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  • Finding header files

    - by rwallace
    A C or C++ compiler looks for header files using a strict set of rules: relative to the directory of the including file (if "" was used), then along the specified and default include paths, fail if still not found. An ancillary tool such as a code analyzer (which I'm currently working on) has different requirements: it may for a number of reasons not have the benefit of the setup performed by a complex build process, and have to make the best of what it is given. In other words, it may find a header file not present in the include paths it knows, and have to take its best shot at finding the file itself. I'm currently thinking of using the following algorithm: Start in the directory of the including file. Is the header file found in the current directory or any subdirectory thereof? If so, done. If we are at the root directory, the file doesn't seem to be present on this machine, so skip it. Otherwise move to the parent of the current directory and go to step 2. Is this the best algorithm to use? In particular, does anyone know of any case where a different algorithm would work better?

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  • An ideal way to decode JSON documents in C?

    - by AzizAG
    Assuming I have an API to consume that uses JSON as a data transmission method, what is an ideal way to decode the JSON returned by each API resource? For example, in Java I'd create a class for each API resource then initiate an object of that class and consume data from it. for example: class UserJson extends JsonParser { public function UserJson(String document) { /*Initial document parsing goes here...*/ } //A bunch of getter methods . . . . } The probably do something like this: UserJson userJson = new UserJson(jsonString);//Initial parsing goes in the constructor String username = userJson.getName();//Parse JSON name property then return it as a String. Or when using a programming language with associative arrays(i.e., hash table) the decoding process doesn't require creating a class: (PHP) $userJson = json_decode($jsonString);//Decode JSON as key=>value $username = $userJson['name']; But, when I'm programming in procedural programming languages (C), I can't go with either method, since C is neither OOP nor supports associative arrays(by default, at least). What is the "correct" method of parsing pre-defined JSON strings(i.e., JSON documents specified by the API provider via examples or documentation)? The method I'm currently using is creating a file for each API resource to parse, the problem with this method is that it's basically a lousy version of the OOP method, as it looks exactly like the OOP method but doesn't provide any OOP benefits(e.g., can't pass an object of the parser, etc.). I've been thinking about encapsulating each API resource parser file in a publicly accessed structure(pointing all functions/publicly usable variables to the structure) then accessing the parser file code from within the structure(parser.parse(), parser.getName(), etc.). As this way looks a bit better than the my current method, it still just a rip off the OOP way, isn't it? Any suggestions for methods to parse JSON documents on procedural programming lanauges? Any comments on the methods I'm currently using(either 3 of them)?

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  • Authorization design-pattern / practice?

    - by Lawtonfogle
    On one end, you have users. On the other end, you have activities. I was wondering if there is a best practice to relate the two. The simplest way I can think of is to have every activity have a role, and assign every user every role they need. The problem is that this gets really messy in practice as soon as you go beyond a trivial system. A way I recently designed was to have users who have roles, and roles have privileges, and activities require some combinations of privileges. For the trivial case, this is more complex, but I think it will scale better. But after I implemented it, I felt like it was overkill for the system I had. Another option would be to have users, who have roles, and activities require you to have a certain role to perform with many activities sharing roles. A more complex variant of this would given activities many possible roles, which you only needed one of. And an even more complex variant would be to allow logical statements of role ownership to use an activity (i.e. Must have A and (B exclusive or C) and must not have D). I could continue to list more, but I think this already gives a picture. And many of these have trade offs. But in software design, there are oftentimes solutions, while perhaps not perfect in every possible case, are clearly top of the pack to an extent it isn't even considered opinion based (i.e. how to store passwords, plain text is worse, hashing better, hashing and salt even better, despite the increased complexity of each level) (i.e. 2, Smart UI designs for applications are bad, even if it is subjective as to what the best design is). So, is there a best practice for authorization design that is not purely opinion based/subjective?

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  • How to rotate a sprite using multi-touch with AndEngine?

    - by 786
    I am new to Android game development. I am using AndEngine GLES-2. I have created a box with a sprite. This box is now draggable by using the code below. It works fine. But I want multi-touch on this: I want to rotate the sprite with two fingers on that box, and to keep it draggable. I've no idea how do do that, which way should I go? final float centerX = (CAMERA_WIDTH - this.mBox.getWidth()) / 2; final float centerY = (CAMERA_HEIGHT - this.mBox.getHeight()) / 2; Box = new Sprite(centerX, centerY, this.mBox, this.getVertexBufferObjectManager()) { public boolean onAreaTouched(TouchEvent pSceneTouchEvent, float pTouchAreaLocalX, float pTouchAreaLocalY) { this.setPosition(pSceneTouchEvent.getX() - this.getWidth()/ 2, pSceneTouchEvent.getY() - this.getHeight() / 2); float pValueX = pSceneTouchEvent.getX(); float pValueY = CAMERA_HEIGHT-pSceneTouchEvent.getY(); float dx = pValueX - gun.getX(); float dy = pValueY - gun.getY(); double Radius = Math.atan2(dy,dx); double Angle = Radius * 360 ; Box.setRotation((float)Math.toDegrees(Angle)); return true; }

