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  • DPKG errors after upgrade to 12.10

    - by James Wulfe
    So I was doing fine then i upgraded my system to 12.10 and now i cant get my system to update all of its packages properly. no matter what i do, cleaning apt cache, manual install using dpkg, etc, i just cant get them to install. what is happening here and how do i fix this. if i would have thought 12.10 would be this much of a hassle i would have never upgraded..... here is a sampling of the code that returns from "apt-get -f install" Preparing to replace usb-modeswitch-data 20120120-0ubuntu1 (using .../usb-modeswitch-data_20120815-1_all.deb) ... /var/lib/dpkg/info/usb-modeswitch-data.prerm: 4: /var/lib/dpkg/info/usb-modeswitch-data.prerm: dpkg-maintscript-helper: Input/output error dpkg: warning: subprocess old pre-removal script returned error exit status 2 dpkg: trying script from the new package instead ... /var/lib/dpkg/tmp.ci/prerm: 4: /var/lib/dpkg/tmp.ci/prerm: dpkg-maintscript-helper: Input/output error dpkg: error processing /var/cache/apt/archives/usb-modeswitch-data_20120815-1_all.deb (--unpack): subprocess new pre-removal script returned error exit status 2 /var/lib/dpkg/info/usb-modeswitch-data.postinst: 7: /var/lib/dpkg/info/usb-modeswitch-data.postinst: dpkg-maintscript-helper: Input/output error dpkg: error while cleaning up: subprocess installed post-installation script returned error exit status 2 Errors were encountered while processing: /var/cache/apt/archives/network-manager_0.9.6.0-0ubuntu7_i386.deb /var/cache/apt/archives/pcmciautils_018-8_i386.deb /var/cache/apt/archives/unity-common_6.10.0-0ubuntu2_all.deb /var/cache/apt/archives/whoopsie_0.2.7_i386.deb /var/cache/apt/archives/usb-modeswitch_1.2.3+repack0-1ubuntu3_i386.deb /var/cache/apt/archives/usb-modeswitch-data_20120815-1_all.deb E: Sub-process /usr/bin/dpkg returned an error code (1) It is also just these 6 packages only. no other packages have given me this kind of trouble. well i should say as of now. It was just 5, but them i got an update for unity, and now unity-common is added to the trouble makers. which prevents me from further upgrading the actual unity package as this package is a dependancy.....

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  • Is it possible to power up ports on a USB hub from Ubuntu?

    - by James Henstridge
    I have a D-Link DUB-H7 powered USB 2.0 hub connected to my computer. Occasionally when I reboot the system, I've noticed that some of the ports on the hub get powered down: the green light next to the port is turned off, and the device attached to that port is not visible to lsusb or similar commands. Devices attached to the other ports on the hub function as normal. I am able to restore the ports by disconnecting power to the hub temporarily (from the computer, AC adapter and any devices that might provide any power such as my phone), but this is a bit of a hassle. It seems like something that might be related to power management, so is there some way you can tell the USB hub to power up through software?

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  • VertTwoFingerScroll and VertEdgeScroll not settable via xorg.conf

    - by James Wood
    I've just upgraded to Saucy (this was working in Raring). I've tried rebooting. Here's /etc/X11/xorg.conf: Section "InputClass" Identifier "Touchpad" Driver "synaptics" MatchIsTouchpad "on" Option "PressureMotionMinZ" "60" Option "MaxTapMove" "4" Option "PalmDetect" "1" Option "VertTwoFingerScroll" "1" Option "VertEdgeScroll" "0" EndSection And here's the output from synclient: LeftEdge = 100 RightEdge = 2408 TopEdge = 71 BottomEdge = 1249 FingerLow = 1 FingerHigh = 1 MaxTapTime = 180 MaxTapMove = 4 MaxDoubleTapTime = 180 SingleTapTimeout = 180 ClickTime = 100 EmulateMidButtonTime = 75 EmulateTwoFingerMinZ = 282 EmulateTwoFingerMinW = 7 VertScrollDelta = 56 HorizScrollDelta = 56 VertEdgeScroll = 1 HorizEdgeScroll = 1 CornerCoasting = 0 VertTwoFingerScroll = 0 HorizTwoFingerScroll = 0 MinSpeed = 1 MaxSpeed = 1.75 AccelFactor = 0.0705716 TouchpadOff = 2 LockedDrags = 0 LockedDragTimeout = 5000 RTCornerButton = 2 RBCornerButton = 3 LTCornerButton = 0 LBCornerButton = 0 TapButton1 = 1 TapButton2 = 3 TapButton3 = 0 ClickFinger1 = 1 ClickFinger2 = 1 ClickFinger3 = 0 CircularScrolling = 0 CircScrollDelta = 0.1 CircScrollTrigger = 0 PalmDetect = 1 PalmMinWidth = 10 PalmMinZ = 200 CoastingSpeed = 20 CoastingFriction = 50 PressureMotionMinZ = 60 PressureMotionMaxZ = 160 PressureMotionMinFactor = 1 PressureMotionMaxFactor = 1 ResolutionDetect = 1 GrabEventDevice = 1 TapAndDragGesture = 1 AreaLeftEdge = 0 AreaRightEdge = 0 AreaTopEdge = 0 AreaBottomEdge = 0 HorizHysteresis = 14 VertHysteresis = 14 ClickPad = 0 Notice that PressureMotionMinZ, MaxTapMove and PalmDetect are as specified in xorg.conf, but VertEdgeScroll and VertTwoFingerScroll aren't. I can set them temporarily via synclient VertEdgeScroll=0 and synclient VertTwoFingerScroll=1, but these changes are lost when I reboot. What's the best way of fixing this?

