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  • Why lock statements don't scale

    - by Alex.Davies
    We are going to have to stop using lock statements one day. Just like we had to stop using goto statements. The problem is similar, they're pretty easy to follow in small programs, but code with locks isn't composable. That means that small pieces of program that work in isolation can't necessarily be put together and work together. Of course actors scale fine :) Why lock statements don't scale as software gets bigger Deadlocks. You have a program with lots of threads picking up lots of locks. You already know that if two of your threads both try to pick up a lock that the other already has, they will deadlock. Your program will come to a grinding halt, and there will be fire and brimstone. "Easy!" you say, "Just make sure all the threads pick up the locks in the same order." Yes, that works. But you've broken composability. Now, to add a new lock to your code, you have to consider all the other locks already in your code and check that they are taken in the right order. Algorithm buffs will have noticed this approach means it takes quadratic time to write a program. That's bad. Why lock statements don't scale as hardware gets bigger Memory bus contention There's another headache, one that most programmers don't usually need to think about, but is going to bite us in a big way in a few years. Locking needs exclusive use of the entire system's memory bus while taking out the lock. That's not too bad for a single or dual-core system, but already for quad-core systems it's a pretty large overhead. Have a look at this blog about the .NET 4 ThreadPool for some numbers and a weird analogy (see the author's comment). Not too bad yet, but I'm scared my 1000 core machine of the future is going to go slower than my machine today! I don't know the answer to this problem yet. Maybe some kind of per-core work queue system with hierarchical work stealing. Definitely hardware support. But what I do know is that using locks specifically prevents any solution to this. We should be abstracting our code away from the details of locks as soon as possible, so we can swap in whatever solution arrives when it does. NAct uses locks at the moment. But my advice is that you code using actors (which do scale well as software gets bigger). And when there's a better way of implementing actors that'll scale well as hardware gets bigger, only NAct needs to work out how to use it, and your program will go fast on it's own.

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  • Why Clonezilla needs to reinstall grub?

    - by Pablo
    By default CloneZilla Live will reinstall grub after restore. In my particular case I am restoring a disk image to same phisical disk without any partitioning/size change. I am expecting to have exact same state as I had right after backup. However, reinstalling grub will render my system to unbootable. If I remove that option [-g] then everything is fine. My question is in what cases and why CloneZilla ever need to re-install grub when restoring disk image?

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  • Why it is so difficult to find a good Ads SDK for Windows Phone 7

    - by help.net
    This post try to address an issue with the Microsoft Advertising SDK, the main fact that today Microsoft is still refusing access to the Ad Center worldwide. Yesterday they generously increase the number of free apps we can develop from 5 to 100. According to talks with other developers and the Windows Phone 7 team, I have the strong feeling the model of publishing free apps supported by apps is the right course to take today. This probably why Microsoft has moved to a bigger figure. Am I the only...(read more)

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  • Why should you document code?

    - by Edwin Tripp
    I am a graduate software developer for a financial company that uses an old COBOL-like language/flat-file record storage system. The code is completely undocumented, both code comments and overall system design and there is no help on the web (unused outside the industry). The current developers have been working on the system for between 10 and 30 years and are adamant that documentation is unnecessary as you can just read the code to work out what's going on and that you can't trust comments. Why should such a system be documented?

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  • Why Solid-State Drives Slow Down As You Fill Them Up

    - by Chris Hoffman
    The benchmarks are clear: Solid-state drives slow down as you fill them up. Fill your solid-state drive to near-capacity and its write performance will decrease dramatically. The reason why lies in the way SSDs and NAND Flash storage work. Filling the drive to capacity is one of the things you should never do with a solid-state drive. A nearly full solid-state drive will have much slower write operations, slowing down your computer.    

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  • Why do iterators in Python raise an exception?

    - by NullUserException
    Here's the syntax for iterators in Java (somewhat similar syntax in C#): Iterator it = sequence.iterator(); while (it.hasNext()) { System.out.println(it.next()); } Which makes sense. Here's the equivalent syntax in Python: it = iter(sequence) while True: try: value = it.next() except StopIteration: break print(value) I thought Exceptions were supposed to be used only in, well, exceptional circumstances. Why does Python use exceptions to stop iteration?

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  • Why was Scala not implemented with C or C++

    - by jpartogi
    Does anybody know why was Scala implemented in Java and .NET instead of C or C++? Most languages are implemented with Cor C++ [i.e Erlang, Python, PHP, Ruby, Perl]. What are the advantages for Scala implemented in Java and .NET other than giving access to Java and .NET libraries? UPDATE Woudln't Scala gain more benefit if it is implemented in C because it can be tuned better rather than relying on JVM?

