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  • How meaningful is the Big-O time complexity of an algorithm?

    - by james creasy
    Programmers often talk about the time complexity of an algorithm, e.g. O(log n) or O(n^2). Time complexity classifications are made as the input size goes to infinity, but ironically infinite input size in computation is not used. Put another way, the classification of an algorithm is based on a situation that algorithm will never be in: where n = infinity. Also, consider that a polynomial time algorithm where the exponent is huge is just as useless as an exponential time algorithm with tiny base (e.g., 1.00000001^n) is useful. Given this, how much can I rely on the Big-O time complexity to advise choice of an algorithm?

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  • The Three Laws of Robotics; As Told by Asimov Himself

    - by Jason Fitzpatrick
    Many Sci-Fi fans and certainly most Isaac Asimov fans are familiar with the Three Laws of Robotics–but how many of us have heard the man himself explain them? In this archival clip a young Isaac Asimov explains the Three Laws of Robotics–the organizing principle behind his robot-based short stories and novels. [via Neatorama] 6 Start Menu Replacements for Windows 8 What Is the Purpose of the “Do Not Cover This Hole” Hole on Hard Drives? How To Log Into The Desktop, Add a Start Menu, and Disable Hot Corners in Windows 8

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  • problem connecting to magento connect

    - by amir
    hi, I'm using magento 1.4.0 and when I try to get to magento connect and download a plugin the page will say Error: Please check for sufficient write file permissions Your Magento folder does not have sufficient write permissions, which this web based downloader requires. If you wish to proceed downloading Magento packages online, please set all Magento folders to have writable permission for the web server user (example: apache) and press the "Refresh" button to try again. does anyone know how I can fix this problem, thanks Update: the plugin I'm trying to use is MagentoPycho light box so I unpacked the folder into the app/code/local but it still doesn't show in the admin area

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  • Oracle Database Appliance Now Certified by SAP

    - by Bandari Huang
    All SAP products based on SAP NetWeaver 7.x that are also certified for Oracle Database 11g Release 2 (single node or RAC) can now be used with the Oracle Database Appliance. RAC One Node is NOT supported. Only Three-Tier SAP Installations. Only the Oracle database can run on the Oracle Database Appliance.  No SAP instance can be deployed on the Oracle Database Appliance. SAP instances have to run on different middle-tier machines of any hardware architecture and operating system. Central Services (ASCS and/or SCS) can be configured to run on the Oracle Database Appliance for Unicode installations of SAP. SAP BR*Tools support is now available for the Oracle Database Appliance. For more information about SAP on ODA, please refer: Using SAP NetWeaver with the Oracle Database Appliance New Nov2012 Note 1760737 - SAP Software and Oracle Database Appliance (ODA) Note 1785353 - ODA 11.2.0: Patches for 11.2.0.3  

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  • How can an experienced web developer transition to desktop development?

    - by Craige
    I'm a web developer, first and foremost. I've been programming for 5 or 6 years now, all of which has been web-based. I'm good at my job, both specifically as a web developer and as a programmer in general. I have decided recently that I would like to learn some desktop programming to to beef up my skill-set. My question is this: How can an experienced web developer transition to desktop development? To elaborate: I have always been a web-developer, and I can design and build web-applications without any problem. When it comes to sitting down with a to learn some desktop oriented programming, my problem isn't with any of the technical matters, but rather coming up with an idea to program. I draw a blank.

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  • Getting overwhelmed after starting a new project

    - by Kian Mayne
    I started a project (a Windows based timetable program that helps you stay organised with your subjects and assignments). The problem is that I'm not sure how I should manage this project and what order to build things. I.e. Should I build all the different interface elements then write the code or should I make an interface, code it, make another interface then code that? So my question is; how do I split up this longish project into small, ordered pieces to complete; and how should I order this?

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  • Best approach for a flexible layout for ASP.NET application

    - by Rohith Nair
    I am looking for a best approach for designing a dynamic page. I want my users to be able to determine the position of set of controls to be loaded into a page. Should be able to add new controls or swap in and out new controls into an existing page. Eg: Portal based applications,iGoogle kind of websites I am afraid that I will be re-inventing the wheel if I go and create a portal structure for my web application. There are a couple of things in my mind to look into: Good third-party suites which can do the same Should I look into Silverlight RIA application? I have researched about the Infragistics and Telerik controls and the price is high for just a control like LayoutManager which I need. Any alternatives? What is the best approach for this kind of situation, to add to the list?

