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• Which network protocol to use for lightweight notification of remote apps?

  - by Chris Thornton

  I have this situation.... Client-initiated SOAP 1.1 communication between one server and let's say, tens of thousands of clients. Clients are external, coming in through our firewall, authenticated by certificate, https, etc.. They can be anywhere, and usually have their own firewalls, NAT routers, etc... They're truely external, not just remote corporate offices. They could be in a corporate/campus network, DSL/Cable, even Dialup. Client uses Delphi (2005 + SOAP fixes from 2007), and the server is C#, but from an architecture/design standpoint, that shouldn't matter. Currently, clients push new data to the server and pull new data from the server on 15-minute polling loop. The server currently does not push data - the client hits the "messagecount" method, to see if there is new data to pull. If 0, it sleeps for another 15 min and checks again. We're trying to get that down to 7 seconds. If this were an internal app, with one or just a few dozen clients, we'd write a cilent "listener" soap service, and would push data to it. But since they're external, sit behind their own firewalls, and sometimes private networks behind NAT routers, this is not practical. So we're left with polling on a much quicker loop. 10K clients, each checking their messagecount every 10 seconds, is going to be 1000/sec messages that will mostly just waste bandwidth, server, firewall, and authenticator resources. So I'm trying to design something better than what would amount to a self-inflicted DoS attack. I don't think it's practical to have the server send soap messages to the client (push) as this would require too much configuration at the client end. But I think there are alternatives that I don't know about. Such as: 1) Is there a way for the client to make a request for GetMessageCount() via Soap 1.1, and get the response, and then perhaps, "stay on the line" for perhaps 5-10 minutes to get additional responses in case new data arrives? i.e the server says "0", then a minute later in response to some SQL trigger (the server is C# on Sql Server, btw), knows that this client is still "on the line" and sends the updated message count of "5"? 2) Is there some other protocol that we could use to "ping" the client, using information gathered from their last GetMessageCount() request? 3) I don't even know. I guess I'm looking for some magic protocol where the client can send a GetMessageCount() request, which would include info for "oh by the way, in case the answer changes in the next hour, ping me at this address...". Also, I'm assuming that any of these "keep the line open" schemes would seriously impact the server sizing, as it would need to keep many thousands of connections open, simultaneously. That would likely impact the firewalls too, I think. Is there anything out there like that? Or am I pretty much stuck with polling? TIA, Chris

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• Where can I learn more about datastructure tricky questions?

  - by Sandbox

  I am relatively new to programming (around 1 year programming C#-winforms). Also, I come from a non CS background (no formal degree) Recently, while being interviewed for a job, I was asked about implementing a queue using a stack. I fumbled and wan't able to answer the question. After, the interview I could do it(had to spend some time). I have learnt (and think that I know it well) basic algorithms in datastructures using the book Data Structures: A Pseudocode Approach with C - Richard F. Gilberg (Author) . I want to know about sites/ books which have such questions along with answers. I think this will allow me to develop my CS specific problem solving skills. Any help is appreciated. BOUNTY: I am looking at some blog/website with datastructure and algorithms Q&A.

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• How to inject dependencies into a CustomUserNamePasswordValidator in WCF?

  - by Dannerbo

  I'm using a UserNamePasswordValidator in WCF along with Unity for my dependency injection, but since WCF creates the instance of the UserNamePasswordValidator, I cannot inject my container into the class. So how would one go about this? The simplest solution I can think of is to create a static proxy/wrapper class around a static instance of a UnityContainer, which exposes all the same methods... This way, any class can access the container, and I don't need to inject it everywhere. So I could just do UnityContainerWrapper.Resolve() anywhere in code. So basically this solution solves 2 problems for me, I can use it in classes that I'm not creating an instance of, and I can use it anywhere without having to inject the container into a bunch of classes. The only downside I can think of is that I'm now potentially exposing my container to a bunch of classes that wouldn't of had access to the container before. Not really sure if this is even a problem though?

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• does a switch idiom make sense in this case?

