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  • How does the rsync algorithm correctly identify repeating blocks?

    - by Kai
    I'm on a personal quest to learn how the rsync algorithm works. After some reading and thinking, I've come up with a situation where I think the algorithm fails. I'm trying to figure out how this is resolved in an actual implementation. Consider this example, where A is the receiver and B is the sender. A = abcde1234512345fghij B = abcde12345fghij As you can see, the only change is that 12345 has been removed. Now, to make this example interesting, let's choose a block size of 5 bytes (chars). Hashing the values on the sender's side using the weak checksum gives the following values list. abcde|12345|fghij abcde -> 495 12345 -> 255 fghij -> 520 values = [495, 255, 520] Next we check to see if any hash values differ in A. If there's a matching block we can skip to the end of that block for the next check. If there's a non-matching block then we've found a difference. I'll step through this process. Hash the first block. Does this hash exist in the values list? abcde -> 495 (yes, so skip) Hash the second block. Does this hash exist in the values list? 12345 -> 255 (yes, so skip) Hash the third block. Does this hash exist in the values list? 12345 -> 255 (yes, so skip) Hash the fourth block. Does this hash exist in the values list? fghij -> 520 (yes, so skip) No more data, we're done. Since every hash was found in the values list, we conclude that A and B are the same. Which, in my humble opinion, isn't true. It seems to me this will happen whenever there is more than one block that share the same hash. What am I missing?

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  • How to know when a user has really released a key in Java?

    - by Luis Soeiro
    (Edited for clarity) I want to detect when a user presses and releases a key in Java Swing, ignoring the keyboard auto repeat feature. I also would like a pure Java approach the works on Linux, Mac OS and Windows. Requirements: When the user presses some key I want to know what key is that; When the user releases some key, I want to know what key is that; I want to ignore the system auto repeat options: I want to receive just one keypress event for each key press and just one key release event for each key release; If possible, I would use items 1 to 3 to know if the user is holding more than one key at a time (i.e, she hits 'a' and without releasing it, she hits "Enter"). The problem I'm facing in Java is that under Linux, when the user holds some key, there are many keyPress and keyRelease events being fired (because of the keyboard repeat feature). I've tried some approaches with no success: Get the last time a key event occurred - in Linux, they seem to be zero for key repeat, however, in Mac OS they are not; Consider an event only if the current keyCode is different from the last one - this way the user can't hit twice the same key in a row; Here is the basic (non working) part of code: import java.awt.event.KeyListener; public class Example implements KeyListener { public void keyTyped(KeyEvent e) { } public void keyPressed(KeyEvent e) { System.out.println("KeyPressed: "+e.getKeyCode()+", ts="+e.getWhen()); } public void keyReleased(KeyEvent e) { System.out.println("KeyReleased: "+e.getKeyCode()+", ts="+e.getWhen()); } } When a user holds a key (i.e, 'p') the system shows: KeyPressed: 80, ts=1253637271673 KeyReleased: 80, ts=1253637271923 KeyPressed: 80, ts=1253637271923 KeyReleased: 80, ts=1253637271956 KeyPressed: 80, ts=1253637271956 KeyReleased: 80, ts=1253637271990 KeyPressed: 80, ts=1253637271990 KeyReleased: 80, ts=1253637272023 KeyPressed: 80, ts=1253637272023 ... At least under Linux, the JVM keeps resending all the key events when a key is being hold. To make things more difficult, on my system (Kubuntu 9.04 Core 2 Duo) the timestamps keep changing. The JVM sends a key new release and new key press with the same timestamp. This makes it hard to know when a key is really released. Any ideas? Thanks

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  • DCVS + hosting for a startup commercial multiplatform phone app

    - by AG
    I'm in lean startup mode, working on a simple phone app that will be published initially as a iThingy app and an Android app with, possibly, Blackberry and Symbian versions to follow. I'm about to go from no repository to needing a central repository that up to 4 very part-time resources will be sharing. Two of us have no version control background, one has used Subversion, and I've used most of the major centralized VCS systems. I'm not going to be pushing the technical limitations of any VCS for a long time; I'm sure that any of the major systems would work fine. And the hosting accounts I've looked at seem reasonable. So I'm really focussed on minimizing the downside risks. That is, I'd like to find a stable setup that is easy to learn in general, easy to use from Windows/Eclipse, and won't paint me into any obvious corners for the next 12 months or so. A quick search of the web had led me to consider the following pairs of DVCS and hosting service, with what I think I'm hearing as their strengths and weaknesses (for my purposes): Bazaar/Launchpad -- My initial choice since I need to get more familiar with this pair for the Google Summer of Code mentoring I'm doing. But, whatever the technical merits, a non-starter for me because they are purely open source, no private repositories plans to purchase that I can see. Git/GitHub -- Git: Fast, light, ultimately flexible, but relatively less Windows friendly, Eclipse plugin (eGit) available but relatively young, GitHub: widely used, pricing is fine Mercurial/BitBucket -- Mercurial: a little less flexible, a little more Windows friendly, Eclipse plugin seems a bit more mature, BitBucket: widely used, pricing is fine, includes a wiki and an issue tracker that we might be able to use instead of something like BaseCamp, at least for a while. Mercurial/BitBucket seem like the winning pair so far for my particular situation; at least two of us are definitely going to be working mostly from Eclipse on Windows and reducing my own learning curve is a priority. ;-) But I have two specific questions: 1) Am I wrong about Bazaar/Launchpad and is there a viable, secure way to use them for proprietary code? 2) Any reason to think that the Mecurial/Bitbucket pair will end up being a headache for my Mac developer, soon, or for Blackberry or Symbian developers a little later? ag

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  • Spring.NET & Immediacy CMS (or how to inject to server side controls without using PageHandlerFactor

