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  • What do neglected O'Reilly book topics tell us about that topic?

    - by Peter Turner
    Does anybody know how O'Reilly chooses topics to publish? For some reason, I don't see how it can be based on demand. The reason, I ask, is because they haven't published a Delphi book in almost 12 years and Object Pascal is at least as esoteric as Erlang and as practical as PHP and as robust as C++. So, maybe someone knows what rationale is behind O'Reilly's publishing methodology or what it is supposed to tell us about the relative popularity or usefulness of any given language or programming technique? Oh, I forgot about pig and robotlegs

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  • Why do we need fork to create new process

    - by user3671483
    In Unix whenever we want to create a new process, we fork the current process i.e. we create a new child process which is exactly the same as the parent process and then we do exec system call to replace the child process with a new process i.e. we replace all the data for the parent process eith that for the new process. Why do we create a copy of the parent process in the first place and why don't we create a new process directly? I am new to Unix please explain in lay-man terms.

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  • Podcast interview with Michael Kane

    - by mhornick
    In this podcast interview with Michael Kane, Data Scientist and Associate Researcher at Yale University, Michael discusses the R statistical programming language, computational challenges associated with big data, and two projects involving data analysis he conducted on the stock market "flash crash" of May 6, 2010, and the tracking of transportation routes bird flu H5N1. Michael also worked with Oracle on Oracle R Enterprise, a component of the Advanced Analytics option to Oracle Database Enterprise Edition. In the closing segment of the interview, Michael comments on the relationship between the data analyst and the database administrator and how Oracle R Enterprise provides secure data management, transparent access to data, and improved performance to facilitate this relationship. Listen now...

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  • How to render axometric/isometric tiles that are a 2d array in logic, but inclined 45º visually?

    - by TheLima
    I am making a tile-based strategy game which i plan to have 2.5D visuals in an axometric/isometric fashion. Right now i'm programming it's logic and rendering it as a literal 2-dimensional array (perfect squares, like an isometric top-down-view). In short, i have something like this: And i want to turn it to something like this: Do i keep going on the 2d-array logic? Is it all just a change in rendering behavior, as i'm thinking it is? or 2d-array is the wrong approach for my objective and I should change before it's too late? What are the ways of doing it, anyways? How should i apply the 2.5D axometric/isometric view (45º rotation to the side, and 45º rotation upwards)?

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  • Defining the Features we would like to see

    - by Patrick Liekhus
    OK, now that we have a very rough idea of what we are building, let’s get a list of the top features that this application needs to allow us to do.  In this next list we are not prioritizing them yet, just getting on paper the high level backlog of items that this system must do. Add a new task to my work queue Change the status of the task Print a hard copy of the task list by day for my records Log a phone conversation A manager should be able to assign tasks to another user How do we login? Change the Covey roles per user Manage the statuses used Manage the Covey quadrants Can we make this available on the following user interfaces? Windows Desktop Web Browser Sliverlight (WPF) Excel Add-in Outlook Add-in Android Devices iPhone Devices Windows Mobile Devices Blackberry Devices While this looks like a simple spread sheet, it can get pretty complex and busy quickly.  Next time we will work on making this into a Product Backlog and prioritizing the features we would like to see.

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  • The Modern Marketer’s Guide to Connected Customer Journeys

    - by Richard Lefebvre
    By Amanda Batista on Thursday, August 14, 2014 in Marketing Efficiency Organizations are striving to deliver consistent experiences but very few feel they are there yet. It’s a simple consideration for marketers, really. Not only does industry data continue to support that customers demand personalized experiences when engaging with brands, but if you think about your own consumer driven shopping experiences, you, too, expect that stellar experience at every touch point. And when you don’t get it, that brand has potentially alienated the experience, as well as their shot at engaging with you in more meaningful ways. Oracle Marketing Cloud partnered with marketingfinder.co.uk to conduct a survey exploring how marketers are adapting to this new age of the customer and the challenges they face. Less than half (40%) of marketers in the study were able to track the customer journey across channels. These findings, as well as other data points showcasing marketers’ challenges, are explored in our latest eBook, “The Modern Marketer's Guide to Connected Customer Journeys.” Read the entire article and order your copy of the full report here

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  • Properly Label Your Dangerous Projects

    - by Jason Fitzpatrick
    In the pursuit of science, fun, and laser-fueled hijinks, we often undertake projects that really should be labeled more properly. Download this effective label to visually warn “No really, you’ll burn the house down”. Courtesy of Flattr at Thingiverse, you can grab a copy of the “Warning: Will Burn Your House Down” graphic in high resolution image formats suitable for silk screening, laser engraving, or plain old fashioned sign printing. Warning: Will Burn Your House Down [Thingiverse via Make] How To Encrypt Your Cloud-Based Drive with BoxcryptorHTG Explains: Photography with Film-Based CamerasHow to Clean Your Dirty Smartphone (Without Breaking Something)