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  • Oracle Utilities Framework Batch Easy Steps

    - by ACShorten
    Oracle Support have compiled a list of common Questions and Answers for Batch Processing in Oracle Utilities Application Framework. Customers and partners should take a look at these questions and answers before posting any question to support to save time. The Knowledge Base article is available from My Oracle Support under FW - Oracle Utilities Framework Batch Easy Steps (Doc ID 1306282.1). This article answers the questions but also posts links to other documents including the Batch Best Practices for Oracle Utilities Application Framework based products (Doc Id: 836362.1) and Oracle Utilities CCB Batch Operations And Configuration Guide (Doc Id: 753301.1) for more detailed information and explanation. Customers of Oracle Utilities Meter Data Management V2.0 and above, Oracle Utilities Mobile Workforce Management V2.0 and above, Oracle Enterprise Taxation and Policy Management V2.0 and above, and Oracle Utilities Smart Grid Gateway V2.0 (all editions) and above should refer to the Batch Server Administration Guide shipped with their products on eDelivery instead of using Doc Id: 753301.1.

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  • SilverlightShow for Jan 3-9, 2011

    - by Dave Campbell
    Check out the Top Five most popular news at SilverlightShow for Jan 3-9, 2011. SilverlightShow's review of their top 10 visited articles in 2010 got most hits last week. MicrosoftFeed's review of the Facebook application Picturize.me got the second place. Among the top5 is also an interesting review of the top Silverlight books for 2010 by Michael Crump. Here is SilverlightShow's weekly top 5: Top 10 SilverlightShow Articles for Year 2010 Picturize.me - a Silverlight Based Facebook application Face detection in Windows Phone 7 MVVM Navigation with MEF What is the best book on Silverlight 4 Visit and bookmark SilverlightShow. Stay in the 'Light

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  • How to install iodbc in Ubuntu 12.10

