cache what other problems should I be thinking about when locking the cache insert method for a public facing website. The actual data retrieval and insert into the cache should take no more than 1 second, which we can live with. More importantly i don't want multiple thread potentially all hitting the Insert method at the same time. The sample code looks something like: public static readonly object _syncRoot = new object(); if (HttpContext.Current.Cache["key"] == null) { lock (_syncRoot) { HttpContext.Current.Cache.Insert("key", "DATA", null, DateTime.Now.AddMinutes(5), Cache.NoSlidingExpiration, CacheItemPriority.Normal, null); } } Response.Write(HttpContext.Current.Cache["key"]);

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  • My multithread program works slowly or appear deadlock on dual core machine, please help

    - by Shangping Guo
    I have a program with several threads, one thread will change a global when it exits itself and the other thread will repeatedly poll the global. No any protection on the globals. The program works fine on uni-processor. On dual core machine, it works for a while and then halt either on Sleep(0) or SuspendThread(). Would anyone be able to help me out on this? The code would be like this: Thread 1: do something... while(1) { ..... flag_thread1_running=false; SuspendThread(GetCurrentThread()); continue; } Thread 2 .... while(flag_thread1_running==false) Sleep(0); ....

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  • NSFetchedResultsController not processing certain section driven moves

    - by JK
    I utilize a NSFetchedResultsController (frc) with a Core Data store. I implement all the frc delegate methods. The table is sporadically updated by background threads. All the inserts, deletes and updates work fine, with the exception that updates to the frc's index key for rows toward to the bottom of the table (50 rows), do not result in a section move. e.g. if "name" is the index key and the name "Victor" is changed to "Alex", the victor row now shows the name Alex, but is not moved to the top of the table alongside all other names starting with A. As I noted, this is only for rows towards the bottom of the table. If a row like "Andy" is changed to "Ben", the move is indeed processed correctly by the frc. Any suggestions to fix this would be appreciated. I do not use a frc cache. Thanks

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  • AJAX: Statusbar: force update of UpdatePanel while function executes

    - by John Bourke
    Hi Guys, I have a label inside an update panel which I wouldl ike to use as a status bar. Basically the user clicks a button which executes a main fucntion that performs a series of tasks. I'd like to inform the user as to the state of the function as it progresses e.g.: Stage 1: Retrieving data... Stage 2: Calculating values... Stage 3: Printing values... Stage 4: Done! I've tried updating the updatepanel directly from the function but it only updates the panel at the end of function (stage 4) and shows "Done!" (which I understand is how it should work). I've been looking into timers and threads to try and update the panel seperate to the main function but I thought I'd post here incase anyone has any better ideas? Thanks for any help in advance! John bourkeyo is offline Reply With Quote

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  • Wait for tasks to get completed in threadpool.

    - by Alien01
    Hello I have created a thread pool in C++ which stores all tasks in a queue. Thread pool start n number of threads which takes tasks from queue , process each task and then delete tasks from queue. Now , I want to wait till all tasks get completed. Checking for empty queue for completion of tasks may not work as , task can be given to each thread and queue can be emptied but still the tasks can in processing mode. I am not getting idea how to wait for all the tasks completion.This is a design problem. Any suggestions?

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  • LINQ to SQL or Entities, at this point?

    - by orlon
    I'm a bit late to the game and have decided to spend some spare time learning LINQ. As an exercise, I'm going to rewrite a WebForms app in MVC 2 (which is also new to me). I managed to find a few topics regarding LINQ here (http://stackoverflow.com/questions/16322/learning-about-linq, http://stackoverflow.com/questions/8050/beginners-guide-to-linq, http://stackoverflow.com/questions/252683/is-linq-to-sql-doa), which brought the concern of Entities vs SQL to my attention. The threads are all over a year old however, and I can't seem to find any definitive information on which ORM is preferable. Is Entities more or less LINQ to SQL 2.0 at this point? Is it still more difficult to use? Is there any reason to use LINQ to SQL, or should I just jump into Entities? The applications I write at my present employer have a lengthy lifecycle (~10 years), so I'm trying to pick the best technology available.

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  • Log RuntimeException thrown from thread created by Spring via the @Async annotation

    - by Eugen
    I'm having some difficulty logging RuntimeException from a thread. My system is: Java 7 (b118), Spring 3.0.5. The threads are not created by hand, but via Spring's @Async annotation, which creates it's own executor behind the scenes, so I don't really have the option of overriding any methods of the thread, FutureTask or anything low level. So my question is if Spring has any support or if there are any best practices for handling (logging) these type of exceptions? Any suggestions are appreciated. Thanks.

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  • VB .NET Shared Function if called multiple times simultaneously

    - by Mehdi Anis
    Consider I have a shared function:- Public Shared Function CalculateAreaFromRadius(ByVal radius As Double) As Double ' square the radius... Dim radiusSquared As Double radiusSquared = radius * radius ' multiply it by pi... Dim result As Double result = radiusSquared * Math.PI 'Wait a bit, for the sake of testing and 'simulate another call will be made b4 earlier one ended or such for i as Integer = 0 to integer.Max Next ' return the result... Return result End Function My Questions: If I have two or more threads in the same vb .net app and each of them calls the shared function at the same time with different RADIUS, will they each get their own AREA? I want to know for each call to the function if it is using same local variables or each call creates new instances of local variables? Will the answers to above questions be same If I have multiple (2+) single threaded apps and they all call the function at the same time with different RADIUS value? I will appreciate your reponse. Thank you.

