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  • Do the ‘up to date’ guarantees for values of Java's final fields extend to indirect references?

    - by mattbh
    The Java language spec defines semantics of final fields in section 17.5: The usage model for final fields is a simple one. Set the final fields for an object in that object's constructor. Do not write a reference to the object being constructed in a place where another thread can see it before the object's constructor is finished. If this is followed, then when the object is seen by another thread, that thread will always see the correctly constructed version of that object's final fields. It will also see versions of any object or array referenced by those final fields that are at least as up-to-date as the final fields are. My question is - does the 'up-to-date' guarantee extend to the contents of nested arrays, and nested objects? An example scenario: Thread A constructs a HashMap of ArrayLists, then assigns the HashMap to final field 'myFinal' in an instance of class 'MyClass' Thread B sees a (non-synchronized) reference to the MyClass instance and reads 'myFinal', and accesses and reads the contents of one of the ArrayLists In this scenario, are the members of the ArrayList as seen by Thread B guaranteed to be at least as up to date as they were when MyClass's constructor completed? I'm looking for clarification of the semantics of the Java Memory Model and language spec, rather than alternative solutions like synchronization. My dream answer would be a yes or no, with a reference to the relevant text.

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  • WPF Background Thread Invocation

    - by jeffn825
    Maybe I'm mis-remembering how Winforms works or I'm overcomplicating the hell out of this, but here's my problem. I have a WPF client app application that talks to a server over WCF. The current user may "log out" of the WPF client, which closes all open screens, leaves only the navigation pane, and minimizes the program window. When the user re-maximizes the program window, they are prompted to log in. Simple. But sometimes things happen on background threads - like every 5 minutes the client tries to make a WCF calls that refreshes some cached data. And what if the user is logged out when this 5 minute timer triggers? Well, then the user should be prompted to log back in...and this must of course happen on the UI thread. private static ISecurityContext securityContext; public static ISecurityContext SecurityContext { get { if (securityContext == null) { // Login method shows a window and prompts the user to log in Application.Current.Dispatcher.Invoke((Action)Login); } return securityContext; } } So far so good, right? But what happens when multiple threads hit this spot of code? Well, my first intuition was that since I'm syncrhonizing across the Application.Current.Dispatcher, I should be fine, and whichever thread hit first would be responsible for showing the login form and getting the user logged in... Not the case... Thread 1 will hit the code and call ShowDialog on the login form Thread 2 will also hit the code and will call Login as soon as Thread 1 has called ShowDialog, since calling ShowDialog unblocked Thread 1 (I believe because of the way the WPF message pump works) All I want is a synchronized way of getting the user logged back into the application...what am I missing here? Thanks in advance.

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  • What is a good embeddable Java LDAP server?

    - by LeedsSideStreets
    I'm working on a Java web application that integrates with a few other external applications that are deployed along with it. Authentication information must be synchronized across everything and the other applications want to authenticate against LDAP. The application will be deployed in environments where there will be no other LDAP server for everything to use; I have to provide it. My solution so far has been to use Penrose Server as a standalone app, which I set up to examine tables in the main application's database and publish LDAP based on that. It works well, but it would be nice to have something that can be embedded into the main application itself to simplify deployment. It looks like Penrose can be embedded, but the documentation can be a bit spotty or out-of-date (though it seems to be actively developed). It could be an acceptable solution, but if there is another out there that is known to work well in an embedded configuration I might want to check it out. I'm also concerned about GPL issues with Penrose. I'm not at liberty to GPL the source code for the application. I don't believe it was an issue running it standalone, but embedding it may be no-no... anybody know for sure? A permissive license would be good in order to avoid these issues. Requirements: LDAP v3 Must be able to be have the directory contents updated while running, either programmatically or by another means like syncing with the database as Penrose does Easy to configure (no additional configuration for the app at deployment time would be ideal) So far I've briefly looked at ApacheDS and OpenDS which seem to be embeddable. Does anyone have experience with this kind of thing?

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  • best practice for directory polling

    - by Hieu Lam
    Hi all, I have to do batch processing to automate business process. I have to poll directory at regular interval to detect new files and do processing. While old files is being processed, new files can come in. For now, I use quartz scheduler and thread synchronization to ensure that only one thread can process files. Part of the code are: application-context.xml <bean id="methodInvokingJob" class="org.springframework.scheduling.quartz.MethodInvokingJobDetailFactoryBean" <property name="targetObject" ref="documentProcessor" / <property name="targetMethod" value="processDocuments" / </bean DocumentProcessor ..... public void processDocuments() { LOG.info(Thread.currentThread().getName() + " attempt to run."); if (!processing) { synchronized (this) { try { processing = true; LOG.info(Thread.currentThread().getName() + " is processing"); List xmlDocuments = documentManager.getFileNamesFromFolder(incomingFolderPath); // loop over the files and processed unlock files. for (String xmlDocument : xmlDocuments) { processDocument(xmlDocument); } } finally { processing = false; } } } } For the current code, I have to prevent other thread to process files when one thread is processing. Is that a good idea ? or we support multi-threaded processing. In that case how can I know which files is being process and which files has just arrived ? Any idea is really appreciated.

