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• Plagued by multithreaded bugs

  - by koncurrency

  On my new team that I manage, the majority of our code is platform, TCP socket, and http networking code. All C++. Most of it originated from other developers that have left the team. The current developers on the team are very smart, but mostly junior in terms of experience. Our biggest problem: multi-threaded concurrency bugs. Most of our class libraries are written to be asynchronous by use of some thread pool classes. Methods on the class libraries often enqueue long running taks onto the thread pool from one thread and then the callback methods of that class get invoked on a different thread. As a result, we have a lot of edge case bugs involving incorrect threading assumptions. This results in subtle bugs that go beyond just having critical sections and locks to guard against concurrency issues. What makes these problems even harder is that the attempts to fix are often incorrect. Some mistakes I've observed the team attempting (or within the legacy code itself) includes something like the following: Common mistake #1 - Fixing concurrency issue by just put a lock around the shared data, but forgetting about what happens when methods don't get called in an expected order. Here's a very simple example: void Foo::OnHttpRequestComplete(statuscode status) { m_pBar->DoSomethingImportant(status); } void Foo::Shutdown() { m_pBar->Cleanup(); delete m_pBar; m_pBar=nullptr; } So now we have a bug in which Shutdown could get called while OnHttpNetworkRequestComplete is occuring on. A tester finds the bug, captures the crash dump, and assigns the bug to a developer. He in turn fixes the bug like this. void Foo::OnHttpRequestComplete(statuscode status) { AutoLock lock(m_cs); m_pBar->DoSomethingImportant(status); } void Foo::Shutdown() { AutoLock lock(m_cs); m_pBar->Cleanup(); delete m_pBar; m_pBar=nullptr; } The above fix looks good until you realize there's an even more subtle edge case. What happens if Shutdown gets called before OnHttpRequestComplete gets called back? The real world examples my team has are even more complex, and the edge cases are even harder to spot during the code review process. Common Mistake #2 - fixing deadlock issues by blindly exiting the lock, wait for the other thread to finish, then re-enter the lock - but without handling the case that the object just got updated by the other thread! Common Mistake #3 - Even though the objects are reference counted, the shutdown sequence "releases" it's pointer. But forgets to wait for the thread that is still running to release it's instance. As such, components are shutdown cleanly, then spurious or late callbacks are invoked on an object in an state not expecting any more calls. There are other edge cases, but the bottom line is this: Multithreaded programming is just plain hard, even for smart people. As I catch these mistakes, I spend time discussing the errors with each developer on developing a more appropriate fix. But I suspect they are often confused on how to solve each issue because of the enormous amount of legacy code that the "right" fix will involve touching. We're going to be shipping soon, and I'm sure the patches we're applying will hold for the upcoming release. Afterwards, we're going to have some time to improve the code base and refactor where needed. We won't have time to just re-write everything. And the majority of the code isn't all that bad. But I'm looking to refactor code such that threading issues can be avoided altogether. One approach I am considering is this. For each significant platform feature, have a dedicated single thread where all events and network callbacks get marshalled onto. Similar to COM apartment threading in Windows with use of a message loop. Long blocking operations could still get dispatched to a work pool thread, but the completion callback is invoked on on the component's thread. Components could possibly even share the same thread. Then all the class libraries running inside the thread can be written under the assumption of a single threaded world. Before I go down that path, I am also very interested if there are other standard techniques or design patterns for dealing with multithreaded issues. And I have to emphasize - something beyond a book that describes the basics of mutexes and semaphores. What do you think? I am also interested in any other approaches to take towards a refactoring process. Including any of the following: Literature or papers on design patterns around threads. Something beyond an introduction to mutexes and semaphores. We don't need massive parallelism either, just ways to design an object model so as to handle asynchronous events from other threads correctly. Ways to diagram the threading of various components, so that it will be easy to study and evolve solutions for. (That is, a UML equivalent for discussing threads across objects and classes) Educating your development team on the issues with multithreaded code. What would you do?

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• Issue with InnoDB engine while enabling and [ skip-innodb ] - [ERROR] Plugin 'InnoDB' init function returned error

  - by Ahn

  How to enable InnoDB, which was previously disabled with skip-innodb option. Case 1: Disabled the innodb with skip-innodb option and show engines givens as below. Engine | Support ... | InnoDB | NO ...... Case 2: As I want to enable the innodb, I commanded the #skip-innodb option and restarted. But now the show engines even not showing the InnoDB engine in the list. ? Mysql Version : 5.1.57-community-log OS : CentOS release 5.7 (Final) Log: 120622 13:06:36 InnoDB: Initializing buffer pool, size = 8.0M 120622 13:06:36 InnoDB: Completed initialization of buffer pool InnoDB: No valid checkpoint found. InnoDB: If this error appears when you are creating an InnoDB database, InnoDB: the problem may be that during an earlier attempt you managed InnoDB: to create the InnoDB data files, but log file creation failed. InnoDB: If that is the case, please refer to InnoDB: http://dev.mysql.com/doc/refman/5.1/en/error-creating-innodb.html 120622 13:06:36 [ERROR] Plugin 'InnoDB' init function returned error. 120622 13:06:36 [ERROR] Plugin 'InnoDB' registration as a STORAGE ENGINE failed. 120622 13:06:36 [Note] Event Scheduler: Loaded 0 events 120622 13:06:36 [Note] /usr/sbin/mysqld: ready for connections. Version: '5.1.57-community-log' socket: '/data/mysqlsnd/mysql.sock1' port: 3307 MySQL Community Server (GPL)

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• CSV engine on MySQL server

  - by Jeff

  I don't think that this is a programming question so I am going to ask it here - Reading the book high performance mysql, I read about the CSV engine. The paragraph says: The CSV engine can treat comma-separated values (CSV) files as table, but it does not support indexes on them. This engine lets you copy files in and out of the database while the server is running. If you export a CSV file from a spreadsheet and save it in the MySQL server's data directory, the server can read it immediately. Similary, if you write data to a CSV table, an external program can read it right away. CSV tables are especially useful as a data interchange format and for certain kinds of logging. What I get from this paragraph is that I can copy a .CSV file into the data directory of database, and it should show as a table that is able to be read from. However, whenever I copy a test .csv file into the directory, it does not appear as a table. I can't access it. I am using MySQL 5.5 also Does anyone know why this is not working, or what I am doing wrong? Thanks

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• Issue with InnoDB engine while enabling and [ skip-innodb ]

  - by Ahn

  How to enable InnoDB, which was previously disabled with skip-innodb option. Case 1: Disabled the innodb with skip-innodb option and show engines givens as below. Engine | Support ... | InnoDB | NO ...... Case 2: As I want to enable the innodb, I commanded the #skip-innodb option and restarted. But now the show engines even not showing the InnoDB engine in the list. ? Mysql Version : 5.1.57-community-log OS : CentOS release 5.7 (Final) Log: 120622 13:06:36 InnoDB: Initializing buffer pool, size = 8.0M 120622 13:06:36 InnoDB: Completed initialization of buffer pool InnoDB: No valid checkpoint found. InnoDB: If this error appears when you are creating an InnoDB database, InnoDB: the problem may be that during an earlier attempt you managed InnoDB: to create the InnoDB data files, but log file creation failed. InnoDB: If that is the case, please refer to InnoDB: http://dev.mysql.com/doc/refman/5.1/en/error-creating-innodb.html 120622 13:06:36 [ERROR] Plugin 'InnoDB' init function returned error. 120622 13:06:36 [ERROR] Plugin 'InnoDB' registration as a STORAGE ENGINE failed. 120622 13:06:36 [Note] Event Scheduler: Loaded 0 events 120622 13:06:36 [Note] /usr/sbin/mysqld: ready for connections. Version: '5.1.57-community-log' socket: '/data/mysqlsnd/mysql.sock1' port: 3307 MySQL Community Server (GPL)

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• Parking domains and avoiding so called "search engine penalities"