    - by Simon Rice
    Is there any way to inject dependencies into an Immediacy CMS control using Spring.NET, ideally without having to use to ContextRegistry when initialising the control? Update, with my own answer The issue here is that Immediacy already has a handler defined in web.config that deals with all aspx pages, & so it's not possible add an entry for Spring.NET's PageHandlerFactory in web.config as per a normal webforms app. That rules out making the control implement ISupportsWebDependencyInjection. Furthermore, most of Immediacy's generated pages are aspx pages that don't physically exist on the drive. I have changed the title of the question to reflect this. What I have done to get Dependency Injection working is: Add the usual entries to web.config for Spring.NET as outlined in the documentation, except for the adding the entry to the <httpHandlers> section. In this case I've got my object definitions in Spring.config. Create the following abstract base class that will deal with all of the Dependency Injection work: DIControl.cs public abstract class DIControl : ImmediacyControl { protected virtual string DIName { get { return this.GetType().Name; } } protected override void OnInit(EventArgs e) { if (ContextRegistry.GetContext().GetObject(DIName, this.GetType()) != null) ContextRegistry.GetContext().ConfigureObject(this, DIName); base.OnInit(e); } } For non-immediacy controls, you can make this server side control inherit from Control or whatever subclass of that you like. For any control with which you wish to use with Spring.NET's Inversion of Control container, define it to inherit from DIControl & add the relelvant entry to Spring.config, for example: SampleControl.cs public class SampleControl : DIControl, INamingContainer { public string Text { get; set; } protected string InjectedText { get; set; } public SampleControl() : base() { Text = "Hello world"; } protected override void RenderContents(HtmlTextWriter output) { output.Write(string.Format("{0} {1}", Text, InjectedText)); } } Spring.config <objects xmlns="http://www.springframework.net"> <object id="SampleControl" type="MyProject.SampleControl, MyAssembly"> <property name="InjectedText" value="from Spring.NET" /> </object> </objects> You can optionally override DIName if you wish to name your entry in Spring.config differently from the name of your class. Provided everything's done correctly, you will have the control writing out "Hello world from Spring.NET!" when used in a page. This solution uses Spring.NET's ContextRegistry from within the control, but I would be surprised if there's no way around that for Immediacy at least since the page objects themselves aren't accessible. However, can this be improved at all from a Spring.NET perspective? Is there maybe an Immediacy plugin that already does this that I'm completely unaware of? Or is there an approach that does this in a more elegant way? I'm open to suggestions.

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  • Consolidating coding styles: Funcs, private method, single method classes

    - by jdoig
    Hi all, We currently have 3 devs with, some, conflicting styles and I'm looking for a way to bring peace to the kingdom... The Coders: Foo 1: Likes to use Func's & Action's inside public methods. He uses actions to alias off lengthy method calls and Func's to perform simple tasks that can be expressed in 1 or 2 lines and will be used frequently through out the code Pros: The main body of his code is succinct and very readable, often with only one or 2 public methods per class and rarely any private methods. Cons: The start of methods contain blocks of lambda rich code that other developers don't enjoy reading; and, on occasion, can contain higher order functions that other dev's REALLY don't like reading. Foo 2: Likes to create a private method for (almost) everything the public method will have to do . Pros: Public methods remain small and readable (to all developers). Cons: Private methods are numerous. With private methods that call into other private methods, that call into... etc, etc. Making code hard to navigate. Foo 3: Likes to create a public class with a, single, public method for every, non-trivial, task that needs performing, then dependency inject them into other objects. Pros: Easily testable, easy to understand (one object, one responsibility). Cons: project gets littered by classes, opening multiple class files to understand what code does makes navigation awkward. It would be great to take the best of all these techniques... Foo-1 Has really nice, readable (almost dsl-like) code... for the most part, except for all the Action and Func lambda shenanigans bulked together at the start of a method. Foo-3 Has highly testable and extensible code that just feels a bit "belt-&-braces" for some solutions and has some code-navigation niggles (constantly hitting F12 in VS and opening 5 other .cs files to find out what a single method does). And Foo-2... Well I'm not sure I like anything about the one-huge .cs file with 2 public methods and 12 private ones, except for the fact it's easier for juniors to dig into. I admit I grossly over-simplified the explanations of those coding styles; but if any one knows of any patterns, practices or diplomatic-manoeuvres that can help unite our three developers (without just telling any of them to just "stop it!") that would be great. From a feasibility standpoint : Foo-1's style meets with the most resistance due to some developers finding lambda and/or Func's hard to read. Foo-2's style meets with a less resistance as it's just so easy to fall into. Foo-3's style requires the most forward thinking and is difficult to enforce when time is short. Any ideas on some coding styles or conventions that can make this work?

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  • Make a compiled binary run at native speed flawlessly without recompiling from source on a another system?

    - by unknownthreat
    I know that many people, at a first glance of the question, may immediately yell out "Java", but no, I know Java's qualities. Allow me to elaborate my question first. Normally, when we want our program to run at a native speed on a system, whether it be Windows, Mac OS X, or Linux, we need to compile from source codes. If you want to run a program of another system in your system, you need to use a virtual machine or an emulator. While these tools allow you to use the program you need on the non-native OS, they sometimes have problems of performance and glitches. We also have a newer compiler called "JIT Compiler", where the compiler will parse the bytecode program to native machine language before execution. The performance may increase to a very good extent with JIT Compiler, but the performance is still not the same as running it on a native system. Another program on Linux, WINE, is also a good tool for running Windows program on Linux system. I have tried running Team Fortress 2 on it, and tried experiment with some settings. I got ~40 fps on Windows at its mid-high setting on 1280 x 1024. On Linux, I need to turn everything low at 1280 x 1024 to get ~40 fps. There are 2 notable things though: Polygon model settings do not seem to affect framerate whether I set it low or high. When there are post-processing effects or some special effects that require manipulation of drawn pixels of the current frame, the framerate will drop to 10-20 fps. From this point, I can see that normal polygon rendering is just fine, but when it comes to newer rendering methods that requires graphic card to the job, it slows down to a crawl. Anyway, this question is rather theoretical. Is there anything we can do at all? I see that WINE can run STEAM and Team Fortress 2. Although there are flaws, they can run at lower setting. Or perhaps, I should also ask, "is it possible to translate one whole program on a system to another system without recompiling from source and get native speed?" I see that we also have AOT Compiler, is it possible to use it for something like this? Or there are so many constraints (such as DirectX call or differences in software architecture) that make it impossible to have a flawless and not native to the system program that runs at native speed?

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  • How can I structure and recode messy categorical data in R?

    - by briandk
    I'm struggling with how to best structure categorical data that's messy, and comes from a dataset I'll need to clean. The Coding Scheme I'm analyzing data from a university science course exam. We're looking at patterns in student responses, and we developed a coding scheme to represent the kinds of things students are doing in their answers. A subset of the coding scheme is shown below. Note that within each major code (1, 2, 3) are nested non-unique sub-codes (a, b, ...). What the Raw Data Looks Like I've created an anonymized, raw subset of my actual data which you can view here. Part of my problem is that those who coded the data noticed that some students displayed multiple patterns. The coders' solution was to create enough columns (reason1, reason2, ...) to hold students with multiple patterns. That becomes important because the order (reason1, reason2) is arbitrary--two students (like student 41 and student 42 in my dataset) who correctly applied "dependency" should both register in an analysis, regardless of whether 3a appears in the reason column or the reason2 column. How Can I Best Structure Student Data? Part of my problem is that in the raw data, not all students display the same patterns, or the same number of them, in the same order. Some students may do just one thing, others may do several. So, an abstracted representation of example students might look like this: Note in the example above that student002 and student003 both are coded as "1b", although I've deliberately shown the order as different to reflect the reality of my data. My (Practical) Questions Should I concatenate reason1, reason2, ... into one column? How can I (re)code the reasons in R to reflect the multiplicity for some students? Thanks I realize this question is as much about good data conceptualization as it is about specific features of R, but I thought it would be appropriate to ask it here. If you feel it's inappropriate for me to ask the question, please let me know in the comments, and stackoverflow will automatically flood my inbox with sadface emoticons. If I haven't been specific enough, please let me know and I'll do my best to be clearer.

