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  • database schema eligible for delta synchronization

    - by WilliamLou
    it's a question for discussion only. Right now, I need to re-design a mysql database table. Basically, this table contains all the contract records I synchronized from another database. The contract record can be modified, deleted or users can add new contract records via GUI interface. At this stage, the table structure is exactly the same as the Contract info (column: serial number, expiry date etc.). In that case, I can only synchronize the whole table (delete all old records, replace with new ones). If I want to delta(only synchronize with modified, new, deleted records) synchronize the table, how should I change the database schema? here is the method I come up with, but I need your suggestions because I think it's a common scenario in database applications. 1)introduce a sequence number concept/column: for each sequence, mark the new added records, modified records, deleted records with this sequence number. By recording the last synchronized sequence number, only pass those records with higher sequence number; 2) because deleted contracts can be added back, and the original table has primary key constraints, should I create another table for those deleted records? or add a flag column to indicate if this contract has been deleted? I hope I explain my question clearly. Anyway, if you know any articles or your own suggestions about this, please let me know. Thanks!

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  • Understanding Java Wait and Notify methods

    - by Maddy
    Hello all: I have a following program: import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; public class SimpleWaitNotify implements Runnable { final static Object obj = new Object(); static boolean value = true; public synchronized void flag() { System.out.println("Before Wait"); try { obj.wait(); } catch (InterruptedException e) { System.out.println("Thread interrupted"); } System.out.println("After Being Notified"); } public synchronized void unflag() { System.out.println("Before Notify All"); obj.notifyAll(); System.out.println("After Notify All Method Call"); } public void run() { if (value) { flag(); } else { unflag(); } } public static void main(String[] args) throws InterruptedException { ExecutorService pool = Executors.newFixedThreadPool(4); SimpleWaitNotify sWait = new SimpleWaitNotify(); pool.execute(sWait); SimpleWaitNotify.value = false; SimpleWaitNotify sNotify = new SimpleWaitNotify(); pool.execute(sNotify); pool.shutdown(); } } When I wait on obj, I get the following exception Exception in thread "pool-1-thread-1" java.lang.IllegalMonitorStateException: current thread not owner for each of the two threads. But if I use SimpleWaitNotify's monitor then the program execution is suspended. In other words, I think it suspends current execution thread and in turn the executor. Any help towards understanding what's going on would be duly appreciated. This is an area1 where the theory and javadoc seem straightforward, and since there aren't many examples, conceptually left a big gap in me.

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  • Java: Implement own message queue (threadsafe)

    - by derMax
    The task is to implement my own messagequeue that is thread safe. My approach: public class MessageQueue { /** * Number of strings (messages) that can be stored in the queue. */ private int capacity; /** * The queue itself, all incoming messages are stored in here. */ private Vector<String> queue = new Vector<String>(capacity); /** * Constructor, initializes the queue. * * @param capacity The number of messages allowed in the queue. */ public MessageQueue(int capacity) { this.capacity = capacity; } /** * Adds a new message to the queue. If the queue is full, it waits until a message is released. * * @param message */ public synchronized void send(String message) { //TODO check } /** * Receives a new message and removes it from the queue. * * @return */ public synchronized String receive() { //TODO check return "0"; } } If the queue is empty and I call remove(), I want to call wait() so that another thread can use the send() method. Respectively, I have to call notifyAll() after every iteration. Question: Is that possible? I mean does it work that when I say wait() in one method of an object, that I can then execute another method of the same object? And another question: Does that seem to be clever?

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  • Finding leaks under GeneralBlock-16?

    - by erastusnjuki
    If ObjectAlloc cannot deduce type information for the block, it uses 'GeneralBlock'. Any strategies to get leaks from this block that may eliminate the need of my 'trial and error' methods that I use? The Extended Detail thing doesn't really do it for me as I just keep guessing.