  - by senthilkumar-c

  I have purchased two domains from one particular registrar and hosting from GoDaddy. Assume they are domain1.com and domain2.com Assume my hosting IP address is 111.111.111.111 I added both domain1.com and domain2.com in my domain management control panel and gave the same two nameservers for both domains at my registrar's control panel. So, now, both domains should show the same website. When I ping "domain1.com" or "domain2.com" the results say - Pinging domain1.com [111.111.111.111] with 32 bytes of data: Pinging domain2.com [111.111.111.111] with 32 bytes of data: respectively. So, they both point to the same hosting IP. BUT, internally, I have configured IIS to point them to different folders so that different websites are shown. (My hosting plan is expensive and I intend to use the space and bandwidth for many websites). But still, technically, all domains point to same IP address. Is this a bad thing? Is this what is called "domain parking"? I read some search engine forum posts that two domains pointing to the same IP/Website will be penalised by search engines and stuff. I have also read that simply "parking" the domains won't attract penality. I don't know whether what I have done is parking or the so called "wrong" thing. Can someone shed light on what I have done and what I should do? I don't want to be blacklisted by any search engine. P.S. I know this is not a search engine forum, but I am new to website hosting and domains and I am very weak in nearly all technical terms and concepts relating to web hosting and domains. I thought this will be a good place to understand these things.

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• How to resolve: 'cmd' is not recognized as an internal or external command?

