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  • XNA on the TechNet Wiki

    - by Michael B. McLaughlin
    Many months ago I came across an interesting Microsoft website, the TechNet Wiki, when I was looking for information about something that I can’t even remember anymore. I noticed at the time that its section on gaming technologies was sparse and even exchanged a few emails with one of the friendly Microsoft employees who contributes there regularly about some ideas I had for the site. I seem to recall mentioning my intentions to add some articles on XNA when I found the time but between one thing and another it seemed like I was busy from the end of last Summer straight through ‘til now. Yesterday I came across the TechNet Wiki link in my miscellaneous links collection and remembered my intentions many months ago. I decided that adding XNA pages to it would make a nice project to work on while taking breaks from my other projects. So I wrote my first two articles for it: XNA Framework Overview and Content Pipeline Overview. I hope to add more in the coming days and weeks. I’d be delighted if some of my fellow XNA enthusiasts out there joined in, time permitting. Anyone else who’d like to add a page or two on a topic area you’re familiar with, this seems like a great opportunity to contribute to the community and help build a nice knowledge base to benefit all of us who are always interested in learning something new!

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  • First ATMs programming language

    - by revo
    First ATMs performed tasks like a cash dispenser, they were offline machines which worked with punch cards impregnated with Carbon and a 6-digit PIN code. Maximum withdrawal with a card was 10 pounds and each one was a one-time use card - ATM swallowed cards! The first ATM was installed in London in the year 1967, as I looked at time line of programming languages, there were many programming languages made before that decade. I don't know about the hardware neither, but in which programming language it was written? *I didn't find a detailed biography of John Shepherd-Barron (ATM inventor at 70s) Update I found this picture, which is taken from a newspaper back to the year 1972 in Iran. Translated PS : Shows Mr. Rad-lon (if spelled correctly), The manager of Barros (if spelled correctly) International Educational Institute in United Kingdom at the right, and Mr. Jim Sutherland - Expert of Computer Kiosks. In the rest of the text I found on this paper, these kind of ATMs which called "Automated Computer Kiosk" were advertised with this: Mr. Rad-lon (if spelled correctly) puts his card to one specific location of Automated Computer Kiosk and after 10 seconds he withdraws his cash. Two more questions are: 1- How those ATMs were so fast? (withdrawal in 10 seconds in that year) 2- I didn't find any text on Internet which state about "Automated Computer Kiosk", Is it valid or were they being called Computer in that time?

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  • Moving while doing loop animation in RPGMaker

    - by AzDesign
    I made a custom class to display character portrait in RPGMaker XP Here is the class : class Poser attr_accessor :images def initialize @images = Sprite.new @images.bitmap = RPG::Cache.picture('Character.png') #100x300 @images.x = 540 #place it on the bottom right corner of the screen @images.y = 180 end end Create an event on the map to create an instance as global variable, tada! image popped out. Ok nice. But Im not satisfied, Now I want it to have bobbing-head animation-like (just like when we breathe, sometimes bob our head up and down) so I added another method : def move(x,y) @images.x += x @images.y += y end def animate(x,y,step,delay) forward = true 2.times { step.times { wait(delay) if forward move(x/step,y/step) else move(-x/step,-y/step) end } wait(delay*3) forward = false } end def wait(time) while time > 0 time -= 1 Graphics.update end end I called the method to run the animation and it works, so far so good, but the problem is, WHILE the portrait goes up and down, I cannot move my character until the animation is finished. So that's it, I'm stuck in the loop block, what I want is to watch the portrait moving up and down while I walk around village, talk to npc, etc. Anyone can solve my problem ? Or better solution ? Thanks in advance

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  • "Unable to install GRUB in /dev/sda" when installing GRUB