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  • Send/cache multidimensional array to php with jQuery

    - by robertdd
    hy, i have a little, big problem here :) after i upload some images i get a list with all the images. I have some jQuery function for rotate, duplicate, delete, shuffle images! when i select a image and hit delete i send a post to php with the alt="" value of the image,i identify the picture and edit. I want to make a save button, Instead of sending a post every time i rotate a image, better send a post after editing the list of images with an array that contains all data? my php array after upload looks like this: [files] => Array ( [lcxkijgr] => lcxkijgr.jpg [xcewxpfv] => xcewxpfv.jpg [rtiurwxf] => rtiurwxf.jpg [gsbxdsdc] => gsbxdsdc.jpg ) say that I uploaded 4 pictures, firs picture i rotate 90 degrees second i want to duplicate third i rotate 270 degrees and the fourth image i delete i can do all this only with jQuery, but on the server the images are the same, after a refresh the images are the same this is the list with the images: <div class="upimage"> <ul id="upimagesQueue"> <li id="upimagesHPVEJM"> <a href="javascript:jQuery('#upimagesHPVEJM').showlargeimage('HPVEJM')"> <img alt="lcxkijgr" src="uploads/s6id9r9icnp8q9102h8md9kfd7/lcxkijgr.jpg?1272087830477" id="HPVEJM" style="display: block;" > </a> </li> <li id="upimagesSTCSAV"> <a href="javascript:jQuery('#upimagesSTCSAV').showlargeimage('STCSAV')"> <img alt="xcewxpfv" src="uploads/s6id9r9icnp8q9102h8md9kfd7/xcewxpfv.jpg?1272087831360" id="STCSAV" style="display: block;" > </a> </li> <li id="upimagesBFPUEQ"> <a href="javascript:jQuery('#upimagesBFPUEQ').showlargeimage('BFPUEQ')"> <img alt="rtiurwxf" src="uploads/s6id9r9icnp8q9102h8md9kfd7/rtiurwxf.jpg?1272087832162" id="BFPUEQ" style="display: block;" > </a> </li> <li id="upimagesRKXNSV"> <a href="javascript:jQuery('#upimagesRKXNSV').showlargeimage('RKXNSV')"> <img alt="gsbxdsdc" src="uploads/s6id9r9icnp8q9102h8md9kfd7/gsbxdsdc.jpg?1272087832957" id="RKXNSV" style="display: block;"> </a> </li> <ul> </div> is ok if i make one array like this: array{ imgFromLi = array(img1,img2,img3,img4,img5,img6) rotate = array{img1=90, img2=270, img3=90} delete = array{img4,img5,img6} duplicate = array{img2, img3} } how i can send/cache this array?? sorry for my very bad english

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  • java and threads: very strange behaviour

    - by Derk
    private synchronized Map<Team, StandingRow> calculateStanding() { System.out.println("Calculate standing for group " + getName()); Map<Team, StandingRow> standing = new LinkedHashMap<Team, StandingRow>(); for (Team team : teams) { standing.put(team, new StandingRow(team)); } StandingRow homeTeamRow, awayTeamRow; for (Match match : matches.values()) { homeTeamRow = standing.get(match.getHomeTeam()); awayTeamRow = standing.get(match.getAwayTeam()); System.out.println("Contains key for " + match.getHomeTeam() + ": " + standing.containsKey(match.getHomeTeam())); System.out.println("Contains key for " + match.getAwayTeam() + ": " + standing.containsKey(match.getAwayTeam())); } } This is my code. matches contains 6 elements, but the problem is that after two matches no keys are anymore found in the standing map. The output is for example Contains key for Zuid-Afrika: true Contains key for Mexico: true Contains key for Uruguay: true Contains key for Frankrijk: true Contains key for Zuid-Afrika: false Contains key for Uruguay: false Contains key for Frankrijk: false Contains key for Mexico: false Contains key for Mexico: false Contains key for Uruguay: false Contains key for Frankrijk: false Contains key for Zuid-Afrika: false This is in a threaded environment, but the method is synchronized so I thought that this would not give a problem? I have also a simple unit test for this method and that works well.

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  • How do I use the information about exceptions a method throws in .NET in my code?