  - by the ungoverned

  I'm writing a parser/handler for a network protocol; the protocol is predefined and I am writing an adapter, in python. In the process of decoding the incoming messages, I've been considering using the idiom I've seen suggested elsewhere for "switch" in python: use a hash table whose keys are the field you want to match on (a string in this case) and whose values are callable expressions: self.switchTab = { 'N': self.handleN, 'M': self.handleM, ... } Where self.handleN, etc., are methods on the current class. The actual switch looks like this: self.switchTab[selector]() According to some profiling I've done with cProfile (and Python 2.5.2) this is actually a little bit faster than a chain of if..elif... statements. My question is, do folks think this is a reasonable choice? I can't imagine that re-framing this in terms of objects and polymorphism would be as fast, and I think the code looks reasonably clear to a reader.

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• how to change color of text following function in javascript

  - by OVERTONE

  Ok before i make spaghetti of this code i thought id ask around here. ive made a quiz for an online site. The answers are stored in an array, and ive a function that checks the answers array to what youve clicked. then it counts them and gives you your score. but i want to change the clor of the right answer wen the user clicks the score button. so the correct answers are highlighted. something like this https://www.shutterpoint.com/Home-Quiz.cfm (just hit submit at the bottom, no need to do the quiz). the little answer icon at the side looks flashy but id rather just have the text change color. heres how my questions are formatted <p>Depth of field is controlled by :?</p> <p id = "question2"><input type="radio" name="question2" id="Answer1" value = "a" onClick ="recordAnswer(2,this.value)"/> The focal length of the lens. <br/> <input type="radio" name="question2" id="Answer2" value = "b" onClick = "recordAnswer(2,this.value)"/> The size of the aperture opening. <br/> <input type="radio" name="question2" id="Answer3" value = "c" onClick = "recordAnswer(2,this.value)"/> The distance between the camera and lens. <br/> <input type="radio" name="question2" id="Answer4" value = "d" onClick = "recordAnswer(2,this.value)"/> All of these. <br/></p> and these are the two functions that are called throughout. record answer is called every time the user clicks a button function recordAnswer(question,answer) { answers[question-1] = answer; } this is the final button which calculates the score function scoreQuiz() { var totalCorrect = 0; for(var count = 0; count<correctAnswers.length;count++) { if(answers[count]== correctAnswers[count]) totalCorrect++; } <!-- alert("You scored " + totalCorrect + " out of 12 correct!"); --> } another function is best i think. ive already made attemots at it and know i have to set the color using document.getElementById('question2').style.color = '#0000ff'; question2 being the p id i think if i take in the value part of (input type....) ill be able to compare it to the answers array. but im not quite sure how to do this. any helpers? maybe something like this document.getElementById("Answer1").style.color = '#0000ff'; using the id part of the (input type line) i think i got it actually. ill post my answer in a sec

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• Combining Session and Cache

  - by Zyphrax

  To make my extranet web application even faster/more scalable I think of using some of the caching mechanisms. For some of the pages we'll use HTML caching, please ignore that technique for this question. E.g.: at some point in time 2500 managers will simultaneously login on our application (most of them with the same Account/Project) I think of storing an Account-cachekey and Project-cachekey into the user's Session and use that to get the item from the Cache. I could have simply stored the Account into the session, but that would result in 2500 of the same Accounts in memory. Is there a better solution to this or does it make sense :)?

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• How to find largest common sub-tree in the given two binary search trees?

  - by Bhushan

  Two BSTs (Binary Search Trees) are given. How to find largest common sub-tree in the given two binary trees? EDIT 1: Here is what I have thought: Let, r1 = current node of 1st tree r2 = current node of 2nd tree There are some of the cases I think we need to consider: Case 1 : r1.data < r2.data 2 subproblems to solve: first, check r1 and r2.left second, check r1.right and r2 Case 2 : r1.data > r2.data 2 subproblems to solve: - first, check r1.left and r2 - second, check r1 and r2.right Case 3 : r1.data == r2.data Again, 2 cases to consider here: (a) current node is part of largest common BST compute common subtree size rooted at r1 and r2 (b)current node is NOT part of largest common BST 2 subproblems to solve: first, solve r1.left and r2.left second, solve r1.right and r2.right I can think of the cases we need to check, but I am not able to code it, as of now. And it is NOT a homework problem. Does it look like?

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• How to estimate the quality of a web page?

  - by roddik

  Hello, I'm doing a university project, that must gather and combine data on a user provided topic. The problem I've encountered is that Google search results for many terms are polluted with low quality autogenerated pages and if I use them, I can end up with wrong facts. How is it possible to estimate the quality/trustworthiness of a page? You may think "nah, Google engineers are working on the problem for 10 years and he's asking for a solution", but if you think about it, SE must provide up-to-date content and if it marks a good page as a bad one, users will be dissatisfied. I don't have such limitations, so if the algorithm accidentally marks as bad some good pages, that wouldn't be a problem.