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  • Remote Working & Relocation

    - by James Burgess
    Sorry if this question is a duplicate, I did some extensive searching and found nothing on quite the same topic (though a couple on partially-overlapping topics). Recently, whilst on holiday in Munich, Germany, I was taken aback by the sheer number of programming-related posts available in the city that I easily qualify for (both in terms of knowledge, and experience). The advertised working environments seemed good and the pay seemed to be at least as good as what I'd expect here in the UK. Probably 80% of the advertisements I saw on the underground were for IT-related jobs, and a good 60% of those I was easily qualified for. At the moment, I work as a freelancer mostly on web and small software projects, but seeing the vast availability of jobs in Munich versus my local area has me thinking about remote working. I'm unable to relocate for a job for the next 3 years (my wife has a contract to continue being a doctor at her current hospital for that time) but would almost certainly be open to it after that (after all, my wife and I both love Munich). In the meanwhile, I would be very interested in remote-working. So, my question is thus do companies ever take on remote workers (even with semi-frequent trips to the office) from abroad, with a view to later relocation? And, if so, how do you go about broaching the topic with a recruiter when getting in contact about a job posting? Language isn't a barrier for me, here, as 90% of the jobs I've looked up in Munich don't require German speakers (seems they have a big recruiting market abroad). I'm also under no illusions about the disadvantages of remote working, but I'm more interested in the viability of the scenario rather than the intricacies (at least at this point). I'd really appreciate any contributions, especially from those who have experience with working in such a scenario!

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  • Tetris Movement - Implementation

    - by James Brauman
    Hi gamedev, I'm developing a Tetris clone and working on the input at the moment. When I was prototyping, movement was triggered by releasing a directional key. However, in most Tetris games I've played the movement is a bit more complex. When a directional key is pressed, the shape moves one space in that direction. After a short interval, if the key is still held down, the shape starts moving in the direction continuously until the key is released. In the case of the down key being pressed, there is no pause between the initial movement and the subsequent continuous movement. I've come up with a solution, and it works well, but it's totally over-engineered. Hey, at least I can recognize when things are getting silly, right? :) public class TetrisMover { List registeredKeys; Dictionary continuousPressedTime; Dictionary totalPressedTime; Dictionary initialIntervals; Dictionary continousIntervals; Dictionary keyActions; Dictionary initialActionDone; KeyboardState currentKeyboardState; public TetrisMover() { *snip* } public void Update(GameTime gameTime) { currentKeyboardState = Keyboard.GetState(); foreach (Keys currentKey in registeredKeys) { if (currentKeyboardState.IsKeyUp(currentKey)) { continuousPressedTime[currentKey] = TimeSpan.Zero; totalPressedTime[currentKey] = TimeSpan.Zero; initialActionDone[currentKey] = false; } else { if (initialActionDone[currentKey] == false) { keyActions[currentKey](); initialActionDone[currentKey] = true; } totalPressedTime[currentKey] += gameTime.ElapsedGameTime; if (totalPressedTime[currentKey] = initialIntervals[currentKey]) { continuousPressedTime[currentKey] += gameTime.ElapsedGameTime; if (continuousPressedTime[currentKey] = continousIntervals[currentKey]) { keyActions[currentKey](); continuousPressedTime[currentKey] = TimeSpan.Zero; } } } } } public void RegisterKey(Keys key, TimeSpan initialInterval, TimeSpan continuousInterval, Action keyAction) { if (registeredKeys.Contains(key)) throw new InvalidOperationException( string.Format("The key %s is already registered.", key)); registeredKeys.Add(key); continuousPressedTime.Add(key, TimeSpan.Zero); totalPressedTime.Add(key, TimeSpan.Zero); initialIntervals.Add(key, initialInterval); continousIntervals.Add(key, continuousInterval); keyActions.Add(key, keyAction); initialActionDone.Add(key, false); } public void UnregisterKey(Keys key) { *snip* } } I'm updating it every frame, and this is how I'm registering keys for movement: tetrisMover.RegisterKey( Keys.Left, keyHoldStartSpecialInterval, keyHoldMovementInterval, () = { Move(Direction.Left); }); tetrisMover.RegisterKey( Keys.Right, keyHoldStartSpecialInterval, keyHoldMovementInterval, () = { Move(Direction.Right); }); tetrisMover.RegisterKey( Keys.Down, TimeSpan.Zero, keyHoldMovementInterval, () = { PerformGravity(); }); Issues that this doesn't address: If both left and right are held down, the shape moves back and forth really quick. If a directional key is held down and the turn finishes and the shape is replaced by a new one, the new one will move quickly in that direction instead of the little pause it is supposed to have. I could fix the issues, but I think it will make the solution even worse. How would you implement this?