  - by qwer1234

  I have searched other forums to solve this error where it would either end with: 1.) re-install OS 2.) Setting path variable C:/Windows/System32 The latter did not work, and as you can probably imagine, I do not want to have to re-install my OS... I am running the command "mvn jetty:run" and the following is my stack trace, finishing with the message: "'cmd' is not recognized as an internal or external command, operable problem or batch file" as stated in the title of this question. [INFO] Scanning for projects... [INFO] ------------------------------------------------------------------------ [INFO] Building Test Tool [INFO] task-segment: [jetty:run] [INFO] ------------------------------------------------------------------------ [INFO] Preparing jetty:run [WARNING] Removing: run from forked lifecycle, to prevent recursive invocation. [INFO] [resources:resources] [WARNING] Using platform encoding (Cp1252 actually) to copy filtered resources, i.e. build is platform dependent! [INFO] Copying 32 resources [INFO] Copying 192 resources [INFO] [compiler:compile] [INFO] Compiling 1854 source files to C:\Development\global_stock_record\test\java\Turtle\target\classes [INFO] ------------------------------------------------------------------------ [ERROR] BUILD FAILURE [INFO] ------------------------------------------------------------------------ [INFO] Compilation failure C:\Development\global_stock_record\test\java\Turtle\src\main\java\net\sf\jasperreports\compilers\JavaScriptClassCompiler.java:[45,29] cannot find symbol symbol : class CompilerEnvirons location: package org.mozilla.javascript C:\Development\global_stock_record\test\java\Turtle\src\main\java\net\sf\jasperreports\compilers\JavaScriptClassCompiler.java:[47,29] cannot find symbol symbol : class ContextFactory location: package org.mozilla.javascript C:\Development\global_stock_record\test\java\Turtle\src\main\java\net\sf\jasperreports\compilers\JavaScriptClassCompiler.java:[49,39] cannot find symbol symbol : class ClassCompiler location: package org.mozilla.javascript.optimizer C:\Development\global_stock_record\test\java\Turtle\src\main\java\net\sf\jasperreports\compilers\JavaScriptClassCompiler.java:[181,55] cannot find symbol symbol : class CompilerEnvirons location: class net.sf.jasperreports.compilers.JavaScriptClassCompiler C:\Development\global_stock_record\test\java\Turtle\src\main\java\net\sf\jasperreports\engine\export\JRXmlExporter.java:[99,26] package org.w3c.tools.codec does not exist C:\Development\global_stock_record\test\java\Turtle\src\main\java\net\sf\jasperreports\engine\xml\JRBaseFactory.java:[26,34] package org.apache.commons.digester does not exist C:\Development\global_stock_record\test\java\Turtle\src\main\java\net\sf\jasperreports\engine\xml\JRBaseFactory.java:[27,34] package org.apache.commons.digester does not exist C:\Development\global_stock_record\test\java\Turtle\src\main\java\net\sf\jasperreports\engine\xml\JRBaseFactory.java:[34,47] cannot find symbol symbol: class ObjectCreationFactory public abstract class JRBaseFactory implements ObjectCreationFactory C:\Development\global_stock_record\test\java\Turtle\src\main\java\net\sf\jasperreports\engine\xml\JRBaseFactory.java:[41,21] cannot find symbol symbol : class Digester location: class net.sf.jasperreports.engine.xml.JRBaseFactory C:\Development\global_stock_record\test\java\Turtle\src\main\java\net\sf\jasperreports\engine\xml\JRBaseFactory.java:[47,8] cannot find symbol symbol : class Digester location: class net.sf.jasperreports.engine.xml.JRBaseFactory C:\Development\global_stock_record\test\java\Turtle\src\main\java\net\sf\jasperreports\engine\xml\JRBaseFactory.java:[56,25] cannot find symbol symbol : class Digester location: class net.sf.jasperreports.engine.xml.JRBaseFactory C:\Development\global_stock_record\test\java\Turtle\src\main\java\net\sf\jasperreports\components\barcode4j\Code39Component.java:[28,29] package org.krysalis.barcode4j does not exist C:\Development\global_stock_record\test\java\Turtle\src\main\java\net\sf\jasperreports\components\barcode4j\BarcodeComponent.java:[41,29] package org.krysalis.barcode4j does not exist C:\Development\global_stock_record\test\java\Turtle\src\main\java\net\sf\jasperreports\components\barcode4j\Code39Component.java:[66,29] cannot find symbol symbol : class ChecksumMode location: class net.sf.jasperreports.components.barcode4j.Code39Component C:\Development\global_stock_record\test\java\Turtle\src\main\java\net\sf\jasperreports\components\barcode4j\BarcodeComponent.java:[179,29] cannot find symbol symbol : class HumanReadablePlacement location: class net.sf.jasperreports.components.barcode4j.BarcodeComponent C:\Development\global_stock_record\test\java\Turtle\src\main\java\net\sf\jasperreports\components\barcode4j\EAN128Component.java:[26,29] package org.krysalis.barcode4j does not exist C:\Development\global_stock_record\test\java\Turtle\src\main\java\net\sf\jasperreports\components\barcode4j\DataMatrixComponent.java:[26,45] package org.krysalis.barcode4j.impl.datamatrix does not exist C:\Development\global_stock_record\test\java\Turtle\src\main\java\net\sf\jasperreports\components\barcode4j\FourStateBarcodeComponent.java:[26,29] package org.krysalis.barcode4j does not exist C:\Development\global_stock_record\test\java\Turtle\src\main\java\net\sf\jasperreports\components\barcode4j\UPCAComponent.java:[28,29] package org.krysalis.barcode4j does not exist C:\Development\global_stock_record\test\java\Turtle\src\main\java\net\sf\jasperreports\components\barcode4j\UPCEComponent.java:[28,29] package org.krysalis.barcode4j does not exist C:\Development\global_stock_record\test\java\Turtle\src\main\java\net\sf\jasperreports\components\barcode4j\EAN13Component.java:[28,29] package org.krysalis.barcode4j does not exist C:\Development\global_stock_record\test\java\Turtle\src\main\java\net\sf\jasperreports\components\barcode4j\EAN8Component.java:[28,29] package org.krysalis.barcode4j does not exist C:\Development\global_stock_record\test\java\Turtle\src\main\java\net\sf\jasperreports\components\barcode4j\Interleaved2Of5Component.java:[28,29] package org.krysalis.barcode4j does not exist C:\Development\global_stock_record\test\java\Turtle\src\main\java\net\sf\jasperreports\components\barcode4j\EAN128Component.java:[57,29] cannot find symbol symbol : class ChecksumMode location: class net.sf.jasperreports.components.barcode4j.EAN128Component C:\Development\global_stock_record\test\java\Turtle\src\main\java\net\sf\jasperreports\components\barcode4j\DataMatrixComponent.java:[62,22] cannot find symbol symbol : class SymbolShapeHint location: class net.sf.jasperreports.components.barcode4j.DataMatrixComponent C:\Development\global_stock_record\test\java\Turtle\src\main\java\net\sf\jasperreports\components\barcode4j\FourStateBarcodeComponent.java:[76,29] cannot find symbol symbol : class ChecksumMode location: class net.sf.jasperreports.components.barcode4j.FourStateBarcodeComponent C:\Development\global_stock_record\test\java\Turtle\src\main\java\net\sf\jasperreports\components\barcode4j\UPCAComponent.java:[56,29] cannot find symbol symbol : class ChecksumMode location: class net.sf.jasperreports.components.barcode4j.UPCAComponent C:\Development\global_stock_record\test\java\Turtle\src\main\java\net\sf\jasperreports\components\barcode4j\UPCEComponent.java:[56,29] cannot find symbol symbol : class ChecksumMode location: class net.sf.jasperreports.components.barcode4j.UPCEComponent C:\Development\global_stock_record\test\java\Turtle\src\main\java\net\sf\jasperreports\components\barcode4j\EAN13Component.java:[56,29] cannot find symbol symbol : class ChecksumMode location: class net.sf.jasperreports.components.barcode4j.EAN13Component C:\Development\global_stock_record\test\java\Turtle\src\main\java\net\sf\jasperreports\components\barcode4j\EAN8Component.java:[56,29] cannot find symbol symbol : class ChecksumMode location: class net.sf.jasperreports.components.barcode4j.EAN8Component C:\Development\global_stock_record\test\java\Turtle\src\main\java\net\sf\jasperreports\components\barcode4j\Interleaved2Of5Component.java:[60,29] cannot find symbol symbol : class ChecksumMode location: class net.sf.jasperreports.components.barcode4j.Interleaved2Of5Component C:\Development\global_stock_record\test\java\Turtle\src\main\java\net\sf\jasperreports\engine\data\JRHibernateAbstractDataSource.java:[36,25] package org.hibernate.type does not exist C:\Development\global_stock_record\test\java\Turtle\src\main\java\net\sf\jasperreports\engine\query\JRHibernateQueryExecuter.java:[49,20] package org.hibernate does not exist C:\Development\global_stock_record\test\java\Turtle\src\main\java\net\sf\jasperreports\engine\query\JRHibernateQueryExecuter.java:[50,20] package org.hibernate does not exist C:\Development\global_stock_record\test\java\Turtle\src\main\java\net\sf\jasperreports\engine\query\JRHibernateQueryExecuter.java:[51,20] package org.hibernate does not exist C:\Development\global_stock_record\test\java\Turtle\src\main\java\net\sf\jasperreports\engine\query\JRHibernateQueryExecuter.java:[52,20] package org.hibernate does not exist C:\Development\global_stock_record\test\java\Turtle\src\main\java\net\sf\jasperreports\engine\query\JRHibernateQueryExecuter.java:[53,20] package org.hibernate does not exist C:\Development\global_stock_record\test\java\Turtle\src\main\java\net\sf\jasperreports\engine\query\JRHibernateQueryExecuter.java:[54,25] package org.hibernate.type does not exist C:\Development\global_stock_record\test\java\Turtle\src\main\java\net\sf\jasperreports\engine\data\JRHibernateAbstractDataSource.java:[173,38] cannot find symbol symbol : class Type location: class net.sf.jasperreports.engine.data.JRHibernateAbstractDataSource C:\Development\global_stock_record\test\java\Turtle\src\main\java\net\sf\jasperreports\engine\query\JRHibernateQueryExecuter.java:[66,35] cannot find symbol symbol : class Type location: class net.sf.jasperreports.engine.query.JRHibernateQueryExecuter C:\Development\global_stock_record\test\java\Turtle\src\main\java\net\sf\jasperreports\engine\query\JRHibernateQueryExecuter.java:[89,9] cannot find symbol symbol : class Session location: class net.sf.jasperreports.engine.query.JRHibernateQueryExecuter C:\Development\global_stock_record\test\java\Turtle\src\main\java\net\sf\jasperreports\engine\query\JRHibernateQueryExecuter.java:[90,9] cannot find symbol symbol : class Query location: class net.sf.jasperreports.engine.query.JRHibernateQueryExecuter C:\Development\global_stock_record\test\java\Turtle\src\main\java\net\sf\jasperreports\engine\query\JRHibernateQueryExecuter.java:[92,9] cannot find symbol symbol : class ScrollableResults location: class net.sf.jasperreports.engine.query.JRHibernateQueryExecuter C:\Development\global_stock_record\test\java\Turtle\src\main\java\net\sf\jasperreports\engine\query\JRHibernateQueryExecuter.java:[359,8] cannot find symbol symbol : class Type location: class net.sf.jasperreports.engine.query.JRHibernateQueryExecuter C:\Development\global_stock_record\test\java\Turtle\src\main\java\net\sf\jasperreports\engine\query\JRHibernateQueryExecuter.java:[474,8] cannot find symbol symbol : class ScrollableResults location: class net.sf.jasperreports.engine.query.JRHibernateQueryExecuter