    - by dotnetdev
    For many methods in .NET, the exceptions they can potentially throw can be as many as 7-8 (one or two methods in XmlDocument, Load() being one I think, can throw this many exceptions). Does this mean I have to write 8 catch blocks to catch all of these exceptions (it is best practise to catch an exception with a specific exception block and not just a general catch block of type Exception). How do I use this information? Thanks

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  • Unity 2 and Enterprise library configuration tool

    - by nachid
    Hi, Can someone show me how to use Enterprise library configuration tool with Unity2 Whatever I did, when I open the Enterprise library configuration tool, I could not have it working with a Unity config file. When I click on the menu to add a new block, there is no Unity configuration block What am I doing wrong? Thank you for your help

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  • an x86 question

    - by wide
    i'm working for my exam. i didn't resolved this question. does anyone help me? assume that there are two block, BLOCK1 AND BLOCK2. every block has 50 bytes. write a program to add BLOCK1 with BLOCK2 , and store result to BLOCK2 using LODS, STOS and LOOP etc. assembly commands?

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  • how to restart a Thread?

    - by wizztjh
    It is a RMI Server object , so many sethumanActivity() might be run , how do i make sure the previous changeToFalse thread will be stop or halt before the new changeToFalse run? t. interrupt ? Basically when sethumanActivity() is invoke , the humanActivity will be set to true , but a thread will be run to set it back to false. But I am thinking for how to disable or kill the thread when another sethumanActivity() invoked? public class VitaminDEngine implements VitaminD { public boolean humanActivity = false; changeToFalse cf = new changeToFalse(); Thread t = new Thread(cf); private class changeToFalse implements Runnable{ @Override public void run() { try { Thread.sleep(4000); } catch (InterruptedException e) { // TODO Auto-generated catch block e.printStackTrace(); } humanActivity = false; } } @Override public void sethumanActivity() throws RemoteException { // TODO Auto-generated method stub humanActivity = true; t.start(); } public boolean gethumanActivity() throws RemoteException { // TODO Auto-generated method stub return humanActivity; } } Edited after the help of SOer package smartOfficeJava; import java.rmi.RemoteException; import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; public class VitaminDEngine implements VitaminD { public volatile boolean humanActivity = false; changeToFalse cf = new changeToFalse(); ExecutorService service = Executors.newSingleThreadExecutor(); private class changeToFalse implements Runnable{ @Override public void run() { try { Thread.sleep(4000); } catch (InterruptedException e) { // TODO Auto-generated catch block e.printStackTrace(); } humanActivity = false; } } @Override public synchronized void sethumanActivity() throws RemoteException { humanActivity = true; service.submit(cf); } public synchronized boolean gethumanActivity() throws RemoteException { return humanActivity; } }

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  • Designing a database file format

    - by RoliSoft
    I would like to design my own database engine for educational purposes, for the time being. Designing a binary file format is not hard nor the question, I've done it in the past, but while designing a database file format, I have come across a very important question: How to handle the deletion of an item? So far, I've thought of the following two options: Each item will have a "deleted" bit which is set to 1 upon deletion. Pro: relatively fast. Con: potentially sensitive data will remain in the file. 0x00 out the whole item upon deletion. Pro: potentially sensitive data will be removed from the file. Con: relatively slow. Recreating the whole database. Pro: no empty blocks which makes the follow-up question void. Con: it's a really good idea to overwrite the whole 4 GB database file because a user corrected a typo. I will sell this method to Twitter ASAP! Now let's say you already have a few empty blocks in your database (deleted items). The follow-up question is how to handle the insertion of a new item? Append the item to the end of the file. Pro: fastest possible. Con: file will get huge because of all the empty blocks that remain because deleted items aren't actually deleted. Search for an empty block exactly the size of the one you're inserting. Pro: may get rid of some blocks. Con: you may end up scanning the whole file at each insert only to find out it's very unlikely to come across a perfectly fitting empty block. Find the first empty block which is equal or larger than the item you're inserting. Pro: you probably won't end up scanning the whole file, as you will find an empty block somewhere mid-way; this will keep the file size relatively low. Con: there will still be lots of leftover 0x00 bytes at the end of items which were inserted into bigger empty blocks than they are. Rigth now, I think the first deletion method and the last insertion method are probably the "best" mix, but they would still have their own small issues. Alternatively, the first insertion method and scheduled full database recreation. (Probably not a good idea when working with really large databases. Also, each small update in that method will clone the whole item to the end of the file, thus accelerating file growth at a potentially insane rate.) Unless there is a way of deleting/inserting blocks from/to the middle of the file in a file-system approved way, what's the best way to do this? More importantly, how do databases currently used in production usually handle this?