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  • How to troubleshoot a Highcharts script that's not rendering data when date is added and hanging the JS engine with large datasets?

    - by ylluminate
    I have a Highchart JS graph that I'm building in Rails (although I don't think Ruby has real bearing on this problem unless it's the Date output format) to which I'm adding the timestamp of each datapoint. Presently the array of floats is rendering fine without timestamps, however when I add the timestamp to the series it fails to rend. What's worse is that when the series has hundreds of entries all sorts of problems arise, not the least of which is the browser entirely hanging and requiring a force quit / kill. I'm using the following to build the array of arrays data series: series1 = readings.map{|row| [(row.date.to_i * 1000), (row.data1.to_f if BigDecimal(row.data1) != BigDecimal("-1000.0"))] } This yields a result like this: series: [{"name":"Data 1","data":[[1326262980000,1.79e-09],[1326262920000,1.29e-09],[1326262860000,1.22e-09],[1326262800000,1.42e-09],[1326262740000,1.29e-09],[1326262680000,1.34e-09],[1326262620000,1.31e-09],[1326262560000,1.51e-09],[1326262500000,1.24e-09],[1326262440000,1.7e-09],[1326262380000,1.24e-09],[1326262320000,1.29e-09],[1326262260000,1.53e-09],[1326262200000,1.23e-09],[1326262140000,1.21e-09]],"color":"blue"}] Yet nothing appears on the graph as noted. Notwithstanding, when I compare the data series in one of their very similar examples here: http://www.highcharts.com/demo/spline-irregular-time It appears that really the data series are formatted identically (except in mine I use the timestamp vs date method). This leads me to think I've got a problem with the timestamp output, but I'm just not able to figure out where / how as I'm converting the date output to an integer multipled by 1000 to convert it to milliseconds as per explained in a similar Railscasts tutorial. I would very much appreciate it if someone could point me in the right direction here as to what I may be doing wrong. What could cause no data to appear on the graph in smaller sized sets (<100 points) and when into the hundreds causes an apparent hang in the javascript engine in this case? Perhaps ultimately the key lies here as this is the entire js that's being generated and not rendering: jQuery(function() { // 1. Define JSON options var options = { chart: {"defaultSeriesType":"spline","renderTo":"chart_name"}, title: {"text":"Title"}, legend: {"layout":"vertical","style":{}}, xAxis: {"title":{"text":"UTC Time"},"type":"datetime"}, yAxis: [{"title":{"text":"Left Title","margin":10}},{"title":{"text":"Right Groups Title"},"opposite":true}], tooltip: {"enabled":true}, credits: {"enabled":false}, plotOptions: {"areaspline":{}}, series: [{"name":"Data 1","data":[[1326262980000,1.79e-08],[1326262920000,1.69e-08],[1326262860000,1.62e-08],[1326262800000,1.42e-08],[1326262740000,1.29e-08],[1326262680000,1.34e-08],[1326262620000,1.31e-08],[1326262560000,1.51e-08],[1326262500000,1.64e-08],[1326262440000,1.7e-08],[1326262380000,1.64e-08],[1326262320000,1.69e-08],[1326262260000,1.53e-08],[1326262200000,1.23e-08],[1326262140000,1.21e-08]],"color":"blue"},{"name":"Data 2","data":[[1326262980000,9.79e-09],[1326262920000,9.78e-09],[1326262860000,9.8e-09],[1326262800000,9.82e-09],[1326262740000,9.88e-09],[1326262680000,9.89e-09],[1326262620000,1.3e-06],[1326262560000,1.32e-06],[1326262500000,1.33e-06],[1326262440000,1.33e-06],[1326262380000,1.34e-06],[1326262320000,1.33e-06],[1326262260000,1.32e-06],[1326262200000,1.32e-06],[1326262140000,1.32e-06]],"color":"red"}], subtitle: {} }; // 2. Add callbacks (non-JSON compliant) // 3. Build the chart var chart = new Highcharts.StockChart(options); });

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  • bottom uicomponent does not receive mouse events

    - by firemonkey
    HI, I am sure this is very basic, however I am not able to find the solution. I have a base ShapeContainer(UIComponent). I add a uicomponent which has mouse down listener to ShapeContainer. the listener works great. When I add a simple sprite(draw square) on the ShapeContainer, The listener does not work any more. In the code, if I comment below lines, The event listener works fine. var square:Sprite = new Sprite(); square.graphics.lineStyle(4,0x00FF00); square.graphics.drawRect(0,0,20,20); square.mouseEnabled=false; shapeContainer.addChildAt(square,1); I have tried few things like, mouseenabled=false on top sprite. also tried to add addChildAt but non of them did any help. How can I draw a shape and also have the event listener work. enter code here protected function application1_creationCompleteHandler(event:FlexEvent):void { var shapeContainer:UIComponent = new UIComponent(); shapeContainer.x=100; shapeContainer.y=100; shapeContainer.width=200; shapeContainer.height=200; rawChildren.addChild(shapeContainer); var EventListenerShape:UIComponent = new UIComponent(); EventListenerShape.x=100; EventListenerShape.y=100; EventListenerShape.width=200;a EventListenerShape.height=200; EventListenerShape.graphics.clear(); EventListenerShape.graphics.beginFill(0xf1f1f1, 0.1); EventListenerShape.graphics.drawRoundRect(0, 0, 200, 200, 10, 10); EventListenerShape.alpha = 0; EventListenerShape.graphics.endFill(); EventListenerShape.addEventListener(MouseEvent.MOUSE_DOWN, mouseDownfunc); shapeContainer.addChild(EventListenerShape); var square:Sprite = new Sprite(); square.graphics.lineStyle(4,0x00FF00); square.graphics.drawRect(0,0,20,20); square.mouseEnabled=false; shapeContainer.addChildAt(square,1); } private function mouseDownfunc(e:MouseEvent){ trace("mouse Down **"); }    ]]> </mx:Script> <mx:Canvas id="uic" width="100%" height="100%" backgroundColor="0xFFFFFF"> </mx:Canvas>

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  • What is the difference between NULL in C++ and null in Java?