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  • Receive MMS images and make album using iamge using j2me

    - by Abdul Basit
    I am trying to made application which receive MMS images and make a album from them user can view the pictures while running this application. I am facing problem while running application on mobile. while this application is fully working in wireless tookit emulator. Please guide me to fix this problem.`//package hello; import javax.microedition.midlet.; import javax.microedition.lcdui.; import javax.wireless.messaging.*; import java.io.IOException; import java.util.Vector; import javax.microedition.io.Connector; import javax.microedition.lcdui.Display; //, ItemStateListener public class MMSS extends MIDlet implements CommandListener, Runnable, MessageListener { //-----------------------------------Receive MMS --------------------------- private Thread mReceiver = null; private boolean mEndNow = false; private Message msg = null; String msgReceived = null; private Image[] receivedImage = new Image[5]; private Command mExitCommand = new Command("Exit", Command.EXIT, 2); private Command mRedCommand = new Command("Back", Command.SCREEN, 1); private Command mBlueCommand = new Command("Next", Command.SCREEN, 1); private Command mPlay = new Command("Play", Command.SCREEN, 1); protected static final String DEFAULT_IMAGE = "/MMSS_logo.jpg"; //protected static final String DEFAULT_IMAGE = "/wait.png"; private Display mDisplay = null; //protected ImageItem mColorSquare = null; protected Image mInitialImage = null; private String mAppID = "MMSMIDlet"; private TextField imageName = null; //private Form mForm = null; private int count = 0; private int next = 0; private Integer mMonitor = new Integer(0); //----------------------------------- End Receive MMS --------------------------- private boolean midletPaused = false; private Command exitCommand; private Command exitCommand1; private Command backCommand; private Form form; private StringItem stringItem; private ImageItem imageItem; private Image image1; private Alert alert; private List locationList; private Alert cannotAddLocationAlert; public MMSS() { } /** * Initilizes the application. * It is called only once when the MIDlet is started. The method is called before the startMIDlet method. */ private void initialize() { } /** * Performs an action assigned to the Mobile Device - MIDlet Started point. */ public void startMIDlet() { // write pre-action user code here switchDisplayable(null, getForm()); // write post-action user code here } /** * Performs an action assigned to the Mobile Device - MIDlet Resumed point. */ public void resumeMIDlet() { } /** * Switches a current displayable in a display. The display instance is taken from getDisplay method. This method is used by all actions in the design for switching displayable. * @param alert the Alert which is temporarily set to the display; if null, then nextDisplayable is set immediately * @param nextDisplayable the Displayable to be set / public void switchDisplayable(Alert alert, Displayable nextDisplayable) {//GEN-END:|5-switchDisplayable|0|5-preSwitch // write pre-switch user code here Display display = getDisplay();//GEN-BEGIN:|5-switchDisplayable|1|5-postSwitch if (alert == null) { display.setCurrent(nextDisplayable); } else { display.setCurrent(alert, nextDisplayable); } } /* * Called by a system to indicated that a command has been invoked on a particular displayable. * @param command the Command that was invoked * @param displayable the Displayable where the command was invoked */ public void commandAction(Command command, Displayable displayable) { // write pre-action user code here if (displayable == form) { if (command == exitCommand) { // write pre-action user code here exitMIDlet(); // write post-action user code here } } // write post-action user code here } /** * Returns an initiliazed instance of exitCommand component. * @return the initialized component instance */ public Command getExitCommand() { if (exitCommand == null) { // write pre-init user code here exitCommand = new Command("Exit", Command.EXIT, 0); // write post-init user code here } return exitCommand; } /** * Returns an initiliazed instance of form component. * @return the initialized component instance */ public Form getForm() { if (form == null) { // write pre-init user code here form = new Form("Welcome to MMSS", new Item[] { getStringItem(), getImageItem() }); form.addCommand(getExitCommand()); form.setCommandListener(this); // write post-init user code here } return form; } /** * Returns an initiliazed instance of stringItem