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  • Design Patterns - Why the need for interfaces?

    - by Kyle Johnson
    OK. I am learning design patterns. Every time I see someone code an example of a design pattern they use interfaces. Here is an example: http://visualstudiomagazine.com/Articles/2013/06/18/the-facade-pattern-in-net.aspx?Page=1 Can someone explain to me why was the interfaces needed in this example to demonstrate the facade pattern? The program work if you pass in the classes to the facade instead of the interface. If I don't have interfaces does that mean

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  • Why can we recognize game engines?

    - by Bart van Heukelom
    About many games you can say "oh that's the Unreal engine for sure", "this was made by upgrading GTA 4", etc. We can often recognize the engine used for a game just by looking at its graphics (disregarding menus and such). I'm wondering, why is this? All game engines use the same 3D rendering technology that we all use, and the different games usually have a distinct art style, so what's left to recognize?

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  • Why Use !boolean_variable Over boolean_variable == false

    - by ell
    A comment on this question: Calling A Method that returns a boolean value inside a conditional statement says that you should use !boolean instead of boolean == false when testing conditions. Why? To me boolean == false is much more natural in English and is more explicit. I apologise if this is just a matter of style, but I was wondering if there was some other reason for this preference of !boolean?

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  • Why does XCode convert PNGs to CgBI format?

    - by Gdeglin
    According to the research done here http://imageoptim.com/tweetbot.html, Xcode's conversion of PNGs to the proprietary Apple CgBI format does not create a noticeable performance improvement. Their claim is that the conversion only reduces PNG loading speed by 1 nanosecond. If this is true, why does apple bother with the CgBI format at all? Has anyone else benchmarked loading CgBI images vs regular PNG images on iOS devices to see if they perform differently?

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  • Why is iOS "jailbreaking" CPU specific? [closed]

    - by Ted Wong
    Recently, iOS 6 was "jailbroken" but only on the Apple A4 CPU. Why is the "jailbreaking" process specific to a CPU? From Wikipedia: ... "iOS jailbreaking is the process of removing the limitations imposed by Apple on devices running the iOS operating system through the use of hardware/software exploits – such devices include the iPhone, iPod touch, iPad, and second generation Apple TV. Jailbreaking allows iOS users to gain root access to the operating system""" ...

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  • why do we need to put private members in headers

    - by Simon
    Private variables are a way to hide complexity and implementation details to the user of a class. This is a rather nice feature. But I do not understand why in c++ we need to put them in the header of a class. I see some annoying downsides to this: it clutters the header from the user it force recompilation of all client libraries whenever the internals are modified Is there a conceptual reason behind this requirement? Is it only to ease the work of the compiler?

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  • Why SEO Hosting Reviews Are Important

    Read about why and how webmasters are finding out SEO Hosting Reviews to be able to find the ideal web host to make the most of their domains and sites. This is the new age of internet marketing and it begins with SEO Hosting.

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  • Why many designs ignore normalization in RDBMS?

    - by Yosi
    I got to see many designs that normalization wasn't the first consideration in decision making phase. In many cases those designs included more than 30 columns, and the main approach was "to put everything in the same place" According to what I remember normalization is one of the first, most important things, so why is it dropped so easily sometimes? Edit: Is it true that good architects and experts choose a denormalized design while non-experienced developers choose the opposite? What are the arguments against starting your design with normalization in mind?

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  • Why is my system freezing when I switch users

