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• How to estimate the thread context switching overhead?

  - by Ignas Limanauskas

  I am trying to improve the performance of the threaded application with real-time deadlines. It is running on Windows Mobile and written in C / C++. I have a suspicion that high frequency of thread switching might be causing tangible overhead, but can neither prove it or disprove it. As everybody knows, lack of proof is not a proof of opposite :). Thus my question is twofold: If exists at all, where can I find any actual measurements of the cost of switching thread context? Without spending time writing a test application, what are the ways to estimate the thread switching overhead in the existing application? Does anyone know a way to find out the number of context switches (on / off) for a given thread?

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• Database indexes - what should they be

  - by WebweaverD

  Most of my database tables have a clear unique index through which lookups are done 90% of the time but I am a bit unsure on this one - I have a table which keeps track of user rating totals for items in my database, I now want to add another table, to track individual ratings with an ip address column to make sure no one can rate something twice. Since I can see this becoming a big, high use table it is important to optimize it correctly. (MYSQL table) This table will have the following fields: rating_id(always - unique), item_id (always - not unique), user_id (optional - not unique), ip_address (always - not unique), rating_value(always - not unique), has_review(bool) Now I envisions 90% the queries going something like this: When a user rates something - select where item_id = x and ip_address = y, (if rows = 0) insert rating When in user account pages - select where ip_address = x or username = y Now none of the fields searched on are unique, can I still use them as indexes (for example item _id and ip_address), can I have two indexes and will this still improve performance over a non indexed table?

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• Minimalistic PHP template engine with caching but not Smarty?

  - by Pekka

  There are loads of questions for "the right" PHP template engine, but none of them is focused on caching. Does anybody know a lightweight, high-quality, PHP 5 based template engine that does the following out of the box: Low-level templating functions (Replacements, loops, and filtering, maybe conditionals) Caching of the parsed results with the possibility to set an individual TTL per item, and of course to force a reload programmatically Extremely easy usage (like Smarty's) Modest in polluting the namespace (the ideal solution would be one class to interact with from the outside application) But not Smarty. I have nothing against, and often use, Smarty, but I am looking for something a bit simpler and leaner. I took a look at Fabien Potencier's Twig that looks very nice and compiles templates into PHP code, but it doesn't do any actual caching beyond that. I need and want a template engine, as I need to completely separate code and presentation in a way that a HTML designer can understand later on, so please no fundamental discussions about whether template engines in PHP make sense. Those discussions are important, but they already exist on SO.

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• Problem with Python 3.1(syntax error). Im a beginner please help!

  - by Jonathan

  Hi there, im new to pragraming :) I got a problem with sytax error while making a guessing game. the problem is in (if Gender = boy or Boy), the equal(=) letter is a syntax error. Please help! Answer = 23 Guess = () Gender = input("Are you a boy, a girl or an alien? ") if Gender = boy or Boy: print("Nice!", Gender) if Gender = girl or Girl: print("Prepare do die!", Gender) if Gender = alien or Alien: print("AWESOME my", Gender, "Friend!") While Guess != Answer: if Guess < Answer: print("Too low! try again") else: print("too high!" print("Congratulations you guessed correct!", Gender, "Have fun!" Thank

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• How to find good looking font color if background color is known?

  - by Mecki

  There seem to be so many color wheel, color picker, and color matcher web apps out there, where you give one color and the they'll find a couple of other colors that will create a harmonic layout when being used in combination. However most of them focus on background colors only and any text printed on each background color (if text is printed at all in the preview) is either black or white. My problem is different. I know the background color I want to use for a text area. What I need help with is choosing a couple of colors (the more, the merrier) I can use as font colors on this background. Most important is that the color will make sure the font is readable (contrast not being too low, also maybe not being too high to avoid that eyes are stressed) and of course that the combination of foreground and background just looks good. Anyone being aware of such an application? I'd prefer a web application to anything I have to download. Thanks.

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• Shadow maps unable to properly project shadows in some situations?

  - by meds

  In the shadow map sample provided by Microsoft I've noticed an issue where shadows are not properly projected when thin geometry is projected at high angles, see here the shadows being projected, notice the poles from the lights are not projected: http://imgur.com/QwOBa.png And in this screenshot we see things from the lights perspective, not ethe poles are clearly visible: http://imgur.com/k2woZ.png So two questions really, is this an actual bug or a limitation with shadow mapping and if it's a bug how can I fix it? The source is directly from the Microsoft DirectX Sample Browser 'ShadowMap' sample from July 2004, the sample browser is the latest August 2009 one.