component. * @return the initialized component instance */ public StringItem getStringItem() { if (stringItem == null) { // write pre-init user code here stringItem = new StringItem("Hello", "Hello, World!"); // write post-init user code here } return stringItem; } /** * Returns an initiliazed instance of exitCommand1 component. * @return the initialized component instance / public Command getExitCommand1() { if (exitCommand1 == null) { // write pre-init user code here exitCommand1 = new Command("Exit", Command.EXIT, 0); // write post-init user code here } return exitCommand1; } /* * Returns an initiliazed instance of imageItem component. * @return the initialized component instance */ public ImageItem getImageItem() { if (imageItem == null) { // write pre-init user code here imageItem = new ImageItem("imageItem", getImage1(), ImageItem.LAYOUT_CENTER | Item.LAYOUT_TOP | Item.LAYOUT_BOTTOM | Item.LAYOUT_VCENTER | Item.LAYOUT_EXPAND | Item.LAYOUT_VEXPAND, "");//GEN-LINE:|26-getter|1|26-postInit // write post-init user code here } return imageItem; } /** * Returns an initiliazed instance of image1 component. * @return the initialized component instance */ public Image getImage1() { if (image1 == null) { // write pre-init user code here try { image1 = Image.createImage("/B.jpg"); } catch (java.io.IOException e) { e.printStackTrace(); } // write post-init user code here } return image1; } /** * Returns a display instance. * @return the display instance. */ public Display getDisplay () { return Display.getDisplay(this); } /** * Exits MIDlet. */ public void exitMIDlet() { switchDisplayable (null, null); destroyApp(true); notifyDestroyed(); } /** * Called when MIDlet is started. * Checks whether the MIDlet have been already started and initialize/starts or resumes the MIDlet. */ public void startApp() { if (midletPaused) { resumeMIDlet (); } else { initialize (); startMIDlet (); } midletPaused = false; /////////////////////////////////////////////////////////////////////// /////////////////////////////////////////////////////////////////////// try { conn = (MessageConnection) Connector.open("mms://:" + mAppID); conn.setMessageListener(this); } catch (Exception e) { System.out.println("startApp caught: "); e.printStackTrace(); } if (conn != null) { startReceive(); } /////////////////////////////////////////////////////////////////////// /////////////////////////////////////////////////////////////////////// } /** * Called when MIDlet is paused. */ public void pauseApp() { midletPaused = true; mEndNow = true; try { conn.setMessageListener(null); conn.close(); } catch (IOException ex) { System.out.println("pausetApp caught: "); ex.printStackTrace(); } } /** * Called to signal the MIDlet to terminate. * @param unconditional if true, then the MIDlet has to be unconditionally terminated and all resources has to be released. */ public void destroyApp(boolean unconditional) { mEndNow = true; try { conn.close(); } catch (IOException ex) { System.out.println("destroyApp caught: "); ex.printStackTrace(); } } private void startReceive() { mEndNow = false; //---- Start receive thread mReceiver = new Thread(this); mReceiver.start(); } protected MessageConnection conn = null; protected int mMsgAvail = 0; // -------------------- Get Next Images ------------------------------------ private void getMessage() { synchronized(mMonitor) { mMsgAvail++; mMonitor.notify(); } } // -------------------- Display Images Thread ------------------------------ public void notifyIncomingMessage(MessageConnection msgConn) { if (msgConn == conn) getMessage(); } public void itemStateChanged(Item item) { throw new UnsupportedOperationException("Not supported yet."); } class SetImage implements Runnable { private Image img = null; public SetImage(Image inImg) { img = inImg; } public void run() { imageItem.setImage(img); imageName.setString(Integer.toString(count)); } } public void run() { mMsgAvail = 0; while (!mEndNow) { synchronized(mMonitor) { // Enter monitor if (mMsgAvail <= 0) try { mMonitor.wait(); } catch (InterruptedException ex) { } mMsgAvail--; } try { msg = conn.receive(); if (msg instanceof MultipartMessage) { MultipartMessage mpm = (MultipartMessage)msg; MessagePart[] parts = mpm.getMessageParts(); if (parts != null) { for (int i = 0; i < parts.length; i++) { MessagePart mp = parts[i]; byte[] ba = mp.getContent(); receivedImage[count] = Image.createImage(ba, 0, ba.length); } Display.getDisplay(this).callSerially(new SetImage(receivedImage[count])); } } } catch (IOException e) { System.out.println("Receive thread caught: "); e.printStackTrace(); } count++; } // of while } } `