    - by Stephano
    I've been trying to figure out why C++ is making me crazy typing NULL. Suddenly it hits me the other day; I've been typing null (lower case) in Java for years. Now suddenly I'm programming in C++ and that little chunk of muscle memory is making me crazy. Wikiperipatetic defines C++ NULL as part of the stddef: A macro that expands to a null pointer constant. It may be defined as ((void*)0), 0 or 0L depending on the compiler and the language. Sun's docs tells me this about Java's "null literal": The null type has one value, the null reference, represented by the literal null, which is formed from ASCII characters. A null literal is always of the null type. So this is all very nice. I know what a null pointer reference is, and thank you for the compiler notes. Now I'm a little fuzzy on the idea of a literal in Java so I read on... A literal is the source code representation of a fixed value; literals are represented directly in your code without requiring computation. There's also a special null literal that can be used as a value for any reference type. null may be assigned to any variable, except variables of primitive types. There's little you can do with a null value beyond testing for its presence. Therefore, null is often used in programs as a marker to indicate that some object is unavailable. Ok, so I think I get it now. In C++ NULL is a macro that, when compiled, defines the null pointer constant. In Java, null is a fixed value that any non-primitive can be assigned too; great for testing in a handy if statement. Java does not have pointers, so I can see why they kept null a simple value rather than anything fancy. But why did java decide to change the all caps NULL to null? Furthermore, am I missing anything here?

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  • E4X in ActionScript help needed

    - by voipsecuritydigest.com
    Here is the XML How using E4X read values of nodes <status>??</status> and of node <invisible value="false"/> ? <?xml version="1.0" encoding="utf-8"?> <s:Application xmlns:fx="http://ns.adobe.com/mxml/2009" xmlns:s="library://ns.adobe.com/flex/spark" creationComplete="init()"> <fx:Declarations> <!-- Place non-visual elements (e.g., services, value objects) here --> </fx:Declarations> <fx:Script> <![CDATA[ var xml:XML = <iq type="result" id="ss-1"> <query status-min-ver="1" status-max="512" status-list-contents-max="5" status-list-max="3" xmlns="google:shared-status"> <status> ?? </status> <show> default </show> <status-list show="default"> <status> ?? </status> <status> ? </status> <status> ?? </status> </status-list> <status-list show="dnd"> <status> ?? </status> <status> dnd, i have bad mood </status> <status> showering </status> <status> ??_???¦ </status> <status> ? </status> </status-list> <invisible value="false"/> </query> </iq> public function init() { trace(xml.query.invisible.@value); } ]]> </fx:Script> </s:Application>

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  • How to do the processing and keep GUI refreshed using databinding?

    - by macias
    History of the problem This is continuation of my previous question How to start a thread to keep GUI refreshed? but since Jon shed new light on the problem, I would have to completely rewrite original question, which would make that topic unreadable. So, new, very specific question. The problem Two pieces: CPU hungry heavy-weight processing as a library (back-end) WPF GUI with databinding which serves as monitor for the processing (front-end) Current situation -- library sends so many notifications about data changes that despite it works within its own thread it completely jams WPF data binding mechanism, and in result not only monitoring the data does not work (it is not refreshed) but entire GUI is frozen while processing the data. The aim -- well-designed, polished way to keep GUI up to date -- I am not saying it should display the data immediately (it can skip some changes even), but it cannot freeze while doing computation. Example This is simplified example, but it shows the problem. XAML part: <StackPanel Orientation="Vertical"> <Button Click="Button_Click">Start</Button> <TextBlock Text="{Binding Path=Counter}"/> </StackPanel> C# part (please NOTE this is one piece code, but there are two sections of it): public partial class MainWindow : Window,INotifyPropertyChanged { // GUI part public MainWindow() { InitializeComponent(); DataContext = this; } private void Button_Click(object sender, RoutedEventArgs e) { var thread = new Thread(doProcessing); thread.IsBackground = true; thread.Start(); } // this is non-GUI part -- do not mess with GUI here public event PropertyChangedEventHandler PropertyChanged; public void OnPropertyChanged(string property_name) { if (PropertyChanged != null) PropertyChanged(this, new PropertyChangedEventArgs(property_name)); } long counter; public long Counter { get { return counter; } set { if (counter != value) { counter = value; OnPropertyChanged("Counter"); } } } void doProcessing() { var tmp = 10000.0; for (Counter = 0; Counter < 10000000; ++Counter) { if (Counter % 2 == 0) tmp = Math.Sqrt(tmp); else tmp = Math.Pow(tmp, 2.0); } } } Known workarounds (Please do not repost them as answers) Those two first are based on Jon ideas: pass GUI dispatcher to library and use it for sending notifications -- why it is ugly? because it could be no GUI at all give up with data binding COMPLETELY (one widget with databinding is enough for jamming), and instead check from time to time data and update the GUI manually -- well, I didn't learn WPF just to give up with it now ;-) and this is mine, it is ugly, but simplicity of it kills -- before sending notification freeze a thread -- Thread.Sleep(1) -- to let the potential receiver "breathe" -- it works, it is minimalistic, it is ugly though, and it ALWAYS slows down computation even if no GUI is there So... I am all ears for real solutions, not some tricks.

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  • How to use constraint programming for optimizing shopping baskets?

    - by tangens
    I have a list of items I want to buy. The items are offered by different shops and different prices. The shops have individual delivery costs. I'm looking for an optimal shopping strategy (and a java library supporting it) to purchase all of the items with a minimal total price. Example: Item1 is offered at Shop1 for $100, at Shop2 for $111. Item2 is offered at Shop1 for $90, at Shop2 for $85. Delivery cost of Shop1: $10 if total order < $150; $0 otherwise Delivery cost of Shop2: $5 if total order < $50; $0 otherwise If I buy Item1 and Item2 at Shop1 the total cost is $100 + $90 +$0 = $190. If I buy Item1 and Item2 at Shop2 the total cost is $111 + $85 +$0 = $196. If I buy Item1 at Shop1 and Item2 at Shop2 the total cost is $100 + $10 + $85 + $0 = 195. I get the minimal price if I order Item1 and Item2 at Shop1: $190 What I tried so far I asked another question before that led me to the field of constraint programming. I had a look at cream and choco, but I did not figure out how to create a model to solve my problem. | shop1 | shop2 | shop3 | ... ----------------------------------------- item1 | p11 | p12 | p13 | item2 | p21 | p22 | p23 | . | | | | . | | | | ----------------------------------------- shipping | s1 | s2 | s3 | limit | l1 | l2 | l3 | ----------------------------------------- total | t1 | t2 | t3 | ----------------------------------------- My idea was to define these constraints: each price "p xy" is defined in the domain (0, c) where c is the price of the item in this shop only one price in a line should be non zero if one or more items are bought from one shop and the sum of the prices is lower than limit, then add shipping cost to the total cost shop total cost is the sum of the prices of all items in a shop total cost is the sum of all shop totals The objective is "total cost". I want to minimize this. In cream I wasn't able to express the "if then" constraint for conditional shipping costs. In choco these constraints exist, but even for 5 items and 10 shops the program was running for 10 minutes without finding a solution. Question How should I express my constraints to make this problem solvable for a constraint programming solver?

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  • Difficulty adding widgets to django form.