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  • JavaOne Latin America Sessions

    - by Tori Wieldt
    The stars of Java are gathering in São Paulo next week. Here are just a few of the outstanding sessions you can attend at JavaOne Latin America: “Designing Java EE Applications in the Age of CDI” Michel Graciano, Michael Santos “Don’t Get Hacked! Tips and Tricks for Securing Your Java EE Web Application” Fabiane Nardon, Fernando Babadopulos “Java and Security Programming” Juan Carlos Herrera “Java Craftsmanship: Lessons Learned on How to Produce Truly Beautiful Java Code” Edson Yanaga “Internet of Things with Real Things: Java + Things – API + Raspberry PI + Toys!” Vinicius Senger “OAuth 101: How to Protect Your Resources in a Web-Connected Environment” Mauricio Leal “Approaching Pure REST in Java: HATEOAS and HTTP Tuning” Eder Ignatowicz “Open Data in Politics: Using Java to Follow Your Candidate” Bruno Gualda, Thiago Galbiatti Vespa "Java EE 7 Platform: More Productivity and Integrated HTML" Arun Gupta  Go to the JavaOne site for a complete list of sessions. JavaOne Latin America will in São Paulo, 4-6 December 2012 at the Transamerica Expo Center. Register by 3 December and Save R$ 300,00! Para mais informações ou inscrição ligue para (11) 2875-4163. 

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  • grub workaround for cannot find UUID in dual boot system fails and now grub won't boot anything

    - by keepitsimpleengineer
    New clean install of x86 11.10 desktop. Dual boot with windows XP and Linux on separate drives. After install grub will not boot Windows, but by changing boot drive boots fine. When I go to fix this I find from http://bootinfoscript.sourceforge.net/ and a link to http://sourceforge.net/apps/mediawiki/bootinfoscript/index.php?title=Boot_Problems:search my problem, the message on the grub boot error screen: error: no such device: 6??????? So I follow the Step2 and compare the output of: sudo blkid and sudo nano /boot/grub/grub.cfg The UUIDs in both match for the Windows drive, so I do the fix in Step 4 "remove the search lines for …" in /usr/lib/grub/grub-mkconfig_lib, commenting out the three lines as before? # if fs_uuid="`${grub_probe} --device ${device} --target=fs_uuid 2> /dev/null`" ; then # echo "search --no-floppy --fs-uuid --set ${fs_uuid}" # fi I run sudo update-grub and check /etc/default/grub.cfg and see that it now identifies the Windows partition not by UUID, which I suppose is the workaround. But now when I try to boot 11.10 Desktop, I get: error: no such partition… … and when I try to boot Windows, I get: error: invalid signature. So Now, how do I fix this… The boot problem and find a workaround that works?

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  • How is software used in critical life-or-death systems tested?

    - by waiwai933
    An airplane, as opposed to, for example, a website, is a system where any failure in certain systems is completely unacceptable, since errors in e.g. flight monitoring can cause the autopilot to malfunction and do a dive. Obviously, this doesn't happen since the brilliant engineers at Boeing and Airbus have checks in the autopilot to make sure it doesn't suddenly decide a dive is a perfectly acceptable and safe maneuver. Or perhaps the computer crashes, and the pilots in the newer fly-by-wire aircraft can no longer actually fly the plane. Of course, there are various safety procedures and redundancies built into these systems to prevent a crash (of both the software and the aircraft). However, on the other hand, it's quite obvious that software isn't perfect—both open source and closed source software do crash regularly, and only the simplest "Hello World" program doesn't fail. How can the engineers who design the software systems in the aeronautic, medical, and other life-or-death industries manage to test their software so that it doesn't fail (and if it does fail, at least fail gracefully)? I'm desperately hoping that you're not all going to go: "Oh, I work for Boeing/Airbus/(some other company) and it's not! Have fun on your next flight/hospital visit."

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  • Reading OpenDocument spreadsheets using C#