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  • Create ABPerson Records in a Shared CardDAV (10.6/Server Hosted) AddressBook

    - by Woodster
    Hello, My app presently reads and writes to the local Mac OS X 10.6 client addressbook using the AddressBook.framework. It works fine. 10.6 Server introduced AddressBook Server, which 10.6 clients can connect to by setting up a CardDAV Account. User and Group records can be stored in that account, which is synchronized to the 10.6 server and made available to other clients who access the same CardDAV account. Mail.app is able to autocomplete the email addresses from accounts that are in the local datastore as well as the remote CardDAV datastore. ABPeoplePicker can see both. But, programatically, I'm not getting any CardDAV-based data returned from my queries against the shared AddressBook. I'm not sure if I need to ask it for a different AddressBook, or if I need to modify my fetch-request to indicate that I want it to be able to use the shared data too. My goal is to adapt the current code so that it can read/write to the CardDAV account too, instead of just the local addressbook. Thoughts?

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  • evaluation of a java thread dump

    - by raticulin
    I got a thread dump of one of my processes. It has a bunch of these threads. I guess they are keeping a bunch of memory so I am getting OOM. "Thread-8264" prio=6 tid=0x4c94ac00 nid=0xf3c runnable [0x4fe7f000] java.lang.Thread.State: RUNNABLE at java.util.zip.Inflater.inflateBytes(Native Method) at java.util.zip.Inflater.inflate(Inflater.java:223) - locked <0x0c9bc640 (a java.util.zip.Inflater) at org.apache.commons.compress.archivers.zip.ZipArchiveInputStream.read(ZipArchiveInputStream.java:235) at com.my.ZipExtractorCommonsCompress.extract(ZipExtractorCommonsCompress.java:48) at com.my.CustomThreadedExtractorWrapper$ExtractionThread.run(CustomThreadedExtractorWrapper.java:151) Locked ownable synchronizers: - None "Thread-8241" prio=6 tid=0x4c94a400 nid=0xb8c runnable [0x4faef000] java.lang.Thread.State: RUNNABLE at java.util.zip.Inflater.inflateBytes(Native Method) at java.util.zip.Inflater.inflate(Inflater.java:223) - locked <0x0c36b808 (a java.util.zip.Inflater) at org.apache.commons.compress.archivers.zip.ZipArchiveInputStream.read(ZipArchiveInputStream.java:235) at com.my.ZipExtractorCommonsCompress.extract(ZipExtractorCommonsCompress.java:48) at com.my.CustomThreadedExtractorWrapper$ExtractionThread.run(CustomThreadedExtractorWrapper.java:151) Locked ownable synchronizers: - None I am trying to find out how it arrived to this situation. CustomThreadedExtractorWrapper is a wrapper class that fires a thread to do some work (ExtractionThread, which uses ZipExtractorCommonsCompress to extract zip contents from a compressed stream). If the task is taking too long, ExtractionThread.interrupt(); is called to cancel the operation. I can see in my logs that the cancellation happened 25 times. And I see 21 of these threads in my dump. My questions: What is the status of these threads? Alive and running? Blocked somehow? They did not die with .interrupt() apparently? Is there a sure way to really kill a thread? What does really mean 'locked ' in the stack trace? Line 223 in Inflater.java is: public synchronized int inflate(byte[] b, int off, int len) { ... //return is line 223 return inflateBytes(b, off, len); }

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  • Custom Database integration with MOSS 2007

    - by Bob
    Hopefully someone has been down this road before and can offer some sound advice as far as which direction I should take. I am currently involved in a project in which we will be utilizing a custom database to store data extracted from excel files based on pre-established templates (to maintain consistency). We currently have a process (written in C#.Net 2008) that can extract the necessary data from the spreadsheets and import it into our custom database. What I am primarily interested in is figuring out the best method for integrating that process with our portal. What I would like to do is let SharePoint keep track of the metadata about the spreadsheet itself and let the custom database keep track of the data contained within the spreadsheet. So, one thing I need is a way to link spreadsheets from SharePoint to the custom database and vice versa. As these spreadsheets will be updated periodically, I need tried and true way of ensuring that the data remains synchronized between SharePoint and the custom database. I am also interested in finding out how to use the data from the custom database to create reports within the SharePoint portal. Any and all information will be greatly appreciated.

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  • Java: volatile guarantees and out-of-order execution

    - by WizardOfOdds
    Note that this question is solely about the volatile keyword and the volatile guarantees: it is not about the synchronized keyword (so please don't answer "you must use synchronize" for I don't have any issue to solve: I simply want to understand the volatile guarantees (or lack of guarantees) regarding out-of-order execution). Say we have an object containing two volatile String references that are initialized to null by the constructor and that we have only one way to modify the two String: by calling setBoth(...) and that we can only set their references afterwards to non-null reference (only the constructor is allowed to set them to null). For example (it's just an example, there's no question yet): public class SO { private volatile String a; private volatile String b; public SO() { a = null; b = null; } public void setBoth( @NotNull final String one, @NotNull final String two ) { a = one; b = two; } public String getA() { return a; } public String getB() { return b; } } In setBoth(...), the line assigning the non-null parameter "a" appears before the line assigning the non-null parameter "b". Then if I do this (once again, there's no question, the question is coming next): if ( so.getB() != null ) { System.out.println( so.getA().length ); } Am I correct in my understanding that due to out-of-order execution I can get a NullPointerException? In other words: there's no guarantee that because I read a non-null "b" I'll read a non-null "a"? Because due to out-of-order (multi)processor and the way volatile works "b" could be assigned before "a"? volatile guarantees that reads subsequent to a write shall always see the last written value, but here there's an out-of-order "issue" right? (once again, the "issue" is made on purpose to try to understand the semantics of the volatile keyword and the Java Memory Model, not to solve a problem).

