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• Tweeting about Oracle Applications Usability: Points to Consider

  - by ultan o'broin

  Here are a few pointers to anyone interested in tweeting about Oracle Applications usability or user experience (UX). These are based on my own experiences and practice, and may not necessarily reflect the views of Oracle, of course (touché, see the footer). If you are an Oracle employee and tweet about our offerings, then read up and follow the corporate social media policy. For the record, I tweet under the following account names: @ultan, @localization, @gamifyOracle, and @usableapps. The last two are supposedly Oracle subject-dedicated, but I mix it up on occassion. Fill out your Twitter account profile, and add a profile picture too. Disclose your interest. Don’t leave either the profile or image blank if you want to be taken seriously (or followed by me). Don’t tweet from a locked down Twitter account, as the message cannot be circulated to anyone who doesn't follow you. Open up the account if you really want to get that UX message out. Stay on message. The usable apps website, Misha Vaughan's VoX blog, and the Oracle Applications blog are good sources of UX messages and information, but you can find many other product team, individual, and corporate-wide sources with a little bit of searching. Set up a Google Alert with pertinent related keywords to get a daily digest of new information right in your inbox. Be original about it. Add your own insight and wit to the message, were relevant. Just circulating and RTing stock headlines adds no value to your effort or to the reader, and is somewhat lazy, in my opinion. Leave room for RTing of your tweet. So, don’t max out those 140 characters. Keep it under 130 if you want to be RTed without modification (or at all-I am not a fan of modifying tweets [MT], way too much effort for the medium). Remove articles and punctuation marks and use fragments, abbreviations, and so on at will to keep the tweet short enough, but leave keywords intact, as people search on those. Follow any Fusion UX Advocates who are on Twitter too (you can search for these names), and not just Oracle employees. Don't just follow people you like or think like you, or those who you think like you or are like-minded. Take a look at who is following or being followed by other tweeters and er, follow up. Create and socialize others to use an easily remembered or typed hashtag, or use what’s already popularized (for an event or conference, for example). We used #gamifyOracle for the applications UX gamification design jam, and other popular applications UX ones are #fusionapps and #usableapps (or at least I’m trying to popularize it). But, before you start the messaging, if you want to keep a record of the hashtag traffic, then set it up with an archiving service. Twitter’s own tweet lifespan is short. Don't mix up hashtags (#) with Twitter handles (@) that have the same name. Sending a tweet to @gamifyOracle will just be seen by @gamifyOracle (me) and any followers we have in common. Sending it to #gamifyOracle is seen by anyone following or searching for that hashtag. No dissing the competition. But there is no rule about not following them on Twitter to see the market reactions to Oracle announcements and this can even let you can tailor your own message accordingly. Don’t be boring. Mix it up a bit. Every 10th or so tweet, divert into other areas of interest, personal ones, even. No constant “I just received K+ in this and that” or “I just checked into wherever” on foursquare pouring into the Twittersteam, please. I just don’t care and will probably unfollow such people pretty quickly. And now, your Twitter tips and experiences with this subject? Them go in the comments...

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• Managing game state / 'what to update' within an XNA game 'screen'

  - by codinghands

  Note - having read through other GDev questions suggested when writing this question I'm confident this isn't a dupe. Of course, it's 3am and I'm likely wrong, so please mod as such if so. I'm trying to figure out how best to manage state within my game screens - please bare with me though! At the moment I'm using a heavily modified version of the fantastic game state management example on the XNA site available here. This is working perfectly for my 'Screens' - 'IntroScreen' with some shiny logos, 'TitleScreen' and a 'MenuScreen' stacked on top for the title and menu, 'PlayScreen' for the actual gameplay, etc. Each screen has the a bunch of sprites, and an 'Update' and 'Draw', managed by a 'ScreenManager'. In addition to the above, and as suggested as an answer to my other question here, most screens have a 'GameProcessQueue' class full of 'GameProcess'es which lets me do just about anything (animations, youbetcha!), in any order, in sequence or parallel. Why mention all this? When I talk about managing game state I'm thinking more for complex scenarios within a 'Screen'. 'TitleScreen', 'MenuScreen' and the like are all relatively simple. 'Play Screen' less so. How do people manage the different 'states' within the screen (or whatever you call it) that 'does' gameplay? (for me, the 'PlayScreen') I've thought about the following: Enum of different states in the Screen, 'activeState' enum-type variable, switching on the enum in the Screen Update() loop to determine what Screen Update 'sub'-function is called. I can see this getting hairy pretty fast though as screens get more complex and with the 'PlayScreen' becoming a behemoth mega-class. 'State' class with Update loop - a Screen can have any number of 'States', 1+ of which are 'active'. Screen update loop calls update on all active states. States themselves know which screen they belong to, and may even belong to a 'StateManager' which handles transitioning from one state to the next. Once a state is over it's removed from the ScreenState list. The Screen doesn't need a bunch of GameProcessQueues, each State has its own. Abstract Screen further to be more flexible - I can see the similarities between what I've got (game 'Screens' handled by a ScreenManager) and what I want (states within a screen, and a mechanism to manage them). However at the moment I see 'Screens' as high level and very distinct ('PlayScreen' with baddies != 'MenuScreen' with 4 words and event handlers), where as my proposed 'States' are more intrinsically tied to a specific screen with complex requirements. I think. This is for a turn-based board game, so it's easier to define things as a discrete series of steps (IntroAnimation - P1Turn - P2Turn - P1Turn ... - GameOver - .... Obviously with an open-world RPG things are very different, but any advice in this scenario is appreciated. If I'm just going OOP-crazy please say so. Similarly I'm concious there's a huge amount on this site re: state management. But as my first 'serious' game after a couple of false starts I'd like to get this right, and would rather be harassed and modded down than never ask :)

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• Clever memory usage through the years

  - by Ben Emmett

  A friend and I were recently talking about the really clever tricks people have used to get the most out of memory. I thought I’d share my favorites, and would love to hear yours too! Interleaving on drum memory Back in the ye olde days before I’d been born (we’re talking the 50s / 60s here), working memory commonly took the form of rotating magnetic drums. These would spin at a constant speed, and a fixed head would read from memory when the correct part of the drum passed it by, a bit like a primitive platter disk. Because each revolution took a few milliseconds, programmers took to manually arranging information non-sequentially on the drum, timing when an instruction or memory address would need to be accessed, then spacing information accordingly around the edge of the drum, thus reducing the access delay. Similar techniques were still used on hard disks and floppy disks into the 90s, but have become irrelevant with modern disk technologies. The Hashlife algorithm Conway’s Game of Life has attracted numerous implementations over the years, but Bill Gosper’s Hashlife algorithm is particularly impressive. Taking advantage of the repetitive nature of many cellular automata, it uses a quadtree structure to store the hashes of pieces of the overall grid. Over time there are fewer and fewer new structures which need to be evaluated, so it starts to run faster with larger grids, drastically outperforming other algorithms both in terms of speed and the size of grid which can be simulated. The actual amount of memory used is huge, but it’s used in a clever way, so makes the list . Elite’s procedural generation Ok, so this isn’t exactly a memory optimization – more a storage optimization – but it gets an honorable mention anyway. When writing Elite, David Braben and Ian Bell wanted to build a rich world which gamers could explore, but their 22K memory was something of a limitation (for comparison that’s about the size of my avatar picture at the top of this page). They procedurally generated all the characteristics of the 2048 planets in their virtual universe, including the names, which were stitched together using a lookup table of parts of names. In fact the original plans were for 2^52 planets, but it was decided that that was probably too many. Oh, and they did that all in assembly language. Other games of the time used similar techniques too – The Sentinel’s landscape generation algorithm being another example. Modern Garbage Collectors Garbage collection in managed languages like Java and .NET ensures that most of the time, developers stop needing to care about how they use and clean up memory as the garbage collector handles it automatically. Achieving this without killing performance is a near-miraculous feet of software engineering. Much like when learning chemistry, you find that every time you think you understand how the garbage collector works, it turns out to be a mere simplification; that there are yet more complexities and heuristics to help it run efficiently. Of course introducing memory problems is still possible (and there are tools like our memory profiler to help if that happens to you) but they’re much, much rarer. A cautionary note In the examples above, there were good and well understood reasons for the optimizations, but cunningly optimized code has usually had to trade away readability and maintainability to achieve its gains. Trying to optimize memory usage without being pretty confident that there’s actually a problem is doing it wrong. So what have I missed? Tell me about the ingenious (or stupid) tricks you’ve seen people use. Ben

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• Question on the implementation of my Entity System