    - by vicban3d
    I recently bought a shiny new Lenovo Yoga 2 Pro and I want to dual boot it with Ubuntu for studying purposes. Its built-in OS is Windows 8.1 and it has a 256GB SSD. I've made a separate 90GB partition just for Ubuntu and a live USB to install it. The first time everything seemed to work great, I solved the wifi issued by blacklisting ideapad_laptop, the installation went flawlessly and Ubuntu worked fine. When I got up the next morning and turned on my laptop it booted into Windows right away without ever showing the GRUB menu. So I tried to reset, and checked my partitions with the Disk Manager and everything looked fine. Since I couldn't find a solution online I went ahead and formatted the partition to try and install again. This time and every time since, the installation was aborted and I got a fatal error saying: Unable to install GRUB in /dev/sda Executing `grub-install /dev/sda` failed. This is a fatal error. Can anyone please suggest a solution to this problem? If any further information is needed I would be happy to provide it. Thanks. When installing I get the following in details: ubuntu kernel: [ 1946.372741] FAT-fs (sda2): error, fat_get_cluster: invalid cluster chain (i_pos 0). ubuntu grub-installer: error: Running 'grub-install --force failed.

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  • Developing Functional Specifications based on the UML Model

    A few days ago I found this white paper I did around 2004 way before I started really blogging:The Process OverviewUse-case to Specifications is a processing using UML use-cases to identify user requirements and model systems to be able to properly define functionality. This document is intended to serve as an execution based walk-through of this process.As background: The Unified Modeling Language (UML) is a language for specifying, visualizing, constructing, and documenting the artifacts of software...Did you know that DotNetSlackers also publishes .net articles written by top known .net Authors? We already have over 80 articles in several categories including Silverlight. Take a look: here.

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  • Authenticate native mobile app using a REST API

    - by Supercell
    I'm starting a new project soon, which is targeting mobile application for all major mobile platforms (iOS, Android, Windows). It will be a client-server architecture. The app is both informational and transactional. For the transactional part, they're required to have an account and log in before a transaction can be made. I'm new to mobile development, so I don't know how the authentication part is done on these platforms. The clients will communicate with the server through a REST API. Will be using HTTPS ofcourse. I haven't yet decided if I want the user to log in when they open the app, or only when they perform a transaction. I got the following questions: 1) Like the Facebook application, you only enter your credentials when you open the application for the first time. After that, you're automatically signed in every time you open the app. How does one accomplish this? Just simply by encrypting and storing the credentials on the device and sending them every time the app starts? 2) Do I need to authenticate the user for each (transactional) request made to the REST API or use a token based approach? Please feel free to suggest other ways for authentication. Thanks!

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  • Constituent Experience Counts In Public Sector

    - by Michael Seback
      Businesses and government organizations are operating in an era of the empowered customer where service  and communication channels are challenged every day.  Consumers in the private sector have high expectations from purchasing gifts online, reading reviews on social sites, and expecting the companies they do business with to know and reward them.   In the Public Sector, constituents also expect government organizations to provide consistent and timely service across agencies and touch points.  Examples include requesting critical city services, applying for social assistance or reviewing insurance plans for a health insurance exchange. If an individual does not receive the services they need at the right time and place, it can create a dire situation – involving housing, food or healthcare assistance. Government organizations need to deliver a fast, reliable and personalized experience to constituents. Look at a few recent statistics from a Government focused survey: How do you define good customer service? 70 % improved services, 48% shortest time to provide information, 44% shortest time to resolve complaints What are ways/opportunities to improve customer service? 69% increased collaboration across agencies and 41% increased customer service channels Are you using data collected to make informed decisionsto improve customer service efforts? 39% data collection is limited, not used to improve decision making Source: Re-Imagining Customer Service in Government, 2012 Click here to see the highlights.  Would you like to get started – read Eight Steps to great constituent experiences for government.

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  • Oracle R Enterprise 1.1 Download Available

    - by Sherry LaMonica
    Oracle just released the latest update to Oracle R Enterprise, version 1.1. This release includes the Oracle R Distribution (based on open source R, version 2.13.2), an improved server installation, and much more.  The key new features include: Extended Server Support: New support for Windows 32 and 64-bit server components, as well as continuing support for Linux 64-bit server components Improved Installation: Linux 64-bit server installation now provides robust status updates and prerequisite checks Performance Improvements: Improved performance for embedded R script execution calculations In addition, the updated ROracle package, which is used with Oracle R Enterprise, now reads date data by conversion to character strings. We encourage you download Oracle software for evaluation from the Oracle Technology Network. See these links for R-related software: Oracle R Distribution, Oracle R Enterprise, ROracle, Oracle R Connector for Hadoop.  As always, we welcome comments and questions on the Oracle R Forum.