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  • How to dispatch a new property value in an object to the same property of two other objects

    - by WPFadvocate
    In WPF, I've three objects exposing the same DependencyProperty (let's say it's an integer). I want all three property values to remain synchronized, i.e. that whenever the int value changes in an object, this value is propagated to the two other objects. I think of multibinding to do the job, but I don't know how to detect which object changed, thus which value should be used and propagated to the other objects. Edited: here is my tentative code for multibinding, with the false hope that it would work without additional code: // create the multibinding MultiBinding mb = new MultiBinding() { Mode = BindingMode.TwoWay, UpdateSourceTrigger = UpdateSourceTrigger.PropertyChanged }; // create individual bindings to associate object_2 and object_3 to object_1 Binding b2 = new Binding() { Source = object_2, Path = new PropertyPath("X") }; Binding b3 = new Binding() { Source = object_3, Path = new PropertyPath("X") }; // add individual bindings to multibinding mb.Bindings.Add(b2); mb.Bindings.Add(b3); // bind object_2 and _3 to object_1 BindingOperations.SetBinding(object_1, TypeObject_1.XProperty, mb); But actually, there is a runtime error, saying the binding set by the last instruction is lacking a converter. But again I don't know how to write this converter (there is nothing to convert (as this is the case in the related MS sample of code linking 3 rgb properties to a color property), only to forward the value of the property changed to the two other properties). I understand I could solve the problem by creating an X_Changed event in the 3 types and then have each object registering to the two other objects event. I don't like this "manual" way and would prefer to bind the 3 properties together.

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  • NSUserDefaults not saving properly

    - by BWC
    Hey Guys I'm having issues with NSUserDefaults and I don't quite understand what's going on My App has 5 levels and each level does the exact same thing with NSUserDefaults (Retrieves the levels defaults, changes the value as the user plays the level and then sets the defaults and syncronizes at the end of the level) the first 4 levels...work without a hitch but the last level doesn't save the values. The app doesn't crash and the last level isn't the very last thing that happens, And I even have the defaults synchronized when the application terminates. Is there a max size on the NSUserDefaults or is there anything anyone can think of that I haven't, I'll post the code below but like I said the first four levels work perfectly //header NSUserDefaults *userData; @property(nonatomic,retain) NSUserDefaults *userData; //class file //Sets the boolean variables for the class to use userData = [NSUserDefaults standardUserDefaults]; boolOne = [userData boolForKey:@"LevelFiveBoolOne"]; boolTwo = [userData boolForKey:@"LevelFiveBoolTwo"]; boolThree = [userData boolForKey:@"LevelFiveBoolThree"]; boolFour = [userData boolForKey:@"LevelFiveBoolFour"]; boolFive = [userData boolForKey:@"LevelFiveBoolFive"]; boolSix = [userData boolForKey:@"LevelFiveBoolSix"]; boolSeven = [userData boolForKey:@"LevelFiveBoolSeven"]; //End Of Level [userData setBool:boolOne forKey:@"LevelFiveBoolOne"]; [userData setBool:boolTwo forKey:@"LevelFiveBoolTwo"]; [userData setBool:boolThree forKey:@"LevelFiveBoolThree"]; [userData setBool:boolFour forKey:@"LevelFiveBoolFour"]; [userData setBool:boolFive forKey:@"LevelFiveBoolFive"]; [userData setBool:boolSix forKey:@"LevelFiveBoolSix"]; [userData setBool:boolSeven forKey:@"LevelFiveBoolSeven"]; [userData synchronize]; When when I switch to the view that uses these defaults they values are correct but when I terminate the application and restart it, these values aren't saved, every other level does the exact same process this is the only level that doesn't work. I've stared at this for quite awhile and I'm hoping someone out there has run into the same problem and can give me some insight on how they resolved it. Thank you in Advance BWC

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  • Boost Thread Synchronization

    - by Dave18
    I don't see synchronized output when i comment the the line wait(1) in thread(). can I make them run at the same time (one after another) without having to use 'wait(1)'? #include <boost/thread.hpp> #include <iostream> void wait(int seconds) { boost::this_thread::sleep(boost::posix_time::seconds(seconds)); } boost::mutex mutex; void thread() { for (int i = 0; i < 100; ++i) { wait(1); mutex.lock(); std::cout << "Thread " << boost::this_thread::get_id() << ": " << i << std::endl; mutex.unlock(); } } int main() { boost::thread t1(thread); boost::thread t2(thread); t1.join(); t2.join(); }

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  • Synchronizing a collection of wrapped objects with a collection of unwrapped objects

    - by Kenneth Cochran
    I have two classes: Employee and EmployeeGridViewAdapter. Employee is composed of several complex types. EmployeeGridViewAdapter wraps a single Employee and exposes its members as a flattened set of system types so a DataGridView can handle displaying, editing, etc. I'm using VS's builtin support for turning a POCO into a data source, which I then attach to a BindingSource object. When I attach the DataGridView to the BindingSource it creates the expected columns and at runtime I can perform the expected CRUD operations. All is good so far. The problem is the collection of adapters and the collection of employees aren't being synchronized. So all the employees I create an runtime never get persisted. Here's a snippet of the code that generates the collection of EmployeeGridViewAdapter's: var employeeCollection = new List<EmployeeGridViewAdapter>(); foreach (var employee in this.employees) { employeeCollection.Add(new EmployeeGridViewAdapter(employee)); } this.view.Employees = employeeCollection; Pretty straight forward but I can't figure out how to synchronize changes back to the original collection. I imagine edits are already handled because both collections reference the same objects but creating new employees and deleting employees aren't happening so I can't be sure.