  - by miguel.martin

  I am currently creating an Entity System, in C++, it is almost completed (I have all the code there, I just have to add a few things and test it). The only thing is, I can't figure out how to implement some features. This Entity System is based off a bit from the Artemis framework, however it is different. I'm not sure if I'll be able to type this out the way my head processing it. I'm going to basically ask whether I should do something over something else. Okay, now I'll give a little detail on my Entity System itself. Here are the basic classes that my Entity System uses to actually work: Entity - An Id (and some methods to add/remove/get/etc Components) Component - An empty abstract class ComponentManager - Manages ALL components for ALL entities within a Scene EntitySystem - Processes entities with specific components Aspect - The class that is used to help determine what Components an Entity must contain so a specific EntitySystem can process it EntitySystemManager - Manages all EntitySystems within a Scene EntityManager - Manages entities (i.e. holds all Entities, used to determine whether an Entity has been changed, enables/disables them, etc.) EntityFactory - Creates (and destroys) entities and assigns an ID to them Scene - Contains an EntityManager, EntityFactory, EntitySystemManager and ComponentManager. Has functions to update and initialise the scene. Now in order for an EntitySystem to efficiently know when to check if an Entity is valid for processing (so I can add it to a specific EntitySystem), it must recieve a message from the EntityManager (after a call of activate(Entity& e)). Similarly the EntityManager must know when an Entity is destroyed from the EntityFactory in the Scene, and also the ComponentManager must know when an Entity is created AND destroyed. I do have a Listener/Observer pattern implemented at the moment, but with this pattern I may remove a Listener (which is this case is dependent on the method being called). I mainly have this implemented for specific things related to a game, i.e. Teams, Tagging of entities, etc. So... I was thinking maybe I should call a private method (using friend classes) to send out when an Entity has been activated, deleted, etc. i.e. taken from my EntityFactory void EntityFactory::killEntity(Entity& e) { // if the entity doesn't exsist in the entity manager within the scene if(!getScene()->getEntityManager().doesExsist(e)) { return; // go back to the caller! (should throw an exception or something..) } // tell the ComponentManager and the EntityManager that we killed an Entity getScene()->getComponentManager().doOnEntityWillDie(e); getScene()->getEntityManager().doOnEntityWillDie(e); // notify the listners for(Mouth::iterator i = getMouth().begin(); i != getMouth().end(); ++i) { (*i)->onEntityWillDie(*this, e); } _idPool.addId(e.getId()); // add the ID to the pool delete &e; // delete the entity } As you can see on the lines where I am telling the ComponentManager and the EntityManager that an Entity will die, I am calling a method to make sure it handles it appropriately. Now I realise I could do this without calling it explicitly, with the help of that for loop notifying all listener objects connected to the EntityFactory's Mouth (an object used to tell listeners that there's an event), however is this a good idea (good design, or what)? I've gone over the PROS and CONS, I just can't decide what I want to do. Calling Explicitly: PROS Faster? Since these functions are explicitly called, they can't be "removed" CONS Not flexible Bad design? (friend functions) Calling through Listener objects (i.e. ComponentManager/EntityManager inherits from a EntityFactoryListener) PROS More Flexible? Better Design? CONS Slower? (virtual functions) Listeners can be removed, i.e. may be removed and not get called again during the program, which could cause in a crash. P.S. If you wish to view my current source code, I am hosting it on BitBucket.

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• Comparing Isis, Google, and Paypal

  - by David Dorf

  Back in 2010 I was sure NFC would make great strides, but here we are two years later and NFC doesn't seem to be sticking. The obvious reason being the chicken-and-egg problem.  Retailers don't want to install the terminals until the phones support NFC, and vice-versa. So consumers continue to sit on the sidelines waiting for either side to blink and make the necessary investment.  In the meantime, EMV is looking for a way to sneak into the US with the help of the card brands. There are currently three major solutions that are battling in the marketplace.  All three know that replacing mag-stripe alone is not sufficient to move consumers.  Long-term it's the offers and loyalty programs combined with tendering that make NFC attractive. NFC solutions cross lots of barriers, so a strong partner system is required.  The solutions need to include the carriers, card brands, banks, handset manufacturers, POS terminals, and most of all lots of merchants.  Lots of coordination is necessary to make the solution seamless to the consumer. Google Wallet Google's problem has always been that only the Nexus phone has an NFC chip that supports their wallet.  There are a couple of additional phones out there now, but adoption is still slow.  They acquired Zavers a while back to incorporate digital coupons, but the the bulk of their users continue to be non-NFC.  They have taken an open approach by not specifying particular payment brands.  Google is piloting in San Francisco and New York, supporting both MasterCard PayPass and stored value. I suppose the other card brands may eventually follow.  There's no cost for consumers or merchants -- Google will make money via targeted ads. Isis Not long after Google announced its wallet, AT&T, Verizon, and T-Mobile announced a joint venture called Isis.  They are in the unique position of owning the SIM in the phones they issue.  At first it seemed Isis was a vehicle for the carriers to compete with the existing card brands, but Isis later switched to a generic wallet that supports the major card brands.  Isis reportedly charges issuers a $5 fee per customer per year.  Isis will pilot this summer in Salt Lake City and Austin. PayPal PayPal, the clear winner in the online payment space beyond traditional credit cards, is trying to move into physical stores.  After negotiations with Google to provide a wallet broke off, PayPal decided to avoid NFC altogether, at least for now, and focus on payments without any physical card or phone.  By avoiding NFC, consumers don't need an NFC-enabled phone and merchants don't need a new reader.  Consumers must enter their phone number and PIN in the merchant's existing device, or they can enter their PIN in the PayPal inStore app running on their phone, then show the merchant a unique barcode which authorizes payment. Paypal is free for consumers and charges a fee for merchants.  Its not clear, at least to me, how PayPal handles fraudulent transactions and whether the consumer is protected. The wildcard is, of course, Apple.  Their mobile technologies set the standard, so incorporating NFC chips would certainly accelerate adoption of many payment solutions.  Their announcement today of the iOS Passbook is a step in the right direction, but stops short of handling payments. For those retailers that have invested in modern terminals, it seems the best strategy is to support all the emerging solutions and let the consumers choose the winner.

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• Syntax of passing lambda

  - by Astara

  Right now, I'm working on refactoring a program that calls its parts by polling to a more event-driven structure. I've created sched and task classes with the sced to become a base class of the current main loop. The tasks will be created for each meter so they can be called off of that instead of polling. Each of the events main calls are a type of meter that gather info and display it. When the program is coming up, all enabled meters get 'constructed' by a main-sub. In that sub, I want to store off the "this" pointer associated with the meter, as well as the common name for the "action routine. void MeterMaker::Meter_n_Task (Meter * newmeter,) { push(newmeter); // handle non-timed draw events Task t = new Task(now() + 0.5L); t.period={0,1U}; t.work_meter = newmeter; t.work = [&newmeter](){newmeter.checkevent();};<<--attempt at lambda t.flags = T_Repeat; t.enable_task(); _xos->sched_insert(t); } A sample call to it: Meter_n_Task(new CPUMeter(_xos, "CPU ")); 've made the scheduler a base class of the main routine (that handles the loop), and I've tried serveral variations to get the task class to be a base of the meter class, but keep running into roadblocks. It's alot like "whack-a-mole" -- pound in something to fix something one place, and then a new probl pops out elsewhere. Part of the problem, is that the sched.h file that is trying to hold the Task Q, includes the Task header file. The task file Wants to refer to the most "base", Meter class. The meter class pulls in the main class of the parent as it passes a copy of the parent to the children so they can access the draw routines in the parent. Two references in the task file are for the 'this' pointer of the meter and the meter's update sub (to be called via this). void *this_data= NULL; void (*this_func)() = NULL; Note -- I didn't really want to store these in the class, as I wanted to use a lamdba in that meter&task routine above to store a routine+context to be used to call the meter's action routine. Couldn't figure out the syntax. But am running into other syntax problems trying to store the pointers...such as g++: COMPILE lsched.cc In file included from meter.h:13:0, from ltask.h:17, from lsched.h:13, from lsched.cc:13: xosview.h:30:47: error: expected class-name before ‘{’ token class XOSView : public XWin, public Scheduler { Like above where it asks for a class, where the classname "Scheduler" is. !?!? Huh? That IS a class name. I keep going in circles with things that don't make sense... Ideally I'd get the lamba to work right in the Meter_n_Task routine at the top. I wanted to only store 1 pointer in the 'Task' class that was a pointer to my lambda that would have already captured the "this" value ... but couldn't get that syntax to work at all when I tried to start it into a var in the 'Task' class. This project, FWIW, is my teething project on the new C++... (of course it's simple!.. ;-))... I've made quite a bit of progress in other areas in the code, but this lambda syntax has me stumped...its at times like thse that I appreciate the ease of this type of operation in perl. Sigh. Not sure the best way to ask for help here, as this isn't a simple question. But thought I'd try!... ;-) Too bad I can't attach files to this Q.

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• XNA Multiplayer Games and Networking

  - by JoshReuben

  ·        XNA communication must by default be lightweight – if you are syncing game state between players from the Game.Update method, you must minimize traffic. That game loop may be firing 60 times a second and player 5 needs to know if his tank has collided with any player 3 and the angle of that gun turret. There are no WCF ServiceContract / DataContract niceties here, but at the same time the XNA networking stack simplifies the details. The payload must be simplistic - just an ordered set of numbers that you would map to meaningful enum values upon deserialization.   Overview ·        XNA allows you to create and join multiplayer game sessions, to manage game state across clients, and to interact with the friends list ·        Dependency on Gamer Services - to receive notifications such as sign-in status changes and game invitations ·        two types of online multiplayer games: system link game sessions (LAN) and LIVE sessions (WAN). ·        Minimum dev requirements: 1 Xbox 360 console + Creators Club membership to test network code - run 1 instance of game on Xbox 360, and 1 on a Windows-based computer   Network Sessions ·        A network session is made up of players in a game + up to 8 arbitrary integer properties describing the session ·        create custom enums – (e.g. GameMode, SkillLevel) as keys in NetworkSessionProperties collection ·        Player state: lobby, in-play   Session Types ·        local session - for split-screen gaming - requires no network traffic. ·        system link session - connects multiple gaming machines over a local subnet. ·        Xbox LIVE multiplayer session - occurs on the Internet. Ranked or unranked   Session Updates ·        NetworkSession class Update method - must be called once per frame. ·        performs the following actions: o   Sends the network packets. o   Changes the session state. o   Raises the managed events for any significant state changes. o   Returns the incoming packet data. ·        synchronize the session à packet-received and state-change events à no threading issues   Session Config ·        Session host - gaming machine that creates the session. XNA handles host migration ·        NetworkSession properties: AllowJoinInProgress , AllowHostMigration ·        NetworkSession groups: AllGamers, LocalGamers, RemoteGamers   Subscribe to NetworkSession events ·        GamerJoined ·        GamerLeft ·        GameStarted ·        GameEnded – use to return to lobby ·        SessionEnded – use to return to title screen   Create a Session session = NetworkSession.Create(         NetworkSessionType.SystemLink,         maximumLocalPlayers,         maximumGamers,         privateGamerSlots,         sessionProperties );   Start a Session if (session.IsHost) {     if (session.IsEveryoneReady)     {        session.StartGame();        foreach (var gamer in SignedInGamer.SignedInGamers)        {             gamer.Presence.PresenceMode =                 GamerPresenceMode.InCombat;   Find a Network Session AvailableNetworkSessionCollection availableSessions = NetworkSession.Find(     NetworkSessionType.SystemLink,       maximumLocalPlayers,     networkSessionProperties); availableSessions.AllowJoinInProgress = true;   Join a Network Session NetworkSession session = NetworkSession.Join(     availableSessions[selectedSessionIndex]);   Sending Network Data var packetWriter = new PacketWriter(); foreach (LocalNetworkGamer gamer in session.LocalGamers) {     // Get the tank associated with this player.     Tank myTank = gamer.Tag as Tank;     // Write the data.     packetWriter.Write(myTank.Position);     packetWriter.Write(myTank.TankRotation);     packetWriter.Write(myTank.TurretRotation);     packetWriter.Write(myTank.IsFiring);     packetWriter.Write(myTank.Health);       // Send it to everyone.     gamer.SendData(packetWriter, SendDataOptions.None);     }   Receiving Network Data foreach (LocalNetworkGamer gamer in session.LocalGamers) {     // Keep reading while packets are available.     while (gamer.IsDataAvailable)     {         NetworkGamer sender;          // Read a single packet.         gamer.ReceiveData(packetReader, out sender);          if (!sender.IsLocal)         {             // Get the tank associated with this packet.             Tank remoteTank = sender.Tag as Tank;              // Read the data and apply it to the tank.             remoteTank.Position = packetReader.ReadVector2();             …   End a Session if (session.AllGamers.Count == 1)         {             session.EndGame();             session.Update();         }   Performance •        Aim to minimize payload, reliable in order messages •        Send Data Options: o   Unreliable, out of order -(SendDataOptions.None) o   Unreliable, in order (SendDataOptions.InOrder) o   Reliable, out of order (SendDataOptions.Reliable) o   Reliable, in order (SendDataOptions.ReliableInOrder) o   Chat data (SendDataOptions.Chat) •        Simulate: NetworkSession.SimulatedLatency , NetworkSession.SimulatedPacketLoss •        Voice support – NetworkGamer properties: HasVoice ,IsTalking , IsMutedByLocalUser