    - by Hanynowsky
    I need to install the library iodbc (depends on libodbc2) in my Quantal machine. Yet there is creepy dependency problem. This was replaced somehow by unixodbc which I don't have, installed. Here is what I get when I try to install : sudo apt-get install libiodbc2-dev Reading package lists... Done Building dependency tree Reading state information... Done Some packages could not be installed. This may mean that you have requested an impossible situation or if you are using the unstable distribution that some required packages have not yet been created or been moved out of Incoming. The following information may help to resolve the situation: The following packages have unmet dependencies: libiodbc2-dev : Depends: libiodbc2 (= 3.52.7-2build2) but it is not going to be installed Depends: iodbc (= 3.52.7-2build2) but it is not going to be installed E: Unable to correct problems, you have held broken packages. I can tell that iodbc conflicts with odbcinst. Yet, I cannot remove it due to the following: sudo apt-get remove odbcinst Reading package lists... Done Building dependency tree Reading state information... Done The following packages were automatically installed and are no longer required: akonadi-backend-mysql calligra-l10n-engb kde-l10n-engb kdevelop-l10n kdevelop-php-docs-l10n kdevelop-php-l10n libakonadi-kabc4 libakonadi-notes4 libakonadiprotocolinternals1 libboost-thread1.49.0 libdmtx0a libgpgme++2 libkcalcore4 libkdgantt2 libkholidays4 libkimap4 libkldap4 libkmbox4 libkmime4 libkolabxml0 libkpgp4 libkresources4 libksieve4 libprison0 libqgpgme1 libqrencode3 libxerces-c3.1 Use 'apt-get autoremove' to remove them. The following packages will be REMOVED: akonadi-server k3b k3b-i18n katepart kde-runtime kdelibs-bin kdelibs5-plugins kdepim-runtime kdepim-strigi-plugins kdepimlibs-kio-plugins kdoctools kget kmag kmail kmix kmousetool ksystemlog kubuntu-debug-installer language-pack-kde-ar language-pack-kde-en libakonadi-calendar4 libakonadi-contact4 libakonadi-kcal4 libakonadi-kde4 libakonadi-kmime4 libcalendarsupport4 libincidenceeditorsng4 libk3b6 libkabc4 libkactivities-bin libkactivities6 libkalarmcal2 libkatepartinterfaces4 libkcal4 libkcalutils4 libkcddb4 libkde3support4 libkdepim4 libkdepimdbusinterfaces4 libkdewebkit5 libkemoticons4 libkfile4 libkgapi0 libkhtml5 libkio5 libkleo4 libkmanagesieve4 libkmediaplayer4 libknewstuff3-4 libknotifyconfig4 libkolab0 libkonq-common libkonq5abi1 libkontactinterface4 libkparts4 libkpimidentities4 libkpimtextedit4 libkpimutils4 libkprintutils4 libksieveui4 libktexteditor4 libktnef4 libktorrent4 libkworkspace4abi2 libkxmlrpcclient4 libmailcommon4 libmailimporter4 libmailtransport4 libmessagecomposer4 libmessagecore4 libmessagelist4 libmessageviewer4 libmicroblog4 libnepomuk4 libnepomukcore4abi1 libnepomukquery4a libnepomuksync4 libnepomukutils4 libplasma3 libsoprano4 libtemplateparser4 libvirtodbc0 nepomuk-core odbcinst odbcinst1debian2 plasma-scriptengine-javascript qapt-batch soprano-daemon virtuoso-minimal 0 upgraded, 0 newly installed, 89 to remove and 0 not upgraded. After this operation, 126 MB disk space will be freed. Do you want to continue [Y/n]? Other info: Why do the "iodbc" and "libmyodbc" packages conflict with each other? The root problem is that I need to use a new feature introduced in the latest MySQL Workbench builds (DB Migration) which uses odbc for that matter. Here is what Mysql doc says about it : Linux The Migration Wizard uses iODBC as a driver manager for all of its ODBC connections in Linux. This may give you some troubles because most Linux distributions provide ODBC drivers compiled against unixODBC. This is another driver manager not supported by MySQL Workbench so you won’t be able to use those drivers unless you compile them against iODBC. Here’s what you should do. Make sure that you have iODBC installed. If you are using Debian, Ubuntu or another Debian based distro, type this command in your terminal: $ sudo apt-get install iodbc libiodbc2-dev libpq-dev libssl-dev For RPM based distros (RedHat, Fedora, etc.) type this command instead of the previous one: $ sudo yum install iodbc iodbc-dev libpqxx-devel openssl-devel Now we need to install the PostgreSQL ODBC drivers. Download the psqlODBC source tarball from here. Use the latest version available for download. As of this writing the latest version corresponds to the file psqlodbc-09.01.0200.tar.gz. Extract this tarball to a directory in your hard drive and open a terminal and cd into that directory. Type this in the terminal window: $ ./configure --with-iodbc --enable-pthreads $ make $ sudo make install Verify that you have the file psqlodbcw.so in the /usr/local/lib directory. This package seems to pose the problem probably: dpkg -s odbcinst1debian2 Package: odbcinst1debian2 Status: install ok installed Priority: optional Section: libs Installed-Size: 241 Maintainer: Ubuntu Developers <[email protected]> Architecture: amd64 Multi-Arch: same Source: unixodbc Version: 2.2.14p2-5ubuntu4 Replaces: unixodbc (<< 2.1.1-2) Depends: libc6 (>= 2.14), libltdl7 (>= 2.4.2), odbcinst Pre-Depends: multiarch-support Breaks: libiodbc2, libmyodbc (<< 5.1.6-2), odbc-postgresql (<< 1:09.00.0310-1.1), tdsodbc (<< 0.82-8) Conflicts: odbcinst1, odbcinst1debian1 Description: Support library for accessing odbc ini files This package contains the libodbcinst library from unixodbc, a library used by ODBC drivers for reading their configuration settings from /etc/odbc.ini and ~/.odbc.ini. . Also contained in this package are the driver setup plugins, which describe the features supported by individual ODBC drivers. Homepage: http://www.unixodbc.org/ Original-Maintainer: Steve Langasek <[email protected]> I have no broken packages:

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  • USB mouse disconnecting and reconnecting in windows and linux