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  • Rot13 for numbers.

    - by dreeves
    EDIT: Now a Major Motion Blog Post at http://messymatters.com/sealedbids The idea of rot13 is to obscure text, for example to prevent spoilers. It's not meant to be cryptographically secure but to simply make sure that only people who are sure they want to read it will read it. I'd like to do something similar for numbers, for an application involving sealed bids. Roughly I want to send someone my number and trust them to pick their own number, uninfluenced by mine, but then they should be able to reveal mine (purely client-side) when they're ready. They should not require further input from me or any third party. (Added: Note the assumption that the recipient is being trusted not to cheat.) It's not as simple as rot13 because certain numbers, like 1 and 2, will recur often enough that you might remember that, say, 34.2 is really 1. Here's what I'm looking for specifically: A function seal() that maps a real number to a real number (or a string). It should not be deterministic -- seal(7) should not map to the same thing every time. But the corresponding function unseal() should be deterministic -- unseal(seal(x)) should equal x for all x. I don't want seal or unseal to call any webservices or even get the system time (because I don't want to assume synchronized clocks). (Added: It's fine to assume that all bids will be less than some maximum, known to everyone, say a million.) Sanity check: > seal(7) 482.2382 # some random-seeming number or string. > seal(7) 71.9217 # a completely different random-seeming number or string. > unseal(seal(7)) 7 # we always recover the original number by unsealing.

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  • Design suggestion for expression tree evaluation with time-series data

    - by Lirik
    I have a (C#) genetic program that uses financial time-series data and it's currently working but I want to re-design the architecture to be more robust. My main goals are: sequentially present the time-series data to the expression trees. allow expression trees to access previous data rows when needed. to optimize performance of the data access while evaluating the expression trees. keep a common interface so various types of data can be used. Here are the possible approaches I've thought about: I can evaluate the expression tree by passing in a data row into the root node and let each child node use the same data row. I can evaluate the expression tree by passing in the data row index and letting each node get the data row from a shared DataSet (currently I'm passing the row index and going to multiple synchronized arrays to get the data). Hybrid: an immutable data set is accessible by all of the expression trees and each expression tree is evaluated by passing in a data row. The benefit of the first approach is that the data row is being passed into the expression tree and there is no further query done on the data set (which should increase performance in a multithreaded environment). The drawback is that the expression tree does not have access to the rest of the data (in case some of the functions need to do calculations using previous data rows). The benefit of the second approach is that the expression trees can access any data up to the latest data row, but unless I specify what that row is, I'll have to iterate through the rows and figure out which one is the last one. The benefit of the hybrid is that it should generally perform better and still provide access to the earlier data. It supports two basic "views" of data: the latest row and the previous rows. Do you guys know of any design patterns or do you have any tips that can help me build this type of system? Should I use a DataSet to hold and present the data, or are there more efficient ways to present rows of data while maintaining a simple interface? FYI: All of my code is written in C#.

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  • Android: Unable to make httprequest behind firewall

    - by Yang
    The standard getUrlContent works welll when there is no firewall. But I got exceptions when I try to do it behind a firewall. I've tried to set "http proxy server" in AVD manager, but it didn't work. Any idea how to correctly set it up? protected static synchronized String getUrlContent(String url) throws ApiException { if(url.equals("try")){ return "thanks"; } if (sUserAgent == null) { throw new ApiException("User-Agent string must be prepared"); } // Create client and set our specific user-agent string HttpClient client = new DefaultHttpClient(); HttpGet request = new HttpGet(url); request.setHeader("User-Agent", sUserAgent); try { HttpResponse response = client.execute(request); // Check if server response is valid StatusLine status = response.getStatusLine(); if (status.getStatusCode() != HTTP_STATUS_OK) { throw new ApiException("Invalid response from server: " + status.toString()); } // Pull content stream from response HttpEntity entity = response.getEntity(); InputStream inputStream = entity.getContent(); ByteArrayOutputStream content = new ByteArrayOutputStream(); // Read response into a buffered stream int readBytes = 0; while ((readBytes = inputStream.read(sBuffer)) != -1) { content.write(sBuffer, 0, readBytes); } // Return result from buffered stream return new String(content.toByteArray()); } catch (IOException e) { throw new ApiException("Problem communicating with API", e); } }

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  • What is the best software design to use in this scenario