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• Numerically stable(ish) method of getting Y-intercept of mouse position?

  - by Fraser

  I'm trying to unproject the mouse position to get the position on the X-Z plane of a ray cast from the mouse. The camera is fully controllable by the user. Right now, the algorithm I'm using is... Unproject the mouse into the camera to get the ray: Vector3 p1 = Vector3.Unproject(new Vector3(x, y, 0), 0, 0, width, height, nearPlane, farPlane, viewProj; Vector3 p2 = Vector3.Unproject(new Vector3(x, y, 1), 0, 0, width, height, nearPlane, farPlane, viewProj); Vector3 dir = p2 - p1; dir.Normalize(); Ray ray = Ray(p1, dir); Then get the Y-intercept by using algebra: float t = -ray.Position.Y / ray.Direction.Y; Vector3 p = ray.Position + t * ray.Direction; The problem is that the projected position is "jumpy". As I make small adjustments to the mouse position, the projected point moves in strange ways. For example, if I move the mouse one pixel up, it will sometimes move the projected position down, but when I move it a second pixel, the project position will jump back to the mouse's location. The projected location is always close to where it should be, but it does not smoothly follow a moving mouse. The problem intensifies as I zoom the camera out. I believe the problem is caused by numeric instability. I can make minor improvements to this by doing some computations at double precision, and possibly abusing the fact that floating point calculations are done at 80-bit precision on x86, however before I start micro-optimizing this and getting deep into how the CLR handles floating point, I was wondering if there's an algorithmic change I can do to improve this? EDIT: A little snooping around in .NET Reflector on SlimDX.dll: public static Vector3 Unproject(Vector3 vector, float x, float y, float width, float height, float minZ, float maxZ, Matrix worldViewProjection) { Vector3 coordinate = new Vector3(); Matrix result = new Matrix(); Matrix.Invert(ref worldViewProjection, out result); coordinate.X = (float) ((((vector.X - x) / ((double) width)) * 2.0) - 1.0); coordinate.Y = (float) -((((vector.Y - y) / ((double) height)) * 2.0) - 1.0); coordinate.Z = (vector.Z - minZ) / (maxZ - minZ); TransformCoordinate(ref coordinate, ref result, out coordinate); return coordinate; } // ... public static void TransformCoordinate(ref Vector3 coordinate, ref Matrix transformation, out Vector3 result) { Vector3 vector; Vector4 vector2 = new Vector4 { X = (((coordinate.Y * transformation.M21) + (coordinate.X * transformation.M11)) + (coordinate.Z * transformation.M31)) + transformation.M41, Y = (((coordinate.Y * transformation.M22) + (coordinate.X * transformation.M12)) + (coordinate.Z * transformation.M32)) + transformation.M42, Z = (((coordinate.Y * transformation.M23) + (coordinate.X * transformation.M13)) + (coordinate.Z * transformation.M33)) + transformation.M43 }; float num = (float) (1.0 / ((((transformation.M24 * coordinate.Y) + (transformation.M14 * coordinate.X)) + (coordinate.Z * transformation.M34)) + transformation.M44)); vector2.W = num; vector.X = vector2.X * num; vector.Y = vector2.Y * num; vector.Z = vector2.Z * num; result = vector; } ...which seems to be a pretty standard method of unprojecting a point from a projection matrix, however this serves to introduce another point of possible instability. Still, I'd like to stick with the SlimDX Unproject routine rather than writing my own unless it's really necessary.

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• RemoveHandler Issues with Custom Events

  - by Jeff Certain

  This is a case of things being more complicated that I thought they should be. Since it took a while to figure this one out, I thought it was worth explaining and putting all of the pieces to the answer in one spot. Let me set the stage. Architecturally, I have the notion of generic producers and consumers. These put items onto, and remove items from, a queue. This provides a generic, thread-safe mechanism to load balance the creation and processing of work items in our application. Part of the IProducer(Of T) interface is: 1: Public Interface IProducer(Of T) 2: Event ItemProduced(ByVal sender As IProducer(Of T), ByVal item As T) 3: Event ProductionComplete(ByVal sender As IProducer(Of T)) 4: End Interface Nothing sinister there, is there? In order to simplify our developers’ lives, I wrapped the queue with some functionality to manage the produces and consumers. Since the developer can specify the number of producers and consumers that are spun up, the queue code manages adding event handlers as the producers and consumers are instantiated. Now, we’ve been having some memory leaks and, in order to eliminate the possibility that this was caused by weak references to event handles, I wanted to remove them. This is where it got dicey. My first attempt looked like this: 1: For Each producer As P In Producers 2: RemoveHandler producer.ItemProduced, AddressOf ItemProducedHandler 3: RemoveHandler producer.ProductionComplete, AddressOf ProductionCompleteHandler 4: producer.Dispose() 5: Next What you can’t see in my posted code are the warnings this caused. The 'AddressOf' expression has no effect in this context because the method argument to 'AddressOf' requires a relaxed conversion to the delegate type of the event. Assign the 'AddressOf' expression to a variable, and use the variable to add or remove the method as the handler.  Now, what on earth does that mean? Well, a quick Bing search uncovered a whole bunch of talk about delegates. The first solution I found just changed all parameters in the event handler to Object. Sorry, but no. I used generics precisely because I wanted type safety, not because I wanted to use Object. More searching. Eventually, I found this forum post, where Jeff Shan revealed a missing piece of the puzzle. The other revelation came from Lian_ZA in this post. However, these two only hinted at the solution. Trying some of what they suggested led to finally getting an invalid cast exception that revealed the existence of ItemProducedEventHandler. Hold on a minute! I didn’t create that delegate. There’s nothing even close to that name in my code… except the ItemProduced event in the interface. Could it be? Naaaaah. Hmmm…. Well, as it turns out, there is a delegate created by the compiler for each event. By explicitly creating a delegate that refers to the method in question, implicitly cast to the generated delegate type, I was able to remove the handlers: 1: For Each producer As P In Producers 2: Dim _itemProducedHandler As IProducer(Of T).ItemProducedEventHandler = AddressOf ItemProducedHandler 3: RemoveHandler producer.ItemProduced, _itemProducedHandler 4:  5: Dim _productionCompleteHandler As IProducer(Of T).ProductionCompleteEventHandler = AddressOf ProductionCompleteHandler 6: RemoveHandler producer.ProductionComplete, _productionCompleteHandler 7: producer.Dispose() 8: Next That’s “all” it took to finally be able to remove the event handlers and maintain type-safe code. Hopefully, this will save you the same challenges I had in trying to figure out how to fix this issue!

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• ConcurrentDictionary<TKey,TValue> used with Lazy<T>

  - by Reed

  In a recent thread on the MSDN forum for the TPL, Stephen Toub suggested mixing ConcurrentDictionary<T,U> with Lazy<T>.  This provides a fantastic model for creating a thread safe dictionary of values where the construction of the value type is expensive.  This is an incredibly useful pattern for many operations, such as value caches. The ConcurrentDictionary<TKey, TValue> class was added in .NET 4, and provides a thread-safe, lock free collection of key value pairs.  While this is a fantastic replacement for Dictionary<TKey, TValue>, it has a potential flaw when used with values where construction of the value class is expensive. The typical way this is used is to call a method such as GetOrAdd to fetch or add a value to the dictionary.  It handles all of the thread safety for you, but as a result, if two threads call this simultaneously, two instances of TValue can easily be constructed. If TValue is very expensive to construct, or worse, has side effects if constructed too often, this is less than desirable.  While you can easily work around this with locking, Stephen Toub provided a very clever alternative – using Lazy<TValue> as the value in the dictionary instead. This looks like the following.  Instead of calling: MyValue value = dictionary.GetOrAdd( key, () => new MyValue(key)); .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; } We would instead use a ConcurrentDictionary<TKey, Lazy<TValue>>, and write: MyValue value = dictionary.GetOrAdd( key, () => new Lazy<MyValue>( () => new MyValue(key))) .Value; This simple change dramatically changes how the operation works.  Now, if two threads call this simultaneously, instead of constructing two MyValue instances, we construct two Lazy<MyValue> instances. However, the Lazy<T> class is very cheap to construct.  Unlike “MyValue”, we can safely afford to construct this twice and “throw away” one of the instances. We then call Lazy<T>.Value at the end to fetch our “MyValue” instance.  At this point, GetOrAdd will always return the same instance of Lazy<MyValue>.  Since Lazy<T> doesn’t construct the MyValue instance until requested, the actual MyClass instance returned is only constructed once.