    - by DigiMortal
    Excel with its file formats is not the only spreadsheet application that is widely used. There are also users on Linux and Macs and often they are using OpenOffice and other open-source office packages that use ODF instead of OpenXML. In this post I will show you how to read Open Document spreadsheet in C#. Importer as example My previous post about importers showed you how to build flexible importers support to your web application. This post introduces you practical example of one of my importers. Of course, sensitive code is omitted. We start with ODS importer class and we add new methods as we go. public class OdsImporter : ImporterBase {     public OdsImporter()     {     }       public override string[] SupportedFileExtensions     {         get { return new[] { "ods" }; }     }       public override ImportResult Import(Stream fileStream, long companyId, short year)     {         string contentXml = GetContentXml(fileStream);           var result = new ImportResult();         var doc = XDocument.Parse(contentXml);           var rows = doc.Descendants("{urn:oasis:names:tc:opendocument:xmlns:table:1.0}table-row").Skip(1);           foreach (var row in rows)         {             ImportRow(row, companyId, year, result);         }           return result;     } } The class given here just extends base class for importers (previous post uses interface but as I already told there you move to abstract base class when writing code for real projects). Import method reads data from *.ods file, parses it (it is XML), finds all data rows and imports data. As you may see then first row is skipped. This is because the first row on my sheet is always headers row. Reading ODS file Our import method starts with getting XML from *.ods file. ODS files like OpenXml files are zipped containers that contain different files. We need content.xml as all data is kept there. To get the contents of file we use SharpZipLib library to read uploaded file as *.zip file. private static string GetContentXml(Stream fileStream) {     var contentXml = "";       using (var zipInputStream = new ZipInputStream(fileStream))     {         ZipEntry contentEntry = null;         while ((contentEntry = zipInputStream.GetNextEntry()) != null)         {             if (!contentEntry.IsFile)                 continue;             if (contentEntry.Name.ToLower() == "content.xml")                 break;         }           if (contentEntry.Name.ToLower() != "content.xml")         {             throw new Exception("Cannot find content.xml");         }           var bytesResult = new byte[] { };         var bytes = new byte[2000];         var i = 0;           while ((i = zipInputStream.Read(bytes, 0, bytes.Length)) != 0)         {             var arrayLength = bytesResult.Length;             Array.Resize<byte>(ref bytesResult, arrayLength + i);             Array.Copy(bytes, 0, bytesResult, arrayLength, i);         }         contentXml = Encoding.UTF8.GetString(bytesResult);     }     return contentXml; } If here is content.xml file then we stop browsing the file. We read this file to memory and return it as UTF-8 format string. Importing rows Our last task is to import rows. We use special method for this as we have to handle some tricks here. To keep files smaller the cell count on row is not always the same. If we have more than one empty cell one after another then ODS keeps only one cell for sequential empty cells. This cell has attribute called number-columns-repeated and it’s value is set to the number of sequential empty cells. This is why we use two indexers for cells collection. private void ImportRow(XElement row, ImportResult result) {     var cells = (from c in row.Descendants()                 where c.Name == "{urn:oasis:names:tc:opendocument:xmlns:table:1.0}table-cell"                 select c).ToList();       var dto = new DataDto();       var count = cells.Count;     var j = -1;       for (var i = 0; i < count; i++)     {         j++;         var cell = cells[i];         var attr = cell.Attribute("{urn:oasis:names:tc:opendocument:xmlns:table:1.0}number-columns-repeated");         if (attr != null)         {             var numToSkip = 0;             if (int.TryParse(attr.Value, out numToSkip))             {                 j += numToSkip - 1;             }         }           if (i > 30) break;         if (j == 0)         {             dto.SomeProperty = cells[i].Value;         }         if (j == 1)         {             dto.SomeOtherProperty = cells[i].Value;         }         // some more data reading     }       // save data } You can define your own class for import results and add there all problems found during data import. Your application gets the results and shows them to user. Conclusion Reading ODS files may seem to complex task but actually it is very easy if we need only data from those documents. We can use some zip-library to get the content file and then parse it to XML. It is not hard to go through the XML but there are some optimization tricks we have to know. The code here is safe to use in web applications as it is not using any API-s that may have special needs to server and infrastructure.

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  • Logistics of code reuse (OOP)

    - by Ominus
    One of the driving points behind OOP is code reuse. I am curious about the actual logistics of this and how others both in team or solo handle it. For example lets say you have 5 projects you have worked on and between them you have a ton of classes that you think would be useful in other projects. How do you store them? Are they just in the normal project repository or do you break out the relevant classes and have them (as now copies) in another unique source repository that only houses code pieces that are intended to be reused? How do you go about finding or even knowing that there is a good piece of code out there that you should reuse? It's easier if your solo because you remember that you have coded something similar but even then it becomes kind of a stretch. If there is some way that you are storing these pieces of code do you then also have them indexed and searchable by tag or something. I fear that it just boils down to some tribal knowledge that you just know that for situation A i need solution B and we have a good piece of code that already can help here. A bit verbose but I hope you get what I am aiming at. If you think of a better way to make the question clearer please have at it :) TIA!

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  • Desktop application, dependency injection

    - by liori
    I am thinking of applying a real dependency injection library to my toy C#/GTK# desktop application. I chose NInject, but I think this is irrelevant to my question. There is a database object, a main window and several utility window classes. It's clear that I can inject the database into every window object, so here DI is useful. But does it make sense to inject utility window classes into other window classes? Example: I have classes such as: class MainWindow {…} class AddItemWindow {…} class AddAttachmentWindow {…} class BrowseItemsWindow {…} class QueryBuilderWindow {…} class QueryBrowserWindow {…} class PreferencesWindow {…} … Each of the utility classes can be opened from MainWindow. Some utility windows can also be opened from other utility windows. Generally, there might be a really complex graph of who can open whom. So each of those classes might need quite a lot of other window classes injected. I'm worried that such usage will go against the suggestion not to inject too many classes at once and become a code smell. Should I use some kind of a service locator object here?