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  • Teamwork 101 for the solo newbie

    - by clankercrusher
    Forgive my newbishness but I have a question to ask about teamwork...mainly because I stink at it. Most of my projects up until this point have been solo so I have a very limited experience with teamwork. I did make graphics for a game that was being developed by several people, but that was completely different than programming with several different people. Right now I'm working with someone else on an indie MMO along with a few other team members. I've already made some pretty stupid mistakes, (like rewriting EVERYTHING) so I have two questions for you guys: 1) What are some of the most common mistakes that people make in a team environment and how can they be avoided? 2) How can the structure of your program be altered to allow for multiple teams members to work on different parts of the program at the same time? P.S. Is this the right stack exchange site for this type of question? (if not, where does it go? Thanks)

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  • A Quick Primer on SharePoint Customization

    - by PeterBrunone
    Normal 0 false false false EN-US X-NONE X-NONE MicrosoftInternetExplorer4 /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-qformat:yes; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin:0in; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:10.0pt; font-family:"Times New Roman","serif";} This one goes out to all the people who have been asked to change the way a SharePoint site looks.  Management wants to know how long it will take, and you can whip that out by tomorrow, right?  If you don't have time to prepare a treatise on what's involved, or if you just want to lend some extra weight to your case by quoting a blogger who was an MVP for seven years, then dive right in; this post is for you. There are three main components of SharePoint visual customization:   1)       Theme – A theme encompasses all the standardized text formatting and coloring (borders, fonts, etc), including the background images of various sections. All told, there could be around 50 images involved, and a few hundred CSS (style) classes.  Installing a theme once it’s been created is no great feat.  Given the number of pieces, of course, creating a new theme could take anywhere from a day to a week… once decisions have been made about the desired appearance. 2)      Master Page – A master page provides the framework for page layout.  This includes all the top and side menus, where content shows up, et cetera.  Master pages have been around for a long time in ASP.NET (Microsoft’s web development platform), and they do require some .NET programming knowledge.  Beyond that, in SharePoint, there are a few dozen controls which the system expects find on a given page.  They’re not all used at once, but if they’re not there when they’re needed, chaos ensues.  Estimating a custom master page is difficult, as it depends on the level of customization.  I’ve been on projects where I was brought in simply to fix some problems and add a few finishing touches, and it took 2-3 weeks.  Master page customization requires a large amount of testing time to make sure that the HTML, JavaScript, CSS, and control placement all work well together. 3)      Individual page layout – Each page (ideally) uses a master page for its template, but within the content areas defined by the master page, web parts can be added, removed, and configured from within the browser.  The wireframe that Brent provided could most likely be completed simply by manipulating the content on the home page in this fashion, and we had allowed about a day of effort for the task.  If needed, further functionality can be provided by an experienced ASP.NET developer; custom forms are a common example.  This of course is a bit more in-depth than simple content manipulation and could take several days per page (or more; there’s really no way to quantify this without a set of requirements).   That’s basically it.  To recap:  Fonts and coloring are done with themes, and can take anywhere from a day to a week to create (not counting creative time); required technical skills include HTML, CSS, and image manipulation.  Templated layout is done with master pages, and generally requires a developer familiar with both ASP.NET and SharePoint in particular; it can have far-reaching consequences depending on the complexity of the changes, and could add weeks or months to a project.  Page layout can be as simple as content manipulation in the web browser, taking a few hours per page, or it can involve more detail, like custom forms, and can require programming expertise and significantly more development time.

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  • New Exadata Book Available Soon

    - by Rob Reynolds
    Oracle Press is set to released the first book on data warehouse performance and Exadata on March 14th. Achieving Extreme Performance with Oracle Exadata , by my colleagues Rick Greenwald, Robert Stackowiak, Maqsood Alam, and Mans Bhuller will be available at your favorite booksellers next week. I've seen a sneak peak of the content in this book and its a great way to fully grasp the power of Exadata and how to best apply it to achieve extreme data warehouse performance. From the publisher's description: Achieving Extreme Performance with Oracle Exadata and the Sun Oracle Database Machine is filled with best practices for deployments, hardware sizing, architecting the database machine environments for maximum availability, and backup and recovery. Oracle Database 11gR2 features used within these offerings, as well as migration options and paths for Oracle and non-Oracle databases to Oracle Exadata are covered. This Oracle Press guide also discusses architecture, administration, maintenance, monitoring, and tuning of Oracle Exadata Storage Servers and the Sun Oracle Database Machine. If your company is considering Exadata, or if you need more horsepower out of your data warehouse, I highly recommend grabbing a copy of this book next week.