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• Access Master Page Controls II

  - by Bunch

  Here is another way to access master page controls. This way has a bit less coding then my previous post on the subject. The scenario would be that you have a master page with a few navigation buttons at the top for users to navigate the app. After a button is clicked the corresponding aspx page would load in the ContentPlaceHolder. To make it easier for the users to see what page they are on I wanted the clicked navigation button to change color. This would be a quick visual for the user and is useful when inevitably they are interrupted with something else and cannot get back to what they were doing for a little while. Anyway the code is something like this. Master page: <body>     <form id="form1" runat="server">     <div id="header">     <asp:Panel ID="Panel1" runat="server" CssClass="panelHeader" Width="100%">        <center>            <label style="font-size: large; color: White;">Test Application</label>        </center>       <asp:Button ID="btnPage1" runat="server" Text="Page1" PostBackUrl="~/Page1.aspx" CssClass="navButton"/>       <asp:Button ID="btnPage2" runat="server" Text="Page2" PostBackUrl="~/Page2.aspx" CssClass="navButton"/>       <br />     </asp:Panel>     <br />     </div>     <div>         <asp:scriptmanager ID="Scriptmanager1" runat="server"></asp:scriptmanager>         <asp:ContentPlaceHolder id="ContentPlaceHolder1" runat="server">         </asp:ContentPlaceHolder>     </div>     </form> </body> Page 1: VB Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load     Dim clickedButton As Button = Master.FindControl("btnPage1")     clickedButton.CssClass = "navButtonClicked" End Sub CSharp protected void Page_Load(object sender, EventArgs e) {     Button clickedButton;     clickedButton = (Button)Master.FindControl("btnPage1");     clickedButton.CssClass = "navButtonClicked"; } CSS: .navButton {     background-color: White;     border: 1px #4e667d solid;     color: #2275a7;     display: inline;     line-height: 1.35em;     text-decoration: none;     white-space: nowrap;     width: 100px;     text-align: center;     margin-bottom: 10px;     margin-left: 5px;     height: 30px; } .navButtonClicked {     background-color:#FFFF86;     border: 1px #4e667d solid;     color: #2275a7;     display: inline;     line-height: 1.35em;     text-decoration: none;     white-space: nowrap;     width: 100px;     text-align: center;     margin-bottom: 10px;     margin-left: 5px;     height: 30px; } The idea is pretty simple, use FindControl for the master page in the page load of your aspx page. In the example I changed the CssClass for the aspx page's corresponding button to navButtonClicked which has a different background-color and makes the clicked button stand out. Technorati Tags: ASP.Net,CSS,CSharp,VB.Net

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• Wireless device bug on 13.10. BCM4313 registers as eth1 instead of wlan0 and no internet access

  - by user205691

  My Hotel wiFi requires me to login with a username & password after connecting to the hotspot. So, my browser would open a page with username & passwrd fields to login and then connect to internet. But unfortunately, firefox & chromium dont seem to work. i dont think it is browser related but a setting for the wifi router or driver which is creating this issue. using Broadcom 801.11 STA wireless driver (proprietary). tried open source as well but same result !! The image linked below shows my wifi connection setting & Chromium. The login page itself comes up after a long time and after entering the credentials, it keeps loading for ever !! it is the same case for every other browser.. so i dont think its browser issue but something to do with wifi setting or network manager stuff.. interestingly, i am able to connect to WiFi networks with WPA key without any issue. Adhoc hotspot is a problem and that is my regular home network :( .. I hope i can get some help solving this issue ! I have tried repeating the same hotspot after login from my android, by creating a virtual repeater with WPA key and it works. I can browse on ubuntu using this method.. but cant be doing this regularly ! I tried loading the same login page of the hotel wifi while browsing through my repeater wifi created on mobile and screen shot attached below. the page loads up quick and easy.. so this means something is wrong with the way network manager handles adhoc connectivity & login ?? i installed wicd0 but it crashes on startup and not helpful at all ! Screenshot of Chromium page Login page with repeated hotspot ifconfig in my terminal results: krishna@krishna-HP-ENVY-4-Notebook-PC:~$ ifconfig eth0 Link encap:Ethernet HWaddr 28:92:4a:1d:54:fa UP BROADCAST MULTICAST MTU:1500 Metric:1 RX packets:0 errors:0 dropped:0 overruns:0 frame:0 TX packets:0 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:0 (0.0 B) TX bytes:0 (0.0 B) eth1 Link encap:Ethernet HWaddr e0:06:e6:89:fa:49 inet addr:10.24.1.71 Bcast:10.24.1.255 Mask:255.255.255.0 inet6 addr: fe80::e206:e6ff:fe89:fa49/64 Scope:Link UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:10940 errors:0 dropped:0 overruns:0 frame:348431 TX packets:6611 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:7669631 (7.6 MB) TX bytes:864195 (864.1 KB) Interrupt:17 lo Link encap:Local Loopback inet addr:127.0.0.1 Mask:255.0.0.0 inet6 addr: ::1/128 Scope:Host UP LOOPBACK RUNNING MTU:65536 Metric:1 RX packets:2146 errors:0 dropped:0 overruns:0 frame:0 TX packets:2146 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:0 RX bytes:166120 (166.1 KB) TX bytes:166120 (166.1 KB) I wonder why is the wireless configured under eth1 ? I think this is a bug with earlier ubuntu versions, but is this normal in 13.10 or is there a wrong configuration here ? The wireless device in my pc is BCM4313 and i have installed the bcmwl-kernel-sources, wireless-tools to support the device. i also reinstalled the bcmwl-kernel as suggested on broadcom website, via synaptic package manager. Nothing has changed this situation ! I tried booting into liveUSB and then ifconfig results show wireless under wlan0. But then the wireless connects and loads the login page. So is the problem with the device configuration now ? i really want to get this fixed before i start configuring the other stuff like ATI graphics and such on the laptop for overheating.. lack of internet access is too bad a bug for me :P any help is appreciated!

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• The best computer ever

  - by Jeff

  (This is a repost from my personal blog… wow… I need to write more technical stuff!) About three years and three months ago, I bought a 17" MacBook Pro, and it turned out to be the best computer I've ever owned. You might think that every computer with better specs is automatically better than the last, but that hasn't been my experience. My first one was a Sony, back in the Pentium III days, and it cost an astonishing $2,500. That was even more ridiculous in 1999 dollars. It had a dial-up modem, and a CD-ROM, built-in! It may have even played DVD's. A few years later I bought an HP, and it ended up being a pile of shit. The power connector inside came loose from the board, and on occasion would even short. In 2005, I bought a Dell, and it wasn't bad. It had a really high resolution screen (complete with dead pixels, a problem in those days), and it was the first laptop I felt I could do real work on. When 2006 rolled around, Apple started making computers with Intel CPU's, and I bought the very first one the week it came out. I used Boot Camp to run Windows. I still have it in its box somewhere, and I used it for three years. The current 17" was new in 2009. The goodness was largely rooted in having a big screen with lots of dots. This computer has been the source of hundreds of blog posts, tens of thousands of lines of code, video and photo editing, and of course, a whole lot of Web surfing. It connected to corpnet at Microsoft, WiFi in Hawaii and has presented many a deck. It has traveled with me tens of thousands of miles. Last year, I put a solid state drive in it, and it was like getting a new computer. I can boot up a Windows 7 VM in about 19 seconds. Having 8 gigs of RAM has always been fantastic. Everything about it has been fast and fun. When new, the battery (when not using VM's) could get as much as 10 hours. I can still do 7 without much trouble. After 460 charge cycles, the battery health is still between 85 and 90%. The only real negative has been the size and weight. It's only an inch thick, but naturally it's pretty big with a 17" screen. You don't get battery life like that without a huge battery, either, so it's heavy. It was never a deal breaker, but sometimes a long haul across a large airport, you know you're carrying it. Today, Apple announced a new, thinner and lighter 15" laptop, with twice the RAM and CPU cores, and four times the screen resolution. It basically handles my size and weight issues while retaining the resolution, and it still costs less than my 17" did. So I ordered one. Three years is an excellent run, but I kind of budgeted for a new workhorse this year anyway. So if you're interested in a 17" MacBook Pro with a Core 2 Duo 2.66 GHz CPU, 8 gigs of RAM and a 320 gig hard drive (sorry, I'm keeping the SSD), I have one to sell. They've apparently discontinued the 17", which is going to piss off the video community. It's in excellent condition, with a few minor scratches, but I take care of my stuff.

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• Syntax of passing lambda causing hair loss (pulling out)

  - by Astara

  Right now, I'm working on refactoring a program that calls its parts by polling to a more event-driven structure. I've created sched and task classes with the sced to become a base class of the current main loop. The tasks will be created for each meter so they can be called off of that instead of polling. Each of the events main calls are a type of meter that gather info and display it. When the program is coming up, all enabled meters get 'constructed' by a main-sub. In that sub, I want to store off the "this" pointer associated with the meter, as well as the common name for the "action routine. void MeterMaker::Meter_n_Task (Meter * newmeter,) { push(newmeter); // handle non-timed draw events Task t = new Task(now() + 0.5L); t.period={0,1U}; t.work_meter = newmeter; t.work = [&newmeter](){newmeter.checkevent();};<<--attempt at lambda t.flags = T_Repeat; t.enable_task(); _xos->sched_insert(t); } A sample call to it: Meter_n_Task(new CPUMeter(_xos, "CPU ")); 've made the scheduler a base class of the main routine (that handles the loop), and I've tried serveral variations to get the task class to be a base of the meter class, but keep running into roadblocks. It's alot like "whack-a-mole" -- pound in something to fix something one place, and then a new probl pops out elsewhere. Part of the problem, is that the sched.h file that is trying to hold the Task Q, includes the Task header file. The task file Wants to refer to the most "base", Meter class. The meter class pulls in the main class of the parent as it passes a copy of the parent to the children so they can access the draw routines in the parent. Two references in the task file are for the 'this' pointer of the meter and the meter's update sub (to be called via this). void *this_data= NULL; void (*this_func)() = NULL; Note -- I didn't really want to store these in the class, as I wanted to use a lamdba in that meter&task routine above to store a routine+context to be used to call the meter's action routine. Couldn't figure out the syntax. But am running into other syntax problems trying to store the pointers...such as g++: COMPILE lsched.cc In file included from meter.h:13:0, from ltask.h:17, from lsched.h:13, from lsched.cc:13: xosview.h:30:47: error: expected class-name before ‘{’ token class XOSView : public XWin, public Scheduler { Like above where it asks for a class, where the classname "Scheduler" is. !?!? Huh? That IS a class name. I keep going in circles with things that don't make sense... Ideally I'd get the lamba to work right in the Meter_n_Task routine at the top. I wanted to only store 1 pointer in the 'Task' class that was a pointer to my lambda that would have already captured the "this" value ... but couldn't get that syntax to work at all when I tried to start it into a var in the 'Task' class. This project, FWIW, is my teething project on the new C++... (of course it's simple!.. ;-))... I've made quite a bit of progress in other areas in the code, but this lambda syntax has me stumped...its at times like thse that I appreciate the ease of this type of operation in perl. Sigh. Not sure the best way to ask for help here, as this isn't a simple question. But thought I'd try!... ;-) Too bad I can't attach files to this Q.