    - by Kalak
    I have a problem similar to what is described at "Why is my USB mouse disconnecting and reconnecting randomly and often?" except is is happening in both Windows 7 and Linux (Ubuntu 12/04TLS, fully patched), multiple mice, multiple OSs. It stops responding to input for about 3-5 seconds, then starts responding again. It's more frequent and lasts longer when running games (TF2, L4D, Dishonored, Borderlands 2, and more), but happens when just running the OS as well. I was hoping it was the motherboard so I bought a USB 2.0 PCI card to try that, but it's still happening. I've stripped it down to just the keyboard and mouse (different keyboard too just in case the keyboard was the problem), but it's still happening. All the hardware (mice and keyboards) work fine on other computers. I have literally pulled the mouse and keyboard out and plugged them into another computer (laptop) and re-joined the online game and had no problem with the keyboard and mouse combo that just failed on my gaming rig. Please no driver / Windows or Linux only suggestions, as that wouldn't effect both OSs. edit: known good mice I've brought home are now going bad. I suspect the hardware is messed up (voltage?) and has been frying the mice.

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  • Oracle Business Intelligence Advanced - Hands-on Workshop para Parceiros - 18 a 21 de Janeiro

    - by Claudia Costa
    Workshop Description This FREE hands-on workshop highlights strengths of OBIEE 11g by providing attendees a hands-on experience with BI 11g product. OBIEE 11g has adopted the standardized infrastructure of Fusion Middleware to provide robust server capability along with highly anticipated advanced visualization components like Maps, Flash based charts, Scorecards and KPIs. This workshop focuses on new features and infrastructure components for the BI practitioners who are familiar with either OBIEE 10g or previous BI releases. After taking this course, Oracle Business Intelligence 11g Advanced, you will gain insight into OBIEE11g technology, reporting solutions and new features. Workshop provides opportunities to practice with OBIEE11g environment as hands on activities. Participant will gain in-depth understanding of new architecture of OBIEE 11g, security mode, installation/configuration as well as reporting aspects like, new ROLAP/MOLAP style hierarchical browsing, new chart types, Action Framework and Advanced Visualization. If you are a Business Intelligence practitioners and familiar with BI10g - you cannot afford to miss this 3-day workshop. Register Now! PresentationsBusiness Intelligence EE (OBIEE) 11g: Advanced Workshop ·         OBIEE 11g Overview ·         OBIEE 11g Architecture and Infrastructure ·         OBIEE 11g Installation, Configuration and Monitoring ·         OBIEE11g Security Model and BI Components ·         OBIEE 11g Homepage Overview ·         New Visualizations: Master-Detail Events, Charts, Hierarchies ·         Reports Building with OBIEE 11g and Catalog Management ·         Spatial Integration, Action Framework, Scorecards ·         OBIEE 11g Dashboards ·         OBIEE Integration Options  Lab OutlineOracle Business Intelligence (OBIEE) 11g: Advanced Workshop The labs enable OBIEE Core functionality through hands-on activities are based on a Oracle VirtualBox image with software and training samples pre-installed. This Advanced course has few labs optional during the workshop to allow for students to practice them on their own. The primary purpose of the workshop is to provide expertise of 11g features and infrastructure changes from 10g. Labs will allow you to explore concepts to: ·         Have a clear understanding of the OBIEE 11g architecture ·         Have a clear understanding of the OBIEE differentiators ·         OBIEE11g Security Model ·         OBIEE11g Environment Management ·         Report Building with OBIEE11g ·         OBIEE11g Dashboard and Homepage Environment ·         New Visualization features ·         Management of Reports, Dashboards and BI Catalog Objects Audience ·         Business Intelligence Evangelist ·         Business Intelligence Application Developer or Consultant ·         Data Warehouse Developer ·         Enterprise Architects ·         Industry Solutions Architects Prerequisites ·         Experience and Understanding of OBIEE 10g is required. ·         Good understanding of data modeling for reporting purpose ·         Strong experience with database technologies preferred Equipment RequirementsThis workshop requires attendees to provide their own laptops. Attendee laptops must meet the following minimum hardware/software requirements: OBIEE 11g environments requires at least 3 GB of RAM (4GB Preferred), without which student will not be able to complete labs. This workshop has environment that includes VM Image and also a software components that students will install on their laptop for the labs. ·         Minimum 3GB RAM. 25GB free disk space ·         Internet Explorer 7 ·         VirtualBox (the latest version) ·         Downloadable from http://www.virtualbox.org ·         WINRAR or 7zip ·         Downloadable from http://www.win-rar.com/download.html ·         Downloadable from http://www.7zip.com/ Attendees will be given a VirtualBox image for Oraclee BI 11g Workshop containing the software along with required toolset, database and data sets for the labs. AgendaThis class duration is 3 Days9:00am: Sign-in and Technical Set up9:30am : Workshop Starts5:00pm : Workhop Ends LocalHotel Holiday Inn Express - Porto Salvo - Lisboa This class is Free. Register early to confirm a seat! Oracle BI Advanced 11g Hands-on Workshop - Schedule Register Now! January 11-13, 2011: Kista, Sweden January 18-20, 2011: Lisbon, Portugal March 1-3, 2011: Reading, Berkshire, UK March 15-17, 2011: Colombes, Paris, France March 29-31, 2011: Amsterdam, Netherlands Questions? For registration questions please send an email to [email protected]. Para outras informações, por favor contacte Claudia Costa, telf: 214235027 ou pelo email   