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• Sorting NSTableColumn contents

  - by Yahoo

  Hey, I have a problem with sorting NSTableColumn contents. In my NSTableView there are three columns: File, Size, Path. The contents are stored in NSMutableArray. Each object in this array is a NSDictionary containing three keys: file, size and path - value for each is a NSString. In Interface Builder, in each Table Column's attributes I can choose sorting options: Selector: IB entered "compare:" which I think is ok, because I compare NSStrings. Sort Key - and that's the problem I think - I don't know what to enter here. Any clues? If you've got questions about my code, please ask.

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• Multiple Post Requests Occuring in Quick Succession

  - by Samuel

  This is a bit of an open ended question but we have a problem with a web application that on the final step of completing an order, multiple post requests are being made, sometimes up to 10 and all within a couple of seconds to the page. Theirs nothing unusual about the page, the user fills out a form which is then validated using the jQuery form validation plugin. We've seen this behavior exhibited over a couple of different browser types, notably IE6 but also IE8. We've also managed to trigger the bug ourselves but nothing out of the ordinary seems to occur on the browsers end, everything progresses as normal. Apache logs show that multiple post requests where made at the same time and the Rails logs show that multiple posts requests were also received by the application, leading me to think it's a problem with the browser. I've exhausted all avenues that I can think of for debugging so I'm throwing this out there to see if anyone has some ideas of what we could try or look for next.

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• resetting the image in an NSView

  - by Josan

  I think this is a very simple question, but I’m new to programming so I may be going about it in a wrong-headed way. I have a basic understanding of Objective-C writing terminal applications and am teaching myself how to use the Cocoa GUI. I understand how to use IBOutlet and IBAction to connect a simple button to a method that will repeatedly send random numbers to a textfield . I understand how to add a NSView file, connect it to a custom view in interface builder and draw a path through random points in the view when the application launches. (I’ve been putting this code inside the - (void)drawRect:(NSRect)dirtyRect method that is declared when the file is created). What I can’t seem to figure out is how to connect a button to an action that will then ‘refresh’ the view – in this case repopulate it with another set of random points connected with a path. Looking at the documentation, I think I should somehow be using – (void) setNeedsDisplay(BOOL)flag but nothing I have tried so far had worked. Please tell me, what am I missing here?

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• How do you determine when an object is drawn on-screen in OpenGL?

  - by Harry

  I'm extremely new to OpenGL. I'm writing a program that displays flying text on screen. I need to know when certain text string appears (drawn) onto the screen and are visible to the user. The program needs to identify which text strings are displayed. At first, I started to think that I could use OpenGL's picking mechanism, but so far I've only seen examples where the selection area is focused on some sort of user interaction. I want to know what objects are displayed on the entire window area. This leads me to think I'm on the wrong track... Am I missing something? Any suggestions are welcome.

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• Google App Engine - Dealing with concurrency issues of storing an object

  - by Spines

  My User object that I want to create and store in the datastore has an email, and a username. How do I make sure when creating my User object that another User object doesn't also have either the same email or the same username? If I just do a query to see if any other users have already used the username or the email, then there could be a race condition. UPDATE: The solution I'm currently considering is to use the MemCache to implement a locking mechanism. I would acquire 2 locks before trying to store the User object in the datastore. First a lock that locks based on email, then another that locks based on username. Since creating new User objects only happens at user registration time, and it's even rarer that two people try to use either the same username or the same email, I think it's okay to take the performance hit of locking. I'm thinking of using the MemCache locking code that is here: http://appengine-cookbook.appspot.com/recipe/mutex-using-memcache-api/ What do you guys think?

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• Is this class + constructor definition pattern overly redundant?

  - by Protector one

  I often come across a pattern similar to this: class Person { public string firstName, lastName; public Person(string firstName, string lastName) { this.firstName = firstName; this.lastName = lastName; } } This feels overly redundant (I imagine typing "firstName" once, instead of thrice could be enough…), but I can't think of a proper alternative. Any ideas? Maybe I just don't know about a certain design pattern I should be using here? Edit - I think I need to elaborate a little. I'm not asking how to make the example code "better", but rather, "shorter". In its current state, all member names appear 3 times (declaration, initialization, constructor arguments), and it feels rather redundant. So I'm wondering if there is a pattern (or semantic sugar) to get (roughly) the same behavior, but with less bloat. I apologize for being unclear initially.