    - by codingJoe
    I have a django app that tracks activities that can benefit a classroom. Using the django examples, I was able to build a form to enter this data. But when I try to add widgets to that form, things get tricky. What I want is a calendar widget that lets the user enter the 'activity_date' field using a widget. If I use Admin interface. The AdminDateWidget works fine. however. This particular user isn't allowed access to the admin interface so I need a different way to present this widget. Also I couldn't figure out how to make the bring the admin widget over into non-admin pages. So I tried a custom widget. This is the first custom widget I've built, so I'm not quite sure what is supposed to be going on here. Any Expert Advice? How do I get my date widget to work? # The Model class Activity(models.Model): activity_date = models.DateField() activity_type = models.CharField(max_length=50, choices=ACTIVITY_TYPES) activity_description = models.CharField(max_length=200) activity_duration= models.DecimalField(decimal_places=2, max_digits=4) est_attendance = models.IntegerField("Estimated attendance") # The Form class ActivityForm(forms.ModelForm): # The following line causes lockup if enabled. # With the DateTimeWidget removed, the form functions correctly except that there is no widget. #activity_date = forms.DateField(label=_('Date'), widget=DateTimeWidget) ##!!! Point of Error !!! class Meta: model = Activity fields = ('activity_date', 'activity_type', 'activity_description', 'activity_duration', 'est_attendance') def __init__(self, *args, **kwargs): super(ActivityForm, self).__init__(*args, **kwargs) instance = getattr(self, 'instance', None) edit_aid = kwargs.get('edit_aid', False) # On a different approach, the following also didn't work. #self.fields['activity_date'].widget = widgets.AdminDateWidget() # The Widget # Example referenced: http://djangosnippets.org/snippets/391/ calbtn = u""" <button id="calendar-trigger">...</button> <img src="%s/site_media/images/icon_calendar.gif" alt="calendar" id="%s_btn" style="cursor: pointer; border: 1px solid #8888aa;" title="Select date and time" onmouseover="this.style.background='#444444';" onmouseout="this.style.background=''" /> <script type="text/javascript"> Calendar.setup({ trigger : "calendar-trigger", inputField : "%s" }); </script>""" class DateTimeWidget(forms.widgets.TextInput): dformat = '%Y-%m-%d %H:%M' def render(self, name, value, attrs=None): print "DTWgt render name=%s, value=%s" % name, value if value is None: value = '' final_attrs = self.build_attrs(attrs, type=self.input_type, name=name) if value != '': try: final_attrs['value'] = \ force_unicode(value.strftime(self.dformat)) except: final_attrs['value'] = \ force_unicode(value) if not final_attrs.has_key('id'): final_attrs['id'] = u'%s_id' % (name) id = final_attrs['id'] jsdformat = self.dformat #.replace('%', '%%') cal = calbtn % (settings.MEDIA_URL, id, id, jsdformat, id) a = u'<input%s />%s' % (forms.util.flatatt(final_attrs), cal) print "render return %s " % a return mark_safe(a) def value_from_datadict(self, data, files, name): print "DTWgt value_from_datadict" dtf = forms.fields.DEFAULT_DATETIME_INPUT_FORMATS empty_values = forms.fields.EMPTY_VALUES value = data.get(name, None) if value in empty_values: return None if isinstance(value, datetime.datetime): return value if isinstance(value, datetime.date): return datetime.datetime(value.year, value.month, value.day) for format in dtf: try: return datetime.datetime(*time.strptime(value, format)[:6]) except ValueError: continue return None

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  • MVC validation error with strongly typed view

    - by Remnant
    I have a simple form that I would like to validate on form submission. Note I have stripped out the html for ease of viewing <%=Html.TextBox("LastName", "")%> //Lastname entry <%=Html.ValidationMessage("LastName")%> <%=Html.TextBox("FirstName", "")%>//Firstname entry <%=Html.ValidationMessage("FirstName")%> <%=Html.DropDownList("JobRole", Model.JobRoleList)%> //Dropdownlist of job roles <% foreach (var record in Model.Courses) // Checkboxes of different courses for user to select { %> <li><label><input type="checkbox" name="Courses" value="<%=record.CourseName%>" /><%= record.CourseName%></label></li> <% } %> On submission of this form I would like to check that both FirstName and LastName are populated (i.e. non-zero length). In my controller I have: public ActionResult Submit(string FirstName, string LastName) { if (FirstName.Trim().Length == 0) ModelState.AddModelError("FirstName", "You must enter a first name"); if (LastName.Trim().Length == 0) ModelState.AddModelError("LastName", "You must enter a first name"); if (ModelState.IsValid) { //Update database + redirect to action } return View(); //If ModelState not valid, return to View and show error messages } Unfortunately, this code logic produces an error that states that no objects are found for JobRole and Courses. If I remove the dropdownlist and checkboxes then all works fine. The issue appears to be that when I return the View the view is expecting objects for the dropwdownlist and checkboxes (which is sensible as that is what is in my View code) How can I overcome this problem? Things I have considered: In my controller I could create a JobRoleList object and Course object to pass to the View so that it has the objects to render. The issue with this is that it will overwrite any dropdownlist / checkbox selections that the user has already made. In the parameters of my controller method Submit I could aslo capture the JobRoleList object and Course object to pass back to the View. Again, not sure this would capture any items the user has already selected. I have done much googling and reading but I cannot find a good answer. When I look at examples in books or online (e.g. Nerddinner) all the validation examples involve simple forms with TextBox inputs and don't seems to show instances with multiple checkboxes and dropdownlists. Have I missed something obvious here? What would be best practice in this situation? Thanks

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  • FFMPEG-PHP Windows "Can't open movie file"

    - by bah
    Hi, ffmpeg extension is loaded as it is shown at phpinfo(), my file and script are at the same location, but I'm still getting this error. Warning: Can't open movie file Untitled.avi in C:\xampp\htdocs\skelbiu\fetch.php on line 4 Fatal error: Call to a member function getDuration() on a non-object in C:\xampp\htdocs\skelbiu\fetch.php on line 5 My script: extension_loaded('ffmpeg') or die('Error in loading ffmpeg'); $ffmpegInstance = new ffmpeg_movie('Untitled.avi'); echo "getDuration: " . $ffmpegInstance->getDuration() . "getFrameCount: " . $ffmpegInstance->getFrameCount() . "getFrameRate: " . $ffmpegInstance->getFrameRate() . "getFilename: " . $ffmpegInstance->getFilename() . "getComment: " . $ffmpegInstance->getComment() . "getTitle: " . $ffmpegInstance->getTitle() . "getAuthor: " . $ffmpegInstance->getAuthor() . "getCopyright: " . $ffmpegInstance->getCopyright() . "getArtist: " . $ffmpegInstance->getArtist() . "getGenre: " . $ffmpegInstance->getGenre() . "getTrackNumber: " . $ffmpegInstance->getTrackNumber() . "getYear: " . $ffmpegInstance->getYear() . "getFrameHeight: " . $ffmpegInstance->getFrameHeight() . "getFrameWidth: " . $ffmpegInstance->getFrameWidth() . "getPixelFormat: " . $ffmpegInstance->getPixelFormat() . "getBitRate: " . $ffmpegInstance->getBitRate() . "getVideoBitRate: " . $ffmpegInstance->getVideoBitRate() . "getAudioBitRate: " . $ffmpegInstance->getAudioBitRate() . "getAudioSampleRate: " . $ffmpegInstance->getAudioSampleRate() . "getVideoCodec: " . $ffmpegInstance->getVideoCodec() . "getAudioCodec: " . $ffmpegInstance->getAudioCodec() . "getAudioChannels: " . $ffmpegInstance->getAudioChannels() . "hasAudio: " . $ffmpegInstance->hasAudio(); I'm using php 5.2.9 (XAMPP 1.7.1), Windows 7. Thanks in advance!