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  • How to Sync Any Folder With SkyDrive on Windows 8.1

    - by Chris Hoffman
    Before Windows 8.1, it was possible to sync any folder on your computer with SkyDrive using symbolic links. This method no longer works now that SkyDrive is baked into Windows 8.1, but there are other tricks you can use. Creating a symbolic link or directory junction inside your SkyDrive folder will give you an empty folder in your SkyDrive cloud storage. Confusingly, the files will appear inside the SkyDrive Modern app as if they were being synced, but they aren’t. The Solution With SkyDrive refusing to understand and accept symbolic links in its own folder, the best option is probably to use symbolic links anyway — but in reverse. For example, let’s say you have a program that automatically saves important data to a folder anywhere on your hard drive — whether it’s C:\Users\USER\Documents\, C:\Program\Data, or anywhere else. Rather than trying to trick SkyDrive into understanding a symbolic link, we could instead move the actual folder itself to SkyDrive and then use a symbolic link at the folder’s original location to trick the original program. This may not work for every single program out there. But it will likely work for most programs, which use standard Windows API calls to access folders and save files. We’re just flipping the old solution here — we can’t trick SkyDrive anymore, so let’s try to trick other programs instead. Moving a Folder and Creating a Symbolic Link First, ensure no program is using the external folder. For example, if it’s a program data or settings folder, close the program that’s using the folder. Next, simply move the folder to your SkyDrive folder. Right-click the external folder, select Cut, go to the SkyDrive folder, right-click and select Paste. The folder will now be located in the SkyDrive folder itself, so it will sync normally. Next, open a Command Prompt window as Administrator. Right-click the Start button on the taskbar or press Windows Key + X and select Command Prompt (Administrator) to open it. Run the following command to create a symbolic link at the original location of the folder: mklink /d “C:\Original\Folder\Location” “C:\Users\NAME\SkyDrive\FOLDERNAME\” Enter the correct paths for the exact location of the original folder and the current location of the folder in your SkyDrive. Windows will then create a symbolic link at the folder’s original location. Most programs should hopefully be tricked by this symbolic location, saving their files directly to SkyDrive. You can test this yourself. Put a file into the folder at its original location. It will be saved to SkyDrive and sync normally, appearing in your SkyDrive storage online. One downside here is that you won’t be able to save a file onto SkyDrive without it taking up space on the same hard drive SkyDrive is on. You won’t be able to scatter folders across multiple hard drives and sync them all. However, you could always change the location of the SkyDrive folder on Windows 8.1 and put it on a drive with a larger amount of free space. To do this, right-click the SkyDrive folder in File Explorer, select Properties, and use the options on the Location tab. You could even use Storage Spaces to combine the drives into one larger drive. Automatically Copy the Original Files to SkyDrive Another option would be to run a program that automatically copies files from another folder on your computer to your SkyDrive folder. For example, let’s say you want to sync copies of important log files that a program creates in a specific folder. You could use a program that allows you to schedule automatic folder-mirroring, configuring the program to regularly copy the contents of your log folder to your SkyDrive folder. This may be a useful alternative for some use cases, although it isn’t the same as standard syncing. You’ll end up with two copies of the files taking up space on your system, which won’t be ideal for large files. The files also won’t be instantly uploaded to your SkyDrive storage after they’re created, but only after the scheduled task runs. There are many options for this, including Microsoft’s own SyncToy, which continues to work on Windows 8. If you were using the symbolic link trick to automatically sync copies of PC game save files with SkyDrive, you could just install GameSave Manager. It can be configured to automatically create backup copies of your computer’s PC game save files on a schedule, saving them to SkyDrive where they’ll be synced and backed up online. SkyDrive support was completely rewritten for Windows 8.1, so it’s not surprising that this trick no longer works. The ability to use symbolic links in previous versions of SkyDrive was never officially supported, so it’s not surprising to see it break after a rewrite. None of the methods above are as convenient and quick as the old symbolic link method, but they’re the best we can do with the SkyDrive integration Microsoft has given us in Windows 8.1. It’s still possible to use symbolic links to easily sync other folders with competing cloud storage services like Dropbox and Google Drive, so you may want to consider switching away from SkyDrive if this feature is critical to you.     

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  • How I understood monads, part 1/2: sleepless and self-loathing in Seattle

    For some time now, I had been noticing some interest for monads, mostly in the form of unintelligible (to me) blog posts and comments saying oh, yeah, thats a monad about random stuff as if it were absolutely obvious and if I didnt know what they were talking about, I was probably an uneducated idiot, ignorant about the simplest and most fundamental concepts of functional programming. Fair enough, I am pretty much exactly that. Being the kind of guy who can spend eight years in college just to...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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  • Do Not Optimize Without Measuring