C:\Development\global_stock_record\test\java\Turtle\src\main\java\net\sf\jasperreports\components\barbecue\BarbecueFillComponent.java:[40,31] package net.sourceforge.barbecue does not exist C:\Development\global_stock_record\test\java\Turtle\src\main\java\net\sf\jasperreports\ant\JRAntXmlExportTask.java:[38,27] package org.apache.tools.ant does not exist C:\Development\global_stock_record\test\java\Turtle\src\main\java\net\sf\jasperreports\ant\JRAntXmlExportTask.java:[39,27] package org.apache.tools.ant does not exist C:\Development\global_stock_record\test\java\Turtle\src\main\java\net\sf\jasperreports\ant\JRAntXmlExportTask.java:[40,27] package org.apache.tools.ant does not exist C:\Development\global_stock_record\test\java\Turtle\src\main\java\net\sf\jasperreports\ant\JRAntXmlExportTask.java:[41,33] package org.apache.tools.ant.types does not exist C:\Development\global_stock_record\test\java\Turtle\src\main\java\net\sf\jasperreports\ant\JRAntXmlExportTask.java:[42,33] package org.apache.tools.ant.types does not exist C:\Development\global_stock_record\test\java\Turtle\src\main\java\net\sf\jasperreports\ant\JRAntXmlExportTask.java:[43,43] package org.apache.tools.ant.types.resources does not exist C:\Development\global_stock_record\test\java\Turtle\src\main\java\net\sf\jasperreports\ant\JRAntXmlExportTask.java:[44,32] package org.apache.tools.ant.util does not exist C:\Development\global_stock_record\test\java\Turtle\src\main\java\net\sf\jasperreports\ant\JRAntXmlExportTask.java:[45,32] package org.apache.tools.ant.util does not exist C:\Development\global_stock_record\test\java\Turtle\src\main\java\net\sf\jasperreports\ant\JRBaseAntTask.java:[34,36] package org.apache.tools.ant.taskdefs does not exist C:\Development\global_stock_record\test\java\Turtle\src\main\java\net\sf\jasperreports\ant\JRBaseAntTask.java:[41,35] cannot find symbol symbol: class MatchingTask public class JRBaseAntTask extends MatchingTask C:\Development\global_stock_record\test\java\Turtle\src\main\java\net\sf\jasperreports\ant\JRAntXmlExportTask.java:[74,9] cannot find symbol symbol : class Path location: class net.sf.jasperreports.ant.JRAntXmlExportTask C:\Development\global_stock_record\test\java\Turtle\src\main\java\net\sf\jasperreports\ant\JRAntXmlExportTask.java:[76,9] cannot find symbol symbol : class Path location: class net.sf.jasperreports.ant.JRAntXmlExportTask C:\Development\global_stock_record\test\java\Turtle\src\main\java\net\sf\jasperreports\ant\JRAntXmlExportTask.java:[86,23] cannot find symbol symbol : class Path location: class net.sf.jasperreports.ant.JRAntXmlExportTask C:\Development\global_stock_record\test\java\Turtle\src\main\java\net\sf\jasperreports\ant\JRAntXmlExportTask.java:[104,8] cannot find symbol symbol : class Path location: class net.sf.jasperreports.ant.JRAntXmlExportTask C:\Development\global_stock_record\test\java\Turtle\src\main\java\net\sf\jasperreports\ant\JRAntXmlExportTask.java:[131,8] cannot find symbol symbol : class Path location: class net.sf.jasperreports.ant.JRAntXmlExportTask C:\Development\global_stock_record\test\java\Turtle\src\main\java\net\sf\jasperreports\ant\JRAntXmlExportTask.java:[145,30] cannot find symbol symbol : class BuildException location: class net.sf.jasperreports.ant.JRAntXmlExportTask C:\Development\global_stock_record\test\java\Turtle\src\main\java\net\sf\jasperreports\ant\JRAntXmlExportTask.java:[183,41] cannot find symbol symbol : class BuildException location: class net.sf.jasperreports.ant.JRAntXmlExportTask C:\Development\global_stock_record\test\java\Turtle\src\main\java\net\sf\jasperreports\ant\JRAntXmlExportTask.java:[211,33] cannot find symbol symbol : class BuildException location: class net.sf.jasperreports.ant.JRAntXmlExportTask C:\Development\global_stock_record\test\java\Turtle\src\main\java\net\sf\jasperreports\ant\JRAntXmlExportTask.java:[276,32] cannot find symbol symbol : class BuildException location: class net.sf.jasperreports.ant.JRAntXmlExportTask C:\Development\global_stock_record\test\java\Turtle\src\main\java\net\sf\jasperreports\engine\xml\TransformedPropertyRule.java:[27,34] package org.apache.commons.digester does not exist C:\Development\global_stock_record\test\java\Turtle\src\main\java\net\sf\jasperreports\engine\xml\TransformedPropertyRule.java:[37,54] cannot find symbol symbol: class Rule public abstract class TransformedPropertyRule extends Rule C:\Development\global_stock_record\test\java\Turtle\src\main\java\net\sf\jasperreports\data\mondrian\MondrianDataAdapterService.java:[29,20] package mondrian.olap does not exist C:\Development\global_stock_record\test\java\Turtle\src\main\java\net\sf\jasperreports\data\mondrian\MondrianDataAdapterService.java:[30,20] package mondrian.olap does not exist C:\Development\global_stock_record\test\java\Turtle\src\main\java\net\sf\jasperreports\data\mondrian\MondrianDataAdapterService.java:[31,20] package mondrian.olap does not exist C:\Development\global_stock_record\test\java\Turtle\src\main\java\net\sf\jasperreports\data\mondrian\MondrianDataAdapterService.java:[45,9] cannot find symbol symbol : class Connection location: class net.sf.jasperreports.data.mondrian.MondrianDataAdapterService C:\Development\global_stock_record\test\java\Turtle\src\main\java\net\sf\jasperreports\engine\data\JRXlsDataSource.java:[40,10] package jxl does not exist C:\Development\global_stock_record\test\java\Turtle\src\main\java\net\sf\jasperreports\engine\data\JRXlsDataSource.java:[41,10] package jxl does not exist C:\Development\global_stock_record\test\java\Turtle\src\main\java\net\sf\jasperreports\engine\data\JRXlsDataSource.java:[42,10] package jxl does not exist C:\Development\global_stock_record\test\java\Turtle\src\main\java\net\sf\jasperreports\engine\data\JRXlsDataSource.java:[43,20] package jxl.read.biff does not exist C:\Development\global_stock_record\test\java\Turtle\src\main\java\net\sf\jasperreports\engine\data\JRXlsDataSource.java:[66,9] cannot find symbol symbol : class Workbook location: class net.sf.jasperreports.engine.data.JRXlsDataSource C:\Development\global_stock_record\test\java\Turtle\src\main\java\net\sf\jasperreports\engine\data\JRXlsDataSource.java:[83,24] cannot find symbol symbol : class Workbook location: class net.sf.jasperreports.engine.data.JRXlsDataSource C:\Development\global_stock_record\test\java\Turtle\src\main\java\net\sf\jasperreports\olap\xmla\JRXmlaMember.java:[26,20] package mondrian.olap does not exist C:\Development\global_stock_record\test\java\Turtle\src\main\java\net\sf\jasperreports\olap\result\JROlapMember.java:[26,20] package mondrian.olap does not exist C:\Development\global_stock_record\test\java\Turtle\src\main\java\net\sf\jasperreports\olap\xmla\JRXmlaMember.java:[89,8] cannot find symbol symbol : class Member location: class net.sf.jasperreports.olap.xmla.JRXmlaMember C:\Development\global_stock_record\test\java\Turtle\src\main\java\net\sf\jasperreports\olap\result\JROlapMember.java:[46,1] cannot find symbol symbol : class Member location: interface net.sf.jasperreports.olap.result.JROlapMember C:\Development\global_stock_record\test\java\Turtle\src\main\java\net\sf\jasperreports\web\actions\AbstractAction.java:[43,36] package org.codehaus.jackson.annotate does not exist C:\Development\global_stock_record\test\java\Turtle\src\main\java\net\sf\jasperreports\web\actions\AbstractAction.java:[49,1] cannot find symbol symbol: class JsonTypeInfo @JsonTypeInfo(use=JsonTypeInfo.Id.NAME, include=JsonTypeInfo.As.PROPERTY, property="actionName") C:\Development\global_stock_record\test\java\Turtle\src\main\java\net\sf\jasperreports\components\barcode4j\AbstractBarcodeEvaluator.java:[32,29] package org.krysalis.barcode4j does not exist C:\Development\global_stock_record\test\java\Turtle\src\main\java\net\sf\jasperreports\components\barcode4j\AbstractBarcodeEvaluator.java:[33,29] package org.krysalis.barcode4j does not exist C:\Development\global_stock_record\test\java\Turtle\src\main\java\net\sf\jasperreports\components\barcode4j\AbstractBarcodeEvaluator.java:[34,29] package org.krysalis.barcode4j does not exist C:\Development\global_stock_record\test\java\Turtle\src\main\java\net\sf\jasperreports\components\barcode4j\AbstractBarcodeEvaluator.java:[35,34] package org.krysalis.barcode4j.impl does not exist C:\Development\global_stock_record\test\java\Turtle\src\main\java\net\sf\jasperreports\components\barcode4j\AbstractBarcodeEvaluator.java:[36,42] package org.krysalis.barcode4j.impl.codabar does not exist C:\Development\global_stock_record\test\java\Turtle\src\main\java\net\sf\jasperreports\components\barcode4j\AbstractBarcodeEvaluator.java:[37,42] package org.krysalis.barcode4j.impl.code128 does not exist C:\Development\global_stock_record\test\java\Turtle\src\main\java\net\sf\jasperreports\components\barcode4j\AbstractBarcodeEvaluator.java:[38,42] package org.krysalis.barcode4j.impl.code128 does not exist C:\Development\global_stock_record\test\java\Turtle\src\main\java\net\sf\jasperreports\components\barcode4j\AbstractBarcodeEvaluator.java:[39,41] package org.krysalis.barcode4j.impl.code39 does not exist C:\Development\global_stock_record\test\java\Turtle\src\main\java\net\sf\jasperreports\components\barcode4j\AbstractBarcodeEvaluator.java:[40,45] package org.krysalis.barcode4j.impl.datamatrix does not exist C:\Development\global_stock_record\test\java\Turtle\src\main\java\net\sf\jasperreports\components\barcode4j\AbstractBarcodeEvaluator.java:[41,45] package org.krysalis.barcode4j.impl.datamatrix does not exist C:\Development\global_stock_record\test\java\Turtle\src\main\java\net\sf\jasperreports\components\barcode4j\AbstractBarcodeEvaluator.java:[42,44] package org.krysalis.barcode4j.impl.fourstate does not exist C:\Development\global_stock_record\test\java\Turtle\src\main\java\net\sf\jasperreports\components\barcode4j\AbstractBarcodeEvaluator.java:[43,44] package org.krysalis.barcode4j.impl.fourstate does not exist C:\Development\global_stock_record\test\java\Turtle\src\main\java\net\sf\jasperreports\components\barcode4j\AbstractBarcodeEvaluator.java:[44,44] package org.krysalis.barcode4j.impl.fourstate does not exist C:\Development\global_stock_record\test\java\Turtle\src\main\java\net\sf\jasperreports\components\barcode4j\AbstractBarcodeEvaluator.java:[45,42] package org.krysalis.barcode4j.impl.int2of5 does not exist C:\Development\global_stock_record\test\java\Turtle\src\main\java\net\sf\jasperreports\components\barcode4j\AbstractBarcodeEvaluator.java:[46,41] package org.krysalis.barcode4j.impl.pdf417 does not exist C:\Development\global_stock_record\test\java\Turtle\src\main\java\net\sf\jasperreports\components\barcode4j\AbstractBarcodeEvaluator.java:[47,42] package org.krysalis.barcode4j.impl.postnet does not exist C:\Development\global_stock_record\test\java\Turtle\src\main\java\net\sf\jasperreports\components\barcode4j\AbstractBarcodeEvaluator.java:[48,41] package org.krysalis.barcode4j.impl.upcean does not exist [INFO] ------------------------------------------------------------------------ [INFO] For more information, run Maven with the -e switch [INFO] ------------------------------------------------------------------------ [INFO] Total time: 17 seconds [INFO] Finished at: Fri Dec 07 11:46:28 EST 2012 [INFO] Final Memory: 27M/63M [INFO] ------------------------------------------------------------------------