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  • How to write your unit tests to switch between NUnit and MSTest

    - by Justin Jones
    On my current project I found it useful to use both NUnit and MsTest for unit testing. When using ReSharper for running unit tests, it just simply works better with NUnit, and on large scale projects NUnit tends to run faster. We would have just simply used NUnit for everything, but MSTest gave us a few bonuses out of the box that were hard to pass up. Namely code coverage (without having to shell out thousands of extra dollars for the privilege) and integrated tests into the build process. I’m one of those guys who wants the build to fail if the unit tests don’t pass. If they don’t pass, there’s no point in sending that build on to QA. So making the build work with MsTest is easiest if you just create a unit test project in your solution. This adds the right references and project type Guids in the project file so that everything just automagically just works. Then (using NuGet of course) you add in NUnit. At the top of your test file, remove the using statements that refer to MsTest and replace it with the following: #if NUNIT using NUnit.Framework; #else using TestFixture = Microsoft.VisualStudio.TestTools.UnitTesting.TestClassAttribute; using Test = Microsoft.VisualStudio.TestTools.UnitTesting.TestMethodAttribute; using TestFixtureSetUp = Microsoft.VisualStudio.TestTools.UnitTesting.TestInitializeAttribute; using SetUp = Microsoft.VisualStudio.TestTools.UnitTesting.TestInitializeAttribute; using Microsoft.VisualStudio.TestTools.UnitTesting; #endif Basically I’m taking the NUnit naming conventions, and redirecting them to MsTest. You can go the other way, of course. I only chose this direction because I had already written the tests as NUnit tests. NUnit and MsTest provide largely the same functionality with slightly differing class names. There’s few actual differences between then, and I have not run into them on this project so far. To run the tests as NUnit tests, simply open up the project properties tab and add the compiler directive NUNIT. Remove it, and you’re back in MsTest land.

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  • New Feature! Automatic Categories for Geekswithblogs.net

    - by Jeff Julian
    One of the features we have been working on is a way to categorize posts without the need of all our bloggers getting on the same page with what categories we have and making them select the categories.  Johnny Kauffman, one of our team members at AJI Software, developed what we call the Sherlock Project over the past few months.  Sherlock is a category suggestion engine based on the content within the posts.  Now, after a post is published, Sherlock will investigate the content and come up with the suggested categories that content fits in.  This will now allow you to go to the specific topics you are interested in and see all the related posts. This is just the beginning, so many more opportunities will arise now that we have our content organized.  One of the first features I will be adding is RSS feeds for each category and sub category.  If you are into ALM, we will have a feed for that! I hope you enjoy these and the engine will continue to get better as we start testing the data.  I hope you are as excited about this as I am :D.  Technorati Tags: Geekswithblogs.net,Categories,Sherlock

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  • cpu use goes to 100% when I lock the screen

    - by gianni
    Whenever I lock the screen, after a certain amount of time, the cpu and the cpu fan use go up near the limit, and it returns back to normal the moment I unlock the screen again (as shown by psensor). How can I find out what process is responsible for this? I've tried with "top -S", and the result is this... PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND 2114 me 20 0 326m 104m 40m R 16 2.6 66:50.03 compiz 1234 root 20 0 396m 152m 98m R 6 3.8 20:23.88 Xorg 2204 me 20 0 160m 38m 30m S 4 1.0 0:33.35 yakuake 2446 me 20 0 206m 18m 12m S 4 0.5 6:32.18 psensor 2280 me 20 0 220m 18m 10m S 2 0.5 5:01.60 unity-panel 9138 me 20 0 154m 27m 15m S 2 0.7 0:03.63 plugin-cont 2282 me 20 0 65800 5272 3316 S 1 0.1 4:36.90 hud-service 2143 me 20 0 140m 11m 8352 S 1 0.3 2:50.16 indicator-m 9095 me 20 0 720m 253m 36m S 1 6.4 0:26.34 firefox 2076 me 20 0 7168 3484 828 S 1 0.1 1:46.53 dbus-daemon 2307 me 20 0 55000 5132 3632 S 1 0.1 2:01.55 indicator-a 2557 me 20 0 86328 6028 4576 S 0 0.1 1:44.71 conky 6290 me 20 0 2836 1296 964 R 0 0.0 0:29.64 top 6291 me 20 0 2836 1188 884 S 0 0.0 0:29.49 top 1 root 20 0 3644 1984 1284 S 0 0.0 60:57.76 init specs: ubuntu 12.04 fresh install intel core i5 4gB ram

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  • Assigning valid moves on board game