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  • Persistent (purely functional) Red-Black trees on disk performance

    - by Waneck
    I'm studying the best data structures to implement a simple open-source object temporal database, and currently I'm very fond of using Persistent Red-Black trees to do it. My main reasons for using persistent data structures is first of all to minimize the use of locks, so the database can be as parallel as possible. Also it will be easier to implement ACID transactions and even being able to abstract the database to work in parallel on a cluster of some kind. The great thing of this approach is that it makes possible implementing temporal databases almost for free. And this is something quite nice to have, specially for web and for data analysis (e.g. trends). All of this is very cool, but I'm a little suspicious about the overall performance of using a persistent data structure on disk. Even though there are some very fast disks available today, and all writes can be done asynchronously, so a response is always immediate, I don't want to build all application under a false premise, only to realize it isn't really a good way to do it. Here's my line of thought: - Since all writes are done asynchronously, and using a persistent data structure will enable not to invalidate the previous - and currently valid - structure, the write time isn't really a bottleneck. - There are some literature on structures like this that are exactly for disk usage. But it seems to me that these techniques will add more read overhead to achieve faster writes. But I think that exactly the opposite is preferable. Also many of these techniques really do end up with a multi-versioned trees, but they aren't strictly immutable, which is something very crucial to justify the persistent overhead. - I know there still will have to be some kind of locking when appending values to the database, and I also know there should be a good garbage collecting logic if not all versions are to be maintained (otherwise the file size will surely rise dramatically). Also a delta compression system could be thought about. - Of all search trees structures, I really think Red-Blacks are the most close to what I need, since they offer the least number of rotations. But there are some possible pitfalls along the way: - Asynchronous writes -could- affect applications that need the data in real time. But I don't think that is the case with web applications, most of the time. Also when real-time data is needed, another solutions could be devised, like a check-in/check-out system of specific data that will need to be worked on a more real-time manner. - Also they could lead to some commit conflicts, though I fail to think of a good example of when it could happen. Also commit conflicts can occur in normal RDBMS, if two threads are working with the same data, right? - The overhead of having an immutable interface like this will grow exponentially and everything is doomed to fail soon, so this all is a bad idea. Any thoughts? Thanks! edit: There seems to be a misunderstanding of what a persistent data structure is: http://en.wikipedia.org/wiki/Persistent_data_structure

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  • C# output of running command prompt

    - by Kaushal Singh
    In this following code whenever I send any command like dir or anything this function get stuck in while loop... I want the output of the command prompt each time I send it command to execute without closing the process after the execution of command. public void shell(String cmd) { ProcessStartInfo PSI = new ProcessStartInfo(); PSI.FileName = "c:\\windows\\system32\\cmd.exe"; PSI.RedirectStandardInput = true; PSI.RedirectStandardOutput = true; PSI.RedirectStandardError = true; PSI.UseShellExecute = false; Process p = Process.Start(PSI); StreamWriter CSW = p.StandardInput; StreamReader CSR = p.StandardOutput; CSW.WriteLine(cmd); CSW.Flush(); while(!(CSR.EndOfStream)) { Console.WriteLine(CSR.ReadLine()); } CSR.Close(); }

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  • What should I recommend a small company looking for C# developers