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• How to Correct & Improve the Design of this Code?

  - by DaveDev

  HI Guys, I've been working on a little experiement to see if I could create a helper method to serialize any of my types to any type of HTML tag I specify. I'm getting a NullReferenceException when _writer = _viewContext.Writer; is called in protected virtual void Dispose(bool disposing) {/*...*/} I think I'm at a point where it almost works (I've gotten other implementations to work) and I was wondering if somebody could point out what I'm doing wrong? Also, I'd be interested in hearing suggestions on how I could improve the design? So basically, I have this code that will generate a Select box with a number of options: // the idea is I can use one method to create any complete tag of any type // and put whatever I want in the content area <% using (Html.GenerateTag<SelectTag>(Model, new { href = Url.Action("ActionName") })) { %> <%foreach (var fund in Model.Funds) {%> <% using (Html.GenerateTag<OptionTag>(fund)) { %> <%= fund.Name %> <% } %> <% } %> <% } %> This Html.GenerateTag helper is defined as: public static MMTag GenerateTag<T>(this HtmlHelper htmlHelper, object elementData, object attributes) where T : MMTag { return (T)Activator.CreateInstance(typeof(T), htmlHelper.ViewContext, elementData, attributes); } Depending on the type of T it'll create one of the types defined below, public class HtmlTypeBase : MMTag { public HtmlTypeBase() { } public HtmlTypeBase(ViewContext viewContext, params object[] elementData) { base._viewContext = viewContext; base.MergeDataToTag(viewContext, elementData); } } public class SelectTag : HtmlTypeBase { public SelectTag(ViewContext viewContext, params object[] elementData) { base._tag = new TagBuilder("select"); //base.MergeDataToTag(viewContext, elementData); } } public class OptionTag : HtmlTypeBase { public OptionTag(ViewContext viewContext, params object[] elementData) { base._tag = new TagBuilder("option"); //base.MergeDataToTag(viewContext, _elementData); } } public class AnchorTag : HtmlTypeBase { public AnchorTag(ViewContext viewContext, params object[] elementData) { base._tag = new TagBuilder("a"); //base.MergeDataToTag(viewContext, elementData); } } all of these types (anchor, select, option) inherit from HtmlTypeBase, which is intended to perform base.MergeDataToTag(viewContext, elementData);. This doesn't happen though. It works if I uncomment the MergeDataToTag methods in the derived classes, but I don't want to repeat that same code for every derived class I create. This is the definition for MMTag: public class MMTag : IDisposable { internal bool _disposed; internal ViewContext _viewContext; internal TextWriter _writer; internal TagBuilder _tag; internal object[] _elementData; public MMTag() {} public MMTag(ViewContext viewContext, params object[] elementData) { } public void Dispose() { Dispose(true /* disposing */); GC.SuppressFinalize(this); } protected virtual void Dispose(bool disposing) { if (!_disposed) { _disposed = true; _writer = _viewContext.Writer; _writer.Write(_tag.ToString(TagRenderMode.EndTag)); } } protected void MergeDataToTag(ViewContext viewContext, object[] elementData) { Type elementDataType = elementData[0].GetType(); foreach (PropertyInfo prop in elementDataType.GetProperties()) { if (prop.PropertyType.IsPrimitive || prop.PropertyType == typeof(Decimal) || prop.PropertyType == typeof(String)) { object propValue = prop.GetValue(elementData[0], null); string stringValue = propValue != null ? propValue.ToString() : String.Empty; _tag.Attributes.Add(prop.Name, stringValue); } } var dic = new Dictionary<string, object>(StringComparer.OrdinalIgnoreCase); var attributes = elementData[1]; if (attributes != null) { foreach (PropertyDescriptor descriptor in TypeDescriptor.GetProperties(attributes)) { object value = descriptor.GetValue(attributes); dic.Add(descriptor.Name, value); } } _tag.MergeAttributes<string, object>(dic); _viewContext = viewContext; _viewContext.Writer.Write(_tag.ToString(TagRenderMode.StartTag)); } } Thanks Dave

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• I'm looking for a web host to put a search java engine. What are the best options?

  - by Nisanio

  I wrote a java search engine and I don't have the money to have my own servers. Can someone recommend me a goo java web host? Thanks in advance

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• Converting 2D Physics to 3D.