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  • Help me understand this "Programming pearls" bitsort program

    - by ardsrk
    Jon Bentley in Column 1 of his book programming pearls introduces a technique for sorting a sequence of non-zero positive integers using bit vectors. I have taken the program bitsort.c from here and pasted it below: /* Copyright (C) 1999 Lucent Technologies */ /* From 'Programming Pearls' by Jon Bentley */ /* bitsort.c -- bitmap sort from Column 1 * Sort distinct integers in the range [0..N-1] */ #include <stdio.h> #define BITSPERWORD 32 #define SHIFT 5 #define MASK 0x1F #define N 10000000 int a[1 + N/BITSPERWORD]; void set(int i) { int sh = i>>SHIFT; a[i>>SHIFT] |= (1<<(i & MASK)); } void clr(int i) { a[i>>SHIFT] &= ~(1<<(i & MASK)); } int test(int i){ return a[i>>SHIFT] & (1<<(i & MASK)); } int main() { int i; for (i = 0; i < N; i++) clr(i); /*Replace above 2 lines with below 3 for word-parallel init int top = 1 + N/BITSPERWORD; for (i = 0; i < top; i++) a[i] = 0; */ while (scanf("%d", &i) != EOF) set(i); for (i = 0; i < N; i++) if (test(i)) printf("%d\n", i); return 0; } I understand what the functions clr, set and test are doing and explain them below: ( please correct me if I am wrong here ). clr clears the ith bit set sets the ith bit test returns the value at the ith bit Now, I don't understand how the functions do what they do. I am unable to figure out all the bit manipulation happening in those three functions. Please help.

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  • Which programming language to choose? (for a specific problem/domain, details inside)

    - by Bijan
    I am building a trading portfolio management system that is responsible for production, optimization, and simulation of non-high frequency trading portfolios (dealing with 1min or 3min bars of data, not tick data). I plan on employing Amazon web services to take on the entire load of the application. I have four choices that I am considering as language. a) Java b) C++ c) C# d) Python Here is the scope of the extremes of the project scope. This isn't how it will be, maybe ever, but it's within the scope of the requirements: Weekly simulation of 10,000,000 trading systems. (Each trading system is expected to have its own data mining methods, including feature selection algorithms which are extremely computationally-expensive. Imagine 500-5000 features using wrappers. These are not run often by any means, but it's still a consideration) Real-time production of portfolio w/ 100,000 trading strategies Taking in 1 min or 3 min data from every stock/futures market around the globe (approx 100,000) Portfolio optimization of portfolios with up to 100,000 strategies. (rather intensive algorithm) Speed is a concern, but I believe that Java can handle the load. I just want to make sure that Java CAN handle the above requirements comfortably. I don't want to do the project in C++, but I will if it's required. The reason C# is on there is because I thought it was a good alternative to Java, even though I don't like Windows at all and would prefer Java if all things are the same. Python - I've read somethings on PyPy and pyscho that claim python can be optimized with JIT compiling to run at near C-like speeds.... That's pretty much the only reason it is on this list, besides that fact that Python is a great language and would probably be the most enjoyable language to code in, which is not a factor at all for this project, but a perk. To sum up: - real time production - weekly simulations of a large number of systems - weekly/monthly optimizations of portfolios - large numbers of connections to collect data from There is no dealing with millisecond or even second based trades. The only consideration is if Java can possibly deal with this kind of load when spread out of a necessary amount of EC2 servers. Thank you guys so much for your wisdom.

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  • Is there a scheduling algorithm that optimizes for "maker's schedules"?

    - by John Feminella
    You may be familiar with Paul Graham's essay, "Maker's Schedule, Manager's Schedule". The crux of the essay is that for creative and technical professionals, meetings are anathema to productivity, because they tend to lead to "schedule fragmentation", breaking up free time into chunks that are too small to acquire the focus needed to solve difficult problems. In my firm we've seen significant benefits by minimizing the amount of disruption caused, but the brute-force algorithm we use to decide schedules is not sophisticated enough to handle scheduling large groups of people well. (*) What I'm looking for is if there's are any well-known algorithms which minimize this productivity disruption, among a group of N makers and managers. In our model, There are N people. Each person pi is either a maker (Mk) or a manager (Mg). Each person has a schedule si. Everyone's schedule is H hours long. A schedule consists of a series of non-overlapping intervals si = [h1, ..., hj]. An interval is either free or busy. Two adjacent free intervals are equivalent to a single free interval that spans both. A maker's productivity is maximized when the number of free intervals is minimized. A manager's productivity is maximized when the total length of free intervals is maximized. Notice that if there are no meetings, both the makers and the managers experience optimum productivity. If meetings must be scheduled, then makers prefer that meetings happen back-to-back, while managers don't care where the meeting goes. Note that because all disruptions are treated as equally harmful to makers, there's no difference between a meeting that lasts 1 second and a meeting that lasts 3 hours if it segments the available free time. The problem is to decide how to schedule M different meetings involving arbitrary numbers of the N people, where each person in a given meeting must place a busy interval into their schedule such that it doesn't overlap with any other busy interval. For each meeting Mt the start time for the busy interval must be the same for all parties. Does an algorithm exist to solve this problem or one similar to it? My first thought was that this looks really similar to defragmentation (minimize number of distinct chunks), and there are a lot of algorithms about that. But defragmentation doesn't have much to do with scheduling. Thoughts? (*) Practically speaking this is not really a problem, because it's rare that we have meetings with more than ~5 people at once, so the space of possibilities is small.

