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• Organizations &amp; Architecture UNISA Studies &ndash; Chap 7

  - by MarkPearl

  Learning Outcomes Name different device categories Discuss the functions and structure of I/.O modules Describe the principles of Programmed I/O Describe the principles of Interrupt-driven I/O Describe the principles of DMA Discuss the evolution characteristic of I/O channels Describe different types of I/O interface Explain the principles of point-to-point and multipoint configurations Discuss the way in which a FireWire serial bus functions Discuss the principles of InfiniBand architecture External Devices An external device attaches to the computer by a link to an I/O module. The link is used to exchange control, status, and data between the I/O module and the external device. External devices can be classified into 3 categories… Human readable – e.g. video display Machine readable – e.g. magnetic disk Communications – e.g. wifi card I/O Modules An I/O module has two major functions… Interface to the processor and memory via the system bus or central switch Interface to one or more peripheral devices by tailored data links Module Functions The major functions or requirements for an I/O module fall into the following categories… Control and timing Processor communication Device communication Data buffering Error detection I/O function includes a control and timing requirement, to coordinate the flow of traffic between internal resources and external devices. Processor communication involves the following… Command decoding Data Status reporting Address recognition The I/O device must be able to perform device communication. This communication involves commands, status information, and data. An essential task of an I/O module is data buffering due to the relative slow speeds of most external devices. An I/O module is often responsible for error detection and for subsequently reporting errors to the processor. I/O Module Structure An I/O module functions to allow the processor to view a wide range of devices in a simple minded way. The I/O module may hide the details of timing, formats, and the electro mechanics of an external device so that the processor can function in terms of simple reads and write commands. An I/O channel/processor is an I/O module that takes on most of the detailed processing burden, presenting a high-level interface to the processor. There are 3 techniques are possible for I/O operations Programmed I/O Interrupt[t I/O DMA Access Programmed I/O When a processor is executing a program and encounters an instruction relating to I/O it executes that instruction by issuing a command to the appropriate I/O module. With programmed I/O, the I/O module will perform the requested action and then set the appropriate bits in the I/O status register. The I/O module takes no further actions to alert the processor. I/O Commands To execute an I/O related instruction, the processor issues an address, specifying the particular I/O module and external device, and an I/O command. There are four types of I/O commands that an I/O module may receive when it is addressed by a processor… Control – used to activate a peripheral and tell it what to do Test – Used to test various status conditions associated with an I/O module and its peripherals Read – Causes the I/O module to obtain an item of data from the peripheral and place it in an internal buffer Write – Causes the I/O module to take an item of data form the data bus and subsequently transmit that data item to the peripheral The main disadvantage of this technique is it is a time consuming process that keeps the processor busy needlessly I/O Instructions With programmed I/O there is a close correspondence between the I/O related instructions that the processor fetches from memory and the I/O commands that the processor issues to an I/O module to execute the instructions. Typically there will be many I/O devices connected through I/O modules to the system – each device is given a unique identifier or address – when the processor issues an I/O command, the command contains the address of the address of the desired device, thus each I/O module must interpret the address lines to determine if the command is for itself. When the processor, main memory and I/O share a common bus, two modes of addressing are possible… Memory mapped I/O Isolated I/O (for a detailed explanation read page 245 of book) The advantage of memory mapped I/O over isolated I/O is that it has a large repertoire of instructions that can be used, allowing more efficient programming. The disadvantage of memory mapped I/O over isolated I/O is that valuable memory address space is sued up. Interrupts driven I/O Interrupt driven I/O works as follows… The processor issues an I/O command to a module and then goes on to do some other useful work The I/O module will then interrupts the processor to request service when is is ready to exchange data with the processor The processor then executes the data transfer and then resumes its former processing Interrupt Processing The occurrence of an interrupt triggers a number of events, both in the processor hardware and in software. When an I/O device completes an I/O operations the following sequence of hardware events occurs… The device issues an interrupt signal to the processor The processor finishes execution of the current instruction before responding to the interrupt The processor tests for an interrupt – determines that there is one – and sends an acknowledgement signal to the device that issues the interrupt. The acknowledgement allows the device to remove its interrupt signal The processor now needs to prepare to transfer control to the interrupt routine. To begin, it needs to save information needed to resume the current program at the point of interrupt. The minimum information required is the status of the processor and the location of the next instruction to be executed. The processor now loads the program counter with the entry location of the interrupt-handling program that will respond to this interrupt. It also saves the values of the process registers because the Interrupt operation may modify these The interrupt handler processes the interrupt – this includes examination of status information relating to the I/O operation or other event that caused an interrupt When interrupt processing is complete, the saved register values are retrieved from the stack and restored to the registers Finally, the PSW and program counter values from the stack are restored. Design Issues Two design issues arise in implementing interrupt I/O Because there will be multiple I/O modules, how does the processor determine which device issued the interrupt? If multiple interrupts have occurred, how does the processor decide which one to process? Addressing device recognition, 4 general categories of techniques are in common use… Multiple interrupt lines Software poll Daisy chain Bus arbitration For a detailed explanation of these approaches read page 250 of the textbook. Interrupt driven I/O while more efficient than simple programmed I/O still requires the active intervention of the processor to transfer data between memory and an I/O module, and any data transfer must traverse a path through the processor. Thus is suffers from two inherent drawbacks… The I/O transfer rate is limited by the speed with which the processor can test and service a device The processor is tied up in managing an I/O transfer; a number of instructions must be executed for each I/O transfer Direct Memory Access When large volumes of data are to be moved, an efficient technique is direct memory access (DMA) DMA Function DMA involves an additional module on the system bus. The DMA module is capable of mimicking the processor and taking over control of the system from the processor. It needs to do this to transfer data to and from memory over the system bus. DMA must the bus only when the processor does not need it, or it must force the processor to suspend operation temporarily (most common – referred to as cycle stealing). When the processor wishes to read or write a block of data, it issues a command to the DMA module by sending to the DMA module the following information… Whether a read or write is requested using the read or write control line between the processor and the DMA module The address of the I/O device involved, communicated on the data lines The starting location in memory to read from or write to, communicated on the data lines and stored by the DMA module in its address register The number of words to be read or written, communicated via the data lines and stored in the data count register The processor then continues with other work, it delegates the I/O operation to the DMA module which transfers the entire block of data, one word at a time, directly to or from memory without going through the processor. When the transfer is complete, the DMA module sends an interrupt signal to the processor, this the processor is involved only at the beginning and end of the transfer. I/O Channels and Processors Characteristics of I/O Channels As one proceeds along the evolutionary path, more and more of the I/O function is performed without CPU involvement. The I/O channel represents an extension of the DMA concept. An I/O channel ahs the ability to execute I/O instructions, which gives it complete control over I/O operations. In a computer system with such devices, the CPU does not execute I/O instructions – such instructions are stored in main memory to be executed by a special purpose processor in the I/O channel itself. Two types of I/O channels are common A selector channel controls multiple high-speed devices. A multiplexor channel can handle I/O with multiple characters as fast as possible to multiple devices. The external interface: FireWire and InfiniBand Types of Interfaces One major characteristic of the interface is whether it is serial or parallel parallel interface – there are multiple lines connecting the I/O module and the peripheral, and multiple bits are transferred simultaneously serial interface – there is only one line used to transmit data, and bits must be transmitted one at a time With new generation serial interfaces, parallel interfaces are becoming less common. In either case, the I/O module must engage in a dialogue with the peripheral. In general terms the dialog may look as follows… The I/O module sends a control signal requesting permission to send data The peripheral acknowledges the request The I/O module transfers data The peripheral acknowledges receipt of data For a detailed explanation of FireWire and InfiniBand technology read page 264 – 270 of the textbook