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  • Visual Studio Async CTP

    - by Daniel Moth
    While most of the buzz at the recent PDC here at Microsoft's headquarters has been about Windows Azure and Windows Phone, there is a truly noteworthy technology that as a .NET developer (of any kind of application) you should pay attention to, even in its early technology preview stage: Visual Studio Async CTP. I could provide many more direct links, but you do not need them: just visit the home page of this technology to download whitepapers, watch videos on how this technology integrates with C# and with VB, (through the new async and await language keywords) as well as videos on how the technology works under the covers (based largely on the Task Parallel Library). More importantly, download the actual bits (they install on top of your Visual Studio 2010), which include many samples. Get ready for a revolution in Asynchronous Programming with C# and Visual Basic. Comments about this post welcome at the original blog.

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  • Email Service or CRM

    - by MG1
    I am creating a process for a client who is a chapel. They have people who sign up to receive notifications of a death anniversary. I exported a CSV from the db, imported it into Mailchimp and I was about to launch a Mailchimp automation based on a date. Not I realized that are many instances where the same person singed up for multiple death reminders. Mailchimp doesn't allow for duplicate email addresses in one list. Is there another service or application that I can use for this?

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  • I need to develop a parser. Can I use Lex and Yacc for the purpose?

    - by Scrooge
    I need to extract very particular data from log files(of different types and formats). Since I am a recent college passout; my mind ran to using Lex and Yacc for the purpose. Now I have the following Questions 1. Will it be legal to do so ? (This product I am working for belongs to one of the biggest tech companies in the world.) 2. Also ; I would like to know if I am being too afraid to write my own parser? 3. How can I use Lex and Yacc if my product is Windows based? Please tell me if you need any clarification or extra information.

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  • OVM Templates: Oracle Solaris Container with Oracle Database 11gR2

    - by Roman Ivanov
    I am delighted to inform you that Oracle just made available new Oracle Solaris Virtual Machine (VM) Templates: Oracle Solaris Container with Oracle Database 11gR2. This VM Templates available for SPARC and x86 platforms. Both Oracle VM Templates based on encapsulating an Oracle Solaris 10 Container which can then be attached to SPARC or x86 system running Oracle Solaris 10 10/09 or later. Make sure your select correct SPARC or x86 platform. The download includes Oracle Solaris 10 10/09 Container Oracle Database 11gR2 pre-installed in the Container.

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  • Dynamically switching the theme in Orchard