  - by static void main

  I'm new to game physics and I am trying to adapt a simple 2D ball simulation for a 3D simulation with the Java3D library. I have this problem: Two things: 1) I noted down the values generated by the engine: X/Y are too high and minX/minY/maxY/maxX values are causing trouble. Sometimes the balls are drawing but not moving Sometimes they are going out of the panel Sometimes they're moving on little area Sometimes they just stick at one place... 2) I'm unable to select/define/set the default correct/suitable values considering the 3D graphics scaling/resolution while they are set with respect to 2D screen coordinates, that is my only problem. Please help. This is the code: public class Ball extends GameObject { private float x, y; // Ball's center (x, y) private float speedX, speedY; // Ball's speed per step in x and y private float radius; // Ball's radius // Collision detected by collision detection and response algorithm? boolean collisionDetected = false; // If collision detected, the next state of the ball. // Otherwise, meaningless. private float nextX, nextY; private float nextSpeedX, nextSpeedY; private static final float BOX_WIDTH = 640; private static final float BOX_HEIGHT = 480; /** * Constructor The velocity is specified in polar coordinates of speed and * moveAngle (for user friendliness), in Graphics coordinates with an * inverted y-axis. */ public Ball(String name1,float x, float y, float radius, float speed, float angleInDegree, Color color) { this.x = x; this.y = y; // Convert velocity from polar to rectangular x and y. this.speedX = speed * (float) Math.cos(Math.toRadians(angleInDegree)); this.speedY = speed * (float) Math.sin(Math.toRadians(angleInDegree)); this.radius = radius; } public void move() { if (collisionDetected) { // Collision detected, use the values computed. x = nextX; y = nextY; speedX = nextSpeedX; speedY = nextSpeedY; } else { // No collision, move one step and no change in speed. x += speedX; y += speedY; } collisionDetected = false; // Clear the flag for the next step } public void collideWith() { // Get the ball's bounds, offset by the radius of the ball float minX = 0.0f + radius; float minY = 0.0f + radius; float maxX = 0.0f + BOX_WIDTH - 1.0f - radius; float maxY = 0.0f + BOX_HEIGHT - 1.0f - radius; double gravAmount = 0.9811111f; double gravDir = (90 / 57.2960285258); // Try moving one full step nextX = x + speedX; nextY = y + speedY; System.out.println("In serializedBall in collision."); // If collision detected. Reflect on the x or/and y axis // and place the ball at the point of impact. if (speedX != 0) { if (nextX > maxX) { // Check maximum-X bound collisionDetected = true; nextSpeedX = -speedX; // Reflect nextSpeedY = speedY; // Same nextX = maxX; nextY = (maxX - x) * speedY / speedX + y; // speedX non-zero } else if (nextX < minX) { // Check minimum-X bound collisionDetected = true; nextSpeedX = -speedX; // Reflect nextSpeedY = speedY; // Same nextX = minX; nextY = (minX - x) * speedY / speedX + y; // speedX non-zero } } // In case the ball runs over both the borders. if (speedY != 0) { if (nextY > maxY) { // Check maximum-Y bound collisionDetected = true; nextSpeedX = speedX; // Same nextSpeedY = -speedY; // Reflect nextY = maxY; nextX = (maxY - y) * speedX / speedY + x; // speedY non-zero } else if (nextY < minY) { // Check minimum-Y bound collisionDetected = true; nextSpeedX = speedX; // Same nextSpeedY = -speedY; // Reflect nextY = minY; nextX = (minY - y) * speedX / speedY + x; // speedY non-zero } } speedX += Math.cos(gravDir) * gravAmount; speedY += Math.sin(gravDir) * gravAmount; } public float getSpeed() { return (float) Math.sqrt(speedX * speedX + speedY * speedY); } public float getMoveAngle() { return (float) Math.toDegrees(Math.atan2(speedY, speedX)); } public float getRadius() { return radius; } public float getX() { return x; } public float getY() { return y; } public void setX(float f) { x = f; } public void setY(float f) { y = f; } } Here's how I'm drawing the balls: public class 3DMovingBodies extends Applet implements Runnable { private static final int BOX_WIDTH = 800; private static final int BOX_HEIGHT = 600; private int currentNumBalls = 1; // number currently active private volatile boolean playing; private long mFrameDelay; private JFrame frame; private int currentFrameRate; private Ball[] ball = new Ball[currentNumBalls]; private Random rand; private Sphere[] sphere = new Sphere[currentNumBalls]; private Transform3D[] trans = new Transform3D[currentNumBalls]; private TransformGroup[] objTrans = new TransformGroup[currentNumBalls]; public 3DMovingBodies() { rand = new Random(); float angleInDegree = rand.nextInt(360); setLayout(new BorderLayout()); GraphicsConfiguration config = SimpleUniverse .getPreferredConfiguration(); Canvas3D c = new Canvas3D(config); add("Center", c); ball[0] = new Ball(0.5f, 0.0f, 0.5f, 0.4f, angleInDegree, Color.yellow); // ball[1] = new Ball(1.0f, 0.0f, 0.25f, 0.8f, angleInDegree, // Color.yellow); // ball[2] = new Ball(0.0f, 1.0f, 0.15f, 0.11f, angleInDegree, // Color.yellow); trans[0] = new Transform3D(); // trans[1] = new Transform3D(); // trans[2] = new Transform3D(); sphere[0] = new Sphere(0.5f); // sphere[1] = new Sphere(0.25f); // sphere[2] = new Sphere(0.15f); // Create a simple scene and attach it to the virtual universe BranchGroup scene = createSceneGraph(); SimpleUniverse u = new SimpleUniverse(c); u.getViewingPlatform().setNominalViewingTransform(); u.addBranchGraph(scene); startSimulation(); } public BranchGroup createSceneGraph() { // Create the root of the branch graph BranchGroup objRoot = new BranchGroup(); for (int i = 0; i < currentNumBalls; i++) { // Create a simple shape leaf node, add it to the scene graph. objTrans[i] = new TransformGroup(); objTrans[i].setCapability(TransformGroup.ALLOW_TRANSFORM_WRITE); Transform3D pos1 = new Transform3D(); pos1.setTranslation(randomPos()); objTrans[i].setTransform(pos1); objTrans[i].addChild(sphere[i]); objRoot.addChild(objTrans[i]); } BoundingSphere bounds = new BoundingSphere(new Point3d(0.0, 0.0, 0.0), 100.0); Color3f light1Color = new Color3f(1.0f, 0.0f, 0.2f); Vector3f light1Direction = new Vector3f(4.0f, -7.0f, -12.0f); DirectionalLight light1 = new DirectionalLight(light1Color, light1Direction); light1.setInfluencingBounds(bounds); objRoot.addChild(light1); // Set up the ambient light Color3f ambientColor = new Color3f(1.0f, 1.0f, 1.0f); AmbientLight ambientLightNode = new AmbientLight(ambientColor); ambientLightNode.setInfluencingBounds(bounds); objRoot.addChild(ambientLightNode); return objRoot; } public void startSimulation() { playing = true; Thread t = new Thread(this); t.start(); } public void stop() { playing = false; } public void run() { long previousTime = System.currentTimeMillis(); long currentTime = previousTime; long elapsedTime; long totalElapsedTime = 0; int frameCount = 0; while (true) { currentTime = System.currentTimeMillis(); elapsedTime = (currentTime - previousTime); // elapsed time in // seconds totalElapsedTime += elapsedTime; if (totalElapsedTime > 1000) { currentFrameRate = frameCount; frameCount = 0; totalElapsedTime = 0; } for (int i = 0; i < currentNumBalls; i++) { ball[i].move(); ball[i].collideWith(); drawworld(); } try { Thread.sleep(88); } catch (Exception e) { e.printStackTrace(); } previousTime = currentTime; frameCount++; } } public void drawworld() { for (int i = 0; i < currentNumBalls; i++) { printTG(objTrans[i], "SteerTG"); trans[i].setTranslation(new Vector3f(ball[i].getX(), ball[i].getY(), 0.0f)); objTrans[i].setTransform(trans[i]); } } private Vector3f randomPos() /* * Return a random position vector. The numbers are hardwired to be within * the confines of the box. */ { Vector3f pos = new Vector3f(); pos.x = rand.nextFloat() * 5.0f - 2.5f; // -2.5 to 2.5 pos.y = rand.nextFloat() * 2.0f + 0.5f; // 0.5 to 2.5 pos.z = rand.nextFloat() * 5.0f - 2.5f; // -2.5 to 2.5 return pos; } // end of randomPos() public static void main(String[] args) { System.out.println("Program Started"); 3DMovingBodiesbb = new 3DMovingBodies(); bb.addKeyListener(bb); MainFrame mf = new MainFrame(bb, 600, 400); } }

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• Light on every model and not in the whole scene