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• How'd they do it: Millions of tiles in Terraria

  - by William 'MindWorX' Mariager

  I've been working up a game engine similar to Terraria, mostly as a challenge, and while I've figured out most of it, I can't really seem to wrap my head around how they handle the millions of interactable/harvestable tiles the game has at one time. Creating around 500.000 tiles, that is 1/20th of what's possible in Terraria, in my engine causes the frame-rate to drop from 60 to around 20, even tho I'm still only rendering the tiles in view. Mind you, I'm not doing anything with the tiles, only keeping them in memory. Update: Code added to show how I do things. This is part of a class, which handles the tiles and draws them. I'm guessing the culprit is the "foreach" part, which iterates everything, even empty indexes. ... public void Draw(SpriteBatch spriteBatch, GameTime gameTime) { foreach (Tile tile in this.Tiles) { if (tile != null) { if (tile.Position.X < -this.Offset.X + 32) continue; if (tile.Position.X > -this.Offset.X + 1024 - 48) continue; if (tile.Position.Y < -this.Offset.Y + 32) continue; if (tile.Position.Y > -this.Offset.Y + 768 - 48) continue; tile.Draw(spriteBatch, gameTime); } } } ... Also here is the Tile.Draw method, which could also do with an update, as each Tile uses four calls to the SpriteBatch.Draw method. This is part of my autotiling system, which means drawing each corner depending on neighboring tiles. texture_* are Rectangles, are set once at level creation, not each update. ... public virtual void Draw(SpriteBatch spriteBatch, GameTime gameTime) { if (this.type == TileType.TileSet) { spriteBatch.Draw(this.texture, this.realm.Offset + this.Position, texture_tl, this.BlendColor); spriteBatch.Draw(this.texture, this.realm.Offset + this.Position + new Vector2(8, 0), texture_tr, this.BlendColor); spriteBatch.Draw(this.texture, this.realm.Offset + this.Position + new Vector2(0, 8), texture_bl, this.BlendColor); spriteBatch.Draw(this.texture, this.realm.Offset + this.Position + new Vector2(8, 8), texture_br, this.BlendColor); } } ... Any critique or suggestions to my code is welcome. Update: Solution added. Here's the final Level.Draw method. The Level.TileAt method simply checks the inputted values, to avoid OutOfRange exceptions. ... public void Draw(SpriteBatch spriteBatch, GameTime gameTime) { Int32 startx = (Int32)Math.Floor((-this.Offset.X - 32) / 16); Int32 endx = (Int32)Math.Ceiling((-this.Offset.X + 1024 + 32) / 16); Int32 starty = (Int32)Math.Floor((-this.Offset.Y - 32) / 16); Int32 endy = (Int32)Math.Ceiling((-this.Offset.Y + 768 + 32) / 16); for (Int32 x = startx; x < endx; x += 1) { for (Int32 y = starty; y < endy; y += 1) { Tile tile = this.TileAt(x, y); if (tile != null) tile.Draw(spriteBatch, gameTime); } } } ...

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• Oracle Applications Cloud Release 8 Customization: Your User Interface, Your Text

  - by ultan o'broin

  Introducing the User Interface Text Editor In Oracle Applications Cloud Release 8, there’s an addition to the customization tool set, called the User Interface Text Editor  (UITE). When signed in with an application administrator role, users launch this new editing feature from the Navigator's Tools > Customization > User Interface Text menu option. See how the editor is in there with other customization tools? User Interface Text Editor is launched from the Navigator Customization menu Applications customers need a way to make changes to the text that appears in the UI, without having to initiate an IT project. Business users can now easily change labels on fields, for example. Using a composer and activated sandbox, these users can take advantage of the Oracle Metadata Services (MDS), add a key to a text resource bundle, and then type in their preferred label and its description (as a best practice for further work, I’d recommend always completing that description). Changing a simplified UI field label using Oracle Composer In Release 8, the UITE enables business users to easily change UI text on a much wider basis. As with composers, the UITE requires an activated sandbox where users can make their changes safely, before committing them for others to see. The UITE is used for editing UI text that comes from Oracle ADF resource bundles or from the Message Dictionary (or FND_MESSAGE_% tables, if you’re old enough to remember such things). Functionally, the Message Dictionary is used for the text that appears in business rule-type error, warning or information messages, or as a text source when ADF resource bundles cannot be used. In the UITE, these Message Dictionary texts are referred to as Multi-part Validation Messages.   If the text comes from ADF resource bundles, then it’s categorized as User Interface Text in the UITE. This category refers to the text that appears in embedded help in the UI or in simple error, warning, confirmation, or information messages. The embedded help types used in the application are explained in an Oracle Fusion Applications User Experience (UX) design pattern set. The message types have a UX design pattern set too. Using UITE  The UITE enables users to search and replace text in UI strings using case sensitive options, as well as by type. Users select singular and plural options for text changes, should they apply. Searching and replacing text in the UITE The UITE also provides users with a way to preview and manage changes on an exclusion basis, before committing to the final result. There might, for example, be situations where a phrase or word needs to remain different from how it’s generally used in the application, depending on the context. Previewing replacement text changes. Changes can be excluded where required. Multi-Part Messages The Message Dictionary table architecture has been inherited from Oracle E-Business Suite days. However, there are important differences in the Oracle Applications Cloud version, notably the additional message text components, as explained in the UX Design Patterns. Message Dictionary text has a broad range of uses as indicated, and it can also be reserved for internal application use, for use by PL/SQL and C programs, and so on. Message Dictionary text may even concatenate together at run time, where required. The UITE handles the flexibility of such text architecture by enabling users to drill down on each message and see how it’s constructed in total. That way, users can ensure that any text changes being made are consistent throughout the different message parts. Multi-part (Message Dictionary) message components in the UITE Message Dictionary messages may also use supportability-related numbers, the ones that appear appended to the message text in the application’s UI. However, should you have the requirement to remove these numbers from users' view, the UITE is not the tool for the job. Instead, see my blog about using the Manage Messages UI.

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• SQL Server: Writing CASE expressions properly when NULLs are involved

  - by Mladen Prajdic

  We’ve all written a CASE expression (yes, it’s an expression and not a statement) or two every now and then. But did you know there are actually 2 formats you can write the CASE expression in? This actually bit me when I was trying to add some new functionality to an old stored procedure. In some rare cases the stored procedure just didn’t work correctly. After a quick look it turned out to be a CASE expression problem when dealing with NULLS. In the first format we make simple “equals to” comparisons to a value: SELECT CASE <value> WHEN <equals this value> THEN <return this> WHEN <equals this value> THEN <return this> -- ... more WHEN's here ELSE <return this> END Second format is much more flexible since it allows for complex conditions. USE THIS ONE! SELECT CASE WHEN <value> <compared to> <value> THEN <return this> WHEN <value> <compared to> <value> THEN <return this> -- ... more WHEN's here ELSE <return this> END Now that we know both formats and you know which to use (the second one if that hasn’t been clear enough) here’s an example how the first format WILL make your evaluation logic WRONG. Run the following code for different values of @i. Just comment out any 2 out of 3 “SELECT @i =” statements. DECLARE @i INTSELECT  @i = -1 -- first resultSELECT  @i = 55 -- second resultSELECT  @i = NULL -- third resultSELECT @i AS OriginalValue, -- first CASE format. DON'T USE THIS! CASE @i WHEN -1 THEN '-1' WHEN NULL THEN 'We have a NULL!' ELSE 'We landed in ELSE' END AS DontUseThisCaseFormatValue, -- second CASE format. USE THIS! CASE WHEN @i = -1 THEN '-1' WHEN @i IS NULL THEN 'We have a NULL!' ELSE 'We landed in ELSE' END AS UseThisCaseFormatValue When the value of @i is –1 everything works as expected, since both formats go into the –1 WHEN branch. When the value of @i is 55 everything again works as expected, since both formats go into the ELSE branch. When the value of @i is NULL the problems become evident. The first format doesn’t go into the WHEN NULL branch because it makes an equality comparison between two NULLs. Because a NULL is an unknown value: NULL = NULL is false. That is why the first format goes into the ELSE Branch but the second format correctly handles the proper IS NULL comparison.   Please use the second more explicit format. Your future self will be very grateful to you when he doesn’t have to discover these kinds of bugs.