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  • C#/.NET Little Wonders: Getting Caller Information

    - by James Michael Hare
    Originally posted on: http://geekswithblogs.net/BlackRabbitCoder/archive/2013/07/25/c.net-little-wonders-getting-caller-information.aspx Once again, in this series of posts I look at the parts of the .NET Framework that may seem trivial, but can help improve your code by making it easier to write and maintain. The index of all my past little wonders posts can be found here. There are times when it is desirable to know who called the method or property you are currently executing.  Some applications of this could include logging libraries, or possibly even something more advanced that may server up different objects depending on who called the method. In the past, we mostly relied on the System.Diagnostics namespace and its classes such as StackTrace and StackFrame to see who our caller was, but now in C# 5, we can also get much of this data at compile-time. Determining the caller using the stack One of the ways of doing this is to examine the call stack.  The classes that allow you to examine the call stack have been around for a long time and can give you a very deep view of the calling chain all the way back to the beginning for the thread that has called you. You can get caller information by either instantiating the StackTrace class (which will give you the complete stack trace, much like you see when an exception is generated), or by using StackFrame which gets a single frame of the stack trace.  Both involve examining the call stack, which is a non-trivial task, so care should be done not to do this in a performance-intensive situation. For our simple example let's say we are going to recreate the wheel and construct our own logging framework.  Perhaps we wish to create a simple method Log which will log the string-ified form of an object and some information about the caller.  We could easily do this as follows: 1: static void Log(object message) 2: { 3: // frame 1, true for source info 4: StackFrame frame = new StackFrame(1, true); 5: var method = frame.GetMethod(); 6: var fileName = frame.GetFileName(); 7: var lineNumber = frame.GetFileLineNumber(); 8: 9: // we'll just use a simple Console write for now 10: Console.WriteLine("{0}({1}):{2} - {3}", 11: fileName, lineNumber, method.Name, message); 12: } So, what we are doing here is grabbing the 2nd stack frame (the 1st is our current method) using a 2nd argument of true to specify we want source information (if available) and then taking the information from the frame.  This works fine, and if we tested it out by calling from a file such as this: 1: // File c:\projects\test\CallerInfo\CallerInfo.cs 2:  3: public class CallerInfo 4: { 5: Log("Hello Logger!"); 6: } We'd see this: 1: c:\projects\test\CallerInfo\CallerInfo.cs(5):Main - Hello Logger! This works well, and in fact CallStack and StackFrame are still the best ways to examine deeper into the call stack.  But if you only want to get information on the caller of your method, there is another option… Determining the caller at compile-time In C# 5 (.NET 4.5) they added some attributes that can be supplied to optional parameters on a method to receive caller information.  These attributes can only be applied to methods with optional parameters with explicit defaults.  Then, as the compiler determines who is calling your method with these attributes, it will fill in the values at compile-time. These are the currently supported attributes available in the  System.Runtime.CompilerServices namespace": CallerFilePathAttribute – The path and name of the file that is calling your method. CallerLineNumberAttribute – The line number in the file where your method is being called. CallerMemberName – The member that is calling your method. So let’s take a look at how our Log method would look using these attributes instead: 1: static int Log(object message, 2: [CallerMemberName] string memberName = "", 3: [CallerFilePath] string fileName = "", 4: [CallerLineNumber] int lineNumber = 0) 5: { 6: // we'll just use a simple Console write for now 7: Console.WriteLine("{0}({1}):{2} - {3}", 8: fileName, lineNumber, memberName, message); 9: } Again, calling this from our sample Main would give us the same result: 1: c:\projects\test\CallerInfo\CallerInfo.cs(5):Main - Hello Logger! However, though this seems the same, there are a few key differences. First of all, there are only 3 supported attributes (at this time) that give you the file path, line number, and calling member.  Thus, it does not give you as rich of detail as a StackFrame (which can give you the calling type as well and deeper frames, for example).  Also, these are supported through optional parameters, which means we could call our new Log method like this: 1: // They're defaults, why not fill 'em in 2: Log("My message.", "Some member", "Some file", -13); In addition, since these attributes require optional parameters, they cannot be used in properties, only in methods. These caveats aside, they do let you get similar information inside of methods at a much greater speed!  How much greater?  Well lets crank through 1,000,000 iterations of each.  instead of logging to console, I’ll return the formatted string length of each.  Doing this, we get: 1: Time for 1,000,000 iterations with StackTrace: 5096 ms 2: Time for 1,000,000 iterations with Attributes: 196 ms So you see, using the attributes is much, much faster!  Nearly 25x faster in fact.  Summary There are a few ways to get caller information for a method.  The StackFrame allows you to get a comprehensive set of information spanning the whole call stack, but at a heavier cost.  On the other hand, the attributes allow you to quickly get at caller information baked in at compile-time, but to do so you need to create optional parameters in your methods to support it. Technorati Tags: Little Wonders,CSharp,C#,.NET,StackFrame,CallStack,CallerFilePathAttribute,CallerLineNumberAttribute,CallerMemberName