    - by domdefelice
    I need to generate HTML snippets using jQuery. The creation of those snippets depends on some data. The data is stored server-side, in session (where PHP is used). At the moment I achieved this - retrieving the data from the server via AJAX in form of JSON - and building the snippets via specific javascript functions that read those data The problem is that the complexity of the data is getting bigger and hence the serialization into JSON is getting even more difficult since I can't do it automatically. I can't do it automatically because some information are sensible so I generate a "stripped" version to send to the client. I know it is difficult to understand without any code to read, but I am hoping this is a common scenario and would be glad for any tip, suggestion or even design-pattern you can give me. Should I store both a complete and a stripped data on the server and then use some library to automatically generate the JSON from the stripped data? But this also means I have to get the two data synchronized. Or maybe I could move the logic server-side, this way avoiding sending the data. But this means sending javascript code (since I rely on jQuery). Maybe not a good idea. Feel free to ask me more details if this is not clear. Thank you for any help

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  • Java performance issue

    - by Colby77
    Hi, I've got a question related to java performance and method execution. In my app there are a lot of place where I have to validate some parameter, so I've written a Validator class and put all the validation methods into it. Here is an example: public class NumberValidator { public static short shortValidator(String s) throws ValidationException{ try{ short sh = Short.parseShort(s); if(sh < 1){ throw new ValidationException(); } return sh; }catch (Exception e) { throw new ValidationException("The parameter is wrong!"); } } ... But I'm thinking about that. Is this OK? It's OO and modularized, but - considering performance - is it a good idea? What if I had awful lot of invocation at the same time? The snippet above is short and fast, but there are some methods that take more time. What happens when there are a lot of calling to a static method or an instance method in the same class and the method is not synchronized? All the calling methods have to fall in line and the JVM executes them sequentially? Is it a good idea to have some class that are identical to the above-mentioned and randomly call their identical methods? I think it is not, because "Don't repeat yourself " and "Duplication is Evil" etc. But what about performance? Thanks is advance.

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  • What does flushing thread local memory to global memory mean?

    - by Jack Griffith
    Hi, I am aware that the purpose of volatile variables in Java is that writes to such variables are immediately visible to other threads. I am also aware that one of the effects of a synchronized block is to flush thread-local memory to global memory. I have never fully understood the references to 'thread-local' memory in this context. I understand that data which only exists on the stack is thread-local, but when talking about objects on the heap my understanding becomes hazy. I was hoping that to get comments on the following points: When executing on a machine with multiple processors, does flushing thread-local memory simply refer to the flushing of the CPU cache into RAM? When executing on a uniprocessor machine, does this mean anything at all? If it is possible for the heap to have the same variable at two different memory locations (each accessed by a different thread), under what circumstances would this arise? What implications does this have to garbage collection? How aggressively do VMs do this kind of thing? Overall, I think am trying to understand whether thread-local means memory that is physically accessible by only one CPU or if there is logical thread-local heap partitioning done by the VM? Any links to presentations or documentation would be immensely helpful. I have spent time researching this, and although I have found lots of nice literature, I haven't been able to satisfy my curiosity regarding the different situations & definitions of thread-local memory. Thanks very much.

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  • Unable to access Java-created file -- sometimes

    - by BlairHippo
    In Java, I'm working with code running under WinXP that creates a file like this: public synchronized void store(Properties props, byte[] data) { try { File file = filenameBasedOnProperties(props); if ( file.exists() ) { return; } File temp = File.createTempFile("tempfile", null); FileOutputStream out = new FileOutputStream(temp); out.write(data); out.flush(); out.close(); file.getParentFile().mkdirs(); temp.renameTo(file); } catch (IOException ex) { // Complain and whine and stuff } } Sometimes, when a file is created this way, it's just about totally inaccessible from outside the code (though the code responsible for opening and reading the file has no problem), even when the application isn't running. When accessed via Windows Explorer, I can't move, rename, delete, or even open the file. Under Cygwin, I get the following when I ls -l the directory: ls: cannot access [big-honkin-filename] total 0 ?????????? ? ? ? ? ? [big-honkin-filename] As implied, the filenames are big, but under the 260-character max for XP (though they are slightly over 200 characters). To further add to the sense the my computer just wants me to feel stupid, sometimes the files created by this code are perfectly normal. The only pattern I've spotted is that once one file in the directory "locks", the rest are screwed. Anybody ever run into something like this before, or have any insights into what's going on here?

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  • XElement vs Dcitionary

    - by user135498
    Hi All, I need advice. I have application that imports 10,000 rows containing name & address from a text file into XElements that are subsequently added to a synchronized queue. When the import is complete the app spawns worker threads that process the XElements by deenqueuing them, making a database call, inserting the database output into the request document and inserting the processed document into an output queue. When all requests have been processed the output queue is written to disk as an XML doc. I used XElements for the requests because I needed the flexibility to add fields to the request during processing. i.e. Depending on the job type the app might require that it add phone number, date of birth or email address to a request based on a name/address match against a public record database. My questions is; The XElements seems to use quite a bit of memory and I know there is a lot of parsing as the document makes its way through the processing methods. I’m considering replacing the XElements with a Dictionary object but I’m skeptical the gain will be worth the effort. In essence it will accomplish the same thing. Thoughts?

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  • How to use SQLErrorCodeSQLExceptionTranslator and DAO class with @Repository in Spring?