    - by Kunal4536
    I am making a board game in unity 4.3 2d similar to checkers. I have added an empty object to all the points where player can move and added a box collider to each empty object.I attached a click to move script to each player token. Now I want to assign valid moves. e.g. as shown in picture... Players can only move on vertex of each square.Player can only move to adjacent vertex.Thus it can only move from red spot to yellow and cannot move to blue spot.There is another condition which is : if there is the token of another player at the yellow spot then the player cannot move to that spot. Instead it will have to go from red to green spot. How can I find the valid moves of the player by scripting. I have another problem with click to move. When I click all the objects move to that position.But I only want to move a single token. So what can i add to script to select a specific object and then click to move the specific object.Here is my script for click to move. var obj:Transform; private var hitPoint : Vector3; private var move: boolean = false; private var startTime:float; var speed = 1; function Update () { if(Input.GetKeyDown(KeyCode.Mouse0)) { var hit : RaycastHit; // no point storing this really var ray = Camera.main.ScreenPointToRay (Input.mousePosition); if (Physics.Raycast (ray, hit, 10000)) { hitPoint = hit.point; move = true; startTime = Time.time; } } if(move) { obj.position = Vector3.Lerp(obj.position, hitPoint, Time.deltaTime * speed); if(obj.position == hitPoint) { move = false; } } }`

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  • What would be a good filter to create 'magnetic deformers' from a depth map?

    - by sebf
    In my project, I am creating a system for deforming a highly detailed mesh (clothing) so that it 'fits' a convex mesh. To do this I use depth maps of the item and the 'hull' to determine at what point in world space the deviation occurs and the extent. Simply transforming all occluded vertices to the depths as defined by the 'hull' is fairly effective, and has good performance, but it suffers the problem of not preserving the features of the mesh and requires extensive culling to avoid false-positives. I would like instead to generate from the depth deviation map a set of simple 'deformers' which will 'push'* all vertices of the deformed mesh outwards (in world space). This way, all features of the mesh are preserved and there is no need to have complex heuristics to cull inappropriate vertices. I am not sure how to go about generating this deformer set however. I am imagining something like an algorithm that attempts to match a spherical surface to each patch of contiguous deviations within a certain range, but do not know where to start doing this. Can anyone suggest a suitable filter or algorithm for generating deformers? Or to put it another way 'compressing' a depth map? (*Push because its fitting to a convex 'bulgy' humanoid so transforms are likely to be 'spherical' from the POV of the surface.)

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  • Of transactions and Mongo