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• How to change the Target URL of EditForm.aspx, DispForm.aspx and NewForm.aspx

  - by Jayant Sharma

  Hi All, To changing the URL of ListForms we have very limited options. On Inernet if you search you will lots of article about Customization of List Forms using SharePoint Desinger, but the disadvantage of SharePoint Desinger is, you cannot create wsp of the customization means what ever changes you have done in UAT environment you need to repeat the same at Production. This is the main reason I donot like SharePoint Desinger more. I always prefer to create WSP file and Deployment of WSP file will do all of my work. Now, If you want to change the ListForm URL using Visual Studio, either you have create new List Defintion or Create New Content Type. I found some very good article and want to share.. http://www.codeproject.com/Articles/223431/Custom-SharePoint-List-Forms http://community.bamboosolutions.com/blogs/sharepoint-2010/archive/2011/05/12/sharepoint-2010-cookbook-how-to-create-a-customized-list-edit-form-for-development-in-visual-studio-2010.aspx Whenever you create, either List Defintion or Content type and specify the URL for List Forms it will automatically add ListID and ItemID (No ItemID in case of NewForm.aspx) in the URL as Querystring, so if you want to redirect it or do some logic you can, as you got the ItemID as well as ListID.

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• Why a static main method in Java and C#, rather than a constructor?

  - by Konrad Rudolph

  Why did (notably) Java and C# decide to have a static method as their entry point – rather than representing an application instance by an instance of an Application class, with the entry point being an appropriate constructor which, at least to me, seems more natural? I’m interested in a definitive answer from a primary or secondary source, not mere speculations. This has been asked before. Unfortunately, the existing answers are merely begging the question. In particular, the following answers don’t satisfy me, as I deem them incorrect: There would be ambiguity if the constructor were overloaded. – In fact, C# (as well as C and C++) allows different signatures for Main so the same potential ambiguity exists, and is dealt with. A static method means no objects can be instantiated before so order of initialisation is clear. – This is just factually wrong, some objects are instantiated before (e.g. in a static constructor). So they can be invoked by the runtime without having to instantiate a parent object. – This is no answer at all. Just to justify further why I think this is a valid and interesting question: Many frameworks do use classes to represent applications, and constructors as entry points. For instance, the VB.NET application framework uses a dedicated main dialog (and its constructor) as the entry point1. Neither Java nor C# technically need a main method. Well, C# needs one to compile, but Java not even that. And in neither case is it needed for execution. So this doesn’t appear to be a technical restriction. And, as I mentioned in the first paragraph, for a mere convention it seems oddly unfitting with the general design principle of Java and C#. To be clear, there isn’t a specific disadvantage to having a static main method, it’s just distinctly odd, which made me wonder if there was some technical rationale behind it. I’m interested in a definitive answer from a primary or secondary source, not mere speculations. 1 Although there is a callback (Startup) which may intercept this.