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• OpenGL Fast-Object Instancing Error

  - by HJ Media Studios

  I have some code that loops through a set of objects and renders instances of those objects. The list of objects that needs to be rendered is stored as a std::map, where an object of class MeshResource contains the vertices and indices with the actual data, and an object of classMeshRenderer defines the point in space the mesh is to be rendered at. My rendering code is as follows: glDisable(GL_BLEND); glEnable(GL_CULL_FACE); glDepthMask(GL_TRUE); glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); glEnable(GL_DEPTH_TEST); for (std::map<MeshResource*, std::vector<MeshRenderer*> >::iterator it = renderables.begin(); it != renderables.end(); it++) { it->first->setupBeforeRendering(); cout << "<"; for (unsigned long i =0; i < it->second.size(); i++) { //Pass in an identity matrix to the vertex shader- used here only for debugging purposes; the real code correctly inputs any matrix. uniformizeModelMatrix(Matrix4::IDENTITY); /** * StartHere fix rendering problem. * Ruled out: * Vertex buffers correctly. * Index buffers correctly. * Matrices correct? */ it->first->render(); } it->first->cleanupAfterRendering(); } geometryPassShader->disable(); glDepthMask(GL_FALSE); glDisable(GL_CULL_FACE); glDisable(GL_DEPTH_TEST); The function in MeshResource that handles setting up the uniforms is as follows: void MeshResource::setupBeforeRendering() { glEnableVertexAttribArray(0); glEnableVertexAttribArray(1); glEnableVertexAttribArray(2); glEnableVertexAttribArray(3); glEnableVertexAttribArray(4); glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, iboID); glBindBuffer(GL_ARRAY_BUFFER, vboID); glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, sizeof(Vertex), 0); // Vertex position glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, sizeof(Vertex), (const GLvoid*) 12); // Vertex normal glVertexAttribPointer(2, 2, GL_FLOAT, GL_FALSE, sizeof(Vertex), (const GLvoid*) 24); // UV layer 0 glVertexAttribPointer(3, 3, GL_FLOAT, GL_FALSE, sizeof(Vertex), (const GLvoid*) 32); // Vertex color glVertexAttribPointer(4, 1, GL_UNSIGNED_SHORT, GL_FALSE, sizeof(Vertex), (const GLvoid*) 44); //Material index } The code that renders the object is this: void MeshResource::render() { glDrawElements(GL_TRIANGLES, geometry->numIndices, GL_UNSIGNED_SHORT, 0); } And the code that cleans up is this: void MeshResource::cleanupAfterRendering() { glDisableVertexAttribArray(0); glDisableVertexAttribArray(1); glDisableVertexAttribArray(2); glDisableVertexAttribArray(3); glDisableVertexAttribArray(4); } The end result of this is that I get a black screen, although the end of my rendering pipeline after the rendering code (essentially just drawing axes and lines on the screen) works properly, so I'm fairly sure it's not an issue with the passing of uniforms. If, however, I change the code slightly so that the rendering code calls the setup immediately before rendering, like so: void MeshResource::render() { setupBeforeRendering(); glDrawElements(GL_TRIANGLES, geometry->numIndices, GL_UNSIGNED_SHORT, 0); } The program works as desired. I don't want to have to do this, though, as my aim is to set up vertex, material, etc. data once per object type and then render each instance updating only the transformation information. The uniformizeModelMatrix works as follows: void RenderManager::uniformizeModelMatrix(Matrix4 matrix) { glBindBuffer(GL_UNIFORM_BUFFER, globalMatrixUBOID); glBufferSubData(GL_UNIFORM_BUFFER, 0, sizeof(Matrix4), matrix.ptr()); glBindBuffer(GL_UNIFORM_BUFFER, 0); }

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• How to make a stack stable? Need help for an explicit resting contact scheme (2-dimensional)

  - by Register Sole

  Previously, I struggle with the sequential impulse-based method I developed. Thanks to jedediah referring me to this paper, I managed to rebuild the codes and implement the simultaneous impulse based method with Projected-Gauss-Seidel (PGS) iterative solver as described by Erin Catto (mentioned in the reference of the paper as [Catt05]). So here's how it currently is: The simulation handles 2-dimensional rotating convex polygons. Detection is using separating-axis test, with a SKIN, meaning closest points between two polygons is detected and determined if their distance is less than SKIN. To resolve collision, simultaneous impulse-based method is used. It is solved using iterative solver (PGS-solver) as in Erin Catto's paper. Error-correction is implemented using Baumgarte's stabilization (you can refer to either paper for this) using J V = beta/dt*overlap, J is the Jacobian for the constraints, V the matrix containing the velocities of the bodies, beta an error-correction parameter that is better be < 1, dt the time-step taken by the engine, and overlap, the overlap between the bodies (true overlap, so SKIN is ignored). However, it is still less stable than I expected :s I tried to stack hexagons (or squares, doesn't really matter), and even with only 4 to 5 of them, they would swing! Also note that I am not looking for a sleeping scheme. But I would settle if you have any explicit scheme to handle resting contacts. That said, I would be more than happy if you have a way of treating it generally (as continuous collision, instead of explicitly as a special state). Ideas I have tried: Using simultaneous position based error correction as described in the paper in section 5.3.2, turned out to be worse than the current scheme. If you want to know the parameters I used: Hexagons, side 50 (pixels) gravity 2400 (pixels/sec^2) time-step 1/60 (sec) beta 0.1 restitution 0 to 0.2 coeff. of friction 0.2 PGS iteration 10 initial separation 10 (pixels) mass 1 (unit is irrelevant for now, i modified velocity directly<-impulse method) inertia 1/1000 Thanks in advance! I really appreciate any help from you guys!! :) EDIT In response to Cholesky's comment about warm starting the solver and Baumgarte: Oh right, I forgot to mention! I do save the contact history and the impulse determined in this time step to be used as initial guess in the next time step. As for the Baumgarte, here's what actually happens in the code. Collision is detected when the bodies' closest distance is less than SKIN, meaning they are actually still separated. If at this moment, I used the PGS solver without Baumgarte, restitution of 0 alone would be able to stop the bodies, separated by a distance of ~SKIN, in mid-air! So this isn't right, I want to have the bodies touching each other. So I turn on the Baumgarte, where its role is actually to pull the bodies together! Weird I know, a scheme intended to push the body apart becomes useful for the reverse. Also, I found that if I increase the number of iteration to 100, stacks become much more stable, though the program becomes so slow. UPDATE Since the stack swings left and right, could it be something is wrong with my friction model? Current friction constraint: relative_tangential_velocity = 0

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• Is this over-abstraction? (And is there a name for it?)

  - by mwhite

  I work on a large Django application that uses CouchDB as a database and couchdbkit for mapping CouchDB documents to objects in Python, similar to Django's default ORM. It has dozens of model classes and a hundred or two CouchDB views. The application allows users to register a "domain", which gives them a unique URL containing the domain name that gives them access to a project whose data has no overlap with the data of other domains. Each document that is part of a domain has its domain property set to that domain's name. As far as relationships between the documents go, all domains are effectively mutually exclusive subsets of the data, except for a few edge cases (some users can be members of more than one domain, and there are some administrative reports that include all domains, etc.). The code is full of explicit references to the domain name, and I'm wondering if it would be worth the added complexity to abstract this out. I'd also like to know if there's a name for the sort of bound property approach I'm taking here. Basically, I have something like this in mind: Before in models.py class User(Document): domain = StringProperty() class Group(Document): domain = StringProperty() name = StringProperty() user_ids = StringListProperty() # method that returns related document set def users(self): return [User.get(id) for id in self.user_ids] # method that queries a couch view optimized for a specific lookup @classmethod def by_name(cls, domain, name): # the view method is provided by couchdbkit and handles # wrapping json CouchDB results as Python objects, and # can take various parameters modifying behavior return cls.view('groups/by_name', key=[domain, name]) # method that creates a related document def get_new_user(self): user = User(domain=self.domain) user.save() self.user_ids.append(user._id) return user in views.py: from models import User, Group # there are tons of views like this, (request, domain, ...) def create_new_user_in_group(request, domain, group_name): group = Group.by_name(domain, group_name)[0] user = User(domain=domain) user.save() group.user_ids.append(user._id) group.save() in group/by_name/map.js: function (doc) { if (doc.doc_type == "Group") { emit([doc.domain, doc.name], null); } } After models.py class DomainDocument(Document): domain = StringProperty() @classmethod def domain_view(cls, *args, **kwargs): kwargs['key'] = [cls.domain.default] + kwargs['key'] return super(DomainDocument, cls).view(*args, **kwargs) @classmethod def get(cls, *args, **kwargs, validate_domain=True): ret = super(DomainDocument, cls).get(*args, **kwargs) if validate_domain and ret.domain != cls.domain.default: raise Exception() return ret def models(self): # a mapping of all models in the application. accessing one returns the equivalent of class BoundUser(User): domain = StringProperty(default=self.domain) class User(DomainDocument): pass class Group(DomainDocument): name = StringProperty() user_ids = StringListProperty() def users(self): return [self.models.User.get(id) for id in self.user_ids] @classmethod def by_name(cls, name): return cls.domain_view('groups/by_name', key=[name]) def get_new_user(self): user = self.models.User() user.save() views.py @domain_view # decorator that sets request.models to the same sort of object that is returned by DomainDocument.models and removes the domain argument from the URL router def create_new_user_in_group(request, group_name): group = request.models.Group.by_name(group_name) user = request.models.User() user.save() group.user_ids.append(user._id) group.save() (Might be better to leave the abstraction leaky here in order to avoid having to deal with a couchapp-style //! include of a wrapper for emit that prepends doc.domain to the key or some other similar solution.) function (doc) { if (doc.doc_type == "Group") { emit([doc.name], null); } } Pros and Cons So what are the pros and cons of this? Pros: DRYer prevents you from creating related documents but forgetting to set the domain. prevents you from accidentally writing a django view - couch view execution path that leads to a security breach doesn't prevent you from accessing underlying self.domain and normal Document.view() method potentially gets rid of the need for a lot of sanity checks verifying whether two documents whose domains we expect to be equal are. Cons: adds some complexity hides what's really happening requires no model modules to have classes with the same name, or you would need to add sub-attributes to self.models for modules. However, requiring project-wide unique class names for models should actually be fine because they correspond to the doc_type property couchdbkit uses to decide which class to instantiate them as, which should be unique. removes explicit dependency documentation (from group.models import Group)