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  • Good style for handling constructor failure of critical object

    - by mtlphil
    I'm trying to decide between two ways of instantiating an object & handling any constructor exceptions for an object that is critical to my program, i.e. if construction fails the program can't continue. I have a class SimpleMIDIOut that wraps basic Win32 MIDI functions. It will open a MIDI device in the constructor and close it in the destructor. It will throw an exception inherited from std::exception in the constructor if the MIDI device cannot be opened. Which of the following ways of catching constructor exceptions for this object would be more in line with C++ best practices Method 1 - Stack allocated object, only in scope inside try block #include <iostream> #include "simplemidiout.h" int main() { try { SimpleMIDIOut myOut; //constructor will throw if MIDI device cannot be opened myOut.PlayNote(60,100); //..... //myOut goes out of scope outside this block //so basically the whole program has to be inside //this block. //On the plus side, it's on the stack so //destructor that handles object cleanup //is called automatically, more inline with RAII idiom? } catch(const std::exception& e) { std::cout << e.what() << std::endl; std::cin.ignore(); return 1; } std::cin.ignore(); return 0; } Method 2 - Pointer to object, heap allocated, nicer structured code? #include <iostream> #include "simplemidiout.h" int main() { SimpleMIDIOut *myOut; try { myOut = new SimpleMIDIOut(); } catch(const std::exception& e) { std::cout << e.what() << std::endl; delete myOut; return 1; } myOut->PlayNote(60,100); std::cin.ignore(); delete myOut; return 0; } I like the look of the code in Method 2 better, don't have to jam my whole program into a try block, but Method 1 creates the object on the stack so C++ manages the object's life time, which is more in tune with RAII philosophy isn't it? I'm still a novice at this so any feedback on the above is much appreciated. If there's an even better way to check for/handle constructor failure in a siatuation like this please let me know.

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  • Is this ruby code thread safe?

    - by Ben K.
    Is this code threadsafe? It seems like it should be, because @myvar will never be assigned from multiple threads (assuming block completes in < 1s). But do I need to be worried about a situation where the second block is trying to read @myvar as it's being written? require 'rubygems' require 'eventmachine' @myvar = Time.now.to_i EventMachine.run do EventMachine.add_periodic_timer(1) do EventMachine.defer do @myvar = Time.now.to_i # some calculation and reassign end end EventMachine.add_periodic_timer(0.5) do puts @myvar end end

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  • Accessing global variable in multithreaded Tomcat server

    - by jwegan
    I have a singleton object that I construct like thus: private static volatile KeyMapper mapper = null; public static KeyMapper getMapper() { if(mapper == null) { synchronized(Utils.class) { if(mapper == null) { mapper = new LocalMemoryMapper(); } } } return mapper; } The class KeyMapper is basically a synchronized wrapper to HashMap with only two functions, one to add a mapping and one to remove a mapping. When running in Tomcat 6.24 on my 32bit Windows machine everything works fine. However when running on a 64 bit Linux machine (CentOS 5.4 with OpenJDK 1.6.0-b09) I add one mapping and print out the size of the HashMap used by KeyMapper to verify the mapping got added (i.e. verify size = 1). Then I try to retrieve the mapping with another request and I keep getting null and when I checked the size of the HashMap it was 0. I'm confident the mapping isn't accidentally being removed since I've commented out all calls to remove (and I don't use clear or any other mutators, just get and put). The requests are going through Tomcat 6.24 (configured to use 200 threads with a minimum of 4 threads) and I passed -Xnoclassgc to the jvm to ensure the class isn't inadvertently getting garbage collected (jvm is also running in -server mode). I also added a finalize method to KeyMapper to print to stderr if it ever gets garbage collected to verify that it wasn't being garbage collected. I'm at my wits end and I can't figure out why one minute the entry in HashMap is there and the next it isn't :(

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  • Custom Items in Lists in C# forms?

    - by chaz
    I'm a bit new to the C#-form app developing and I want know, what's the best way around at making a control that holds a list of horizontal items. In which each of these items are horizontally ruled to it's parent control, contain a thumbnail to the left and a large text block to the right of image and a smaller text block underneath that. So basically this isn't a predefined control I can find in the toolbox. Any ideas?