    - by Coder
    Here is the issue. I am a senior developer, and one of the start-ups I designed the system (management system/database/web) a long time ago, have grown and need software updates. I have left their system to another developer long time ago, but apparently he has left the job, and so they are asking me if I can suggest them where to find a new one. The problem is that the company has no clue that the IT is not cheap. They expect multiple features to be added for 40$, so that's an issue. Actually one of the reasons why I left the project when I did. Lots of expectations, little pay, also I know those people outside work, so I decided to avoided stressing the nonwork-relationships and left the project gracefully. Today they asked me for an advice, and I told them that the feature list they want is probably going to cost some if they'll get a senior developer for the job. So I guess their best bet is to find someone who loves coding and has just finished the school. Which would give someone a chance to code for money which is good for a student, and at the same time, allow the student to get some hands on experience. Then again, the system is not exactly 20 line console program, there is an MSSQL database, ASP.NET web page and content management system with all the AJAX stuff and some other things. So student straight out of school could have some problems with that. But, I thought about the issue some more, and I think that junior developer is a tricky deal, without mentoring, he can either screw up royally, or just do what's asked. Also, it seems no one is coming to interviews at all, which is weird, or maybe not. What should I suggest them?

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  • DTLoggedExec 1.0.0.2 Released

    - by Davide Mauri
    These last days has been full of work and the next days, up until the end of july, will follow the same ultra-busy scheme. This makes the improvement of DTLoggedExec a little bit slower than what I desire, but nonetheless Friday I’ve been able to relase an updated version of the tool that fixes a bug and add a very convenient option to make even more straightforward the creationg of execution logs: [bugfix] Fixed a bug that prevented loading packages from SSIS Package Store [new] Added support for {filename} placeholder in both Data Flow Profiling and CSV Log Provider The added feature allow to generate DataFlow profile logs and CSV logs that has the same name of the package that generated them, es: DTLoggedExec.exec /FILE:”MyPackage.dtsx” /LPA:"FILE=C:\Log\{filename}_{date}_{time}.dtsCSVLog" Share this post: email it! | bookmark it! | digg it! | reddit! | kick it! | live it!

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  • Is there a name for this functional programming construct/pattern?

    - by dietbuddha
    I wrote a function and I'd like to find out if it is an implementation of some functional programming pattern or construct. I'd like to find out the name of this pattern or construct (if it exists)? I have a function which takes a list of functions and does this to them: wrap(fn1, fn2, fn3, fn4) # returns partial(fn4, partial(fn3, partial(fn2, fn1))) There are strong similarities to compose, reduce, and other fp metaprogramming constructs, since the functions are being arranged together and returned as one function. It also has strong similarities to decorators and Python context managers since it provides a way to encapsulate pre and post execution behaviors in one function. Which was the impetus for writing this function. I wanted the ability that context managers provide, but I wanted to be able to have it defined in one function, and to be able to layer function after function on top.

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  • How to approach scrum task burn down when tasks have multiple peoples involvement?

    - by AgileMan
    In my company, a single task can never be completed by one individual. There is going to be a separate person to QA and Code Review each task. What this means is that each individual will give their estimates, per task, as to how much time it will take to complete. The problem is, how should I approach burn down? If I aggregate the hours together, assume the following estimate: 10 hrs - Dev time 4 hrs - QA 4 hrs - Code Review. Task Estimate = 18hrs At the end of each day I ask that the task be updated with "how much time is left until it is done". However, each person generally just thinks about their part of it. Should they mark the effort remaining, and then ADD the effort estimates to that? How are you guys doing this? UPDATE To help clarify a few things, at my organization each Task within a story requires 3 people. Someone to develop the task. (do unit tests, ect...) A QA specialist to review task (they primarily do integration and regression tests) A Tech lead to do code review. I don't think there is a wrong way or a right way, but this is our way ... and that won't be changing. We work as a team to complete even the smallest level of a story whenever possible. You cannot actually test if something works until it is dev complete, and you cannot review the quality of the code either ... so the best you can do is split things up into small logical slices so that the bare minimum functionality can be tested and reviewed as early into the process as possible. My question to those that work this way would be how to burn down a "task" when they are setup this way. Unless a Task has it's own sub-tasks (which JIRA doesn't allow) ... I'm not sure the best way to accomplish tracking "what's left" on a daily basis.