    - by Bertrand Le Roy
    It may sound a little puzzling at first, but in Orchard CMS, more than one theme can be active at any given time. The reason for that is that we have an extensibility point that allows a module (or a theme) to participate in the choice of the theme to use, for each request. The motivation for building the theme engine this way was to enable developers to switch themes based on arbitrary criteria, such as user preferences or the user agent (if you want to serve a mobile theme for phones for example). The choice is made between the active themes, which is why there is a difference between the default theme and the active themes. In order to have a say in the choice of the theme, all you have to do is implement IThemeSelector. That interface is quite simple as it only has one method, GetTheme, that takes the current RequestContext and returns a ThemeSelectorResult or null if the implementation of the interface does not want to participate in the current request (we'll see an example in a moment). ThemeSelectorResult itself is just a ThemeName string property and an integer Priority. We're using a priority so that an arbitrary number of implementations of IThemeSelector can contribute to the choice of a theme. If you look for existing implementations of the interface in Orchard, you'll find four: AdminThemeSelector: selects the TheAdmin theme with a very high priority (100) if the current request is for a page that is part of the admin. Otherwise, null is returned, which enables other implementations to choose the theme. PreviewThemeSelector: selects the preview theme if there is one, with a high priority (90), and null otherwise. This enables administrators to view the site under a different theme while everybody else continues to see the current default theme. SiteThemeSelector: this is the implementation that is doing what you expect most of the time, which is to get the current theme from site settings and set it with a priority of –5. SafeModeThemeSelector: this is the fallback implementation, which should almost never win. It sets the theme as the safe mode theme, which has no style and just uses the default templates for everything. The priority is very low (-100). While this extensibility mechanism is great to have, I wanted to bring that level of choice into the hands of the site administrator rather than just developers. In order to achieve that, I built the Vandelay Theme Picker module. The module provides administration UI to create rules for theme selection. It provides its own extensibility point (the IThemeSelectionRule interface) and one implementation of a rule: UserAgentThemeSelectorRule. This rule gets the current user agent from the context and tries to match it with a regular expression that the administrator can configure in the admin UI. You can for example configure a rule with a regular expression that matches IE6 and serve a different subtheme where the stylesheet has been tweaked for such an antique browser. Another possible configuration is to detect mobile devices from their agent string and serve the mobile theme. All those operations can be done with this module entirely from the admin UI, without writing a line of code. The module also offers the administrator the opportunity to inject a link into the front-end in a specific zone and with a specific position that enables the user to switch to the default theme if he wishes to. This is especially useful for sites that use a mobile theme but still want to allow users to use the full desktop site. While the module is nice and flexible, it may be overkill. On my own personal blog, I have only two active themes: the desktop theme and the mobile theme. I'm fine with going into code to change the criteria on which to switch the theme, so I'm not using my own Theme Picker module. Instead, I made the mobile theme a theme with code (in other words there is a csproj file in the theme). The project includes a single C# file, my MobileThemeSelector for which the code is the following: public class MobileThemeSelector : IThemeSelector { private static readonly Regex _Msie678 = new Regex(@"^Mozilla\/4\.0 \(compatible; MSIE [678]" + @"\.0; Windows NT \d\.\d(.*)\)$", RegexOptions.IgnoreCase); private ThemeSelectorResult _requestCache; private bool _requestCached; public ThemeSelectorResult GetTheme(RequestContext context) { if (_requestCached) return _requestCache; _requestCached = true; var userAgent = context.HttpContext.Request.UserAgent; if (userAgent.IndexOf("phone", StringComparison.OrdinalIgnoreCase) != -1 || _Msie678.IsMatch(userAgent) || userAgent.IndexOf("windows live writer", StringComparison.OrdinalIgnoreCase) != -1) { _requestCache = new ThemeSelectorResult { Priority = 10, ThemeName = "VuLuMobile" }; } return _requestCache; } } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; } The theme selector selects the current theme for Internet Explorer versions 6 to 8, for phones, and for Windows Live Writer (so that the theme that is used when I write posts is as simple as possible). What's interesting here is that it's the theme that selects itself here, based on its own criteria. This should give you a good panorama of what's possible in terms of dynamic theme selection in Orchard. I hope you find some fun uses for it. As usual, I can't wait to see what you're going to come up with…

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  • PTLQueue : a scalable bounded-capacity MPMC queue