    - by Alois Kraus
    Recently I had to do some performance work which included reading a lot of code. It is fascinating with what ideas people come up to solve a problem. Especially when there is no problem. When you look at other peoples code you will not be able to tell if it is well performing or not by reading it. You need to execute it with some sort of tracing or even better under a profiler. The first rule of the performance club is not to think and then to optimize but to measure, think and then optimize. The second rule is to do this do this in a loop to prevent slipping in bad things for too long into your code base. If you skip for some reason the measure step and optimize directly it is like changing the wave function in quantum mechanics. This has no observable effect in our world since it does represent only a probability distribution of all possible values. In quantum mechanics you need to let the wave function collapse to a single value. A collapsed wave function has therefore not many but one distinct value. This is what we physicists call a measurement. If you optimize your application without measuring it you are just changing the probability distribution of your potential performance values. Which performance your application actually has is still unknown. You only know that it will be within a specific range with a certain probability. As usual there are unlikely values within your distribution like a startup time of 20 minutes which should only happen once in 100 000 years. 100 000 years are a very short time when the first customer tries your heavily distributed networking application to run over a slow WIFI network… What is the point of this? Every programmer/architect has a mental performance model in his head. A model has always a set of explicit preconditions and a lot more implicit assumptions baked into it. When the model is good it will help you to think of good designs but it can also be the source of problems. In real world systems not all assumptions of your performance model (implicit or explicit) hold true any longer. The only way to connect your performance model and the real world is to measure it. In the WIFI example the model did assume a low latency high bandwidth LAN connection. If this assumption becomes wrong the system did have a drastic change in startup time. Lets look at a example. Lets assume we want to cache some expensive UI resource like fonts objects. For this undertaking we do create a Cache class with the UI themes we want to support. Since Fonts are expensive objects we do create it on demand the first time the theme is requested. A simple example of a Theme cache might look like this: using System; using System.Collections.Generic; using System.Drawing; struct Theme { public Color Color; public Font Font; } static class ThemeCache { static Dictionary<string, Theme> _Cache = new Dictionary<string, Theme> { {"Default", new Theme { Color = Color.AliceBlue }}, {"Theme12", new Theme { Color = Color.Aqua }}, }; public static Theme Get(string theme) { Theme cached = _Cache[theme]; if (cached.Font == null) { Console.WriteLine("Creating new font"); cached.Font = new Font("Arial", 8); } return cached; } } class Program { static void Main(string[] args) { Theme item = ThemeCache.Get("Theme12"); item = ThemeCache.Get("Theme12"); } } This cache does create font objects only once since on first retrieve of the Theme object the font is added to the Theme object. When we let the application run it should print “Creating new font” only once. Right? Wrong! The vigilant readers have spotted the issue already. The creator of this cache class wanted to get maximum performance. So he decided that the Theme object should be a value type (struct) to not put too much pressure on the garbage collector. The code Theme cached = _Cache[theme]; if (cached.Font == null) { Console.WriteLine("Creating new font"); cached.Font = new Font("Arial", 8); } does work with a copy of the value stored in the dictionary. This means we do mutate a copy of the Theme object and return it to our caller. But the original Theme object in the dictionary will have always null for the Font field! The solution is to change the declaration of struct Theme to class Theme or to update the theme object in the dictionary. Our cache as it is currently is actually a non caching cache. The funny thing was that I found out with a profiler by looking at which objects where finalized. I found way too many font objects to be finalized. After a bit debugging I found the allocation source for Font objects was this cache. Since this cache was there for years it means that the cache was never needed since I found no perf issue due to the creation of font objects. the cache was never profiled if it did bring any performance gain. to make the cache beneficial it needs to be accessed much more often. That was the story of the non caching cache. Next time I will write something something about measuring.

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  • Ever helpful Windows&hellip;

    - by John Breakwell
    I’m doing some troubleshooting for a relative and asked them to send me a zipped copy of their registry which they dutifully did. When I tried to extract the registry file, though, Windows jumped in the way and said “No”. This made sense as registry files are dangerous things in the hands of the ignorant. So I clicked the link to see if it would tell me how to get at the reg file but found the result less than helpful. So off to the Internet and found an excellent answer on how to get round this: Now on to the much harder part of fixing the original problems.

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  • APress Deal of the Day 13/August/2014 - Pro ASP.NET MVC 4

    - by TATWORTH
    Originally posted on: http://geekswithblogs.net/TATWORTH/archive/2014/08/13/apress-deal-of-the-day-13august2014---pro-asp.net-mvc.aspxToday’s $10 Deal of the Day from APress at http://www.apress.com/9781430242369 is Pro ASP.NET MVC 4. Adam Freeman is an excellent author and I recommend this book to all my readers. “The ASP.NET MVC 4 Framework is the latest evolution of Microsoft’s ASP.NET web platform. It provides a high-productivity programming model that promotes cleaner code architecture, test-driven development, and powerful extensibility, combined with all the benefits of ASP.NET.”

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  • Uploading to a PPA using quickly

    - by Andres
    I am trying to participate in ubuntu showdown. I followed Jono's tutorial to do a browser using quickly. I did some modifications including choosing license (gpl v3), putting my name in copy right ( without special spanish charecters since quicky does not like it) $quickly run to make sure it worked I used bazaar to commit a change with a line of comment. I packaged it using quickly. Managed to install it ignoring some warnings but it would not run. I want to share code to get feedback. I have a launchpad account, signed terms and coditions, created a ppa. I got my commandline to talk to lauchpad using the encription key. But when I run $quickly release or $quickly share and it says the project does not exist. There seems to be another command $dput ... But i don't seem to get the wording right because it requests some sort of signed file that i cannot manage to add the correct way.