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  • How to cache queries in EJB and return result efficient (performance POV)

    - by Maxym
    I use JBoss EJB 3.0 implementation (JBoss 4.2.3 server) At the beginning I created native query all the time using construction like Query query = entityManager.createNativeQuery("select * from _table_"); Of couse it is not that efficient, I performed some tests and found out that it really takes a lot of time... Then I found a better way to deal with it, to use annotation to define native queries: @NamedNativeQuery( name = "fetchData", value = "select * from _table_", resultClass=Entity.class ) and then just use it Query query = entityManager.createNamedQuery("fetchData"); the performance of code line above is two times better than where I started from, but still not that good as I expected... then I found that I can switch to Hibernate annotation for NamedNativeQuery (anyway, JBoss's implementation of EJB is based on Hibernate), and add one more thing: @NamedNativeQuery( name = "fetchData2", value = "select * from _table_", resultClass=Entity.class, readOnly=true) readOnly - marks whether the results are fetched in read-only mode or not. It sounds good, because at least in this case of mine I don't need to update data, I wanna just fetch it for report. When I started server to measure performance I noticed that query without readOnly=true (by default it is false) returns result with each iteration better and better, and at the same time another one (fetchData2) works like "stable" and with time difference between them is shorter and shorter, and after 5 iterations speed of both was almost the same... The questions are: 1) is there any other way to speed query using up? Seems that named queries should be prepared once, but I can't say it... In fact if to create query once and then just use it it would be better from performance point of view, but it is problematic to cache this object, because after creating query I can set parameters (when I use ":variable" in query), and it changes query object (isn't it?). well, is here any way to cache them? Or named query is the best option I can use? 2) any other approaches how to make results retrieveng faster. I mean, for instance I don't need those Entities to be attached, I won't update them, all I need is just fetch collection of data. Maybe readOnly is the only available way, so I can't speed it up, but who knows :) P.S. I don't ask about DB performance, all I need now is how not to create query all the time, so use it efficient, and to "allow" EJB to do less job with the same result concerning data returning.

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  • GLES2.0 3D Android game performance and multi threading the update?

    - by Ofer
    I have profiled my mixed Java\C++ Android game and I got the following result: https://dl.dropbox.com/u/8025882/PompiDev/AndroidProfile.png As you can see, the pink think is a C++ functions that updates the game. It does things like updating the logic but it mostly it generates a "request list" for rendering. The thing is, I generate DrawLists on C++ and then send them to Java to process and draw using GLES2.0. Since then I was able to improve update from 9ms down to about 7ms, but I would like to ask if I would benefit from multi threading the update? As I understand from that diagram is that the function that takes the most time is the one you see it's color on the timeline. So the pink area is taken mostly by update. The other area has MainOpenGL.Handle as it's main contributor(whch is my java function), but since it's not drawn to the top of the diagram I can conclude other things are happening at the same time that use the CPU? Or even GPU stuff that isn't shown in this diagram. I am not sure how the GPU works on this. Does it calculate stuff in parallel to the CPU? Or is it part of the CPU usage as in SoC? I am not sure. Anyway, in case GPU things DO happen in parallel to CPU, then I would guess that if I do this C++ Update in parallel to the thread that makes the OpenGL calls, I might make use of "dead CPU time" due to GPU stalling or maybe have the GPU calls getting processed earlier because it won't have to wait for Update to finish? How do you suggest to improve performance based on that? Thanks.

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  • How do you price your work?

    - by Dr.Kameleon
    Well, let me explain : This has really been an issue for me, for such a long time. And what is worse - since coding is something I simply ADORE (I would definitely do it, even if there was no payment involved whatsoever..) - is that I always end up feeling somewhat awkward... Anyway... So, here's the deal : You start working on a project, you may have something in your mind, and even if you're lucky enough and the client needs no "cost estimates" beforehand, sooner or later you'll face the ultimate dilemma of pricing your own work. So, how do YOU do it? By estimating the time you put into it? (obviously, this is not exact, 'coz perhaps a more capable coder will need much less time for the very same thing than a not-so-competent coder + even the very same coder may not "perform" equally at all times) By the Lines of code you've written? (obviously, this is not a measure either : a 10-line script that does exactly the same with a 1000-line script is, at least for me, "better") By taking into account the level of complexity of the project and, perhaps, how specialised the subject is? By taking into account other factors? (e.g. the value of the project for your customer)