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• Java: design problem with private-final-int-value and empty constructor

  - by HH

  $ javac InitInt.java InitInt.java:7: variable right might not have been initialized InitInt(){} ^ 1 error $ cat InitInt.java import java.util.*; import java.io.*; public class InitInt { private final int right; //DUE to new Klowledge: Design Problem //I think having an empty constructor like this // is an design problem, shall I remove it? What do you think? // When to use an empty constructor? InitInt(){} public static void main(String[] args) { InitInt test = new InitInt(); System.out.println(test.getRight()); } public int getRight(){return right;} } Initialization problem with Constructor InitInt{ // Still the error, "may not be initialized" // How to initialise it? if(snippetBuilder.length()>(charwisePos+25)){ right=charwisePos+25; }else{ right=snippetBuilder.length()-1; } }

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• Best way to store chat messages and files

  - by Stnaire

  I would like to know what do you think about storing chat messages in a database? I need to be able to bind other stuff to them (like files, or contacts) and using a database is the best way I see for now. The same question comes for files, because they can be bound to chat messages, I have to store them in the database too.. With thousands of messages and files I wonder about performance drops and database size. What do you think considering I'm using PHP with MySQL/Doctrine?

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• The framerate of one movieclip slowly declines over time. What could cause this? [Flash CS3]

  - by Miles

  I'm creating a flash rhythm game. I have a looping (at a certain frame I have a gotoAndPlay) movieclip that represents the notes that scroll by, which plays for about three minutes. As the level progresses, the movieclip's framerate begins to lag and stutter. I have no idea how this could occur. It is also worth mentioning that the notes are represented by text, if that makes any difference. As far as posting my code goes, I think it would be far too convoluted to be worth your time. And I think it could be a simple problem. I just don't understand how the framerate of this movieclip could drop independent of the rest of the game.

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• How Does Differential Execution Work?

  - by Brian

  I've seen a few mentions of this on SO, but staring at Wikipedia and at an MFC dynamic dialog demo did nothing to enlighten me. Can someone please explain this? Learning a fundamentally different concept sounds nice. Edit: I think I'm getting a better feel for it. I guess I just didn't look at the source code carefully enough the first time. I have mixed feelings about DE at this point. On the one hand, it can make certain tasks considerably easier. On the other hand, getting it up and running (i.e. setting it up in your language of choice) is not easy (I'm sure it would be if I understood it better)...though I guess the toolbox for it need only be made once, then expanded as necessary. I think in order to really understand it, I'll probably need to try implimenting it in another language.

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• Multiple Payment options within the same order

  - by Rob Y

  I have a requirement to be able to accept different forms of payment within the same order - ie not just the usual credit card or paypal for the whole thing, but perhaps paypal for one item, cheque for another. I know this sounds quite crazy, but there is a good business reason for the requirement so I can't just push back. The best way I can think of implementing it at the moment is to have kind of a hub page, where you can "launch off" into multiple flows for each of the payments by opening new windows. I can't figure out a way of doing this in a linear flow as for example you can't guarantee that a user will come back from paypal, so you'd then lose the user completely. Is there a neater way of doing this that anyone can think of, or can anyone point me to an example of a site that does somethign similar for inspiration?

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• for (i in xxx) ggplot problem

  - by Andreas

  This is strange - I think? library(ggplot2) tf <- which(sapply(diamonds, is.factor)) diamonds.tf <- diamonds[,tf] So far so good. But next comes the trouble: pl.f <- ggplot(diamonds.tf, aes(x=diamonds.tf[,i]))+ geom_bar()+ xlab(names(diamonds.tf[i])) for (i in 1:ncol(diamonds.tf)) { ggsave(paste("plot.f",i,".png",sep=""), plot=pl.f, height=3.5, width=5.5) } This saves the plots in my working directory - but with the wrong x-label. I think this is strange since calling ggplot directly produces the right plot: i <- 2 ggplot(diamonds, aes(x=diamonds[,i]))+geom_bar()+xlab(names(diamonds)[i]) I don't really know how to describe this as a fitting title - suggestions as to a more descriptive question-title is most welcome. Thanks in advance