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• Prevent Eclipse Java Builder from Compiling Java-Like Source

  - by redjamjar

  I'm in the process of writing an eclipse plugin for my programming language Whiley (see http://whiley.org). The plugin is working reasonably well, although there's lots to do. Two pieces of the jigsaw are: I've created a "Whiley Builder" by subclassing incremental project builder. This handles building and cleaning of "*.whiley" files. I've created a content-type called "Whiley Source Files" for "*.whiley" files, which extends "org.eclipse.jdt.core.javaSource" (this follows Andrew Eisenberg suggestion). The advantage of having the content-type extend javaSource is that it immediately fits into the package explorer, etc. In principle, I could fleshout ICompilationUnit to provide more useful info, although I haven't done that yet. The disadvantage is that the Java builder is trying to compile my whiley files ... and it obviously can't. Originally, I had the Java Builder run first, then the Whiley builder. Superficially, this actually worked out quite well since all of the errors from the Java Builder were discarded by the Whiley Builder (for whiley files). However, I actually want the Whiley Builder to run first, as this is the best way for me to resolve dependencies between Java and Whiley files. Which leads me to my question: can I stop the Java builder from trying to compile certain java-like resources? Specifically, in my case, those with the "*.whiley" extension. As an alternative, I was wondering whether my Whiley Builder could somehow update the resource delta to remove those files which it has dealt with. Thoughts?

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• Syntactic sugar in PHP with static functions

  - by Anna

  The dilemma I'm facing is: should I use static classes for the components of an application just to get nicer looking API? Example - the "normal" way: // example component class Cache{ abstract function get($k); abstract function set($k, $v); } class APCCache extends Cache{ ... } class application{ function __construct() $this->cache = new APCCache(); } function whatever(){ $this->cache->add('blabla'); print $this->cache->get('blablabla'); } } Notice how ugly is this->cache->.... But it gets waay uglier when you try to make the application extensible trough plugins, because then you have to pass the application instance to its plugins, and you get $this->application->cache->... With static functions: interface CacheAdapter{ abstract function get($k); abstract function set($k, $v); } class Cache{ public static $ad; public function setAdapter(CacheAdapter $a){ static::$ad = $ad; } public static function get($k){ return static::$ad->get($k); } ... } class APCCache implements CacheAdapter{ ... } class application{ function __construct(){ cache::setAdapter(new APCCache); } function whatever() cache::add('blabla', 5); print cache::get('blabla'); } } Here it looks nicer because you just call cache::get() everywhere. The disadvantage is that I loose the possibility to extend this class easily. But I've added a setAdapter method to make the class extensible to some point. I'm relying on the fact that I won't need to rewrite to replace the cache wrapper, ever, and that I won't need to run multiple application instances simultaneously (it's basically a site - and nobody works with two sites at the same time) So, am doing it wrong?

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• Ways to organize interface and implementation in C++

  - by Felix Dombek

  I've seen that there are several different paradigms in C++ concerning what goes into the header file and what to the cpp file. AFAIK, most people, especially those from a C background, do: foo.h class foo { private: int mem; int bar(); public: foo(); foo(const foo&); foo& operator=(foo); ~foo(); } foo.cpp #include foo.h foo::bar() { return mem; } foo::foo() { mem = 42; } foo::foo(const foo& f) { mem = f.mem; } foo::operator=(foo f) { mem = f.mem; } foo::~foo() {} int main(int argc, char *argv[]) { foo f; } However, my lecturers usually teach C++ to beginners like this: foo.h class foo { private: int mem; int bar() { return mem; } public: foo() { mem = 42; } foo(const foo& f) { mem = f.mem; } foo& operator=(foo f) { mem = f.mem; } ~foo() {} } foo.cpp #include foo.h int main(int argc, char* argv[]) { foo f; } // other global helper functions, DLL exports, and whatnot Originally coming from Java, I have also always stuck to this second way for several reasons, such as that I only have to change something in one place if the interface or method names change, and that I like the different indentation of things in classes when I look at their implementation, and that I find names more readable as foo compared to foo::foo. I want to collect pro's and con's for either way. Maybe there are even still other ways? One disadvantage of my way is of course the need for occasional forward declarations.