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  • sell applications that run only on a GPL v2 Server

    - by gadri mabrouk
    I have been testing Pentaho BI server community edition, and after reading their licensing terms I found out that the community edition is under GPLv2. As you may know the server is intended to host different types of files and applications (like reports, olap cubes,etc...) My question is : are we allowed to sell applications that run on the GPLv2 server ? (we will maybe modify the server source code a bit but we won't charge it to our clients. thus the modified GPL server will be just an execution environment or a container for the reports and applications that we intend to sell) ? this suggests that our clients must install the GPL v2 edition first and then buy from us the reports that work on it but not their source code. Thanks in advance.

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  • Adventures in Lab Management Configuration: CMMI Edition Part 1 of 3

    - by Enrique Lima
    I remember at one point someone telling me how close Migrate was to Migraine. This was a process that included an environment from TFS 2008 to TFS 2010, needed to be migrated too as far as the process template goes.  Here we are talking about CMMI v4.2 to CMMI v5.0.  Now, the process to migrate the TFS Infrastructure is one thing, migrating the Process Template is a different deal, not hard … just involved. Followed a combination of steps that came from a blog post as the main guidance and then MSDN (as suggested on the guidance post) to complement some tasks and steps. Again, the focus I have here is CMMI. The high level steps taken to enable the TFS 2008 CMMI v4.2 migrated to TFS 2010 Process Template are: 1)  Backup the Collection, Configuration and Warehouse Databases. 2)  Downloaded the Process Template using Visual Studio 2010. 3) Exported, modified and imported Bug Type Definition 4) Exported, modified and imported Scenario or Requirement Type Definition. 5) Created and imported bug field mappings. Now, we can attempt to connect using Test Manager, and you should be able to get this going. After that was done, it was time to enroll VMs that already existed in the environment.  This was a bit more challenging, but in the end it was a matter of just analyzing the changes that had been made to had a temporary work around from the time we migrated to the time we converted the Work Items and such and added fields to enable communication between the project and the Test and Lab Manager component. There are 2 more parts to this post, the second will describe the detailed steps taken to complete the Process Template update and the third will talk about the gotchas and fixes for the Lab Management portion.

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  • Microsoft dévoile la version CTP de Dryad et DryadLINQ pour le développement parallèle et distribué

    Microsoft dévoile la version CTP de Dryad et DryadLINQ Pour le développement parallèle et distribué Microsoft vient de publier la version CTP de ses environnements de calculs parallèles et distribués qui seront commercialisés dans les semaines à venir, Dryad et DryadLINQ. Dryad est un moteur de calcul haute performance pour des calculs distribués, conçu pour simplifier la mise en oeuvre d'applications distribuées. DryadLINQ, lui, permet aux développeurs d'implémenter des applications Dryad en code managé à l'aide d'une version étendue du modèle de programmation LINQ. A la base, la technologie Dryad était un projet de recherche de Microsoft pour l'exécution des donnée...

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  • Browser Alert -- cannot download links using Internet Explorer

    - by user554629
    Internet Explorer ( ie8, ie9 ) is mangling downloads from this blog. Links to files on this blog ( eg., dirstats ) are typically downloaded using browser:  R-click, SaveAs This works fine on Chrome, Firefox and Safari.  Internet Explorer is not handling the html reference to the file, and adds .html to the filename.   The file will be saved in an incorrect format.   Relatively harmless for a script file that is plain text, but binary files like obiaix.tar.gz , will be corrupted, and there is nothing you can do about it. "Don't get corrupted, get rid of cable  Internet Explorer, use firefox"  ( sorry, US TV advert reference ) The useful part of the compressed tar file is that you don't have to worry about Windows line-end characters corrupting the scripts, and you don't have to change execution permissions to get the scripts to work. dos2unix dirstats   chmod +x dirstats

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  • Silverlight, JavaScript and HTML 5 - Who wins?