    - by ZeroDivide
    Hello I've recently upgraded from 13.04 to 13.10 64bit. I'm running AMD graphics with the proprietary drivers. I have two user accounts. Mine(administrator) and my girlfriend's(standard) My girlfriend clicks "switch user" from my lock screen and logs in fine. I then try to click "switch user" from her lock screen and everything goes black. Then the monitor blinks on and off with just a single cursor. I have no way to access the terminal, the system is unresponsive and I have to hit the power button. Even ctrl + alt + f4 or ctrl + alt + t doesn't get me a terminal. When I press the power button on my system, it does start printing out the shutdown sequence on the monitor. Here is my .xsession-errors Script for ibus started at run_im. Script for auto started at run_im. Script for default started at run_im. Here is hers: init: at-spi2-registryd main process ended, respawning init: at-spi2-registryd main process ended, respawning init: at-spi2-registryd main process ended, respawning init: at-spi2-registryd main process ended, respawning init: at-spi2-registryd main process ended, respawning init: at-spi2-registryd main process ended, respawning init: at-spi2-registryd main process ended, respawning init: at-spi2-registryd main process ended, respawning init: at-spi2-registryd main process ended, respawning init: at-spi2-registryd main process ended, respawning init: at-spi2-registryd respawning too fast, stopped init: logrotate main process (4726) killed by TERM signal init: upstart-dbus-session-bridge main process (4865) terminated with status 1 init: gnome-settings-daemon main process (4843) terminated with status 1 init: gnome-session main process (4852) terminated with status 1 init: unity-panel-service main process (4863) killed by KILL signal I found some advice in a forum to look for at-spi2-registryd in my system logs. Perhaps it will be useful. executing this: sudo grep -r at-spi2-registryd /var/log/* produces this: /var/log/lightdm/x-1-greeter.log:** (at-spi2-registryd:4384): WARNING **: Failed to register client: GDBus.Error:org.freedesktop.DBus.Error.ServiceUnknown: The name org.gnome.SessionManager was not provided by any .service files /var/log/lightdm/x-1-greeter.log:** (at-spi2-registryd:4384): WARNING **: Unable to register client with session manager /var/log/lightdm/x-2-greeter.log.old:** (at-spi2-registryd:7447): WARNING **: Failed to register client: GDBus.Error:org.freedesktop.DBus.Error.ServiceUnknown: The name org.gnome.SessionManager was not provided by any .service files /var/log/lightdm/x-2-greeter.log.old:** (at-spi2-registryd:7447): WARNING **: Unable to register client with session manager /var/log/lightdm/x-0-greeter.log:** (at-spi2-registryd:1378): WARNING **: Failed to register client: GDBus.Error:org.freedesktop.DBus.Error.ServiceUnknown: The name org.gnome.SessionManager was not provided by any .service files /var/log/lightdm/x-0-greeter.log:** (at-spi2-registryd:1378): WARNING **: Unable to register client with session manager /var/log/lightdm/x-0-greeter.log.old:** (at-spi2-registryd:1357): WARNING **: Failed to register client: GDBus.Error:org.freedesktop.DBus.Error.ServiceUnknown: The name org.gnome.SessionManager was not provided by any .service files /var/log/lightdm/x-0-greeter.log.old:** (at-spi2-registryd:1357): WARNING **: Unable to register client with session manager Any ideas what is going on?

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  • Metaobject protocol:Why is it known as an important concept

    - by sushant
    Metaobject protocol is protocol for metaobjects in a programming languages. Although I understand it on simple terms, I want to know the reason and a summary of real world usage patterns of this protocol. So, why exactly is metaobject and more importantly metaobject protocol is such a good idea. I want to know the problem which led to its evolution and also, its high power usage. Opinions as well as general overview/description/alternate explanations are also welcome.

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  • Why aren't more desktop apps written with Qt?

    - by Dehumanizer
    As far as I know and have understood in my experience with Qt, it's a very good and easy to learn library. It has a very well designed API and is cross-platform, and these are just two of the many features that make it attractive. I'm interested to know why more programmers don't use Qt. Is there a deficiency which speaks against it? Which feature makes other libraries better than Qt? Is the issue related to licensing?

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  • Why Hekaton In-Memory OLTP Truly is Revolutionary

    - by merrillaldrich
    I just returned from the PASS Summit in Charlotte, NC – which was excellent, among the best I have attended – and I have had Dr. David DeWitt’s talk rolling around in my head since he gave it on Thursday. (Dr. DeWitt starts at 27:00 at that link.) I probably cannot do it justice, but I wanted to recap why Hekaton really is revolutionary, and not just a marketing buzzword. I am normally skeptical of product announcements, and I find too often that real technical innovation can be overwhelmed by the...(read more)

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  • Why no icons for pcmanfm when run from remote x server

    - by user75430
    pcmanfm works fine when run from a local console, but does not show file icons when run from a remote x session (ssh -X user@machine). Well, that's not quite true - icons for shell scripts show up OK, there are no icons for regular files and folders. There are a load of errors in the X console window "g_object_unref ... G_IS_OBJECT". Why are there no icons for pcmanfm when I run it from a remote x server?

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  • Why You Need Help Building a Website

    Did you ever wonder that you needed help building a website? I guess not. You are probably taking your way easily into website building. But here's a thing, it's not as easy as you think. There are several factors entering into the scene when you start building a website.

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  • Why Use SEO on Your Website?

    SEO can be a time consuming, difficult and frustrating experience. Many webmasters abandon the process altogether, but there are many good reasons why you should pursue SEO for your internet website. A large amount of consumers use the internet first when attempting to find local businesses.

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