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• How to indicate reliability when reporting availability of competencies

  - by Jan Doggen

  We have employees with competencies: Pete Welder Carpenter Melissa Carpenter Assume they both work 40 hours/week, and have not yet been assigned work. We need to report the availability of these competencies, expressed in hours. As far as I can see now, we can report this in two ways: Method A. When someone has multiple competencies, count them both. Welder 40 hours Carpenter 80 hours Method B. When someone has multiple competencies, count an equal division of hours for each Welder 20 hours Carpenter 60 hours Method A has our preference: - A good planner will know to plan the least available competency first. If 30 hours of welding is planned, we will be left with 10 welder, 50 carpenter. - Method B has the disadvantage that the planner thinks he cannot plan the job when 30 hours of welding is required. However, if we report this we would like to give an estimate of the reliability of the numbers for each competency, i.e. how much are these over-reported? In my example A, would I say that carpenter is 100% over-reported, or 50%, or maybe another number? How would I calculate this for large numbers of competencies? I'm sure we are not the first ones dealing with this, is there a 'usual' way of doing this in planning? Additionally: - Would there be an even better method than A or B? - Optionally, we also have an preference order of competencies (like: use him/her in this order), Pete could be 1. welder 2. carpenter. Does this introduce new options?

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• Can anyone recommend an AI sandbox?

  - by user19433

  I'm passionate person, who has been around AI from a long time [1] but never going in deep enough. Now it's time! I've been really looking for some way to concentrate on AI coding but couldn't succeeded to find an AI environment I can focus on. I just want to use an AI sandbox environment which would let me have tools like: visibility information character controller able to easily define a level, with obstacles of course physics collider management triggers management don't need to be a shiny, eye candy graphical render : this is about pathfinding, tactical reasoning, etc.. I have tried : Unreal Dev Kit : while the new release announce is about C++ coding, this is about external tools and will be released in 2013 Cry Engine : really interesting as AI is presents here but coding with it appears to be an hell: did I got it wrong ? Half Life source, C4, Torque, Dx Studio : either quite old, not very useful or costly these imply to dig in documentation (when provided) to code everything, graphics included. Unity 3D : the most promising platform. While you also need to create your own environment, there are lot of examples. The disadvantage is, in addition to spend time to have this env. working, is the languages choice : C#, Javascript or Boo. C# is not that hard, but this implies you'll allways have to convert papers (I love those from Lars Linden) books codes, or anything you can have in Aigamedev are most often in C++. This is extra work. I've look at "Simple Path", the very good Arong Greenberg work but no source provided and AngryAnt work. AI Sandbox : this seems to be exactly what as AI coder I want to use. I saw some preview but from 2009 we still don't know what it will be about precisely, will it be opensource or free (I strongly doubt), will I be able to buy it? will it really provide me tools I need to focus on AI ? That being said, what is the best environment to be able to focus on AI coding only, is it even possible?

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• For a Javascript library, what is the best or standard way to support extensibility

  - by Michael Best

  Specifically, I want to support "plugins" that modify the behavior of parts of the library. I couldn't find much information on the web about this subject. But here are my ideas for how a library could be extensible. The library exports an object with both public and "protected" functions. A plugin can replace any of those functions, thus modifying the library's behavior. Advantages of this method are that it's simple and that the plugin's functions can have full access to the library's "protected" functions. Disadvantages are that the library may be harder to maintain with a larger set of exposed functions and it could be hard to debug if multiple plugins are involved (how to know which plugin modified which function?). The library provides an "add plugin" function that accepts an object with a specific interface. Internally, the library will use the plugin instead of it's own code if appropriate. With this method, the internals of the library can be rearranged more freely as long as it still supports the same plugin interface. This could also support having different plugin interfaces to modify different parts of the library. A disadvantage of this method is that the plugins may have to re-implement code that is already part of the library since the library's internal functions are not exported. The library provides a "set implementation" function that accepts an object inherited from a specific base object. The library's public API calls functions in the implementation object for any functionality that can be modified and the base implementation object includes the core functionality, with both external (to the API) and internal functions. A plugin creates a new implementation object, which inherits from the base object and replaces any functions it wants to modify. This combines advantages and disadvantages of both the other methods.

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• Ways to organize interface and implementation in C++

  - by Felix Dombek

  I've seen that there are several different paradigms in C++ concerning what goes into the header file and what to the cpp file. AFAIK, most people, especially those from a C background, do: foo.h class foo { private: int mem; int bar(); public: foo(); foo(const foo&); foo& operator=(foo); ~foo(); } foo.cpp #include foo.h foo::bar() { return mem; } foo::foo() { mem = 42; } foo::foo(const foo& f) { mem = f.mem; } foo::operator=(foo f) { mem = f.mem; } foo::~foo() {} int main(int argc, char *argv[]) { foo f; } However, my lecturers usually teach C++ to beginners like this: foo.h class foo { private: int mem; int bar() { return mem; } public: foo() { mem = 42; } foo(const foo& f) { mem = f.mem; } foo& operator=(foo f) { mem = f.mem; } ~foo() {} } foo.cpp #include foo.h int main(int argc, char* argv[]) { foo f; } // other global helper functions, DLL exports, and whatnot Originally coming from Java, I have also always stuck to this second way for several reasons, such as that I only have to change something in one place if the interface or method names change, that I like the different indentation of things in classes when I look at their implementation, and that I find names more readable as foo compared to foo::foo. I want to collect pro's and con's for either way. Maybe there are even still other ways? One disadvantage of my way is of course the need for occasional forward declarations.