    - by Dave
    Title: Fast concurrent MPMC queue -- I've used the following concurrent queue algorithm enough that it warrants a blog entry. I'll sketch out the design of a fast and scalable multiple-producer multiple-consumer (MPSC) concurrent queue called PTLQueue. The queue has bounded capacity and is implemented via a circular array. Bounded capacity can be a useful property if there's a mismatch between producer rates and consumer rates where an unbounded queue might otherwise result in excessive memory consumption by virtue of the container nodes that -- in some queue implementations -- are used to hold values. A bounded-capacity queue can provide flow control between components. Beware, however, that bounded collections can also result in resource deadlock if abused. The put() and take() operators are partial and wait for the collection to become non-full or non-empty, respectively. Put() and take() do not allocate memory, and are not vulnerable to the ABA pathologies. The PTLQueue algorithm can be implemented equally well in C/C++ and Java. Partial operators are often more convenient than total methods. In many use cases if the preconditions aren't met, there's nothing else useful the thread can do, so it may as well wait via a partial method. An exception is in the case of work-stealing queues where a thief might scan a set of queues from which it could potentially steal. Total methods return ASAP with a success-failure indication. (It's tempting to describe a queue or API as blocking or non-blocking instead of partial or total, but non-blocking is already an overloaded concurrency term. Perhaps waiting/non-waiting or patient/impatient might be better terms). It's also trivial to construct partial operators by busy-waiting via total operators, but such constructs may be less efficient than an operator explicitly and intentionally designed to wait. A PTLQueue instance contains an array of slots, where each slot has volatile Turn and MailBox fields. The array has power-of-two length allowing mod/div operations to be replaced by masking. We assume sensible padding and alignment to reduce the impact of false sharing. (On x86 I recommend 128-byte alignment and padding because of the adjacent-sector prefetch facility). Each queue also has PutCursor and TakeCursor cursor variables, each of which should be sequestered as the sole occupant of a cache line or sector. You can opt to use 64-bit integers if concerned about wrap-around aliasing in the cursor variables. Put(null) is considered illegal, but the caller or implementation can easily check for and convert null to a distinguished non-null proxy value if null happens to be a value you'd like to pass. Take() will accordingly convert the proxy value back to null. An advantage of PTLQueue is that you can use atomic fetch-and-increment for the partial methods. We initialize each slot at index I with (Turn=I, MailBox=null). Both cursors are initially 0. All shared variables are considered "volatile" and atomics such as CAS and AtomicFetchAndIncrement are presumed to have bidirectional fence semantics. Finally T is the templated type. I've sketched out a total tryTake() method below that allows the caller to poll the queue. tryPut() has an analogous construction. Zebra stripping : alternating row colors for nice-looking code listings. See also google code "prettify" : https://code.google.com/p/google-code-prettify/ Prettify is a javascript module that yields the HTML/CSS/JS equivalent of pretty-print. -- pre:nth-child(odd) { background-color:#ff0000; } pre:nth-child(even) { background-color:#0000ff; } border-left: 11px solid #ccc; margin: 1.7em 0 1.7em 0.3em; background-color:#BFB; font-size:12px; line-height:65%; " // PTLQueue : Put(v) : // producer : partial method - waits as necessary assert v != null assert Mask = 1 && (Mask & (Mask+1)) == 0 // Document invariants // doorway step // Obtain a sequence number -- ticket // As a practical concern the ticket value is temporally unique // The ticket also identifies and selects a slot auto tkt = AtomicFetchIncrement (&PutCursor, 1) slot * s = &Slots[tkt & Mask] // waiting phase : // wait for slot's generation to match the tkt value assigned to this put() invocation. // The "generation" is implicitly encoded as the upper bits in the cursor // above those used to specify the index : tkt div (Mask+1) // The generation serves as an epoch number to identify a cohort of threads // accessing disjoint slots while s-Turn != tkt : Pause assert s-MailBox == null s-MailBox = v // deposit and pass message Take() : // consumer : partial method - waits as necessary auto tkt = AtomicFetchIncrement (&TakeCursor,1) slot * s = &Slots[tkt & Mask] // 2-stage waiting : // First wait for turn for our generation // Acquire exclusive "take" access to slot's MailBox field // Then wait for the slot to become occupied while s-Turn != tkt : Pause // Concurrency in this section of code is now reduced to just 1 producer thread // vs 1 consumer thread. // For a given queue and slot, there will be most one Take() operation running // in this section. // Consumer waits for producer to arrive and make slot non-empty // Extract message; clear mailbox; advance Turn indicator // We have an obvious happens-before relation : // Put(m) happens-before corresponding Take() that returns that same "m" for T v = s-MailBox if v != null : s-MailBox = null ST-ST barrier s-Turn = tkt + Mask + 1 // unlock slot