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  • Merging .net object graph

    - by Tiju John
    Hi guys, has anyone come across any scenario wherein you needed to merge one object with another object of same type, merging the complete object graph. for e.g. If i have a person object and one person object is having first name and other the last name, some way to merge both the objects into a single object. public class Person { public Int32 Id { get; set; } public string FirstName { get; set; } public string LastName { get; set; } } public class MyClass { //both instances refer to the same person, probably coming from different sources Person obj1 = new Person(); obj1.Id=1; obj1.FirstName = "Tiju"; Person obj2 = new Person(); ojb2.Id=1; obj2.LastName = "John"; //some way of merging both the object obj1.MergeObject(obj2); //?? //obj1.Id // = 1 //obj1.FirstName // = "Tiju" //obj1.LastName // = "John" } I had come across such type of requirement and I wrote an extension method to do the same. public static class ExtensionMethods { private const string Key = "Id"; public static IList MergeList(this IList source, IList target) { Dictionary itemData = new Dictionary(); //fill the dictionary for existing list string temp = null; foreach (object item in source) { temp = GetKeyOfRecord(item); if (!String.IsNullOrEmpty(temp)) itemData[temp] = item; } //if the same id exists, merge the object, otherwise add to the existing list. foreach (object item in target) { temp = GetKeyOfRecord(item); if (!String.IsNullOrEmpty(temp) && itemData.ContainsKey(temp)) itemData[temp].MergeObject(item); else source.Add(item); } return source; } private static string GetKeyOfRecord(object o) { string keyValue = null; Type pointType = o.GetType(); if (pointType != null) foreach (PropertyInfo propertyItem in pointType.GetProperties()) { if (propertyItem.Name == Key) { keyValue = (string)propertyItem.GetValue(o, null); } } return keyValue; } public static object MergeObject(this object source, object target) { if (source != null && target != null) { Type typeSource = source.GetType(); Type typeTarget = target.GetType(); //if both types are same, try to merge if (typeSource != null && typeTarget != null && typeSource.FullName == typeTarget.FullName) if (typeSource.IsClass && !typeSource.Namespace.Equals("System", StringComparison.InvariantCulture)) { PropertyInfo[] propertyList = typeSource.GetProperties(); for (int index = 0; index < propertyList.Length; index++) { Type tempPropertySourceValueType = null; object tempPropertySourceValue = null; Type tempPropertyTargetValueType = null; object tempPropertyTargetValue = null; //get rid of indexers if (propertyList[index].GetIndexParameters().Length == 0) { tempPropertySourceValue = propertyList[index].GetValue(source, null); tempPropertyTargetValue = propertyList[index].GetValue(target, null); } if (tempPropertySourceValue != null) tempPropertySourceValueType = tempPropertySourceValue.GetType(); if (tempPropertyTargetValue != null) tempPropertyTargetValueType = tempPropertyTargetValue.GetType(); //if the property is a list IList ilistSource = tempPropertySourceValue as IList; IList ilistTarget = tempPropertyTargetValue as IList; if (ilistSource != null || ilistTarget != null) { if (ilistSource != null) ilistSource.MergeList(ilistTarget); else propertyList[index].SetValue(source, ilistTarget, null); } //if the property is a Dto else if (tempPropertySourceValue != null || tempPropertyTargetValue != null) { if (tempPropertySourceValue != null) tempPropertySourceValue.MergeObject(tempPropertyTargetValue); else propertyList[index].SetValue(source, tempPropertyTargetValue, null); } } } } return source; } } However, this works when the source property is null, if target has it, it will copy that to source. IT can still be improved to merge when inconsistencies are there e.g. if FirstName="Tiju" and FirstName="John" Any commments appreciated. Thanks TJ

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  • Picking good first estimates for Goldschmidt division

    - by Mads Elvheim
    I'm calculating fixedpoint reciprocals in Q22.10 with Goldschmidt division for use in my software rasterizer on ARM. This is done by just setting the nominator to 1, i.e the nominator becomes the scalar on the first iteration. To be honest, I'm kind of following the wikipedia algorithm blindly here. The article says that if the denominator is scaled in the half-open range (0.5, 1.0], a good first estimate can be based on the denominator alone: Let F be the estimated scalar and D be the denominator, then F = 2 - D. But when doing this, I lose a lot of precision. Say if I want to find the reciprocal of 512.00002f. In order to scale the number down, I lose 10 bits of precision in the fraction part, which is shifted out. So, my questions are: Is there a way to pick a better estimate which does not require normalization? Also, is it possible to pre-calculate the first estimates so the series converges faster? Right now, it converges after the 4th iteration on average. On ARM this is about ~50 cycles worst case, and that's not taking emulation of clz/bsr into account, nor memory lookups. Here is my testcase. Note: The software implementation of clz on line 13 is from my post here. You can replace it with an intrinsic if you want. #include <stdio.h> #include <stdint.h> const unsigned int BASE = 22ULL; static unsigned int divfp(unsigned int val, int* iter) { /* Nominator, denominator, estimate scalar and previous denominator */ unsigned long long N,D,F, DPREV; int bitpos; *iter = 1; D = val; /* Get the shift amount + is right-shift, - is left-shift. */ bitpos = 31 - clz(val) - BASE; /* Normalize into the half-range (0.5, 1.0] */ if(0 < bitpos) D >>= bitpos; else D <<= (-bitpos); /* (FNi / FDi) == (FN(i+1) / FD(i+1)) */ /* F = 2 - D */ F = (2ULL<<BASE) - D; /* N = F for the first iteration, because the nominator is simply 1. So don't waste a 64-bit UMULL on a multiply with 1 */ N = F; D = ((unsigned long long)D*F)>>BASE; while(1){ DPREV = D; F = (2<<(BASE)) - D; D = ((unsigned long long)D*F)>>BASE; /* Bail when we get the same value for two denominators in a row. This means that the error is too small to make any further progress. */ if(D == DPREV) break; N = ((unsigned long long)N*F)>>BASE; *iter = *iter + 1; } if(0 < bitpos) N >>= bitpos; else N <<= (-bitpos); return N; } int main(int argc, char* argv[]) { double fv, fa; int iter; unsigned int D, result; sscanf(argv[1], "%lf", &fv); D = fv*(double)(1<<BASE); result = divfp(D, &iter); fa = (double)result / (double)(1UL << BASE); printf("Value: %8.8lf 1/value: %8.8lf FP value: 0x%.8X\n", fv, fa, result); printf("iteration: %d\n",iter); return 0; }

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  • Why is processing a sorted array faster than an unsorted array?