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• Optimal sprite size for rotations

  - by Panda Pajama

  I am making a sprite based game, and I have a bunch of images that I get in a ridiculously large resolution and I scale them to the desired sprite size (for example 64x64 pixels) before converting them to a game resource, so when draw my sprite inside the game, I don't have to scale it. However, if I rotate this small sprite inside the game (engine agnostically), some destination pixels will get interpolated, and the sprite will look smudged. This is of course dependent on the rotation angle as well as the interpolation algorithm, but regardless, there is not enough data to correctly sample a specific destination pixel. So there are two solutions I can think of. The first is to use the original huge image, rotate it to the desired angles, and then downscale all the reaulting variations, and put them in an atlas, which has the advantage of being quite simple to implement, but naively consumes twice as much sprite space for each rotation (each rotation must be inscribed in a circle whose diameter is the diagonal of the original sprite's rectangle, whose area is twice of that original rectangle, supposing square sprites). It also has the disadvantage of only having a predefined set of rotations available, which may be okay or not depending on the game. So the other choice would be to store a larger image, and rotate and downscale while rendering, which leads to my question. What is the optimal size for this sprite? Optimal meaning that a larger image will have no effect in the resulting image. This is definitely dependent on the image size, the amount of desired rotations without data loss down to 1/256, which is the minimum representable color difference. I am looking for a theoretical general answer to this problem, because trying a bunch of sizes may be okay, but is far from optimal.

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• which style of member-access is preferable

  - by itwasntpete

  the purpose of oop using classes is to encapsulate members from the outer space. i always read that accessing members should be done by methods. for example: template<typename T> class foo_1 { T state_; public: // following below }; the most common doing that by my professor was to have a get and set method. // variant 1 T const& getState() { return state_; } void setState(T const& v) { state_ = v; } or like this: // variant 2 // in my opinion it is easier to read T const& state() { return state_; } void state(T const& v) { state_ = v; } assume the state_ is a variable, which is checked periodically and there is no need to ensure the value (state) is consistent. Is there any disadvantage of accessing the state by reference? for example: // variant 3 // do it by reference T& state() { return state_; } or even directly, if I declare the variable as public. template<typename T> class foo { public: // variant 4 T state; }; In variant 4 I could even ensure consistence by using c++11 atomic. So my question is, which one should I prefer?, Is there any coding standard which would decline one of these pattern? for some code see here

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• Session Tracking - Advantages and Disadvantages

  I use to work for a major internet company that sold Dental Plans to customers through their large customer-driven websiteto consumers. They start tracking their users as soon as they hit their web servers, and then they log everything they can about the user. There are a lot of benefits for using session tracking for both the user and the website. Users can benefit from session tracking due to the fact that a website can retain pertaining information for the user so that they do not have to re-enter the same information repeatedly. In addition, websites can hold specific items in a cart for each user so that they can pay for all of their  items at once when they are ready to complete their purchases. Websites can also benefit from session tracking because they can determine where a specific user came from and which advertising partner gave them a sale. This information is very useful when deciding on where to spend an advertising budget. There is only one real disadvantage when it comes to session tracking, Users can not really control what is actually tracked by a website. Yes, they can disable cookies and this will help, but that means that no tracking can be done at all. Most sites require users to have cookies enabled in order for users to make purchases or login to their accounts.  

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• How to deal with OpenGL and Fullscreen on OS X

  - by Armin Ronacher

  I do most of my development on OS X and for my current game project this is my target environment. However when I play games I play on Windows. As a windows gamer I am used to Alt+Tab switching from within the game to the last application that was open. On OS X I currently can't find either a game that supports that nor can I find a way to make it possible. My current project is based on SDL 1.3 and I can see that cmd+tab is a sequence that is sent directly to my application and not intercepted by the operating system. Now my first attempt was to hide the rendering window on cmd+tab which certainly works, but has the disadvantage that a hidden OpenGL window in SDL cannot be restored when the user tabs back to the application. First of all, there is no event fired for that or I can't find it, secondly the core problem is that when that application window is hidden, my game is still the active application, just that the window disappeared. That is incredible annoying. Any ideas how to approximate the windows / linux behavior for alt+tab?

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• For an ORM supporting data validation, should constraints be enforced in the database as well?

  - by Ramnique Singh

  I have always applied constraints at the database level in addition to my (ActiveRecord) models. But I've been wondering if this is really required? A little background I recently had to unit test a basic automated timestamp generation method for a model. Normally, the test would create an instance of the model and save it without validation. But there are other required fields that aren't nullable at the in the table definition, meaning I cant save the instance even if I skip the ActiveRecord validation. So I'm thinking if I should remove such constraints from the db itself, and let the ORM handle them? Possible advantages if I skip constraints in db, imo - Can modify a validation rule in the model, without having to migrate the database. Can skip validation in testing. Possible disadvantage? If its possible that ORM validation fails or is bypassed, howsoever, the database does not check for constraints. What do you think? EDIT In this case, I'm using the Yii Framework, which generates the model from the database, hence database rules are generated also (though I could always write them post-generation myself too).