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• Which web Tier Framework for a public commercial website with heavy load ?

  - by Maxime ARNSTAMM

  Hello everyone, As a part of an enterprise architecture exercise, i need to find a java-based framework filling these constraints : heavy (i think) load : 5000 concurrent connections widely known : can't be too exotic, the contractors would be too high priced. relatively easy to use : developpement time must be reasonnable must be as compliant as possible with the css/html layout produced by a designer Must look like "web 2.0" from the marketing point of view. What i learned from my limited experience is : jsf : 1, don't know. 2, 3 ok. 4 not ok (at least not without huge effort) wicket : 1, not really. 2, 3 and 4 ok. gwt : 1, don't know. 2, 3 ok. 4 not ok (but more ok than jsf) others : not really "web 2.0" or not really known I'm really junior, so my ideas about those frameworks are probably wrong, that's why i come to you, stackoverflowees. Thanks for helping :)

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• feature extraction from acoustic signals

  - by Dolphin

  Hi everyone, It's been a while. I found APIs in Java for extracting features from acoustic audio files and symbolic files separately. But now I have a problem in mapping from low level wav audio features to high level midi features. i.e. I need to write the extracted wav audio features on to midi format. But I cannot think of anything even close to it. Can someone pls provide me some insight as in how I can approach this. Greatly appreciate your responses. Advance thanks

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• How do I draw an ellipse with arbitrary orientation pixel by pixel?

  - by amc

  Hi, I have to draw an ellipse of arbitrary size and orientation pixel by pixel. It seems pretty easy to draw an ellipse whose major and minor axes align with the x and y axes, but rotating the ellipse by an arbitrary angle seems trickier. Initially I though it might work to draw the unrotated ellipse and apply a rotation matrix to each point, but it seems as though that could cause errors do to rounding, and I need rather high precision. Is my suspicion about this method correct? How could I accomplish this task more precisely? I'm programming in C++ (although that shouldn't really matter since this is a more algorithm-oriented question).

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• What database works well with 200+GB of data?

  - by taw

  I've been using mysql (with innodb; on Amazon rds) because it's sort of universal default, but it's been ridiculously under-performing, and tweaking it only delays the inevitable. The data is mostly relatively short (<1kB of bytes each) blobs information about 100Ms of urls. There is (or should be, mysql cannot seem to handle it) very high amount of insert / update / retrieve but few complex queries - not that complex queries wouldn't be useful, but because mysql is so slow that it's far faster to get the data out, process it locally, and cache the results somewhere. I can keep tweaking mysql and throwing more hardware at it, but it seems increasingly futile. So what are the options? SQL/relational model/etc. optional - anything will do as long as it's fast, networked, and language-independent.

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• Grails application hogging too much memory

  - by RN

  Tomcat 5.5.x and 6.0.x Grails 1.6.x Java 1.6.x OS CentOS 5.x (64bit) VPS Server with memory as 384M export JAVA_OPTS='-Xms128M -Xmx512M -XX:MaxPermSize=1024m' I have created a blank Grails application i.e simply by giving the command grails create-app and then WARed it I am running Tomcat on a VPS Server When I simply start the Tomcat server, with no apps deployed, the free memory is about 236M and used memory is about 156M When I deploy my "blank" application, the memory consumption spikes to 360M and finally the Tomcat instance is killed as soon as it takes up all free memory As you have seen, my app is as light as it can be. Not sure why the memory consumption is as high it is. I am actually troubleshooting a real application, but have narrowed down to this scenario which is easier to share and explain.

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• What features of interpreted languages can a compiled one not have?

  - by sub

  Interpreted languages are usually more high-level and therefore have features as dynamic typing (including creating new variables dynamically without declaration), the infamous eval and many many other features that make a programmer's life easier - but why can't compiled languages have these as well? I don't mean languages like Java that run on a VM, but those that compile to binary like C(++). I'm not going to make a list now but if you are going to ask which features I mean, please look into what PHP, Python, Ruby etc. have to offer. Which common features of interpreted languages can't/don't/do exist in compiled languages? Why?