  - by alecnash

  I am using a custom shader and try to pass the effect on my Models like that: foreach (ModelMesh mesh in Model.Meshes) { foreach (ModelMeshPart part in mesh.MeshParts) { part.Effect = effect; } mesh.Draw(); } My only issue is that every Model now has its own light source in it. Why is this happening and is this a problem of my shader? Edit: These are the parameters passed to the shader: private void Get_lambertEffect() { if (_lambertEffect == null) _lambertEffect = Engine.LambertEffect; //Lambert technique (LambertWithShadows, LambertWithShadows2x2PCF, LambertWithShadows3x3PCF) _lambertEffect.CurrentTechnique = _lambertEffect.Techniques["LambertWithShadows3x3PCF"]; _lambertEffect.Parameters["texelSize"].SetValue(Engine.ShadowMap.TexelSize); //ShadowMap parameters _lambertEffect.Parameters["lightViewProjection"].SetValue(Engine.ShadowMap.LightViewProjectionMatrix); _lambertEffect.Parameters["textureScaleBias"].SetValue(Engine.ShadowMap.TextureScaleBiasMatrix); _lambertEffect.Parameters["depthBias"].SetValue(Engine.ShadowMap.DepthBias); _lambertEffect.Parameters["shadowMap"].SetValue(Engine.ShadowMap.ShadowMapTexture); //Camera view and projection parameters _lambertEffect.Parameters["view"].SetValue(Engine._camera.ViewMatrix); _lambertEffect.Parameters["projection"].SetValue(Engine._camera.ProjectionMatrix); _lambertEffect.Parameters["world"].SetValue( Matrix.CreateScale(Size) * world ); //Light and color _lambertEffect.Parameters["lightDir"].SetValue(Engine._sourceLight.Direction); _lambertEffect.Parameters["lightColor"].SetValue(Engine._sourceLight.Color); _lambertEffect.Parameters["materialAmbient"].SetValue(Engine.Material.Ambient); _lambertEffect.Parameters["materialDiffuse"].SetValue(Engine.Material.Diffuse); _lambertEffect.Parameters["colorMap"].SetValue(ColorTexture.Create(Engine.GraphicsDevice, Color.Red)); }

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• Hosting StreamInsight applications using WCF

  - by gsusx

  One of the fundamental differentiators of Microsoft's StreamInsight compared to other Complex Event Processing (CEP) technologies is its flexible deployment model. In that sense, a StreamInsight solution can be hosted within an application or as a server component. This duality contrasts with most of the popular CEP frameworks in the current market which are almost exclusively server based. Whether it's undoubtedly that the ability of embedding a CEP engine in your applications opens new possibilities...(read more)

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• 15 Stylish Navigation Menus For Inspiration

  - by Jyoti

  A site’s navigation menu is one of the most prominent things that users see when they first visit. There are many ways to design a navigation menu  and since almost all websites have some form of navigation designers have to push their creative limits to build one that’s remarkable and outstanding. In this article, you’ll [...]

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• How does 2D Game Physics work? [closed]

  - by StefanE

  Possible Duplicate: How do I build a 2D physics engine? If we take the game Angry Birds that had big success lately I were thinking how do they implement the physics in a game like that? Your are shooting of your birds and they hit something that will fall off and in turn creating a chain reaction of things either falling or exploding.. Are all this happening with calculations with rules considering all collisions together with gravity etc.?

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• Tellago Devlabs: A RESTful API for BizTalk Server Business Rules

  - by gsusx

  Tellago DevLabs keeps growing as the primary example of our commitment to open source! Today, we are very happy to announce the availability of the BizTalk Business Rules Data Service API which extends our existing BizTalk Data Services solution with an OData API for the BizTalk Server Business Rules engine. Tellago’s Vishal Mody led the implementation of this version of the API with some input from other members of our technical staff. The motivation The fundamental motivation behind the BRE Data...(read more)

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• How does I/O work for large graph databases?

  - by tjb1982

  I should preface this by saying that I'm mostly a front end web developer, trained as a musician, but over the past few years I've been getting more and more into computer science. So one idea I have as a fun toy project to learn about data structures and C programming was to design and implement my own very simple database that would manage an adjacency list of posts. I don't want SQL (maybe I'll do my own query language? I'm just having fun). It should support ACID. It should be capable of storing 1TB let's say. So with that, I was trying to think of how a database even stores data, without regard to data structures necessarily. I'm working on linux, and I've read that in that world "everything is a file," including hardware (like /dev/*), so I think that that obviously has to apply to a database, too, and it clearly does--whether it's MySQL or PostgreSQL or Neo4j, the database itself is a collection of files you can see in the filesystem. That said, there would come a point in scale where loading the entire database into primary memory just wouldn't work, so it doesn't make sense to design it with that mindset (I assume). However, reading from secondary memory would be much slower and regardless some portion of the database has to be in primary memory in order for you to be able to do anything with it. I read this post: Why use a database instead of just saving your data to disk? And I found it difficult to understand how other databases, like SQLite or Neo4j, read and write from secondary memory and are still very fast (faster, it would seem, than simply writing files to the filesystem as the above question suggests). It seems the key is indexing. But even indexes need to be stored in secondary memory. They are inherently smaller than the database itself, but indexes in a very large database might be prohibitively large, too. So my question is how is I/O generally done with large databases like the one I described above that would be at least 1TB storing a big adjacency list? If indexing is more or less the answer, how exactly does indexing work--what data structures should be involved?

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• What is a Non-Functional Requirement?

  - by atconway

  In my breakdown of work I have to define work against 'Functional' and 'Non-Functional' design elements / work in my applications. I read the description from Wikipedia here: https://en.wikipedia.org/wiki/Non-functional_requirement but as typical the description did not speak exactly to me to clear up my understanding. Can someone please explain in terms of an example when creating an application from scratch, what would be defined as a 'Non-Functional' requirement?

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• What are the advantages of the delegate pattern over the observer pattern?

  - by JoJo

  In the delegate pattern, only one object can directly listen to another object's events. In the observer pattern, any number of objects can listen to a particular object's events. When designing a class that needs to notify other object(s) of events, why would you ever use the delegate pattern over the observer pattern? I see the observer pattern as more flexible. You may only have one observer now, but a future design may require multiple observers.

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• Advantages and disadvantages of building a single page web application

  - by ryanzec

  I'm nearing the end of a prototyping/proof of concept phase for a side project I'm working on, and trying to decide on some larger scale application design decisions. The app is a project management system tailored more towards the agile development process. One of the decisions I need to make is whether or not to go with a traditional multi-page application or a single page application. Currently my prototype is a traditional multi-page setup, however I have been looking at backbone.js to clean up and apply some structure to my Javascript (jQuery) code. It seems like while backbone.js can be used in multi-page applications, it shines more with single page applications. I am trying to come up with a list of advantages and disadvantages of using a single page application design approach. So far I have: Advantages All data has to be available via some sort of API - this is a big advantage for my use case as I want to have an API to my application anyway. Right now about 60-70% of my calls to get/update data are done through a REST API. Doing a single page application will allow me to better test my REST API since the application itself will use it. It also means that as the application grows, the API itself will grow since that is what the application uses; no need to maintain the API as an add-on to the application. More responsive application - since all data loaded after the initial page is kept to a minimum and transmitted in a compact format (like JSON), data requests should generally be faster, and the server will do slightly less processing. Disadvantages Duplication of code - for example, model code. I am going to have to create models both on the server side (PHP in this case) and the client side in Javascript. Business logic in Javascript - I can't give any concrete examples on why this would be bad but it just doesn't feel right to me having business logic in Javascript that anyone can read. Javascript memory leaks - since the page never reloads, Javascript memory leaks can happen, and I would not even know where to begin to debug them. There are also other things that are kind of double edged swords. For example, with single page applications, the data processed for each request can be a lot less since the application will be asking for the minimum data it needs for the particular request, however it also means that there could be a lot more small request to the server. I'm not sure if that is a good or bad thing. What are some of the advantages and disadvantages of single page web applications that I should keep in mind when deciding which way I should go for my project?

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• Is pixelmator a viable alternative for photoshop? [migrated]

  - by ChrisR

  I've always been a photoshop user, i know the ins and outs and know my way around all the tools i need for my webdesign work. But now i'm faced with a dilemma, for my new job i haven't got the budget for a full photoshop license so i'm wondering, is pixelmator a good alternative? I use Photoshop mainly to slice a design into separate images so enable/disable layers is a must, PSD compatibility too, ... Anyone has experience with Pixelmator?

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• How did you get good practices for your OOP designs?

  - by Darf Zon

  I realized I have a difficulty creating OOP designs. I spent many time deciding if this property is correctly set it to X class. For example, this is a post which has a few days: http://codereview.stackexchange.com/questions/8041/how-to-improve-my-factory-design I'm not convinced of my code. So I want to improve my designs, take less time creating it. How did you learn creating good designs? Some books that you can recommend me?