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  • How to disable the auto resizing of Windows when you touch the top or bottom

    - by L. D. James
    Can someone tell me how to stop the autoresizing behavior of Windows in Ubuntu 14.04 when you touch the top or bottom when resizing the window. There is an undesirable effect of the the bottom resizing all the way to the bottom when you only want to resize the top, or vice-versa. In the past it was possible to disable this effect by unchecking grid in CCSM. Then came Unity Tweak tool which made it easy to remove. You could remove it by turning off Window snapping and Hotcorners. Now in Ubuntu 14.04 I have all those feature turned off and yet I can't resize only the top or only the bottom without the other end automatically moving.

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  • Microsoft Visual C# MVP 2012

    - by James Michael Hare
    I was informed on July 1st, 2012 that I was awarded a Microsoft Visual C# MVP recognition for 2012.  This is my second year now, and I'm doubly thankful to have been nominated and selected, and thankful that you guys all find my posts informative and useful! Even though life has thrown me some curve balls in this past last year, I look forward to continuing my posts (especially the Little Wonders) as much as possible!Thanks again!

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  • Generate texture for a heightmap

    - by James
    I've recently been trying to blend multiple textures based on the height at different points in a heightmap. However i've been getting poor results. I decided to backtrack and just attempt to recreate one single texture from an SDL_Surface (i'm using SDL) and just send that into opengl. I'll put my code for creating the texture and reading the colour values. It is a 24bit TGA i'm loading, and i've confirmed that the rest of my code works because i was able to send the surfaces pixels directly to my createTextureFromData function and it drew fine. struct RGBColour { RGBColour() : r(0), g(0), b(0) {} RGBColour(unsigned char red, unsigned char green, unsigned char blue) : r(red), g(green), b(blue) {} unsigned char r; unsigned char g; unsigned char b; }; // main loading code SDLSurfaceReader* reader = new SDLSurfaceReader(m_renderer); reader->readSurface("images/grass.tga"); // new texture unsigned char* newTexture = new unsigned char[reader->m_surface->w * reader->m_surface->h * 3 * reader->m_surface->w]; for (int y = 0; y < reader->m_surface->h; y++) { for (int x = 0; x < reader->m_surface->w; x += 3) { int index = (y * reader->m_surface->w) + x; RGBColour colour = reader->getColourAt(x, y); newTexture[index] = colour.r; newTexture[index + 1] = colour.g; newTexture[index + 2] = colour.b; } } unsigned int id = m_renderer->createTextureFromData(newTexture, reader->m_surface->w, reader->m_surface->h, RGB); // functions for reading pixels RGBColour SDLSurfaceReader::getColourAt(int x, int y) { Uint32 pixel; Uint8 red, green, blue; RGBColour rgb; pixel = getPixel(m_surface, x, y); SDL_LockSurface(m_surface); SDL_GetRGB(pixel, m_surface->format, &red, &green, &blue); SDL_UnlockSurface(m_surface); rgb.r = red; rgb.b = blue; rgb.g = green; return rgb; } // this function taken from SDL documentation // http://www.libsdl.org/cgi/docwiki.cgi/Introduction_to_SDL_Video#getpixel Uint32 SDLSurfaceReader::getPixel(SDL_Surface* surface, int x, int y) { int bpp = m_surface->format->BytesPerPixel; Uint8 *p = (Uint8*)m_surface->pixels + y * m_surface->pitch + x * bpp; switch (bpp) { case 1: return *p; case 2: return *(Uint16*)p; case 3: if (SDL_BYTEORDER == SDL_BIG_ENDIAN) return p[0] << 16 | p[1] << 8 | p[2]; else return p[0] | p[1] << 8 | p[2] << 16; case 4: return *(Uint32*)p; default: return 0; } } I've been stumped at this, and I need help badly! Thanks so much for any advice.