    - by GManNickG
    Here is a piece of code that shows some very peculiar performance. For some strange reason, sorting the data miraculously speeds up the code by almost 6x: #include <algorithm> #include <ctime> #include <iostream> int main() { // generate data const unsigned arraySize = 32768; int data[arraySize]; for (unsigned c = 0; c < arraySize; ++c) data[c] = std::rand() % 256; // !!! with this, the next loop runs faster std::sort(data, data + arraySize); // test clock_t start = clock(); long long sum = 0; for (unsigned i = 0; i < 100000; ++i) { // primary loop for (unsigned c = 0; c < arraySize; ++c) { if (data[c] >= 128) sum += data[c]; } } double elapsedTime = static_cast<double>(clock() - start) / CLOCKS_PER_SEC; std::cout << elapsedTime << std::endl; std::cout << "sum = " << sum << std::endl; } Without std::sort(data, data + arraySize);, the code runs in 11.54 seconds. With the sorted data, the code runs in 1.93 seconds. Initially I thought this might be just a language or compiler anomaly. So I tried it Java... import java.util.Arrays; import java.util.Random; public class Main { public static void main(String[] args) { // generate data int arraySize = 32768; int data[] = new int[arraySize]; Random rnd = new Random(0); for (int c = 0; c < arraySize; ++c) data[c] = rnd.nextInt() % 256; // !!! with this, the next loop runs faster Arrays.sort(data); // test long start = System.nanoTime(); long sum = 0; for (int i = 0; i < 100000; ++i) { // primary loop for (int c = 0; c < arraySize; ++c) { if (data[c] >= 128) sum += data[c]; } } System.out.println((System.nanoTime() - start) / 1000000000.0); System.out.println("sum = " + sum); } } with a similar but less extreme result. My first thought was that sorting brings the data into cache, but my next thought was how silly that is because the array was just generated. What is going on? Why is a sorted array faster than an unsorted array? The code is summing up some independent terms, the order should not matter.

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  • Optimising speeds in HDF5 using Pytables

    - by Sree Aurovindh
    The problem is with respect to the writing speed of the computer (10 * 32 bit machine) and the postgresql query performance.I will explain the scenario in detail. I have data about 80 Gb (along with approprite database indexes in place). I am trying to read it from Postgresql database and writing it into HDF5 using Pytables.I have 1 table and 5 variable arrays in one hdf5 file.The implementation of Hdf5 is not multithreaded or enabled for symmetric multi processing.I have rented about 10 computers for a day and trying to write them inorder to speed up my data handling. As for as the postgresql table is concerned the overall record size is 140 million and I have 5 primary- foreign key referring tables.I am not using joins as it is not scalable So for a single lookup i do 6 lookup without joins and write them into hdf5 format. For each lookup i do 6 inserts into each of the table and its corresponding arrays. The queries are really simple select * from x.train where tr_id=1 (primary key & indexed) select q_t from x.qt where q_id=2 (non-primary key but indexed) (similarly five queries) Each computer writes two hdf5 files and hence the total count comes around 20 files. Some Calculations and statistics: Total number of records : 14,37,00,000 Total number of records per file : 143700000/20 =71,85,000 The total number of records in each file : 71,85,000 * 5 = 3,59,25,000 Current Postgresql database config : My current Machine : 8GB RAM with i7 2nd generation Processor. I made changes to the following to postgresql configuration file : shared_buffers : 2 GB effective_cache_size : 4 GB Note on current performance: I have run it for about ten hours and the performance is as follows: The total number of records written for each file is about 6,21,000 * 5 = 31,05,000 The bottle neck is that i can only rent it for 10 hours per day (overnight) and if it processes in this speed it will take about 11 days which is too high for my experiments. Please suggest me on how to improve. Questions: 1. Should i use Symmetric multi processing on those desktops(it has 2 cores with about 2 GB of RAM).In that case what is suggested or prefereable? 2. If i change my postgresql configuration file and increase the RAM will it enhance my process. 3. Should i use multi threading.. In that case any links or pointers would be of great help Thanks Sree aurovindh V

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  • translating specifications into query predicates

    - by Jeroen
    I'm trying to find a nice and elegant way to query database content based on DDD "specifications". In domain driven design, a specification is used to check if some object, also known as the candidate, is compliant to a (domain specific) requirement. For example, the specification 'IsTaskDone' goes like: class IsTaskDone extends Specification<Task> { boolean isSatisfiedBy(Task candidate) { return candidate.isDone(); } } The above specification can be used for many purposes, e.g. it can be used to validate if a task has been completed, or to filter all completed tasks from a collection. However, I want to re-use this, nice, domain related specification to query on the database. Of course, the easiest solution would be to retrieve all entities of our desired type from the database, and filter that list in-memory by looping and removing non-matching entities. But clearly that would not be optimal for performance, especially when the entity count in our db increases. Proposal So my idea is to create a 'ConversionManager' that translates my specification into a persistence technique specific criteria, think of the JPA predicate class. The services looks as follows: public interface JpaSpecificationConversionManager { <T> Predicate getPredicateFor(Specification<T> specification, Root<T> root, CriteriaQuery<?> cq, CriteriaBuilder cb); JpaSpecificationConversionManager registerConverter(JpaSpecificationConverter<?, ?> converter); } By using our manager, the users can register their own conversion logic, isolating the domain related specification from persistence specific logic. To minimize the configuration of our manager, I want to use annotations on my converter classes, allowing the manager to automatically register those converters. JPA repository implementations could then use my manager, via dependency injection, to offer a find by specification method. Providing a find by specification should drastically reduce the number of methods on our repository interface. In theory, this all sounds decent, but I feel like I'm missing something critical. What do you guys think of my proposal, does it comply to the DDD way of thinking? Or is there already a framework that does something identical to what I just described?

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  • linq to sql with nservicebus table lock issue

    - by IGoor
    I am building a system using NServiceBus and my DataLayer is using Linq 2 SQL. The system is made up of 2 services. Service1 receives messages from NSB. It will query Table1 in my database and inserts a record into Table1 If a certain condition is met a new NSB message is sent to the 2nd service Service2 will update records also in Table1 when it receives messages from Service1 and it does some other non database related work. Service2 is a long running process. The problem I am having is the moment Service2 updates a record in Table1, the table is locked. The lock seems to be in place until Service2 has completed all it is processing. i.e. The lock is not released after my datacontext is disposed. This causes the query in Service1 to timeout. Once Service2 completes processing, Service1 resumes processing again without problem. So for example Service1 code may look like: int x =0; using (DataContext db = new DataContext()) { x = (from dp in db.Table1 select dp).Count(); // this line will timeout while service2 is processing Table1 t = new Table1(); t.Data = "test"; db.Table1.InsertOnSubmit(t); db.SubmitChanges(); } if(x % 50 == 0) CallService2(); The code in service2 may look like: using (DataContext db = new DataContext()) { Table1 t = db.Table1.Where(t => t.id == myId); t.Data = "updated"; db.SubmitChanges(); } // I would have expected the lock to have been released at this point, but this is not the case. DoSomeLongRunningTasks(); // lock will be released once service2 exits I don't understand why the lock is not released when the datacontext is disposed in Service2. To get around the problem I have been calling: db.ExecuteCommand("SET TRANSACTION ISOLATION LEVEL READ UNCOMMITTED"); and this works, but I am not happy using it. I want to solve this problem properly. Has any one experienced this sort of problem before and does any one know how to solve it? Why is the lock not released after the datacontext has been disposed? Thanks in advance. p.s. sorry for the extremely long post.

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