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• SSH X11 not working

  - by azat

  I have a home and work computer, the home computer has a static IP address. If I ssh from my work computer to my home computer, the ssh connection works but X11 applications are not displayed. In my /etc/ssh/sshd_config at home: X11Forwarding yes X11DisplayOffset 10 X11UseLocalhost yes At work I have tried the following commands: xhost + home HOME_IP ssh -X home ssh -X HOME_IP ssh -Y home ssh -Y HOME_IP My /etc/ssh/ssh_config at work: Host * ForwardX11 yes ForwardX11Trusted yes My ~/.ssh/config at work: Host home HostName HOME_IP User azat PreferredAuthentications password ForwardX11 yes My ~/.Xauthority at work: -rw------- 1 azat azat 269 Jun 7 11:25 .Xauthority My ~/.Xauthority at home: -rw------- 1 azat azat 246 Jun 7 19:03 .Xauthority But it doesn't work After I make an ssh connection to home: $ echo $DISPLAY localhost:10.0 $ kate X11 connection rejected because of wrong authentication. X11 connection rejected because of wrong authentication. X11 connection rejected because of wrong authentication. X11 connection rejected because of wrong authentication. X11 connection rejected because of wrong authentication. X11 connection rejected because of wrong authentication. X11 connection rejected because of wrong authentication. X11 connection rejected because of wrong authentication. kate: cannot connect to X server localhost:10.0 I use iptables at home, but I've allowed port 22. According to what I've read that's all I need. UPD. With -vvv ... debug2: callback start debug2: x11_get_proto: /usr/bin/xauth list :0 2/dev/null debug1: Requesting X11 forwarding with authentication spoofing. debug2: channel 1: request x11-req confirm 1 debug2: client_session2_setup: id 1 debug2: fd 3 setting TCP_NODELAY debug2: channel 1: request pty-req confirm 1 ... When try to launch kate: debug1: client_input_channel_open: ctype x11 rchan 2 win 65536 max 16384 debug1: client_request_x11: request from 127.0.0.1 55486 debug2: fd 8 setting O_NONBLOCK debug3: fd 8 is O_NONBLOCK debug1: channel 2: new [x11] debug1: confirm x11 debug2: X11 connection uses different authentication protocol. X11 connection rejected because of wrong authentication. debug2: X11 rejected 2 i0/o0 debug2: channel 2: read failed debug2: channel 2: close_read debug2: channel 2: input open - drain debug2: channel 2: ibuf empty debug2: channel 2: send eof debug2: channel 2: input drain - closed debug2: channel 2: write failed debug2: channel 2: close_write debug2: channel 2: output open - closed debug2: X11 closed 2 i3/o3 debug2: channel 2: send close debug2: channel 2: rcvd close debug2: channel 2: is dead debug2: channel 2: garbage collecting debug1: channel 2: free: x11, nchannels 3 debug3: channel 2: status: The following connections are open: #1 client-session (t4 r0 i0/0 o0/0 fd 5/6 cc -1) #2 x11 (t7 r2 i3/0 o3/0 fd 8/8 cc -1) # The same as above repeate about 7 times kate: cannot connect to X server localhost:10.0 UPD2 Please provide your Linux distribution & version number. Are you using a default GNOME or KDE environment for X or something else you customized yourself? azat:~$ kded4 -version Qt: 4.7.4 KDE Development Platform: 4.6.5 (4.6.5) KDE Daemon: $Id$ Are you invoking ssh directly on a command line from a terminal window? What terminal are you using? xterm, gnome-terminal, or? How did you start the terminal running in the X environment? From a menu? Hotkey? or ? From terminal emulator `yakuake` Manualy press `Ctrl + N` and write commands Can you run xeyes from the same terminal window where the ssh -X fails? `xeyes` - is not installed But `kate` or another kde app is running Are you invoking the ssh command as the same user that you're logged into the X session as? From the same user UPD3 I also download ssh sources, and using debug2() write why it's report that version is different It see some cookies, and one of them is empty, another is MIT-MAGIC-COOKIE-1

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• Long pause when accessing DFS namespace

  - by Matt

  We've recently migrated our Windows network to use DFS for shared files. DFS is working well, except for one annoying problem: users experience a significant delay when they try to access a DFS namespace that they have not accessed for some time. I have tried to troubleshoot the issue but have not had any success so far, and I was hoping someone here may have some pointers to help resolve the problem. Firstly, some background on our network: The network uses a Windows 2008 functional level Active Directory domain with two Windows 2008 DCs and two DNS servers (one on each of the DCs). The network is DNS only - no WINS. All computers are located at the same site and connected by Gigabit Ethernet. We have approximately 20 Domain-based DFS namespaces in Windows 2008 mode, and each DFS namespace has two Windows 2008 DFS namespace servers (the same two servers for all namespaces). All namespace servers are in FQDN mode and all folder targets are specified using their FQDN. All computers are up-to-date with Service Packs and patches. The actual folder targets (i.e. the SMB shares our DFS folders point to) are scattered across several file and application servers, all running Windows 2008 bar two application servers which run Windows 2003 R2, with no replication setup at all (e.g. all DFS folders currently only have one folder target). Some more detail on the problem: The namespace access delay is generally 1 - 10 seconds long and seems to occur when a particular computer has not accessed the requested namespace for approximately five minutes or more. For example, if the user has not accessed \\domain.name\namespace1\ for more than five minutes and attempts to access \\domain.name\namespace1\ via Windows Explorer, the Explorer window will freeze for 1 - 10 seconds before finally resuming and displaying the folders that exist in \\domain.name\namespace1. If they then close the Explorer window and attempt to access \\domain.name\namespace1\ again within five minutes the contents will be displayed almost instantly - if they wait longer than five minutes it will go through the 1 - 10 second pause again. Once "inside" the namespace everything is nice and snappy, it's just the initial connection to the namespace that is slow. The browsing delays seem to affect all variants of Windows that we use (Windows 2008 x64 SP2, Windows 2003 R2 x86 SP2, Windows XP Pro x86 SP3) - it is possibly a bit worse in Windows XP / 2003 than in Windows 2008, but I'm not sure if the difference isn't just psychological. Accessing the underlying folder targets directly exhibits no delay at all - i.e. if the SMB shares pointed to by DFS are accessed directly (bypassing DFS) then there is no pause. During trouble-shooting I noticed that the "Cache duration" for all of our DFS roots is set to 300 seconds - 5 minutes. Given that this is the same amount of time required to trigger the pause I assume that this caching is somehow related, although I am unsure exactly what is cached on the client and hence what needs to be looked up again after 5 minutes have elapsed. In trying to resolve the problem I have already tried / checked the following (without success): Run dcdiag on both Domain Controllers - no problems found Done some basic DNS server checks without finding any problems - I don't know how to check the DNS servers in detail, but I would add that the network is not exhibiting any other strange behavior that may point to a DNS problem Disabled Anti-virus on clients and servers Removing one of the namespace servers from a couple of namespaces - no difference So that's where I'm up to - and I'm out of ideas. Can anyone suggest what may be causing the delays and/or what I should be trying next?

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• Useful Command-line Commands on Windows

  - by Sung Meister

  The aim for this Wiki is to promote using a command to open up commonly used applications without having to go through many mouse clicks - thus saving time on monitoring and troubleshooting Windows machines. Answer entries need to specify Application name Commands Screenshot (Optional) Shortcut to commands && - Command Chaining %SYSTEMROOT%\System32\rcimlby.exe -LaunchRA - Remote Assistance (Windows XP) appwiz.cpl - Programs and Features (Formerly Known as "Add or Remove Programs") appwiz.cpl @,2 - Turn Windows Features On and Off (Add/Remove Windows Components pane) arp - Displays and modifies the IP-to-Physical address translation tables used by address resolution protocol (ARP) at - Schedule tasks either locally or remotely without using Scheduled Tasks bootsect.exe - Updates the master boot code for hard disk partitions to switch between BOOTMGR and NTLDR cacls - Change Access Control List (ACL) permissions on a directory, its subcontents, or files calc - Calculator chkdsk - Check/Fix the disk surface for physical errors or bad sectors cipher - Displays or alters the encryption of directories [files] on NTFS partitions cleanmgr.exe - Disk Cleanup clip - Redirects output of command line tools to the Windows clipboard cls - clear the command line screen cmd /k - Run command with command extensions enabled color - Sets the default console foreground and background colors in console command.com - Default Operating System Shell compmgmt.msc - Computer Management control.exe /name Microsoft.NetworkAndSharingCenter - Network and Sharing Center control keyboard - Keyboard Properties control mouse(or main.cpl) - Mouse Properties control sysdm.cpl,@0,3 - Advanced Tab of the System Properties dialog control userpasswords2 - Opens the classic User Accounts dialog desk.cpl - opens the display properties devmgmt.msc - Device Manager diskmgmt.msc - Disk Management diskpart - Disk management from the command line dsa.msc - Opens active directory users and computers dsquery - Finds any objects in the directory according to criteria dxdiag - DirectX Diagnostic Tool eventvwr - Windows Event Log (Event Viewer) explorer . - Open explorer with the current folder selected. explorer /e, . - Open explorer, with folder tree, with current folder selected. F7 - View command history find - Searches for a text string in a file or files findstr - Find a string in a file firewall.cpl - Opens the Windows Firewall settings fsmgmt.msc - Shared Folders fsutil - Perform tasks related to FAT and NTFS file systems ftp - Transfers files to and from a computer running an FTP server service getmac - Shows the mac address(es) of your network adapter(s) gpedit.msc - Group Policy Editor gpresult - Displays the Resultant Set of Policy (RSoP) information for a target user and computer httpcfg.exe - HTTP Configuration Utility iisreset - To restart IIS InetMgr.exe - Internet Information Services (IIS) Manager 7 InetMgr6.exe - Internet Information Services (IIS) Manager 6 intl.cpl - Regional and Language Options ipconfig - Internet protocol configuration lusrmgr.msc - Local Users and Groups Administrator msconfig - System Configuration notepad - Notepad? ;) mmsys.cpl - Sound/Recording/Playback properties mode - Configure system devices more - Displays one screen of output at a time mrt - Microsoft Windows Malicious Software Removal Tool mstsc.exe - Remote Desktop Connection nbstat - displays protocol statistics and current TCP/IP connections using NBT ncpa.cpl - Network Connections netsh - Display or modify the network configuration of a computer that is currently running netstat - Network Statistics net statistics - Check computer up time net stop - Stops a running service. net use - Connects a computer to or disconnects a computer from a shared resource, or displays information about computer connections odbcad32.exe - ODBC Data Source Administrator pathping - A traceroute that collects detailed packet loss stats perfmon - Opens Reliability and Performance Monitor ping - Determine whether a remote computer is accessible over the network powercfg.cpl - Power management control panel applet quser - Display information about user sessions on a terminal server qwinsta - See disconnected remote desktop sessions reg.exe - Console Registry Tool for Windows regedit - Registry Editor rasdial - Connects to a VPN or a dialup network robocopy - Backup/Restore/Copy large amounts of files reliably rsop.msc - Resultant Set of Policy (shows the combined effect of all group policies active on the current system/login) runas - Run specific tools and programs with different permissions than the user's current logon provides sc - Manage anything you want to do with services. schtasks - Enables an administrator to create, delete, query, change, run and end scheduled tasks on a local or remote system. secpol.msc - Local Security Settings services.msc - Services control panel set - Displays, sets, or removes cmd.exe environment variables. set DIRCMD - Preset dir parameter in cmd.exe start - Starts a separate window to run a specified program or command start. - opens the current directory in the Windows Explorer. shutdown.exe - Shutdown or Reboot a local/remote machine subst.exe - Associates a path with a drive letter, including local drives systeminfo -Displays a comprehensive information about the system taskkill - terminate tasks by process id (PID) or image name tasklist.exe - List Processes on local or a remote machine taskmgr.exe - Task Manager telephon.cpl - Telephone and Modem properties timedate.cpl - Date and Time title - Change the title of the CMD window you have open tracert - Trace route wmic - Windows Management Instrumentation Command-line winver.exe - Find Windows Version wscui.cpl - Windows Security Center wuauclt.exe - Windows Update AutoUpdate Client