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  • 2D Car Simulation with Throttle Linear Physics

    - by James
    I'm trying to make a simulation game for an automatic cruise control system. The system simulates a car on varying inclinations and throttle speeds. I've coded up to the car physics but these do note make sense. The dynamics of the simulation are specified as follows: a = V' - V T = (k1)V + ?(k2) + ma V' = (1 - (k1 / m) V) + T - ( k2 / m) * ? Where T = throttle position k1 = viscous friction V = speed V' = next speed ? = angle of incline k2 = m g sin ? a = acceleration m = mass Notice that the angle of incline in the equation is not chopped up by sin or cos. Even the equation for acceleration isn't right. Can anyone correct them or am I misinterpreting the physics?

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  • Detecting collision between ball (circle) and brick(rectangle)?

    - by James Harrison
    Ok so this is for a small uni project. My lecturer provided me with a framework for a simple brickbreaker game. I am currently trying to overcome to problem of detecting a collision between the two game objects. One object is always the ball and the other objects can either be the bricks or the bat. public Collision hitBy( GameObject obj ) { //obj is the bat or the bricks //the current object is the ball // if ball hits top of object if(topX + width >= obj.topX && topX <= obj.topX + obj.width && topY + height >= obj.topY - 2 && topY + height <= obj.topY){ return Collision.HITY; } //if ball hits left hand side else if(topY + height >= obj.topY && topY <= obj.topY + obj.height && topX + width >= obj.topX -2 && topX + width <= obj.topX){ return Collision.HITX; } else return Collision.NO_HIT; } So far I have a method that is used to detect this collision. The the current obj is a ball and the obj passed into the method is the the bricks. At the moment I have only added statement to check for left and top collisions but do not want to continue as I have a few problems. The ball reacts perfectly if it hits the top of the bricks or bat but when it hits the ball often does not change directing. It seems that it is happening toward the top of the left hand edge but I cannot figure out why. I would like to know if there is another way of approaching this or if people know where I'm going wrong. Lastly the collision.HITX calls another method later on the changes the x direction likewise with y.

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  • Generic Repositories with DI & Data Intensive Controllers

    - by James
    Usually, I consider a large number of parameters as an alarm bell that there may be a design problem somewhere. I am using a Generic Repository for an ASP.NET application and have a Controller with a growing number of parameters. public class GenericRepository<T> : IRepository<T> where T : class { protected DbContext Context { get; set; } protected DbSet<T> DbSet { get; set; } public GenericRepository(DbContext context) { Context = context; DbSet = context.Set<T>(); } ...//methods excluded to keep the question readable } I am using a DI container to pass in the DbContext to the generic repository. So far, this has met my needs and there are no other concrete implmentations of IRepository<T>. However, I had to create a dashboard which uses data from many Entities. There was also a form containing a couple of dropdown lists. Now using the generic repository this makes the parameter requirments grow quickly. The Controller will end up being something like public HomeController(IRepository<EntityOne> entityOneRepository, IRepository<EntityTwo> entityTwoRepository, IRepository<EntityThree> entityThreeRepository, IRepository<EntityFour> entityFourRepository, ILogError logError, ICurrentUser currentUser) { } It has about 6 IRepositories plus a few others to include the required data and the dropdown list options. In my mind this is too many parameters. From a performance point of view, there is only 1 DBContext per request and the DI container will serve the same DbContext to all of the Repositories. From a code standards/readability point of view it's ugly. Is there a better way to handle this situation? Its a real world project with real world time constraints so I will not dwell on it too long, but from a learning perspective it would be good to see how such situations are handled by others.

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  • wireless driver error after install

    - by James
    after following this command to update wifi drivers:1- Boot into Ubuntu 2- Open a terminal by pressing Ctrl+Alt+T 3- Type in the following (verbatim!) sudo apt-get update && sudo apt-get upgrade press Enter, the command will prompt for your password (the one you use to login into Ubuntu), type it and press Enter. Wait for it to finish updating your system. Now type: sudo apt-get remove bcmwl-kernel-source sudo apt-get install firmware-b43-installer Wait for the command to finish installing the driver, when done restart your computer. i get a message after the first command when installing has done saying not enough space so it aborts! what do i do to fix this

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  • C#/.NET Little Wonders: Interlocked Read() and Exchange()