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• Handling Session ID with Spring

  - by Max

  Hi, I'm trying to build a Spring server for GWT (you can think of it as of Javascript AJAX client). But I can't decide on one point of architecture. How should session be created and used? The obvious easiest way - is to use HTTP sessions (cookies and stuff). Looks fine, but I think that sending session ID separate from the headers would be better (SOAP style). So, what is better: getMyPetsName(String sessionID, int petID) or getMyPetsName(int petID) + session ID through HTTP header (cookies or something). Another question is, if I use the first way (which I like more) - how do I handle session in Spring? I'm really newbie in Spring, and googling did not help. What I mean is: String getMyPetsName(String sessionID, int petID) { Session s = someWayToGetItById(sessionID); } Thanks in advance.

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• remove data layer and put into it's own domain

  - by user334768

  I have a SL4 application that uses EF4 & RIA Services. DB is SQL 2008. All is working well. Now I want to put the Database and web services on one domain (A.com) with the web service exposing the same methods available in my working project. (one listed at top of message) Then put a Silverlight application (same one as above) on domain(B.com) and call the web services on A.com. I thought I had a fair understanding of RIA Services. Enough to get the above application working. Now when I say "working" I do mean on my local dev machine. I have yet to deployed as SL4 & .NET 4 application to my hosting site. But I don't think I understand it well enough. I normally create a new business app, add EF then create the RIA DomainService. Add any [Includes] I need, modify my linq queries and run application. And it works. Now I need to break off my data layer and put it on another hosting site (A.com) And put my UI and business logic on another hosting site (B.com) I think I need to do the following : On the Database & web service site: domain(A.com) create application, create EF4, create RIA Services and deploy. At this time, are the methods exposed available as a "WEB SERVICE" to other applications calling by http:// a.com/serviceName.svc address? I think I need to do the following : On the application site : domain(B.com) create a business application (later will need authentication and navigation). How can I create an EF when I don't have access to the database? (I know I do have access but I want know what happens here when I do not have access to the database, but only data provided by a web service) If I can not create an EF how do I create my RIA Service? I hope any one who takes time to help me understands what I'm asking. Sorry so long.

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• Automatically CONCATENATE text on data entry

  - by Bill T

  I am a newbie and need help. I have a table called "Employees". It has 2 fields [number] and [encode]. I want to automatically take whatever number is entered into [number] and store it in [encode] so that it is preceded by the appropriate amount of 0's to always make 12 digits. Example: user enters '123' into [number], '000000000123' is automatically stored in [encode] user enters '123456789' into [number], '000123456789' is automatically stored in [encode] I think i want to write a trigger to accomplish this. I think that would make it happen at the time of data entry. is that right? The main idea is would be something like this: variable1 = LENGTH [number] variable2 = REPEAT (0,12-variable1) variable3 = CONCATENATE (variable2, [number]) [encode] = variable3 I just don't know enough to make this happen ANY help would be FANTASTIC. I have SQL-SERVER 2005 and both fields are text

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• Are today's young programmers getting wrapped around the axle with patterns and practices?

  - by Robert Harvey

  Recently I have noticed a number of questions on SO that look something like this: I am writing a small program to keep a list of the songs that I keep on my ipod. I'm thinking about writing it as a 3-tier MVC Ruby on Rails web application with TDD, DDD and IOC, using a factory pattern to create the classes and a singleton to store my application settings. Do you think I'm taking the right approach? Do you think that we're handing novice programmers a very sharp knife and telling them, "Don't cut yourself with this"? NOTE: Despite the humorous tone, this is a serious (and programming-related) question.

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• Arrays in javascript, how can i learn manipulating it?

  - by Noor

  I've read alot about the core implementation of arrays in javascript and often i find that experimenting is the best way to learn, Right now i have multiple forms where you can type in different things, i want to be able to pull the value of each one and put it in an array so that i can later on read them in in a dynamically created div.. Can anyone point me in the right direction? There is a way i could get around this and that would be by using just one form, and pulling the text from there seperated by comas (,).. the thing is that i don't have the knowledge to pull the text form the form, search and find the comas, then make a new variable i think is neccessary, and read that in.. i know how to "think" javascript, not how to write it.. how do i learn the easiest/fastest way?

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