    - by Nuri Halperin
    Originally posted on: http://geekswithblogs.net/nuri/archive/2014/05/20/of-transactions-and-mongo-again.aspxWhat's the first thing you hear about NoSQL databases? That they lose your data? That there's no transactions? No joins? No hope for "real" applications? Well, you *should* be wondering whether a certain of database is the right one for your job. But if you do so, you should be wondering that about "traditional" databases as well! In the spirit of exploration let's take a look at a common challenge: You are a bank. You have customers with accounts. Customer A wants to pay B. You want to allow that only if A can cover the amount being transferred. Let's looks at the problem without any context of any database engine in mind. What would you do? How would you ensure that the amount transfer is done "properly"? Would you prevent a "transaction" from taking place unless A can cover the amount? There are several options: Prevent any change to A's account while the transfer is taking place. That boils down to locking. Apply the change, and allow A's balance to go below zero. Charge person A some interest on the negative balance. Not friendly, but certainly a choice. Don't do either. Options 1 and 2 are difficult to attain in the NoSQL world. Mongo won't save you headaches here either. Option 3 looks a bit harsh. But here's where this can go: ledger. See, and account doesn't need to be represented by a single row in a table of all accounts with only the current balance on it. More often than not, accounting systems use ledgers. And entries in ledgers - as it turns out – don't actually get updated. Once a ledger entry is written, it is not removed or altered. A transaction is represented by an entry in the ledger stating and amount withdrawn from A's account and an entry in the ledger stating an addition of said amount to B's account. For sake of space-saving, that entry in the ledger can happen using one entry. Think {Timestamp, FromAccountId, ToAccountId, Amount}. The implication of the original question – "how do you enforce non-negative balance rule" then boils down to: Insert entry in ledger Run validation of recent entries Insert reverse entry to roll back transaction if validation failed. What is validation? Sum up the transactions that A's account has (all deposits and debits), and ensure the balance is positive. For sake of efficiency, one can roll up transactions and "close the book" on transactions with a pseudo entry stating balance as of midnight or something. This lets you avoid doing math on the fly on too many transactions. You simply run from the latest "approved balance" marker to date. But that's an optimization, and premature optimizations are the root of (some? most?) evil.. Back to some nagging questions though: "But mongo is only eventually consistent!" Well, yes, kind of. It's not actually true that Mongo has not transactions. It would be more descriptive to say that Mongo's transaction scope is a single document in a single collection. A write to a Mongo document happens completely or not at all. So although it is true that you can't update more than one documents "at the same time" under a "transaction" umbrella as an atomic update, it is NOT true that there' is no isolation. So a competition between two concurrent updates is completely coherent and the writes will be serialized. They will not scribble on the same document at the same time. In our case - in choosing a ledger approach - we're not even trying to "update" a document, we're simply adding a document to a collection. So there goes the "no transaction" issue. Now let's turn our attention to consistency. What you should know about mongo is that at any given moment, only on member of a replica set is writable. This means that the writable instance in a set of replicated instances always has "the truth". There could be a replication lag such that a reader going to one of the replicas still sees "old" state of a collection or document. But in our ledger case, things fall nicely into place: Run your validation against the writable instance. It is guaranteed to have a ledger either with (after) or without (before) the ledger entry got written. No funky states. Again, the ledger writing *adds* a document, so there's no inconsistent document state to be had either way. Next, we might worry about data loss. Here, mongo offers several write-concerns. Write-concern in Mongo is a mode that marshals how uptight you want the db engine to be about actually persisting a document write to disk before it reports to the application that it is "done". The most volatile, is to say you don't care. In that case, mongo would just accept your write command and say back "thanks" with no guarantee of persistence. If the server loses power at the wrong moment, it may have said "ok" but actually no written the data to disk. That's kind of bad. Don't do that with data you care about. It may be good for votes on a pole regarding how cute a furry animal is, but not so good for business. There are several other write-concerns varying from flushing the write to the disk of the writable instance, flushing to disk on several members of the replica set, a majority of the replica set or all of the members of a replica set. The former choice is the quickest, as no network coordination is required besides the main writable instance. The others impose extra network and time cost. Depending on your tolerance for latency and read-lag, you will face a choice of what works for you. It's really important to understand that no data loss occurs once a document is flushed to an instance. The record is on disk at that point. From that point on, backup strategies and disaster recovery are your worry, not loss of power to the writable machine. This scenario is not different from a relational database at that point. Where does this leave us? Oh, yes. Eventual consistency. By now, we ensured that the "source of truth" instance has the correct data, persisted and coherent. But because of lag, the app may have gone to the writable instance, performed the update and then gone to a replica and looked at the ledger there before the transaction replicated. Here are 2 options to deal with this. Similar to write concerns, mongo support read preferences. An app may choose to read only from the writable instance. This is not an awesome choice to make for every ready, because it just burdens the one instance, and doesn't make use of the other read-only servers. But this choice can be made on a query by query basis. So for the app that our person A is using, we can have person A issue the transfer command to B, and then if that same app is going to immediately as "are we there yet?" we'll query that same writable instance. But B and anyone else in the world can just chill and read from the read-only instance. They have no basis to expect that the ledger has just been written to. So as far as they know, the transaction hasn't happened until they see it appear later. We can further relax the demand by creating application UI that reacts to a write command with "thank you, we will post it shortly" instead of "thank you, we just did everything and here's the new balance". This is a very powerful thing. UI design for highly scalable systems can't insist that the all databases be locked just to paint an "all done" on screen. People understand. They were trained by many online businesses already that your placing of an order does not mean that your product is already outside your door waiting (yes, I know, large retailers are working on it... but were' not there yet). The second thing we can do, is add some artificial delay to a transaction's visibility on the ledger. The way that works is simply adding some logic such that the query against the ledger never nets a transaction for customers newer than say 15 minutes and who's validation flag is not set. This buys us time 2 ways: Replication can catch up to all instances by then, and validation rules can run and determine if this transaction should be "negated" with a compensating transaction. In case we do need to "roll back" the transaction, the backend system can place the timestamp of the compensating transaction at the exact same time or 1ms after the original one. Effectively, once A or B visits their ledger, both transactions would be visible and the overall balance "as of now" would reflect no change.  The 2 transactions (attempted/ reverted) would be visible , since we do actually account for the attempt. Hold on a second. There's a hole in the story: what if several transfers from A to some accounts are registered, and 2 independent validators attempt to compute the balance concurrently? Is there a chance that both would conclude non-sufficient-funds even though rolling back transaction 100 would free up enough for transaction 117 (some random later transaction)? Yes. there is that chance. But the integrity of the business rule is not compromised, since the prime rule is don't dispense money you don't have. To minimize or eliminate this scenario, we can also assign a single validation process per origin account. This may seem non-scalable, but it can easily be done as a "sharded" distribution. Say we have 11 validation threads (or processing nodes etc.). We divide the account number space such that each validator is exclusively responsible for a certain range of account numbers. Sounds cunningly similar to Mongo's sharding strategy, doesn't it? Each validator then works in isolation. More capacity needed? Chop the account space into more chunks. So where  are we now with the nagging questions? "No joins": Huh? What are those for? "No transactions": You mean no cross-collection and no cross-document transactions? Granted - but don't always need them either. "No hope for real applications": well... There are more issues and edge cases to slog through, I'm sure. But hopefully this gives you some ideas of how to solve common problems without distributed locking and relational databases. But then again, you can choose relational databases if they suit your problem.