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  • How to keep menu in a single place without using frames

    - by TJ Ellis
    This is probably a duplicate, but I can't find the answer anywhere (maybe I'm searching for the wrong thing?) and so I'm going to go ahead and ask. What is the accepted standard practice for creating a menu that is stored in a single file, but is included on every page across a site? Back in the day, one used frames, but this seems to be taboo now. I can get things layed out just the way I want, but copy/pasting across every page is a pain. I have seen php-based solutions, but my cheap-o free hosting doesn't support php (which is admittedly a pain, but it's a fairly simple webpage...). Any ideas for doing this that does not require server-side scripting?

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  • how should I network my turn based game?

    - by ddriver1
    I'm writing a very basic turn based strategy game which allows a player to select units and attack enemy units on their turn. The game is written in Java using the slick2d library and I plan to use kyronet for the networking api. I want the game to be networked, but I do not know how I should go about it. My current idea is to connect two users together, and the first one to join the game becomes the game host, while the other becomes the client. However after reading http://gafferongames.com/networking-for-game-programmers/what-every-programmer-needs-to-know-about-game-networking/ it seems my game would be suited to a peer to peer lockstep model. Would that make programming the networking side much easier? Any suggestions on how I should structure my networking would be greatly appreciated

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  • CLR via C# 3rd Edition is out

    - by Abhijeet Patel
    Time for some book news update. CLR via C#, 3rd Edition seems to have been out for a little while now. The book was released in early Feb this year, and needless to say my copy is on it’s way. I can barely wait to dig in and chew on the goodies that one of the best technical authors and software professionals I respect has in store. The 2nd edition of the book was an absolute treat and this edition promises to be no less. Here is a brief description of what’s new and updated from the 2nd edition. Part I – CLR Basics Chapter 1-The CLR’s Execution Model Added about discussion about C#’s /optimize and /debug switches and how they relate to each other. Chapter 2-Building, Packaging, Deploying, and Administering Applications and Types Improved discussion about Win32 manifest information and version resource information. Chapter 3-Shared Assemblies and Strongly Named Assemblies Added discussion of TypeForwardedToAttribute and TypeForwardedFromAttribute. Part II – Designing Types Chapter 4-Type Fundamentals No new topics. Chapter 5-Primitive, Reference, and Value Types Enhanced discussion of checked and unchecked code and added discussion of new BigInteger type. Also added discussion of C# 4.0’s dynamic primitive type. Chapter 6-Type and Member Basics No new topics. Chapter 7-Constants and Fields No new topics. Chapter 8-Methods Added discussion of extension methods and partial methods. Chapter 9-Parameters Added discussion of optional/named parameters and implicitly-typed local variables. Chapter 10-Properties Added discussion of automatically-implemented properties, properties and the Visual Studio debugger, object and collection initializers, anonymous types, the System.Tuple type and the ExpandoObject type. Chapter 11-Events Added discussion of events and thread-safety as well as showing a cool extension method to simplify the raising of an event. Chapter 12-Generics Added discussion of delegate and interface generic type argument variance. Chapter 13-Interfaces No new topics. Part III – Essential Types Chapter 14-Chars, Strings, and Working with Text No new topics. Chapter 15-Enums Added coverage of new Enum and Type methods to access enumerated type instances. Chapter 16-Arrays Added new section on initializing array elements. Chapter 17-Delegates Added discussion of using generic delegates to avoid defining new delegate types. Also added discussion of lambda expressions. Chapter 18-Attributes No new topics. Chapter 19-Nullable Value Types Added discussion on performance. Part IV – CLR Facilities Chapter 20-Exception Handling and State Management This chapter has been completely rewritten. It is now about exception handling and state management. It includes discussions of code contracts and constrained execution regions (CERs). It also includes a new section on trade-offs between writing productive code and reliable code. Chapter 21-Automatic Memory Management Added discussion of C#’s fixed state and how it works to pin objects in the heap. Rewrote the code for weak delegates so you can use them with any class that exposes an event (the class doesn’t have to support weak delegates itself). Added discussion on the new ConditionalWeakTable class, GC Collection modes, Full GC notifications, garbage collection modes and latency modes. I also include a new sample showing how your application can receive notifications whenever Generation 0 or 2 collections occur. Chapter 22-CLR Hosting and AppDomains Added discussion of side-by-side support allowing multiple CLRs to be loaded in a single process. Added section on the performance of using MarshalByRefObject-derived types. Substantially rewrote the section on cross-AppDomain communication. Added section on AppDomain Monitoring and first chance exception notifications. Updated the section on the AppDomainManager class. Chapter 23-Assembly Loading and Reflection Added section on how to deploy a single file with dependent assemblies embedded inside it. Added section comparing reflection invoke vs bind/invoke vs bind/create delegate/invoke vs C#’s dynamic type. Chapter 24-Runtime Serialization This is a whole new chapter that was not in the 2nd Edition. Part V – Threading Chapter 25-Threading Basics Whole new chapter motivating why Windows supports threads, thread overhead, CPU trends, NUMA Architectures, the relationship between CLR threads and Windows threads, the Thread class, reasons to use threads, thread scheduling and priorities, foreground thread vs background threads. Chapter 26-Performing Compute-Bound Asynchronous Operations Whole new chapter explaining the CLR’s thread pool. This chapter covers all the new .NET 4.0 constructs including cooperative cancelation, Tasks, the aralle class, parallel language integrated query, timers, how the thread pool manages its threads, cache lines and false sharing. Chapter 27-Performing I/O-Bound Asynchronous Operations Whole new chapter explaining how Windows performs synchronous and asynchronous I/O operations. Then, I go into the CLR’s Asynchronous Programming Model, my AsyncEnumerator class, the APM and exceptions, Applications and their threading models, implementing a service asynchronously, the APM and Compute-bound operations, APM considerations, I/O request priorities, converting the APM to a Task, the event-based Asynchronous Pattern, programming model soup. Chapter 28-Primitive Thread Synchronization Constructs Whole new chapter discusses class libraries and thread safety, primitive user-mode, kernel-mode constructs, and data alignment. Chapter 29-Hybrid Thread Synchronization Constructs Whole new chapter discussion various hybrid constructs such as ManualResetEventSlim, SemaphoreSlim, CountdownEvent, Barrier, ReaderWriterLock(Slim), OneManyResourceLock, Monitor, 3 ways to solve the double-check locking technique, .NET 4.0’s Lazy and LazyInitializer classes, the condition variable pattern, .NET 4.0’s concurrent collection classes, the ReaderWriterGate and SyncGate classes.