    - by James Michael Hare
    Once again, in this series of posts I look at the parts of the .NET Framework that may seem trivial, but can help improve your code by making it easier to write and maintain. The index of all my past little wonders posts can be found here. Last time we discussed the Interlocked class and its Add(), Increment(), and Decrement() methods which are all useful for updating a value atomically by adding (or subtracting).  However, this begs the question of how do we set and read those values atomically as well? Read() – Read a value atomically Let’s begin by examining the following code: 1: public class Incrementor 2: { 3: private long _value = 0; 4:  5: public long Value { get { return _value; } } 6:  7: public void Increment() 8: { 9: Interlocked.Increment(ref _value); 10: } 11: } 12:  It uses an interlocked increment, as we discuss in my previous post (here), so we know that the increment will be thread-safe.  But, to realize what’s potentially wrong we have to know a bit about how atomic reads are in 32 bit and 64 bit .NET environments. When you are dealing with an item smaller or equal to the system word size (such as an int on a 32 bit system or a long on a 64 bit system) then the read is generally atomic, because it can grab all of the bits needed at once.  However, when dealing with something larger than the system word size (reading a long on a 32 bit system for example), it cannot grab the whole value at once, which can lead to some problems since this read isn’t atomic. For example, this means that on a 32 bit system we may read one half of the long before another thread increments the value, and the other half of it after the increment.  To protect us from reading an invalid value in this manner, we can do an Interlocked.Read() to force the read to be atomic (of course, you’d want to make sure any writes or increments are atomic also): 1: public class Incrementor 2: { 3: private long _value = 0; 4:  5: public long Value 6: { 7: get { return Interlocked.Read(ref _value); } 8: } 9:  10: public void Increment() 11: { 12: Interlocked.Increment(ref _value); 13: } 14: } Now we are guaranteed that we will read the 64 bit value atomically on a 32 bit system, thus ensuring our thread safety (assuming all other reads, writes, increments, etc. are likewise protected).  Note that as stated before, and according to the MSDN (here), it isn’t strictly necessary to use Interlocked.Read() for reading 64 bit values on 64 bit systems, but for those still working in 32 bit environments, it comes in handy when dealing with long atomically. Exchange() – Exchanges two values atomically Exchange() lets us store a new value in the given location (the ref parameter) and return the old value as a result. So just as Read() allows us to read atomically, one use of Exchange() is to write values atomically.  For example, if we wanted to add a Reset() method to our Incrementor, we could do something like this: 1: public void Reset() 2: { 3: _value = 0; 4: } But the assignment wouldn’t be atomic on 32 bit systems, since the word size is 32 bits and the variable is a long (64 bits).  Thus our assignment could have only set half the value when a threaded read or increment happens, which would put us in a bad state. So instead, we could write Reset() like this: 1: public void Reset() 2: { 3: Interlocked.Exchange(ref _value, 0); 4: } And we’d be safe again on a 32 bit system. But this isn’t the only reason Exchange() is valuable.  The key comes in realizing that Exchange() doesn’t just set a new value, it returns the old as well in an atomic step.  Hence the name “exchange”: you are swapping the value to set with the stored value. So why would we want to do this?  Well, anytime you want to set a value and take action based on the previous value.  An example of this might be a scheme where you have several tasks, and during every so often, each of the tasks may nominate themselves to do some administrative chore.  Perhaps you don’t want to make this thread dedicated for whatever reason, but want to be robust enough to let any of the threads that isn’t currently occupied nominate itself for the job.  An easy and lightweight way to do this would be to have a long representing whether someone has acquired the “election” or not.  So a 0 would indicate no one has been elected and 1 would indicate someone has been elected. We could then base our nomination strategy as follows: every so often, a thread will attempt an Interlocked.Exchange() on the long and with a value of 1.  The first thread to do so will set it to a 1 and return back the old value of 0.  We can use this to show that they were the first to nominate and be chosen are thus “in charge”.  Anyone who nominates after that will attempt the same Exchange() but will get back a value of 1, which indicates that someone already had set it to a 1 before them, thus they are not elected. Then, the only other step we need take is to remember to release the election flag once the elected thread accomplishes its task, which we’d do by setting the value back to 0.  In this way, the next thread to nominate with Exchange() will get back the 0 letting them know they are the new elected nominee. Such code might look like this: 1: public class Nominator 2: { 3: private long _nomination = 0; 4: public bool Elect() 5: { 6: return Interlocked.Exchange(ref _nomination, 1) == 0; 7: } 8: public bool Release() 9: { 10: return Interlocked.Exchange(ref _nomination, 0) == 1; 11: } 12: } There’s many ways to do this, of course, but you get the idea.  Running 5 threads doing some “sleep” work might look like this: 1: var nominator = new Nominator(); 2: var random = new Random(); 3: Parallel.For(0, 5, i => 4: { 5:  6: for (int j = 0; j < _iterations; ++j) 7: { 8: if (nominator.Elect()) 9: { 10: // elected 11: Console.WriteLine("Elected nominee " + i); 12: Thread.Sleep(random.Next(100, 5000)); 13: nominator.Release(); 14: } 15: else 16: { 17: // not elected 18: Console.WriteLine("Did not elect nominee " + i); 19: } 20: // sleep before check again 21: Thread.Sleep(1000); 22: } 23: }); And would spit out results like: 1: Elected nominee 0 2: Did not elect nominee 2 3: Did not elect nominee 1 4: Did not elect nominee 4 5: Did not elect nominee 3 6: Did not elect nominee 3 7: Did not elect nominee 1 8: Did not elect nominee 2 9: Did not elect nominee 4 10: Elected nominee 3 11: Did not elect nominee 2 12: Did not elect nominee 1 13: Did not elect nominee 4 14: Elected nominee 0 15: Did not elect nominee 2 16: Did not elect nominee 4 17: ... Another nice thing about the Interlocked.Exchange() is it can be used to thread-safely set pretty much anything 64 bits or less in size including references, pointers (in unsafe mode), floats, doubles, etc.  Summary So, now we’ve seen two more things we can do with Interlocked: reading and exchanging a value atomically.  Read() and Exchange() are especially valuable for reading/writing 64 bit values atomically in a 32 bit system.  Exchange() has value even beyond simply atomic writes by using the Exchange() to your advantage, since it reads and set the value atomically, which allows you to do lightweight nomination systems. There’s still a few more goodies in the Interlocked class which we’ll explore next time! Technorati Tags: C#,CSharp,.NET,Little Wonders,Interlocked