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• Does it make sense to write tests for legacy code when there is no time for a complete refactoring?

  - by is4

  I usually try to follow the advice of the book Working Effectively with Legacy Code. I break dependencies, move parts of the code to @VisibleForTesting public static methods and to new classes to make the code (or at least some part of it) testable. And I write tests to make sure that I don't break anything when I'm modifying or adding new functions. A colleague says that I shouldn't do this. His reasoning: The original code might not work properly in the first place. And writing tests for it makes future fixes and modifications harder since devs have to understand and modify the tests too. If it's GUI code with some logic (~12 lines, 2-3 if/else block, for example), a test isn't worth the trouble since the code is too trivial to begin with. Similar bad patterns could exist in other parts of the codebase, too (which I haven't seen yet, I'm rather new); it will be easier to clean them all up in one big refactoring. Extracting out logic could undermine this future possibility. Should I avoid extracting out testable parts and writing tests if we don't have time for complete refactoring? Is there any disadvantage to this that I should consider?

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• Client/Server game even in solo: any big problem?

  - by Klaim

  I'm making a game which have strong basic design based on multiplayer but also should provide a really interesting and self-sufficient solo game. A bit like a real-time strategy game. The events and actions taken shouldn't be as massive and immediate as in a FPS, so you can also think the networking like for an RTS. It's a PC game, targetting Windows, MacOSX and Linux (Ubuntu & Fedora). It's programmed in C++, using a variety of open source libraries, so I have great (potential) control over the performances. So far I always considered that just making the game work with two applications, client & server, even in solo mode was ok. However, as I'm in the process of starting the network code I'm having doubts about if it's a good idea. I'm not a specialist so I might be missing something in my analysis. I see these pros and cons: Pros: The game works only one way so if I fix a bug it should apply on all game modes, whatever the distance with the server is; Basic networking issues would be detected early, including behaviour with the protection softwares (firewall) installed (i am not specialist so this might be wrong); Cons: I suppose that even if it should be really fast enough, networking client and server on the same computer would still be slower than no networking and message passing in (one) process memory. Maybe debugging would be more difficult? I don't have experience in this case but so far I assume that debugging with Visual Studio allows me to debug multiple process so it shouldn't be really different. Also, remote debugging. My question is: is there a big disadvantage that I missed? Or maybe there are advantages that I missed and that should encourage me to just continue with only client-server game sessions?

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• Users can benefit from Session Tracking

  I use to work for a large Dental Plan marketing website a few years ago and they had a large customer-driven website that sold Dental Plans to consumers. Their website started tracking users as soon as they hit their web servers, and then they logged everything they could about the user. There are a lot of benefits for using session tracking for both the user and the website. Users can benefit from session tracking due to the fact that a website can retain pertaining information for the user so that they do not have to re-enter the same information repeatedly. In addition, websites can hold specific items in a cart for each user so that they can pay for all of their  items at once when they are ready to complete their purchases. Websites can also benefit from session tracking because they can determine where a specific user came from and which advertising partner gave them a sale. This information is very useful when deciding on where to spend an advertising budget. There is only one real disadvantage when it comes to session tracking, Users can not really control what is actually tracked by a website. Yes, they can disable cookies and this will help, but that means that no tracking can be done at all. Most sites require users to have cookies enabled in order for users to make purchases or login to their accounts.

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• @staticmethod vs module-level function

  - by darkfeline

  This is not about @staticmethod and @classmethod! I know how staticmethod works. What I want to know is the proper use cases for @staticmethod vs. a module-level function. I've googled this question, and it seems there's some general agreement that module-level functions are preferred over static methods because it's more pythonic. Static methods have the advantage of being bound to its class, which may make sense if only that class uses it. However, in Python functionality is usually organized by module not class, so usually making it a module function makes sense too. Static methods can also be overridden by subclasses, which is an advantage or disadvantage depending on how you look at it. Although, static methods are usually "functionally pure" so overriding it may not be smart, but it may be convenient sometimes (though this may be one of those "convenient, but NEVER DO IT" kind of things only experience can teach you). Are there any general rule-of-thumbs for using either staticmethod or module-level functions? What concrete advantages or disadvantages do they have (e.g. future extension, external extension, readability)? If possible, also provide a case example.

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• multi-thread in mmorpg server

  - by jean

  For MMORPG, there is a tick function to update every object's state in a map. The function was triggered by a timer in fixed interval. So each map's update can be dispatch to different thread. At other side, server handle player incoming package have its own threads also: I/O threads. Generally, the handler of the corresponding incoming package run in I/O threads. So there is a problem: thread synchronization. I have consider two methods: Synchronize with mutex. I/O thread lock a mutex before execute handler function and map thread lock same mutex before it execute map's update. Execute all handler functions in map's thread, I/O thread only queue the incoming handler and let map thread to pop the queue then call handler function. These two have a disadvantage: delay. For method 1, if the map's tick function is running, then all clients' request need to waiting the lock release. For method 2, if map's tick function is running, all clients' request need to waiting for next tick to be handle. Of course, there is another method: add lock to functions that use data which will be accessed both in I/O thread & map thread. But this is hard to maintain and easy to goes incorrect. It needs carefully check all variables whether or not accessed by both two kinds thread. My problem is: is there better way to do this? Notice that I said map is logic concept means no interactions can happen between two map except transport. I/O thread means thread in 3rd part network lib which used to handle client request.