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• SQL Simple ORDER BY

  - by AeroDroid

  I'm new to SQL and I don't think this question should be hard to answer. I have a high-score table for a game that contains the columns name, score, and rank. I want to know how I can order the table by descending order each time a new score is added so the table can always stay ordered by score. I know this is the wrong way of doing this, but I hope this makes my point kind of clearer. UPDATE `HSTable`.`Highscores` ORDER BY `Highscores`.`score` DESC; What is the correct way of approaching this? One more thing, is there a way I can set it so that the ranking value always stays where it's suppose to be from the SQL, for example, 1st place is always at the top regardless the score? Thanks!

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• Real-time Multiplayer Movement - Flash ActionScript 3 (AS3) - Flash Media Server

  - by Wild Phoenix

  Dear All, I am creating a simple game, where I would like more than one player to be able to connect and play. With regards to a single player game, I am more than comfortable with the coding. I cannot seem to figure out how to connect up more than one player and update their screens when the each player moves. So far I have the players connecting, but I still need to be able update the SharedObject when a player moves, then push it out to the other players. I have searched high and low for a good tutorial / source code to review. Code So Far A tutorial i found so far listened for a click as it was a mouse based movement, then this told the SHaredObject to tell the client (and the others) to update that clients movement. However all of my movement is listend and acted on in the playership class.

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• Windows Azure Table Storage LINQ Operators

  - by Ryan Elkins

  Currently Table Storage supports From, Where, Take, and First. Are there plans to support any of the other 29 operators? If we have to code for these ourselves, how much of a performance difference are we looking at to something similar via SQL and SQL Server? Do you see it being somewhat comparable or will it be far far slower if I need to do a Count or Sum or Group By over a gigantic dataset? I like the Azure platform and the idea of cloud based storage. I like Windows Azure for the amount of data it can store and the schema-less nature of table storage. SQL Azure just won't work due to the high cost to storage space.

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• how to translate Haskell into Scalaz?

  - by TOB

  One of my high school students and I are going to try to do a port of Haskell's Parsec parser combinator library into Scala. (It has the advantage over Scala's built-in parsing library that you can pass state around fairly easily because all the parsers are monads.) The first hitch I've come across is trying to figure out how Functor works in scalaz. Can someone explain how to convert this Haskell code: data Reply s u a = Ok a !(State s u) ParseError | Error ParseError instance Functor (Reply s u) where fmap f (Ok x s e) = Ok (f x) s e fmap _ (Error e) = Error e -- XXX into Scala (using Scalaz, I assume). I got as far as sealed abstract class Reply[S, U, A] case class Ok[S, U, A](a: A, state: State[S, U], error: ParseError) extends Reply[S, U, A] case class Error[S, U, A](error: ParseError) extends Reply[S, U, A] and know that I should make Reply extend the scalaz.Functor trait, but I can't figure out how to do that. (Mostly I'm having trouble figuring out what the F[_] parameter does.) Any help appreciated! Thanks, Todd

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• What fields have job security?

  - by computergeek6

  I can program pretty well, and I'm trying to think of a programming area that I can practice so I have a better chance of getting a job when I finish my education. I'm currently learning game development, but there are a ton of other people trying to get into game dev, so I want to find something a little more secure and sustainable to develop skills in. I've thought of things like financial systems and engineering stuff, but nothing I can think of is accessible to someone in high school. I'm trying to find something that involves physics or networking and isn't as popular a field as game dev. Does anyone have any ideas?

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• Specification: Use cases for CRUD

  - by Mario Ortegón

  I am writing a Product requirements specification. In this document I must describe the ways that the user can interact with the system in a very high level. Several of these operations are "Create-Read-Update-Delete" on some objects. The question is, when writing use cases for these operations, what is the right way to do so? Can I write only one Use Case called "Manage Object x" and then have these operations as included Use Cases? Or do I have to create one use case per operation, per object? The problem I see with the last approach is that I would be writing quite a few pages that I feel do not really contribute to the understanding of the problem. What is the best practice?

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• Alternative to BerkeleyDB?