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  • Keeping files that are often changed in sync between desktop and laptop

    - by N.N.
    I'm looking for a way to keep a desktop and a laptop in sync. What I want to keep in sync are some folders, mainly ~/Documents, that are changed often when working on them. If it matters I can connect to my desktop from anywhere via an URL but my laptop is harder to access since it might be behind NAT and such. I have been looking at Ubuntu One but it seems to not go well with working on documents written in LaTeX. If I work on a .tex file in the Ubuntu One directory and compile it (with pdflatex) every now and then (as often as every 10 sec when working) it will create several new files including a pdf which are uploaded to Ubuntu One and this seems stupid since it will create continuous upload when working on .tex files. I also usually keep .tex documents version controlled by git and then every commit (which also can happen frequently) will cause upload (by changes in ./.git) so that it happens continuously when working. Another example is editing images that are saved often. What I think would be best is for sync to happen every tenth minute or at the end of every working session (but there might be some other way to handle this?).

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  • Distributed Rendering in the UDK and Unity

    - by N0xus
    At the moment I'm looking at getting a game engine to run in a CAVE environment. So far, during my research I've seen a lot of people being able to get both Unity and the Unreal engine up and running in a CAVE (someone did get CryEngine to work in one, but there is little research data about it). As of yet, I have not cemented my final choice of engine for use in the next stage of my project. I've experience in both, so the learning curve will be gentle on both. And both of the engines offer stereoscopic rendering, either already inbuilt with ReadD (Unreal) or by doing it yourself (Unity). Both can also make use of other input devices as well, such as the kinect or other devices. So again, both engines are still on the table. For the last bit of my preliminary research, I was advised to see if either, or both engines could do distributed rendering. I was advised this, as the final game we make could go into a variety of differently sized CAVEs. The one I have access to is roughly 2.4m x 3m cubed, and have been duly informed that this one is a "baby" compared to others. So, finally onto my question: Can either the Unreal Engine, or Unity Engine make it possible for developers to allow distributed rendering? Either through in built devices, or by creating my own plugin / script?

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  • rel="nofollow" SEO impact

    - by Torez
    I saw a technique used where there was a block with three parts: 1. Image (wrapped in an anchor tag) 2. Heading (anchor tag with heading text) 3. Paragraph (regular p tag with synopsis content) e.g. <li class="block"> <a rel="nofollow" class="thumb" href="#"><img src="images/placeholder_service_thumbnail.jpg" alt="" /></a> <a class="h3" href="#"Good SEO Heading</a> <pPellentesque habitant morbi tristique senectus et netus et malesuada fames ac turpis egestas. Vestibulum tortor quam, feugiat vitae, ultricies eget, tempor sit amet, ante. Donec eu...</p> </li> With the image tag there was a rel="nofollow" on the wrapped anchor tag. So the idea is that the users still has the ability to click the image and go to the details page, but the image link does not rank. When users click on the heading text, that is only what ranks for that specific page. Q: Is this the correct approach? Does this even do anything? What is the best practice?

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  • How do I backup my customer's data?

    - by marcamillion
    If you run a SaaS app, or work on one, I would love to hear from you. Where the safety and security of your customer's data is paramount, how do you secure it and back it up? I would love to know your main host (e.g. Heroku, Engine Yard, Rackspace, MediaTemple, etc.) and who you use for your backup. Be as detailed as possible - e.g. a quick overview of your service and the data you store (images for instance), what happens with the images when the user uploads them (e.g. they go to your Linode VPS, and posted to the site for them to see - then they are automatically sent to AWS or wherever, then once a week they are backed up to tape by the managed hosting provider, and you also back them up to your house/office). If you could also give some idea as to what the unit cost (per GB/per user/per month) of storage is - on average, I would really appreciate that. Getting ready to launch my app, and I would love to get some more perspective on the nitty gritty details involved. Thanks!

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  • C# Cursor stuck on busy state

    - by Ben
    So I implemented a fixed time step loop for my C# game. All it does at the moment is make a square bounce around the screen. The problem I'm having is that when I execute the program, the window doesn't allow me to close the program and the cursor is stuck on the busy icon. I have to go into visual studio and stop the program manually. Here's the loop at the moment public void run() { int updates = 0; int frames = 0; double msPerTick = 1000.0 / 60.0; double threshhold = 0; long lastTime = getCurrentTime(); long lastTimer = getCurrentTime(); while (true) { long currTime = getCurrentTime(); threshhold += (currTime - lastTime) / msPerTick; lastTime = currTime; while (threshhold >= 1) { update(); updates++; threshhold -= 1; } this.Refresh(); frames++; if ((getCurrentTime() - lastTimer) >= 1000) { this.Text = updates + " updates and " + frames + " frames per second"; updates = 0; frames = 0; lastTimer += 1000; } } }

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  • Using Behavior Trees and Events together

    - by weichsem
    I am beginning to work with behavior trees and am unsure how events should be handled within the tree. Lets say we have a space game where the player is dogfighting with a handful of other ships, some friendly some not. The player destroys a ship and the rest of the hostile ships should then start to retreat. How was should the shipWasDestroyed event effect the other ship's behavior trees so that they start running the retreat behavior? One way I could think of doing this is have all the conditions I care about be high level nodes that effectively state change the ship. This would mean I'd have to check all of these state change conditions on every frame the behavior tree was run, even if they are very rare occurrences. I'd prefer not doing this for performance and complexity reasons. From looking at the Halo papers on behavior trees it seems that they handled this by dynamically placing nodes into the tree when the event occurred. It seems like calculating where the new node should go could be problematic depending on the current state of the running behavior. How is this normally handled?