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• How to set up a personal Apple developer account now with an eye on transferring app ownership to a company later?

  - by Rinzwind

  I have two Mac applications that I wrote for my own personal use, but I'm considering polishing them up and giving selling them on the Mac App Store a try. It seemed very premature to consider what would happen if either app would become successful enough to make it possible to set up a business around it, or to sell it to another developer. That is, until I read that Apple doesn't make it easy to transfer app ownership. I'm not sure how to best register with the Apple Developer program now to avoid any possible hassle in this respect later. From what I understand, one can really only transfer ownership of a developer account. I'm not sure about the relationship between an Apple ID and an Apple developer account. Does this mean I should at least not use the Apple ID I'm already using for iTunes, but create a second one to use for registering as an Apple Developer? Is there any disadvantage to using separate Apple IDs like this on the same Mac (one ID for Xcode development, the other ID for iTunes/iCloud/App Store/...)? Should one go as far as having a separate Apple ID & Apple developer account per app one develops? Or is there some other solution to take into account the possibility of transferring app ownership?

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• Serve up syntactic XHTML5 using the text/html MIME type?

  - by cboettig

  I have a site currently written with HTML5 tags. I'd like to be able to parse the site as XML, with support for namespaces, etc, to facilitate programmatic extraction of data. Currently I have <!DOCTYPE html> and <meta charset="utf-8"> Which I gather is equivalent in HTML5 to explicitly setting the content-types as <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> for my current setup. In order to serve XML it sounds like the right thing to do is <?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"> Should I also change my Content-Type to <meta http-equiv="content-type" content="application/xhtml+xml; charset=iso-8859-1" /> Or is that not necessary? What is the advantage of having content-type be "application/xhtml+xml"? What is the disadvantage? (Sounds like it may break internet explorer rendering of the site? but maybe that information is out of date now?) Many thanks!

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• Log message Request and Response in ASP.NET WebAPI