    - by GuidoMB
    I'm using Spring 3.0.2 and I have a class called MovieDAO that uses JDBC to handle the db. I have set the @Repository annotations and I want to convert the SQLException to the Spring's DataAccessException I have the following example: @Repository public class JDBCCommentDAO implements CommentDAO { static JDBCCommentDAO instance; ConnectionManager connectionManager; private JDBCCommentDAO() { connectionManager = new ConnectionManager("org.postgresql.Driver", "postgres", "postgres"); } static public synchronized JDBCCommentDAO getInstance() { if (instance == null) instance = new JDBCCommentDAO(); return instance; } @Override public Collection<Comment> getComments(User user) throws DAOException { Collection<Comment> comments = new ArrayList<Comment>(); try { String query = "SELECT * FROM Comments WHERE Comments.userId = ?"; Connection conn = connectionManager.getConnection(); PreparedStatement stmt = conn.prepareStatement(query); stmt = conn.prepareStatement(query); stmt.setInt(1, user.getId()); ResultSet result = stmt.executeQuery(); while (result.next()) { Movie movie = JDBCMovieDAO.getInstance().getLightMovie(result.getInt("movie")); comments.add(new Comment(result.getString("text"), result.getInt("score"), user, result.getDate("date"), movie)); } connectionManager.closeConnection(conn); } catch (SQLException e) { e.printStackTrace(); //CONVERT TO DATAACCESSEXCEPTION } return comments; } } I Don't know how to get the Translator and I don't want to extends any Spring class, because that is why I'm using the @Repository annotation

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  • Help with java executors: wait for task termination.

    - by Raffo
    I need to submit a number of task and then wait for them until all results are available. Each of them adds a String to a Vector (that is synchronized by default). Then I need to start a new task for each result in the Vector but I need to do this only when all the previous tasks have stopped doing their job. I want to use Java Executor, in particular I tried using Executors.newFixedThreadPool(100) in order to use a fixed number of thread (I have a variable number of task that can be 10 or 500) but I'm new with executors and I don't know how to wait for task termination. This is something like a pseudocode of what my program needs to do: EecutorService e = Executors.newFixedThreadPool(100); while(true){ /*do something*/ for(...){ <start task> } <wait for all task termination> for each String in result{ <start task> } <wait for all task termination> } I can't do a e.shutdown because I'm in a while(true) and I need to reuse the executorService... Can you help me? Can you suggest me a guide/book about java executors??

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  • Loading 2 Singletons With Dependencies when an app is opened (appDelegate / appDidBecomeActive) iPhone SDK

    - by taber
    I'm trying to load two standard-issue style singletons: http://cocoawithlove.com/2008/11/singletons-appdelegates-and-top-level.html when my iPhone app is loaded. Here's my code: - (void) applicationDidFinishLaunching:(UIApplication *)application { // first, restore user prefs [AppState loadState]; // then, initialize the camera [[CameraModule sharedCameraModule] initCamera]; } My "camera module" has code that checks a property of the AppState singleton. But I think what's happening is a race condition where the camera module singleton is trying to access the AppState property while it's in the middle of being initialized (so the property is nil, and it's re-initializing AppState). I'd really like to keep these separate, instead of just throwing one (or both) into the App Delegate. Has anyone else seen something like this? What kind of workaround did you use, or what would you suggest? Thanks in advance! Here's the loadState method: + (void)loadState { @synchronized([AppState class]) { NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES); NSString *documentsDirectory = [paths objectAtIndex:0]; NSString *file = [documentsDirectory stringByAppendingPathComponent:@"prefs.archive"]; Boolean saveFileExists = [[NSFileManager defaultManager] fileExistsAtPath:file]; if(saveFileExists) { sharedAppState = [[NSKeyedUnarchiver unarchiveObjectWithFile:file] retain]; } else { [AppState sharedAppState]; } } }

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  • Mix Audio tracks with offset in SOX

    - by Laramie
    From ASP.Net, I am using FFMPEG to convert flv files on a Flash Media Server to wavs that I need to mix into a single MP3 file. I originally attempted this entirely with FFMPEG but eventually gave up on the mixing step because I don't believe it it possible to combine audio only tracks into a single result file. I would love to be wrong. I am now using FFMPEG to access the FLV files and extract the audio track to wav so that SOX can mix them. The problem is that I must offset one of the audio tracks by a few seconds so that they are synchronized. Each file is one half of a conversation between a student and a teacher. For example teacher.wav might need to begin 3.3 seconds after student.wav. I can only figure out how to mix the files with SOX where both tracks begin at the same time. My best attempt at this point is: ffmpeg -y -i rtmp://server/appName/instance/student.flv -ac 1 student.wav ffmpeg -y -i rtmp://server/appName/instance/teacher.flv -ac 1 teacher.wav sox -m student.wav teacher.wav combined.mp3 splice 3.3 These tools (FFMEG/SoX) were chosen based on my best research, but are not required. Any working solution would allow an ASP.Net service to input the two FMS flvs and create a combined MP3 using open-source or free tools.

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