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  • Using thread inter-communication to increase my server app's IO throughput; not sure how

    - by Howard Guo
    My server application creates a new thread for each incoming connection. Incoming requests are serialized in a BlockingQueue. There is one worker thread taking items from the queue, produce a response and send the response through socket. I have noticed a throughput issue: Currently, worker thread is responsible of sending the response message through socket, thus severely wasting processing power and throughput. I am considering: rather than sending the response itself, why not telling network IO threads to send the response? However, when I think about thread inter-communication, I cannot yet figure out how to approach it: Worker thread will produce a response, but how will it inform the response message to IO thread? Is there a standard/best practice? Thank you.

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  • Looking to eventually build a smartphone app...

    - by Brian L
    Hi all- I'm a young, inexperienced programmer (I've had a year of Java, some MATLAB, and HTML/CSS in school) but I've decided that to get better, I'm making it my goal to produce a simple smartphone app of some kind this year- probably either webOS or Android since I'm on a PC and can't afford a Mac just to write an iPhone app. So my question is, where do I start? I've read the threads about How to Write for Android and such, but I'm not sure I have enough Java experience to just jump right in. And then there's webOS which is based on JavaScript, correct? I guess I'd just like some input from more experienced folks. I have some Barnes and Noble book credit I'm looking to get rid of too, so if there's a guide you think would be useful, feel free to request. tl;dr: Programming newbie ultimately wants to build a simple smartphone app. Where do I start?

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  • AudioRecord doesn't work for Motorola Milestone

    - by hcpl
    I'm having this problem only on Motorola Milestone. Code: // init recorder recordInstance = new AudioRecord(MediaRecorder.AudioSource.MIC, 8000, AudioFormat.CHANNEL_CONFIGURATION_MONO, AudioFormat.ENCODING_PCM_16BIT, 8000); recordInstance.startRecording(); //more code here recordInstance.stop(); The errorinformation I have (can't find more for the moment since I don't have a milestone myself for debugging): Uncaught handler: thread main exiting due to uncaught exception java.lang.IllegalStateException: stop() called on an uninitialized AudioRecord. at android.media.AudioRecord.stop(AudioRecord.java:51 6) Apparantly I'm not the only one with this problem. Some very similar threads I found (without solution): http://groups.google.com/group/android-developers/browse_thread/thread/6dd24aeb484b2e40 http://androidcommunity.com/forums/f2/problem-using-audiorecord-in-motorola-milestone-30935/ http://community.developer.motorola.com/t5/Android-App-Development-for/Problem-using-AudioRecord-on-Milestone-device/m-p/3889 http://www.fring.com/forums/showthread.php?t=16194

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  • Linux and I/O completion ports?

    - by someguy
    Using winsock, you can configure sockets or seperate I/O operations to "overlap". This means that calls to perform I/O are returned immediately, while the actual operations are completed asynchronously by separate worker threads. Winsock also provides "completion ports". From what I understand, a completion port acts as a multiplexer of handles (sockets). A handle can be demultiplexed if it isn't in the middle of an I/O operation, i.e. if all its I/O operations are completed. So, on to my question... does linux support completion ports or even asynchronous I/O for sockets?

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  • hibernate not throwing stale state exception nor it is overwriting data

    - by Reddy
    Our application do the following. 1. Start the transaction. 2. Execute a query using prepared statement 3. Check a condition to see the number of rows updated are equal to the required number. 4. It commits on success of above condition otherwise it will roll back However the problem is that when two threads are simultaneously enter this code. Thread-1 is updating a row in step 2. It checked the condition and committed successfully since the condition is successful. Thread-2 started execution somewhere between steps 1 & 4, and it is failing on at condition checking at step 3 (as it is getting number of updated rows as 0). I expected second thread to throw an exception but it is not. What could be the problem?

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  • Fire just once a Thread in Asp.net WebSite Global.asax

    - by Luís Custódio
    I've a legacy application using Asp.Net WebSite (winforms...) and I need run a background thread that collect periodically some files. But this thread must run just one time! My problem start when I put a method in Application_Start: void Application_Start(object sender, EventArgs e) { SetConnection(); SetNHibernate(); SetNinject(); SetExportThread(); } So I start my application on Visual Studio and three threads start to run. I need some singleton? or something?

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  • How to insert arabic characters into sql database?

    - by Pavan Reddy
    How can I insert arabic characters into sql database? I tried to insert arabic data into a table and the arabic characters in the insert script were inserted as '??????' in the table. I tried to directly paste the data into the table through sql management studio and the arabic characters was successfully and accurately inserted. I looked around for resolutions for this problems and some threads suggested changing the datatype to nvarchar instead of varchar. I tried this as well but without any luck. How can we insert arabic characters into sql database?

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  • Jetty with a custom JUL logger

    - by Alan Williamson
    I feel this should be easier, or I am missing something obvious. I am trying to use our custom JUL logging library with Jetty. No matter where I put the JAR file for the custom logger, it is not found. I have tried the usual suspects; /lib/, /lib/ext/, /WEB-INF/lib/ and even manually added it to the classpath. 2011-06-29 15:27:34.518::INFO: Started [email protected]:8080 Can't load log handler "net.aw20.logshot.client.LogShotHandler" java.lang.ClassNotFoundException: net.aw20.logshot.client.LogShotHandler java.lang.ClassNotFoundException: net.aw20.logshot.client.LogShotHandler at java.net.URLClassLoader$1.run(URLClassLoader.java:217) I am starting up Jetty using "-jar start.jar" technique. Searching around, I have spotted a couple of threads that talk about this problem, but with no resolution. Or if there was, they didn't answer with their solution. Can anyone help on this front? Thanks

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