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  • asp.net mvc taking offline for testing

    - by Debra
    I need to test a feature in a live "asp.net mvc" web site and would want to block access to the site while testing, how would you recommend doing that? Is it possible to block access and still be able to test as an anonymous user? (I need to test the process as a user that's not logged in).

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  • jQuery toggling divs, expand collapse all and keep first item selected when page loads

    - by hollyb
    Hi, I have a question about some functionality I'm trying to add to my jQuery to enable a button or text to expand/contract all the divs on click... and I'd like to figure out how to keep the first div open when the page loads. Here is the jQuery: (document).ready(function(){ //Hides containers on load $(".toggle_container").hide(); //Switch "Open" and "Close" state on click $("h2.trigger").toggle(function(){ $(this).addClass("active"); }, function () { $(this).removeClass("active"); }); //Slide up and down on click $("h2.trigger").click(function(){ $(this).next(".toggle_container").slideToggle("slow"); }); }); And the css: // uses a background image with an on (+) and off (-) state stacked on top of each other h2.trigger { background: url(buttonBG.gif) no-repeat;height: 46px;line-height: 46px;width: 300px;font-size: 2em;font-weight: normal;} h2.trigger a {color: #fff;text-decoration: none; display: block;} h2.active {background-position: left bottom;} .toggle_container { overflow: hidden; } .toggle_container .block {padding: 20px;} And the html <h2 class="trigger"><a href="#">Heading</a></h2> <div class="toggle_container"> <div class="block">Stuff goes here</div> </div> <h2 class="trigger"><a href="#">Heading 2</a></h2> <div class="toggle_container"> <div class="block">Stuff goes here</div> </div> So it works great and looks great. However, when I try to get it to keep the first instance open, the background image that should adjust show the (-) state doesn't change. The code I used to this was: $(".toggle_container:first").show(); So, my question is, does anyone know of an easier way to show the first instance of this as open without having to created specials rules/class for the first item? Also, any ideas about how to make an open all/close all link? Thanks!

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  • how to make Xcode indentation from beginning of previous line?

    - by Mikkel
    ok, possibly insanely n00b question or something i have overlooked in Xcode prefs: On pressing return, in stead of Xcode's syntax-aware indentation doing smart indent from whatever brackets i've used on the previous line, how can I make it so Xcode indents just from the beginning of the previous line? From the picture below, first block of code is what i got, second block of code is what I want. Visual representation:

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  • jQuery dynamic css loading weired behavior

    - by jimpsr
    The app I am working on requires dynamic loading of css and js, right now the solution is as follows: myapp.loadCss = function(css){ $("head").append("<link>"); cssDom = $("head").children(":last"); cssDom.attr({rel: "stylesheet", type: "text/css", href: css }); } myapp.loadJs = funciton(js){ ... //$.ajax call is used in synchronized mode to make sure the js is fully loaded } } When some widgets need to be load, the usual call with be myapp.loadCss('/widgets/widget1/css/example.css'); myapp.loadJs('/wiggets/widget1/js/example.js'); The weired thing is that once a while (1 out of 10 or 20), the newly created dom elements from example.js will not be able to get its css from example.css, it seems however my loadCss method does not load the css in a synchronized mode? I have tried to replace my loadCss with the the following code: myapp.loadCss(css){ $('<link href="' + css + '" rel="stylesheet" type="text/css" />').appendTo($('head')); } It seems to be OK then (I refreshed the webpage a hundred times for verification :-( ) But unfortunately this method failed in IE(IE7, not tested in IE6, 8) Is there any better solution for this?

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  • Table clusters in SQLServer

    - by Bruno Martinez
    In Oracle, a table cluster is a group of tables that share common columns and store related data in the same blocks. When tables are clustered, a single data block can contain rows from multiple tables. For example, a block can store rows from both the employees and departments tables rather than from only a single table: http://download.oracle.com/docs/cd/E11882_01/server.112/e10713/tablecls.htm#i25478 Can this be done in SQLServer?

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  • Hide blocks on page not found in Drupal

    - by Tommy
    I have google adsense in a block, and I want to hide the block when the page is a "Page not found" error page. It's against adsenses TOS to show their ads on error pages. I figure there must be a way to write a php script to put in the Page specific visibility options. Does anyone know how to do this?

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