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  • Liskov Substitution Principle and the Oft Forgot Third Wheel

    - by Stacy Vicknair
    Liskov Substitution Principle (LSP) is a principle of object oriented programming that many might be familiar with from the SOLID principles mnemonic from Uncle Bob Martin. The principle highlights the relationship between a type and its subtypes, and, according to Wikipedia, is defined by Barbara Liskov and Jeanette Wing as the following principle:   Let be a property provable about objects of type . Then should be provable for objects of type where is a subtype of .   Rectangles gonna rectangulate The iconic example of this principle is illustrated with the relationship between a rectangle and a square. Let’s say we have a class named Rectangle that had a property to set width and a property to set its height. 1: Public Class Rectangle 2: Overridable Property Width As Integer 3: Overridable Property Height As Integer 4: End Class   We all at some point here that inheritance mocks an “IS A” relationship, and by gosh we all know square IS A rectangle. So let’s make a square class that inherits from rectangle. However, squares do maintain the same length on every side, so let’s override and add that behavior. 1: Public Class Square 2: Inherits Rectangle 3:  4: Private _sideLength As Integer 5:  6: Public Overrides Property Width As Integer 7: Get 8: Return _sideLength 9: End Get 10: Set(value As Integer) 11: _sideLength = value 12: End Set 13: End Property 14:  15: Public Overrides Property Height As Integer 16: Get 17: Return _sideLength 18: End Get 19: Set(value As Integer) 20: _sideLength = value 21: End Set 22: End Property 23: End Class   Now, say we had the following test: 1: Public Sub SetHeight_DoesNotAffectWidth(rectangle As Rectangle) 2: 'arrange 3: Dim expectedWidth = 4 4: rectangle.Width = 4 5:  6: 'act 7: rectangle.Height = 7 8:  9: 'assert 10: Assert.AreEqual(expectedWidth, rectangle.Width) 11: End Sub   If we pass in a rectangle, this test passes just fine. What if we pass in a square?   This is where we see the violation of Liskov’s Principle! A square might "IS A” to a rectangle, but we have differing expectations on how a rectangle should function than how a square should! Great expectations Here’s where we pat ourselves on the back and take a victory lap around the office and tell everyone about how we understand LSP like a boss. And all is good… until we start trying to apply it to our work. If I can’t even change functionality on a simple setter without breaking the expectations on a parent class, what can I do with subtyping? Did Liskov just tell me to never touch subtyping again? The short answer: NO, SHE DIDN’T. When I first learned LSP, and from those I’ve talked with as well, I overlooked a very important but not appropriately stressed quality of the principle: our expectations. Our inclination is to want a logical catch-all, where we can easily apply this principle and wipe our hands, drop the mic and exit stage left. That’s not the case because in every different programming scenario, our expectations of the parent class or type will be different. We have to set reasonable expectations on the behaviors that we expect out of the parent, then make sure that those expectations are met by the child. Any expectations not explicitly expected of the parent aren’t expected of the child either, and don’t register as a violation of LSP that prevents implementation. You can see the flexibility mentioned in the Wikipedia article itself: A typical example that violates LSP is a Square class that derives from a Rectangle class, assuming getter and setter methods exist for both width and height. The Square class always assumes that the width is equal with the height. If a Square object is used in a context where a Rectangle is expected, unexpected behavior may occur because the dimensions of a Square cannot (or rather should not) be modified independently. This problem cannot be easily fixed: if we can modify the setter methods in the Square class so that they preserve the Square invariant (i.e., keep the dimensions equal), then these methods will weaken (violate) the postconditions for the Rectangle setters, which state that dimensions can be modified independently. Violations of LSP, like this one, may or may not be a problem in practice, depending on the postconditions or invariants that are actually expected by the code that uses classes violating LSP. Mutability is a key issue here. If Square and Rectangle had only getter methods (i.e., they were immutable objects), then no violation of LSP could occur. What this means is that the above situation with a rectangle and a square can be acceptable if we do not have the expectation for width to leave height unaffected, or vice-versa, in our application. Conclusion – the oft forgot third wheel Liskov Substitution Principle is meant to act as a guidance and warn us against unexpected behaviors. Objects can be stateful and as a result we can end up with unexpected situations if we don’t code carefully. Specifically when subclassing, make sure that the subclass meets the expectations held to its parent. Don’t let LSP think you cannot deviate from the behaviors of the parent, but understand that LSP is meant to highlight the importance of not only the parent and the child class, but also of the expectations WE set for the parent class and the necessity of meeting those expectations in order to help prevent sticky situations.   Code examples, in both VB and C# Technorati Tags: LSV,Liskov Substitution Principle,Uncle Bob,Robert Martin,Barbara Liskov,Liskov