    - by Sahil Malik
    SharePoint 2010 Training: more information   Disclaimer: These are just opinions. In the past I have expressed opinions about the future of technology, and have been ridiculously accurate. I have no idea if this will be accurate or not, but that is what it’s all about. Its opinions, predicting the future.   This topic has been boiling inside me for a while, and I have discussed it in private gettogethers with fellow minded techies. But I thought it would be a good idea to put this together as a blogpost. There is some debate about the future of Silverlight, especially in light of technologies such as newer faster browsers, and HTML 5. As a .NET developer, where do I invest my time and skills – remember you have limited time and skills, and not everything that comes out of Microsoft is a smashing success. So it is very very wise for you to consider the facts, macro trends, and allocate what you have limited amounts of – “time”. Read full article ....

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  • PHP 5.2 et 5.3 : un bug étrange rend les attaques par Déni de Service enfantines sous Windows et Linux

    PHP : un bug étrange rendrait enfantines les attaques par Déni de Service Il toucherait les versions 5.2 et 5.3 du langage sous Windows et Linux Un bug critique vient d'être découvert dans les branches 5.2 et 5.3 de PHP, le langage de programmation Web parmi les plus populaires. Ce bug est provoqué par certaines valeurs de nombres à virgule flottante ayant un nombre considérable de décimaux. Leurs calculs ou évaluations en PHP provoqueraient une boucle infinie occupant 100% des ressources du CPU. L'exécution de la ligne de code suivante, ou même son équivalent sans la notation scientifique (avec 324 décimales), provoquerait donc le plantage de la machine, et ce sous...

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  • TXPAUSE : polite waiting for hardware transactional memory

    - by Dave
    Classic locks are an appropriate tool to prevent potentially conflicting operations A and B, invoked by different threads, from running at the same time. In a sense the locks cause either A to run before B or vice-versa. Similarly, we can replace the locks with hardware transactional memory, or use transactional lock elision to leverage potential disjoint access parallelism between A and B. But often we want A to wait until B has run. In a Pthreads environment we'd usually use locks in conjunction with condition variables to implement our "wait until" constraint. MONITOR-MWAIT is another way to wait for a memory location to change, but it only allows us to track one cache line and it's only available on x86. There's no similar "wait until" construct for hardware transactions. At the instruction-set level a simple way to express "wait until" in transactions would be to add a new TXPAUSE instruction that could be used within an active hardware transaction. TXPAUSE would politely stall the invoking thread, possibly surrendering or yielding compute resources, while at the same time continuing to track the transaction's address-set. Once a transaction has executed TXPAUSE it can only abort. Ideally that'd happen when some other thread modifies a variable that's in the transaction's read-set or write-set. And since we're aborting all writes would be discarded. In a sense this gives us multi-location MWAIT but with much more flexibility. We could also augment the TXPAUSE with a cycle-count bound to cap the time spent stalled. I should note that we can already enter a tight spin loop in a transaction to wait for updates to address-set to cause an abort. Assuming that the implementation monitors the address-set via cache-coherence probes, by waiting in this fashion we actually communicate via the probes, and not via memory values. That is the updating thread signals the waiter via probes instead of by traditional memory values. But TXPAUSE gives us a polite way to spin.

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  • When should one use "out" parameters?

    - by qegal
    In Objective-C, there are several methods like initWithContentsOfFile:encoding:error: where one passes in a reference to an NSError object for the error: parameter. In this example, the value of the NSError object passed in can change based on what goes on at runtime when the method is being called and whether the body of the method was executed in a certain way successfully. In a way I think of this NSError object as sort of like a second return value from the method, and only differs from an object anObject in the statement return anObject; in that when this statement is called, execution leaves the method. So my question is, not only in the context of error handling in Objective-C, but in general, when should one use an "out" parameter in place of returning said value in a return statement?

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