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  • Trying to find a recent - PHP book - that utilizes SOLID principles! [closed]

    - by darga33
    Pulling my hair out! I have heard of Martin Fowler's book PoEAA and the other book Head First OOA OOD but those are not in PHP. I desperately want to read them, but ONLY in PHP utilizing the - SOLID acronym - principles! Does anyone know of the absolute best, most recent PHP book that utilizes the SOLID principles and GRASP, and all the other best practices? I want to learn from the best possible source! Not beginner books! I already understand OOP. This seems like an almost impossible question to find the answer to and so I thought, hey, might as well post on stackexchange!! Surely someone out there must know!!!!!!!!!! Or if noone happens to know, Maybe they know of an open source application that utilizes these principles that is relatively small that is not a framework. Something that I can go through every single class, and spend time understanding the insides and outs of how the program was developed. Thanks so much in advance! I really really really really appreciate it! Well it looks like we aren't supposed to ask about best books, so nevermind this question! Sorry about that!

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  • Augmenting functionality of subclasses without code duplication in C++

    - by Rob W
    I have to add common functionality to some classes that share the same superclass, preferably without bloating the superclass. The simplified inheritance chain looks like this: Element -> HTMLElement -> HTMLAnchorElement Element -> SVGElement -> SVGAlement The default doSomething() method on Element is no-op by default, but there are some subclasses that need an actual implementation that requires some extra overridden methods and instance members. I cannot put a full implementation of doSomething() in Element because 1) it is only relevant for some of the subclasses, 2) its implementation has a performance impact and 3) it depends on a method that could be overridden by a class in the inheritance chain between the superclass and a subclass, e.g. SVGElement in my example. Especially because of the third point, I wanted to solve the problem using a template class, as follows (it is a kind of decorator for classes): struct Element { virtual void doSomething() {} }; // T should be an instance of Element template<class T> struct AugmentedElement : public T { // doSomething is expensive and uses T virtual void doSomething() override {} // Used by doSomething virtual bool shouldDoSomething() = 0; }; class SVGElement : public Element { /* ... */ }; class SVGAElement : public AugmentedElement<SVGElement> { // some non-trivial check bool shouldDoSomething() { /* ... */ return true; } }; // Similarly for HTMLAElement and others I looked around (in the existing (huge) codebase and on the internet), but didn't find any similar code snippets, let alone an evaluation of the effectiveness and pitfalls of this approach. Is my design the right way to go, or is there a better way to add common functionality to some subclasses of a given superclass?

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  • Screen resolution stuck at 1024x768

    - by Dananjaya
    I just updated from Ubuntu 10.10 to 11.04 and have an issue regarding the screen resolution. I have Intel integrated gfx chip and my monitor supports resolutions larger than 1024x768. (in 10.10 I've been using 1280x1024) But as soon as I upgraded, I'm stuck with 1024x768 resolution and seems I can't change it. running xrandr In terminal yields the following results, Screen 0: minimum 320 x 200, current 1024 x 768, maximum 4096 x 4096 LVDS1 connected 1024x768+0+0 (normal left inverted right x axis y axis) 0mm x 0mm 1280x800 58.1 + 1024x768 60.0* 800x600 60.3 56.2 640x480 59.9 VGA1 connected 1024x768+0+0 (normal left inverted right x axis y axis) 344mm x 194mm 1366x768 59.9 + 1360x768 60.0 1024x768 75.1 72.0 70.1 60.0* 832x624 74.6 800x600 72.2 75.0 60.3 56.2 640x480 72.8 75.0 66.7 60.0 720x400 70.1 1280x1024_60.00 (0xce) 109.0MHz h: width 1280 start 1368 end 1496 total 1712 skew 0 clock 63.7KHz v: height 1024 start 1027 end 1034 total 1063 clock 59.9Hz What maybe the problem? Is it a bug? What kind of steps I should take in order to get a higher resolution? (changing xorg.conf maybe?) Any insight is highly appreciated. Thanks in advance. UPDATE Screenshot after running xrandr --addmode VGA1 1360x768 As you can see, side bar is not completely visible and Ubuntu logo at the task bar is missing. Also when you open an application, the Task bar of the application (where it should go to the top panel) is missing as well..

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