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  • Prevent service from starting

    - by Evan Plaice
    So, I do Arduino development on my system to program arduinos using the FTDI USB programming interface (if you have no idea what this means don't worry). The issue arises because the FTDI interface uses tty to communicate and it conflicts with one of the default ubuntu services. The default service in question is called brltty (which enables braille accessibility for people with impaired vision). Considering that I don't have any particular use for this service and it's annoying to stop it manually (using 'service brltty stop') after I restart my system... Where would I configure this (or any) service to prevent it from loading on startup? Note: I also have this issue with qemu-kvm conflicting with virtualbox.

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  • Computer Science or Computer Engineering for Data Science and Machine Learning

    - by ATMathew
    I'm a 25 year old data consultant who is considering returning to school to get a second bachelors degree in computer science or engineering. My interest is data science and machine learning. I use programming as a means to an end, and use languages like Python, R, C, Java, and Hadoop to find meaning in large data sets. Would a computer science or computer engineering degree be better for this? I realize that a statistics degree may be even more beneficial, but I'll be at a school which dosn't have a stats department or a computational math department.

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  • List of Commonly Used Value Types in XNA Games

    - by Michael B. McLaughlin
    Most XNA programmers are concerned about generating garbage. More specifically about allocating GC-managed memory (GC stands for “garbage collector” and is both the name of the class that provides access to the garbage collector and an acronym for the garbage collector (as a concept) itself). Two of the major target platforms for XNA (Windows Phone 7 and Xbox 360) use variants of the .NET Compact Framework. On both variants, the GC runs under various circumstances (Windows Phone 7 and Xbox 360). Of concern to XNA programmers is the fact that it runs automatically after a fixed amount of GC-managed memory has been allocated (currently 1MB on both systems). Many beginning XNA programmers are unaware of what constitutes GC-managed memory, though. So here’s a quick overview. In .NET, there are two different “types” of types: value types and reference types. Only reference types are managed by the garbage collector. Value types are not managed by the garbage collector and are instead managed in other ways that are implementation dependent. For purposes of XNA programming, the important point is that they are not managed by the GC and thus do not, by themselves, increment that internal 1 MB allocation counter. (n.b. Structs are value types. If you have a struct that has a reference type as a member, then that reference type, when instantiated, will still be allocated in the GC-managed memory and will thus count against the 1 MB allocation counter. Putting it in a struct doesn’t change the fact that it gets allocated on the GC heap, but the struct itself is created outside of the GC’s purview). Both value types and reference types use the keyword ‘new’ to allocate a new instance of them. Sometimes this keyword is hidden by a method which creates new instances for you, e.g. XmlReader.Create. But the important thing to determine is whether or not you are dealing with a value types or a reference type. If it’s a value type, you can use the ‘new’ keyword to allocate new instances of that type without incrementing the GC allocation counter (except as above where it’s a struct with a reference type in it that is allocated by the constructor, but there are no .NET Framework or XNA Framework value types that do this so it would have to be a struct you created or that was in some third-party library you were using for that to even become an issue). The following is a list of most all of value types you are likely to use in a generic XNA game: AudioCategory (used with XACT; not available on WP7) AvatarExpression (Xbox 360 only, but exposed on Windows to ease Xbox development) bool BoundingBox BoundingSphere byte char Color DateTime decimal double any enum (System.Enum itself is a class, but all enums are value types such that there are no GC allocations for enums) float GamePadButtons GamePadCapabilities GamePadDPad GamePadState GamePadThumbSticks GamePadTriggers GestureSample int IntPtr (rarely but occasionally used in XNA) KeyboardState long Matrix MouseState nullable structs (anytime you see, e.g. int? something, that ‘?’ denotes a nullable struct, also called a nullable type) Plane Point Quaternion Ray Rectangle RenderTargetBinding sbyte (though I’ve never seen it used since most people would just use a short) short TimeSpan TouchCollection TouchLocation TouchPanelCapabilities uint ulong ushort Vector2 Vector3 Vector4 VertexBufferBinding VertexElement VertexPositionColor VertexPositionColorTexture VertexPositionNormalTexture VertexPositionTexture Viewport So there you have it. That’s not quite a complete list, mind you. For example: There are various structs in the .NET framework you might make use of. I left out everything from the Microsoft.Xna.Framework.Graphics.PackedVector namespace, since everything in there ventures into the realm of advanced XNA programming anyway (n.b. every single instantiable thing in that namespace is a struct and thus a value type; there are also two interfaces but interfaces cannot be instantiated at all and thus don’t figure in to this discussion). There are so many enums you’re likely to use (PlayerIndex, SpriteSortMode, SpriteEffects, SurfaceFormat, etc.) that including them would’ve flooded the list and reduced its utility. So I went with “any enum” and trust that you can figure out what the enums are (and it’s rare to use ‘new’ with an enum anyway). That list also doesn’t include any of the pre-defined static instances of some of the classes (e.g. BlendState.AlphaBlend, BlendState.Opaque, etc.) which are already allocated such that using them doesn’t cause any new allocations and therefore doesn’t increase that 1 MB counter. That list also has a few misleading things. VertexElement, VertexPositionColor, and all the other vertex types are structs. But you’re only likely to ever use them as an array (for use with VertexBuffer or DynamicVertexBuffer), and all arrays are reference types (even arrays of value types such as VertexPositionColor[ ] or int[ ]). * So that’s it for now. The note below may be a bit confusing (it deals with how the GC works and how arrays are managed in .NET). If so, you can probably safely ignore it for now but feel free to ask any questions regardless. * Arrays of value types (where the value type doesn’t contain any reference type members) are much faster for the GC to examine than arrays of reference types, so there is a definite benefit to using arrays of value types where it makes sense. But creating arrays of value types does cause the GC’s allocation counter to increase. Indeed, allocating a large array of a value type is one of the quickest ways to increment the allocation counter since a .NET array is a sequential block of memory. An array of reference types is just a sequential block of references (typically 4 bytes each) while an array of value types is a sequential block of instances of that type. So for an array of Vector3s it would be 12 bytes each since each float is 4 bytes and there are 3 in a Vector3; for an array of VertexPositionNormalTexture structs it would typically be 32 bytes each since it has two Vector3s and a Vector2. (Note that there are a few additional bytes taken up in the creation of an array, typically 12 but sometimes 16 or possibly even more, which depend on the implementation details of the array type on the particular platform the code is running on).

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  • Flixel Game Over Screen

    - by Jamie Read
    I am new to game development but familiar with programming languages. I have started using Flixel and have a working Breakout game with score and lives. I am just stuck on how I can create a new screen/game over screen if a player runs out of lives. I would like the process to be like following: Check IF lives are equal to 0 Pause the game and display a new screen (probably transparent) that says 'Game Over' When a user clicks or hits ENTER restart the level Here is the function I currently have to update the lives: private function loseLive(_ball:FlxObject, _bottomWall:FlxObject):void { // check for game over if (lives_count == 0) { } else { FlxG:lives_count -= 1; lives.text = 'Lives: ' + lives_count.toString() } } Here is my main game.as: package { import org.flixel.*; public class Game extends FlxGame { private const resolution:FlxPoint = new FlxPoint(640, 480); private const zoom:uint = 2; private const fps:uint = 60; public function Game() { super(resolution.x / zoom, resolution.y / zoom, PlayState, zoom); FlxG.flashFramerate = fps; } } }

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  • HFS+ hard drive being mounted as read only

    - by DNA
    This is a recurring problem and occurs a few times a week. I have an external hard drive which is hfs+. Every couple of weeks, for no obviuous reason, when I mount it by pluggin it in to my Ubuntu 11.10, it is read only and I can't copy any files into it. I gksudo nautlius and change the ownership and it magically works in some time. But returns to the read only state soon in a few hours-days without any rhyme or reason. Right now my fstab doesn't have any entry for my hard drive. What gives? What in the world is going on with Linux/HFS+? This is frustrating. I can't reformat my hard drive because I have almost a terrabyte of data in it and no receptacle to hold it while I reformat it.

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