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  • Documenting a REST interface with a flowchart

    - by James Kassemi
    Does anybody have suggestions on creating a flowchart representation of a REST-style web interface? In the interest of supplying thorough documentation to co-developers, I've been toying around in dia modeling the interface for modifying and generating a product resource: This particular system begins to act differently with user authentication/resource counts, so before I make modifications, I'm looking for some clarification: Complexity: how would you simplify the overall structure to make this easier to read? Display Symbol: is this appropriate for representing a page? Manual Operation Symbol: is this appropriate for representing a user action like a button click? Any other suggestions would be greatly appreciated. My apologies for the re-post. The main stackexchange site suggested this question was better presented on programmers.

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  • .mdf Database Filetype

    - by James Izzard
    Would somebody be kind enough to correct my understanding of the following (if incorrect)? Microsoft's .mdf file-type can be used by both the LocalDB and the full Server database engines (apologies if engine is not the correct word?). The .mdf file does not care which of these two options are accessing it - so you could use either to access any given .mdf file, provided you had permissions and password etc. The LocalDB and the SQL Server are two options that can be interchangeably chosen to access .mdf files depending on the application requirements. Appreciate any clarification. Thanks

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  • Playing part of a sfx audio file in HTML5 using WebAudio

    - by Matthew James Davis
    I have compiled all of my sound effects into one sequenced .ogg file. I have the start and stop times for each sound effect. How do I play the individual effects? That is, how do I play part of an audio file. More specificially, I've created a dictionary { 'sword_hit': { src: 'sfx.ogg', start: 265, // ms length: 212 // ms } } that my play_sound() function can use to look up 'sword_hit' and play the correct audio file at the correct start time for the correct duration. I simply need to know how to tell the WebAudio API to start playing at start ms and only play for length ms.

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  • Why don't C++ Game Developers use the boost library?

    - by James
    So if you spend any time viewing / answering questions over on Stack Overflow under the C++ tag, you will quickly notice that just about everybody uses the boost library; some would even say that if you aren't using it, you're not writing "real' C++ (I disagree, but that's not the point). But then there is the game industry, which is well known for using C++ and not using boost. I can't help but wonder why that is. I don't care to use boost because I write games (now) as a hobby, and part of that hobby is implementing what I need when I am able to and using off-the-shelf libraries when I can't. But that is just me. Why don't game developers, in general, use the boost library? Is it performance or memory concerns? Style? Something Else? I was about to ask this on stack overflow, but I figured the question is better asked here. EDIT : I realize I can't speak for all game programmers and I haven't seen all game projects, so I can't say game developers never use boost; this is simply my experience. Allow me to edit my question to also ask, if you do use boost, why did you choose to use it?

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  • Moving objects colliding when using unalligned collision avoidance (steering)

    - by James Bedford
    I'm having trouble with unaligned collision avoidance for what I think is a rare case. I have set two objects to move towards each other but with a slight offset, so one of the objects is moving slightly upwards, and one of the objects is moving slightly downwards. In my unaligned collision avoidance steering algorithm I'm finding the points on the object's forward line and the other object's forward line where these two lines are the closest. If these closest points are within a collision avoidance distance, and if the distance between them is smaller than the two radii of the two object's bounding spheres, then the objects should steer away in the appropriate direction. The problem is that for my case, the closest points on the lines are calculated to be really far away from the actual collision point. This is because the two forward lines for each object are moving away from each other as the objects pass. The problem is that because of this, no steering takes place, and the two objects partially collide. Does anyone have any suggestions as to how I can correctly calculate the point of collision? Perhaps by somehow taking into account the size of the two objects?