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• Diagnosing packet loss / high latency in Ubuntu

  - by Sam Gammon

  We have a Linux box (Ubuntu 12.04) running Nginx (1.5.2), which acts as a reverse proxy/load balancer to some Tornado and Apache hosts. The upstream servers are physically and logically close (same DC, sometimes same-rack) and show sub-millisecond latency between them: PING appserver (10.xx.xx.112) 56(84) bytes of data. 64 bytes from appserver (10.xx.xx.112): icmp_req=1 ttl=64 time=0.180 ms 64 bytes from appserver (10.xx.xx.112): icmp_req=2 ttl=64 time=0.165 ms 64 bytes from appserver (10.xx.xx.112): icmp_req=3 ttl=64 time=0.153 ms We receive a sustained load of about 500 requests per second, and are currently seeing regular packet loss / latency spikes from the Internet, even from basic pings: sam@AM-KEEN ~> ping -c 1000 loadbalancer PING 50.xx.xx.16 (50.xx.xx.16): 56 data bytes 64 bytes from loadbalancer: icmp_seq=0 ttl=56 time=11.624 ms 64 bytes from loadbalancer: icmp_seq=1 ttl=56 time=10.494 ms ... many packets later ... Request timeout for icmp_seq 2 64 bytes from loadbalancer: icmp_seq=2 ttl=56 time=1536.516 ms 64 bytes from loadbalancer: icmp_seq=3 ttl=56 time=536.907 ms 64 bytes from loadbalancer: icmp_seq=4 ttl=56 time=9.389 ms ... many packets later ... Request timeout for icmp_seq 919 64 bytes from loadbalancer: icmp_seq=918 ttl=56 time=2932.571 ms 64 bytes from loadbalancer: icmp_seq=919 ttl=56 time=1932.174 ms 64 bytes from loadbalancer: icmp_seq=920 ttl=56 time=932.018 ms 64 bytes from loadbalancer: icmp_seq=921 ttl=56 time=6.157 ms --- 50.xx.xx.16 ping statistics --- 1000 packets transmitted, 997 packets received, 0.3% packet loss round-trip min/avg/max/stddev = 5.119/52.712/2932.571/224.629 ms The pattern is always the same: things operate fine for a while (<20ms), then a ping drops completely, then three or four high-latency pings (1000ms), then it settles down again. Traffic comes in through a bonded public interface (we will call it bond0) configured as such: bond0 Link encap:Ethernet HWaddr 00:xx:xx:xx:xx:5d inet addr:50.xx.xx.16 Bcast:50.xx.xx.31 Mask:255.255.255.224 inet6 addr: <ipv6 address> Scope:Global inet6 addr: <ipv6 address> Scope:Link UP BROADCAST RUNNING MASTER MULTICAST MTU:1500 Metric:1 RX packets:527181270 errors:1 dropped:4 overruns:0 frame:1 TX packets:413335045 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:0 RX bytes:240016223540 (240.0 GB) TX bytes:104301759647 (104.3 GB) Requests are then submitted via HTTP to upstream servers on the private network (we can call it bond1), which is configured like so: bond1 Link encap:Ethernet HWaddr 00:xx:xx:xx:xx:5c inet addr:10.xx.xx.70 Bcast:10.xx.xx.127 Mask:255.255.255.192 inet6 addr: <ipv6 address> Scope:Link UP BROADCAST RUNNING MASTER MULTICAST MTU:1500 Metric:1 RX packets:430293342 errors:1 dropped:2 overruns:0 frame:1 TX packets:466983986 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:0 RX bytes:77714410892 (77.7 GB) TX bytes:227349392334 (227.3 GB) Output of uname -a: Linux <hostname> 3.5.0-42-generic #65~precise1-Ubuntu SMP Wed Oct 2 20:57:18 UTC 2013 x86_64 GNU/Linux We have customized sysctl.conf in an attempt to fix the problem, with no success. Output of /etc/sysctl.conf (with irrelevant configs omitted): # net: core net.core.netdev_max_backlog = 10000 # net: ipv4 stack net.ipv4.tcp_ecn = 2 net.ipv4.tcp_sack = 1 net.ipv4.tcp_fack = 1 net.ipv4.tcp_tw_reuse = 1 net.ipv4.tcp_tw_recycle = 0 net.ipv4.tcp_timestamps = 1 net.ipv4.tcp_window_scaling = 1 net.ipv4.tcp_no_metrics_save = 1 net.ipv4.tcp_max_syn_backlog = 10000 net.ipv4.tcp_congestion_control = cubic net.ipv4.ip_local_port_range = 8000 65535 net.ipv4.tcp_syncookies = 1 net.ipv4.tcp_synack_retries = 2 net.ipv4.tcp_thin_dupack = 1 net.ipv4.tcp_thin_linear_timeouts = 1 net.netfilter.nf_conntrack_max = 99999999 net.netfilter.nf_conntrack_tcp_timeout_established = 300 Output of dmesg -d, with non-ICMP UFW messages suppressed: [508315.349295 < 19.852453>] [UFW BLOCK] IN=bond1 OUT= MAC=<mac addresses> SRC=118.xx.xx.143 DST=50.xx.xx.16 LEN=68 TOS=0x00 PREC=0x00 TTL=51 ID=43221 PROTO=ICMP TYPE=3 CODE=1 [SRC=50.xx.xx.16 DST=118.xx.xx.143 LEN=40 TOS=0x00 PREC=0x00 TTL=249 ID=10220 DF PROTO=TCP SPT=80 DPT=53817 WINDOW=8190 RES=0x00 ACK FIN URGP=0 ] [517787.732242 < 0.443127>] Peer 190.xx.xx.131:59705/80 unexpectedly shrunk window 1155488866:1155489425 (repaired) How can I go about diagnosing the cause of this problem, on a Debian-family Linux box?

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• What would make a noise in a PC on graphics operations on a passively-cooled system?

  - by T.J. Crowder

  I have this system based on the Intel D510MO motherboard, which is basically an Atom D510 (dual-core HT Atom w/built-in GPU), an Intel NM10 chipset, and a Realtek Gigabit LAN controller. It's entirely passively cooled. I noticed almost immediately that there was a kind of very, very soft noise that corresponded with graphics operations, sort of the noise you'd get if you had a sheet of flat paper and slid something really light across it — but more electronic than that. I wrote it off as observation error and/or disk activity triggered by the graphics operation (although the latter seemed like a lot of unnecessary disk activity). It isn't. I got curious enough that I finally did a few controlled experiments, and here's what I've determined: It isn't the HDD. For one thing, the sounds the HDD makes (when seeking, when reading or writing, when just sitting there spinning) is different. For another, I used sudo hdparm -y /dev/sda (I'm using Ubuntu 10.04 LTS) to temporarily put the disk on standby while making sure that non-disk graphics op was happening in a loop. The disk spun down, but the other sound continued, corresponding perfectly with the timing of the graphics op. (Then the disk spun up again, but it takes long enough that I could rule out the HDD.) It isn't the monitor; I ensured the two were well physically-separated and the sound was definitely coming from the main box. It isn't something else in the room; the sound is coming from the box. It isn't cross-talk to an audio circuit coming out the speakers. (It doesn't have any speakers.) It isn't my mouse (e.g., when I'm trying to make graphics ops happen); the sound happens if I set up a recurring operation and don't use the mouse at all, or if I lift the mouse off the table slightly (but enough that the laser still registers movement). It isn't the voices in my head; they never whisper like that. Other observations: It doesn't seem to matter what the graphics operation is; anything that changes what's on the screen seems to do it. I get the sound when moving the mouse over the Chromium tab bar (which makes the tab backgrounds change); I get it when a web page has a counter on it that changes the text on the page: I get it when dragging window contents around. The sound is very, very slightly louder if the graphics op is larger, like scrolling a text area when writing a question on superuser.com, than for smaller operations like the tick counter on the web page. But it's very slight. It's fairly loud (and of good duration) when the op involves color changes to substantial surface areas. For instance, when asking a question here on superuser and you move the cursor between the question box and the tag box, and the help to the right fades out, changes, and fades back in. (Yet another example related to the web browser, so let me say: I hear it when operations completely unrelated to the web browser as well.) It doesn't sound like arcing or anything like that (I'd've shut off the machine Right Quick Like if it did). Moving windows does it. Scrolling windows (by and large) doesn't. I have the feeling I've heard this sort of thing before, when all system fans were on low and such, with other systems — but (again) written it off as observational error. For all the world it's like I'm hearing the CPU working (as opposed to the GPU; note the window scroll thing above) or data being transferred somewhere, but that just seems...unlikely. So what am I hearing? This may seem like a very localized question, but perhaps other silent PC enthusiasts may be interested as well...

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