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• What advantages do we have when creating a separate mapping table for two relational tables

  - by Pankaj Upadhyay

  In various open source CMS, I have noticed that there is a separate table for mapping two relational tables. Like for categories and products, there is a separate product_category_mapping table. This table just has a primary key and two foreign keys from the categories and product tables. My question is what are the benefits of this database design rather than just linking the tables directly by defining a foreign key in either table? Is it just matter of convenience?

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• Interaction of a GUI-based App and Windows Service

  - by psubsee2003

  I am working on personal project that will be designed to help manage my media library, specifically recordings created by Windows Media Center. So I am going to have the following parts to this application: A Windows Service that monitors the recording folder. Once a new recording is completed that meets specific criteria, it will call several 3rd party CLI Applications to remove the commercials and re-encode the video into a more hard-drive friendly format. A controller GUI to be able to modify settings of the service, specifically add new shows to watch for, and to modify parameters for the CLI Applications A standalone (GUI-based) desktop application that can perform many of the same functions as the windows service, expect manually on specific files instead of automatically based on specific criteria. (It should be mentioned that I have limited experience with an application of this complexity, and I have absolutely zero experience with Windows Services) Since the 1st and 3rd bullet share similar functionality, my design plan is to pull the common functionality into a separate library shared by both parts applications, but these 2 components do not need to interact otherwise. The 2nd and 3rd bullets seem to share some common functionality, both will have a GUI, both will have to help define similar parameters (one to send to the service and the other to send directly to the CLI applications), so I can see some advantage to combining them into the same application. On the other hand, the standalone application (bullet #3) really does not need to interact with the service at all, except for possibly sharing a few common default parameters that can easily be put into an XML in a common location, so it seems to make more sense to just keep everything separate. The controller GUI (2nd bullet) is where I am stuck at the moment. Do I just roll this functionality (allow for user interaction with the service to update settings and criteria) into the standalone application? Or would it be a better design decision to keep them separate? Specifically, I'm worried about adding the complexity of communicating with the Windows Service to the standalone application when it doesn't need it. Is WCF the right approach to allow the controller GUI to interact with the Windows Service? Or is there a better alternative? At the moment, I don't envision a need for a significant amount of interaction, maybe just adding a new task once in a while and occasionally tweaking a parameter, but when something is changed, I do expect the windows service to immediately use the new settings.

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• Started wrong with a project. Should I start over?

  - by solidsnake

  I'm a beginner web developer (one year of experience). A couple of weeks after graduating, I got offered a job to build a web application for a company whose owner is not much of a tech guy. He recruited me to avoid theft of his idea, the high cost of development charged by a service company, and to have someone young he can trust onboard to maintain the project for the long run (I came to these conclusions by myself long after being hired). Cocky as I was back then, with a diploma in computer science, I accepted the offer thinking I can build anything. I was calling the shots. After some research I settled on PHP, and started with plain PHP, no objects, just ugly procedural code. Two months later, everything was getting messy, and it was hard to make any progress. The web application is huge. So I decided to check out an MVC framework that would make my life easier. That's where I stumbled upon the cool kid in the PHP community: Laravel. I loved it, it was easy to learn, and I started coding right away. My code looked cleaner, more organized. It looked very good. But again the web application was huge. The company was pressuring me to deliver the first version, which they wanted to deploy, obviously, and start seeking customers. Because Laravel was fun to work with, it made me remember why I chose this industry in the first place - something I forgot while stuck in the shitty education system. So I started working on small projects at night, reading about methodologies and best practice. I revisited OOP, moved on to object-oriented design and analysis, and read Uncle Bob's book Clean Code. This helped me realize that I really knew nothing. I did not know how to build software THE RIGHT WAY. But at this point it was too late, and now I'm almost done. My code is not clean at all, just spaghetti code, a real pain to fix a bug, all the logic is in the controllers, and there is little object oriented design. I'm having this persistent thought that I have to rewrite the whole project. However, I can't do it... They keep asking when is it going to be all done. I can not imagine this code deployed on a server. Plus I still know nothing about code efficiency and the web application's performance. On one hand, the company is waiting for the product and can not wait anymore. On the other hand I can't see myself going any further with the actual code. I could finish up, wrap it up and deploy, but god only knows what might happen when people start using it. What do you think I should do?

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• How can I solve the same problems a CB-architecture is trying to solve without using hacks? [on hold]

  - by Jefffrey

  A component based system's goal is to solve the problems that derives from inheritance: for example the fact that some parts of the code (that are called components) are reused by very different classes that, hypothetically, would lie in a very different branch of the inheritance tree. That's a very nice concept, but I've found out that CBS is often hard to accomplish without using ugly hacks. Implementations of this system are often far from clean. But I don't want to discuss this any further. My question is: how can I solve the same problems a CBS try to solve with a very clean interface? (possibly with examples, there are a lot of abstract talks about the "perfect" design already). Here's an example I was going for before realizing I was just reinventing inheritance again: class Human { public: Position position; Movement movement; Sprite sprite; // other human specific components }; class Zombie { Position position; Movement movement; Sprite sprite; // other zombie specific components }; After writing that I realized I needed an interface, otherwise I would have needed N containers for N different types of objects (or to use boost::variant to gather them all together). So I've thought of polymorphism (move what systems do in a CBS design into class specific functions): class Entity { public: virtual void on_event(Event) {} // not pure virtual on purpose virtual void on_update(World) {} virtual void on_draw(Window) {} }; class Human { private: Position position; Movement movement; Sprite sprite; public: virtual void on_event(Event) { ... } virtual void on_update(World) { ... } virtual void on_draw(Window) { ... } }; class Zombie { private: Position position; Movement movement; Sprite sprite; public: virtual void on_event(Event) { ... } virtual void on_update(World) { ... } virtual void on_draw(Window) { ... } }; Which was nice, except for the fact that now the outside world would not even be able to know where a Human is positioned (it does not have access to its position member). That would be useful to track the player position for collision detection or if on_update the Zombie would want to track down its nearest human to move towards him. So I added const Position& get_position() const; to both the Zombie and Human classes. And then I realized that both functionality were shared, so it should have gone to the common base class: Entity. Do you notice anything? Yes, with that methodology I would have a god Entity class full of common functionality (which is the thing I was trying to avoid in the first place).

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• Single Responsibility Principle Implementation

  - by Mike S

  In my spare time, I've been designing a CMS in order to learn more about actual software design and architecture, etc. Going through the SOLID principles, I already notice that ideas like "MVC", "DRY", and "KISS", pretty much fall right into place. That said, I'm still having problems deciding if one of two implementations is the best choice when it comes to the Single Responsibility Principle. Implementation #1: class User getName getPassword getEmail // etc... class UserManager create read update delete class Session start stop class Login main class Logout main class Register main The idea behind this implementation is that all user-based actions are separated out into different classes (creating a possible case of the aptly-named Ravioli Code), but following the SRP to a "tee", almost literally. But then I thought that it was a bit much, and came up with this next implementation class UserView extends View getLogin //Returns the html for the login screen getShortLogin //Returns the html for an inline login bar getLogout //Returns the html for a logout button getRegister //Returns the html for a register page // etc... as needed class UserModel extends DataModel implements IDataModel // Implements no new methods yet, outside of the interface methods // Haven't figured out anything special to go here at the moment // All CRUD operations are handled by DataModel // through methods implemented by the interface class UserControl extends Control implements IControl login logout register startSession stopSession class User extends DataObject getName getPassword getEmail // etc... This is obviously still very organized, and still very "single responsibility". The User class is a data object that I can manipulate data on and then pass to the UserModel to save it to the database. All the user data rendering (what the user will see) is handled by UserView and it's methods, and all the user actions are in one space in UserControl (plus some automated stuff required by the CMS to keep a user logged in or to ensure that they stay out.) I personally can't think of anything wrong with this implementation either. In my personal feelings I feel that both are effectively correct, but I can't decide which one would be easier to maintain and extend as life goes on (despite leaning towards Implementation #1.) So what about you guys? What are your opinions on this? Which one is better? What basics (or otherwise, nuances) of that principle have I missed in either design?

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