  - by John

  I'm looking for a dbm-like library that I can use in place of Berkeley DB, which I'm currently using. My main reason for switching is the licensing fees for BDB are pretty high (free for open source apps, but my employer does not want to open source this particular app for various reasons). I've looked briefly at qdbm but it doesn't look like it will fill my needs -- lots of keys (several million) and large data items ( 1-5 megabytes). Before I continue my search I figured I'd ask because it seems there are tons of dbm-like libraries out there.

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• Accessing the DI container from anywhere

  - by ChrisR

  I've implemented the Symfony2 Dependency Injection container in my Zend Framework project and it works fine in the MVC layer of my application. I've initialized the DIC in my bootstrap and can access it anywhere by calling: Zend_Controller_Front::getInstance()->getParam('bootstrap')->getDic() The problem is that there are some parts of my application that do not utilize the Zend Framework application/MVC layer. My CLI tools for example. I could perfectly initialize a new DIC there but that would just be some copy paste work from the Bootstrap file which is asking for trouble down the road (DRY principles, etc) Is it a better solution to make my DIC available in the Zend_Registry or as a singleton called by a static method DIC::getInstance() for example? I know Registry and singletons are considered bad things but the DIC is such a high level part of the application that I will probably never run into the problems that make it a bad thing. Is this a good solution or are there better ways of accomplishing a globally accessible DIC?

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• Learn Obj-C Memory Management

  - by Joshua Brickner

  I come from a web development background. I'm good at XHTML, CSS, JavaScript, PHP and MySQL, because I use all of those technologies at my day job. Recently I've been tinkering with Obj-C in Xcode in the evenings and on weekends. I've written code for both the iPhone and Mac OS X, but I can't wrap my head around the practicalities of memory management. I understand the high-level concepts but am unclear how that plays out in implementation. Web developers typically don't have to worry about these sorts of things, so it is pretty new to me. I've tried adding memory management to my projects, but things usually end up crashing. Any suggestions of how to learn? Any suggestions are appreciated.

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• how to create a particle system on iphone and retain the created particles?

  - by lukya

  Hi all, I need to create a particle system and retain the created particles. I need to shake / move the created particles with the iphone accelerometer. Also, the number of particles needs to be very high (I need to show sand!). I do not have any OpenGLES programming experience. After initial search, I found Cocos2D can be used for particle generation. But there is no way of retaining the particles in the CCParticle system. As a work around, I tried creating many sprites at the end of particle generation and shown them as particles. But moving few number of sprites with accelerometer drops the frame rate considerably. Please suggest how this can be achieved and whether I should look for some other framework or if some kind of similar demo code is available. Thanks, Swapnil

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• Fastest method for SQL Server inserts, updates, selects

  - by Ian

  I use SPs and this isn't an SP vs code-behind "Build your SQL command" question. I'm looking for a high-throughput method for a backend app that handles many small transactions. I use SQLDataReader for most of the returns since forward only works in most cases for me. I've seen it done many ways, and used most of them myself. Methods that define and accept the stored procedure parameters as parameters themselves and build using cmd.Parameters.Add (with or without specifying the DB value type and/or length) Assembling your SP params and their values into an array or hashtable, then passing to a more abstract method that parses the collection and then runs cmd.Parameters.Add Classes that represent tables, initializing the class upon need, setting the public properties that represent the table fields, and calling methods like Save, Load, etc I'm sure there are others I've seen but can't think of at the moment as well. I'm open to all suggestions.

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• Manipulating the address of a variable to store a smaller type?

  - by Sidnicious

  This is what I get for pampering myself with high-level programming languages. I have a function which writes a 32-bit value to a buffer, and a uint64_t on the stack. Is the following code a sane way to store it? uint64_t size = 0; // ... getBytes((uint32_t*)&size+0x1); I'm assuming that this would be the canonical, safe style: uint64_t size = 0; // ... uint32_t smallSize; getBytes(&smallSize); size = smallSize;

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• mongodb read/write performance and mongo hosting in the cloud

  - by z3cko

  we are currently developing a high traffic rails application with facebooker (facebook game). since amazon simpledb (aws-sdb) is really slow, we are thinking of using a dedicated mongodb server as offered by mongoHQ for example. questions: what is the read/writes peak value for a mongodb server running on a amazon ec2 instance? what would be a recommended setup for a ec2 hosted app with mongodb - a master on amazon EBS and replicas on the ec2 instances? any examples or experiences? is there a company that offers mongodb hosting in the cloud? thanks, mz

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