  - by Fredrik N

  By logging both incoming and outgoing messages for services can be useful in many scenarios, such as debugging, tracing, inspection and helping customers with request problems etc.  I have a customer that need to have both incoming and outgoing messages to be logged. They use the information to see strange behaviors and also to help customers when they call in  for help (They can by looking in the log see if the customers sends in data in a wrong or strange way).   Concerns Most loggings in applications are cross-cutting concerns and should not be  a core concern for developers. Logging messages like this:   // GET api/values/5 public string Get(int id) { //Cross-cutting concerns Log(string.Format("Request: GET api/values/{0}", id)); //Core-concern var response = DoSomething(); //Cross-cutting concerns Log(string.Format("Reponse: GET api/values/{0}\r\n{1}", id, response)); return response; } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; } will only result in duplication of code, and unnecessarily concerns for the developers to be aware of, if they miss adding the logging code, no logging will take place. Developers should focus on the core-concern, not the cross-cutting concerns. By just focus on the core-concern the above code will look like this: // GET api/values/5 public string Get(int id) { return DoSomething(); } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; } The logging should then be placed somewhere else so the developers doesn’t need to focus care about the cross-concern. Using Message Handler for logging There are different ways we could place the cross-cutting concern of logging message when using WebAPI. We can for example create a custom ApiController and override the ApiController’s ExecutingAsync method, or add a ActionFilter, or use a Message Handler. The disadvantage with custom ApiController is that we need to make sure we inherit from it, the disadvantage of ActionFilter, is that we need to add the filter to the controllers, both will modify our ApiControllers. By using a Message Handler we don’t need to do any changes to our ApiControllers. So the best suitable place to add our logging would be in a custom Message Handler. A Message Handler will be used before the HttpControllerDispatcher (The part in the WepAPI pipe-line that make sure the right controller is used and called etc). Note: You can read more about message handlers here, it will give you a good understanding of the WebApi pipe-line. To create a Message Handle we can inherit from the DelegatingHandler class and override the SendAsync method: public class MessageHandler : DelegatingHandler { protected override async Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken) { return base.SendAsync(request, cancellationToken); } } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; }   If we skip the call to the base.SendAsync our ApiController’s methods will never be invoked, nor other Message Handlers. Everything placed before base.SendAsync will be called before the HttpControllerDispatcher (before WebAPI will take a look at the request which controller and method it should be invoke), everything after the base.SendAsync, will be executed after our ApiController method has returned a response. So a message handle will be a perfect place to add cross-cutting concerns such as logging. To get the content of our response within a Message Handler we can use the request argument of the SendAsync method. The request argument is of type HttpRequestMessage and has a Content property (Content is of type HttpContent. The HttpContent has several method that can be used to read the incoming message, such as ReadAsStreamAsync, ReadAsByteArrayAsync and ReadAsStringAsync etc. Something to be aware of is what will happen when we read from the HttpContent. When we read from the HttpContent, we read from a stream, once we read from it, we can’t be read from it again. So if we read from the Stream before the base.SendAsync, the next coming Message Handlers and the HttpControllerDispatcher can’t read from the Stream because it’s already read, so our ApiControllers methods will never be invoked etc. The only way to make sure we can do repeatable reads from the HttpContent is to copy the content into a buffer, and then read from that buffer. This can be done by using the HttpContent’s LoadIntoBufferAsync method. If we make a call to the LoadIntoBufferAsync method before the base.SendAsync, the incoming stream will be read in to a byte array, and then other HttpContent read operations will read from that buffer if it’s exists instead directly form the stream. There is one method on the HttpContent that will internally make a call to the  LoadIntoBufferAsync for us, and that is the ReadAsByteArrayAsync. This is the method we will use to read from the incoming and outgoing message. public abstract class MessageHandler : DelegatingHandler { protected override async Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken) { var requestMessage = await request.Content.ReadAsByteArrayAsync(); var response = await base.SendAsync(request, cancellationToken); var responseMessage = await response.Content.ReadAsByteArrayAsync(); return response; } } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; } The above code will read the content of the incoming message and then call the SendAsync and after that read from the content of the response message. The following code will add more logic such as creating a correlation id to combine the request with the response, and create a log entry etc: public abstract class MessageHandler : DelegatingHandler { protected override async Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken) { var corrId = string.Format("{0}{1}", DateTime.Now.Ticks, Thread.CurrentThread.ManagedThreadId); var requestInfo = string.Format("{0} {1}", request.Method, request.RequestUri); var requestMessage = await request.Content.ReadAsByteArrayAsync(); await IncommingMessageAsync(corrId, requestInfo, requestMessage); var response = await base.SendAsync(request, cancellationToken); var responseMessage = await response.Content.ReadAsByteArrayAsync(); await OutgoingMessageAsync(corrId, requestInfo, responseMessage); return response; } protected abstract Task IncommingMessageAsync(string correlationId, string requestInfo, byte[] message); protected abstract Task OutgoingMessageAsync(string correlationId, string requestInfo, byte[] message); } public class MessageLoggingHandler : MessageHandler { protected override async Task IncommingMessageAsync(string correlationId, string requestInfo, byte[] message) { await Task.Run(() => Debug.WriteLine(string.Format("{0} - Request: {1}\r\n{2}", correlationId, requestInfo, Encoding.UTF8.GetString(message)))); } protected override async Task OutgoingMessageAsync(string correlationId, string requestInfo, byte[] message) { await Task.Run(() => Debug.WriteLine(string.Format("{0} - Response: {1}\r\n{2}", correlationId, requestInfo, Encoding.UTF8.GetString(message)))); } } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; }   The code above will show the following in the Visual Studio output window when the “api/values” service (One standard controller added by the default WepAPI template) is requested with a Get http method : 6347483479959544375 - Request: GET http://localhost:3208/api/values 6347483479959544375 - Response: GET http://localhost:3208/api/values ["value1","value2"] .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; }   Register a Message Handler To register a Message handler we can use the Add method of the GlobalConfiguration.Configration.MessageHandlers in for example Global.asax: public class WebApiApplication : System.Web.HttpApplication { protected void Application_Start() { GlobalConfiguration.Configuration.MessageHandlers.Add(new MessageLoggingHandler()); ... } } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; }   Summary By using a Message Handler we can easily remove cross-cutting concerns like logging from our controllers. You can also find the source code used in this blog post on ForkCan.com, feel free to make a fork or add comments, such as making the code better etc. Feel free to follow me on twitter @fredrikn if you want to know when I will write other blog posts etc.

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• Multiple skins in ASP.NET MVC using StringTemplate

  - by Jamie

  I am considering the StringTemplate view engine for my ASP.NET MVC application. This application will be built with one skin, but I then expect many more, often very similar skins to be developed for it. This is primiarly the reason for my choice of StringTemplate as the view engine, as there will be zero logic in the views. In my head, I envisaged having each skin in a directory under the 'Views' directory in the folder structure, then maintaining a data structure which maps hostnames to skin directories. An obvious disadvantage of this approach is that I will have to explicitly specify my view files - an alternative might be to hack the implementation of the View() method to change the /views/controller/action standard path and insert an extra layer. Is anyone aware of any examples of implementations along these lines using ASP.NET MVC and StringTemplate at present? Can anyone forsee any potential problems with my approach? Thanks in advance.

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• SSL Login in iFrame

  - by Karsten

  My UI prototype requires me to show the sites login info all the time. Either I should show the usual username and password textbox or "you are logged in as". The last bit don't have to be secure, as it's only info to the user, nothing I will use server side. But the first part should send secure to the server. It seems that I would have to use https for all pages on the site then. I would like to only use ssl for the things that are required to be secure. One way is putting the login information into a https://../login.aspx and show it on my mainpage as an IFrame. One disadvantage I can see is that the user won't know that https is being used, unless they read the IFrame src in the source code. What do you think?

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