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  • twin view on gnome when monitor is unplugged

    - by james t
    i have a macbook pro which is often connected to a monitor, twin view on gnome works pretty well, but a problem arises when i disconnect the monitor, any window that resided on that workspace is no longer available. another issue is when i start my computer when a monitor is not present, because xorg.conf file has the monitor configuration in it, my mouse pointer often disappears in the other monitor's virtual space, as if it is currently plugged, osx deals with this issue elegantly by refreshing the display every time a plug in/out occurs, is there anything similar that can be done in linux ?

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  • Are there any Java based libraries that provide game mapping features?

    - by James.Elsey
    Hi All, I'm working on a Java web based game in my spare time (springMVC / JSPs etc), and I'm wondering what are my options for dealing with the "game world" or mapping element. My game will be 2d / text based, so I have no need for any OpenGL / Flash etc. My initial idea was to use Google maps and provide a custom overlay, but I want to know if there are any alternatives? For example, if I create a 2d map with all my zones, are there any libraries that will help me plot players, work out distances and so forth? Regards

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  • Page Load Time - "Waiting on..." taking ages. What part of page request process is hung?

    - by James
    I have a new cluster site running on Magento that's on a development server that is made up of 2 x web servers and 1 x database server. I have optimized the site in all areas I know (gzip, increasing php memory limits, increasing database memory limits etc) but sometimes the page loading gets stuck on 'waiting for xxx.xx.xx.xxx' (Chrome and other broswers, chrome just shows it that way). It can sit there for 40 + seconds, sometimes it just never loads and I close it in frustration. What part of the page loading process is this hung at? Is it a server issue, database issue, platform issue? I need to know where to start or whether to push the hosting provider about it.

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  • Uninstalling GRUB from MacBook Air

    - by James Brooke
    So... I have a MacBook Air and I recently tried to install Ubuntu on my external HD. I booted Ubuntu from a flash drive and everything had gone fine. I turned off my computer and when I turned it on again I got a message of error and a "grub rescue" line to enter some code. I rebooted holding the "option" key and I selected the Mac partition and everything is fine with my system, but every time I start my system and I don't hold the "option" key, I get the same error and the grub rescue message. I just want things to go back to normal, as they were before I installed Ubuntu on my external HD (which, btw, presented a message that said there was no boot loader). What do I do?

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  • Grub Rescue Error: Unknown Filesystem

    - by James
    I was trying to dual boot Windows with Linux (linux installed first). I read that it was easier to do so if windows was installed first. So I tried to install windows, by creating a partition for it. There wasn't enough room on the drive so I tried changing the filesystem of my existing partition to support windows. Now whenever I try to start my computer I get the grub rescue screen. I've tried booting from CD and USB with ubuntu and also with windows, but nothing happens. I ran ls in grub rescue and got hd0, (hd0,msdos5), cd (with an install disc inserted), fd0, and fd1. However if I run ls on any of these I receive the error: unknown filesystem. Can anyone help me out?

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  • Has test driven development (TDD) actually benefited a real world project?

    - by James
    I am not new to coding. I have been coding (seriously) for over 15 years now. I have always had some testing for my code. However, over the last few months I have been learning test driven design/development (TDD) using Ruby on Rails. So far, I'm not seeing the benefit. I see some benefit to writing tests for some things, but very few. And while I like the idea of writing the test first, I find I spend substantially more time trying to debug my tests to get them to say what I really mean than I do debugging actual code. This is probably because the test code is often substantially more complicated than the code it tests. I hope this is just inexperience with the available tools (RSpec in this case). I must say though, at this point, the level of frustration mixed with the disappointing lack of performance is beyond unacceptable. So far, the only value I'm seeing from TDD is a growing library of RSpec files that serve as templates for other projects/files. Which is not much more useful, maybe less useful, than the actual project code files. In reading the available literature, I notice that TDD seems to be a massive time sink up front, but pays off in the end. I'm just wondering, are there any real world examples? Does this massive frustration ever pay off in the real world? I really hope I did not miss this question somewhere else on here. I searched, but all the questions/answers are several years old at this point. It was a rare occasion when I found a developer who would say anything bad about TDD, which is why I have spent as much time on this as I have. However, I noticed that nobody seems to point to specific real-world examples. I did read one answer that said the guy debugging the code in 2011 would thank you for have a complete unit testing suite (I think that comment was made in 2008). So, I'm just wondering, after all these years, do we finally have any examples showing the payoff is real? Has anybody actually inherited or gone back to code that was designed/developed with TDD and has a complete set of unit tests and actually felt a payoff? Or did you find that you were spending so much time trying to figure out what the test was testing (and why it was important) that you just tossed out the whole mess and dug into the code?

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