to admit next producer and consumer return v Pause tryTake() : // total method - returns ASAP with failure indication for auto tkt = TakeCursor slot * s = &Slots[tkt & Mask] if s-Turn != tkt : return null T v = s-MailBox // presumptive return value if v == null : return null // ratify tkt and v values and commit by advancing cursor if CAS (&TakeCursor, tkt, tkt+1) != tkt : continue s-MailBox = null ST-ST barrier s-Turn = tkt + Mask + 1 return v The basic idea derives from the Partitioned Ticket Lock "PTL" (US20120240126-A1) and the MultiLane Concurrent Bag (US8689237). The latter is essentially a circular ring-buffer where the elements themselves are queues or concurrent collections. You can think of the PTLQueue as a partitioned ticket lock "PTL" augmented to pass values from lock to unlock via the slots. Alternatively, you could conceptualize of PTLQueue as a degenerate MultiLane bag where each slot or "lane" consists of a simple single-word MailBox instead of a general queue. Each lane in PTLQueue also has a private Turn field which acts like the Turn (Grant) variables found in PTL. Turn enforces strict FIFO ordering and restricts concurrency on the slot mailbox field to at most one simultaneous put() and take() operation. PTL uses a single "ticket" variable and per-slot Turn (grant) fields while MultiLane has distinct PutCursor and TakeCursor cursors and abstract per-slot sub-queues. Both PTL and MultiLane advance their cursor and ticket variables with atomic fetch-and-increment. PTLQueue borrows from both PTL and MultiLane and has distinct put and take cursors and per-slot Turn fields. Instead of a per-slot queues, PTLQueue uses a simple single-word MailBox field. PutCursor and TakeCursor act like a pair of ticket locks, conferring "put" and "take" access to a given slot. PutCursor, for instance, assigns an incoming put() request to a slot and serves as a PTL "Ticket" to acquire "put" permission to that slot's MailBox field. To better explain the operation of PTLQueue we deconstruct the operation of put() and take() as follows. Put() first increments PutCursor obtaining a new unique ticket. That ticket value also identifies a slot. Put() next waits for that slot's Turn field to match that ticket value. This is tantamount to using a PTL to acquire "put" permission on the slot's MailBox field. Finally, having obtained exclusive "put" permission on the slot, put() stores the message value into the slot's MailBox. Take() similarly advances TakeCursor, identifying a slot, and then acquires and secures "take" permission on a slot by waiting for Turn. Take() then waits for the slot's MailBox to become non-empty, extracts the message, and clears MailBox. Finally, take() advances the slot's Turn field, which releases both "put" and "take" access to the slot's MailBox. Note the asymmetry : put() acquires "put" access to the slot, but take() releases that lock. At any given time, for a given slot in a PTLQueue, at most one thread has "put" access and at most one thread has "take" access. This restricts concurrency from general MPMC to 1-vs-1. We have 2 ticket locks -- one for put() and one for take() -- each with its own "ticket" variable in the form of the corresponding cursor, but they share a single "Grant" egress variable in the form of the slot's Turn variable. Advancing the PutCursor, for instance, serves two purposes. First, we obtain a unique ticket which identifies a slot. Second, incrementing the cursor is the doorway protocol step to acquire the per-slot mutual exclusion "put" lock. The cursors and operations to increment those cursors serve double-duty : slot-selection and ticket assignment for locking the slot's MailBox field. At any given time a slot MailBox field can be in one of the following states: empty with no pending operations -- neutral state; empty with one or more waiting take() operations pending -- deficit; occupied with no pending operations; occupied with one or more waiting put() operations -- surplus; empty with a pending put() or pending put() and take() operations -- transitional; or occupied with a pending take() or pending put() and take() operations -- transitional. The partial put() and take() operators can be implemented with an atomic fetch-and-increment operation, which may confer a performance advantage over a CAS-based loop. In addition we have independent PutCursor and TakeCursor cursors. Critically, a put() operation modifies PutCursor but does not access the TakeCursor and a take() operation modifies the TakeCursor cursor but does not access the PutCursor. This acts to reduce coherence traffic relative to some other queue designs. It's worth noting that slow threads or obstruction in one slot (or "lane") does not impede or obstruct operations in other slots -- this gives us some degree of obstruction isolation. PTLQueue is not lock-free, however. The implementation above is expressed with polite busy-waiting (Pause) but it's trivial to implement per-slot parking and unparking to deschedule waiting threads. It's also easy to convert the queue to a more general deque by replacing the PutCursor and TakeCursor cursors with Left/Front and Right/Back cursors that can move either direction. Specifically, to push and pop from the "left" side of the deque we would decrement and increment the Left cursor, respectively, and to push and pop from the "right" side of the deque we would increment and decrement the Right cursor, respectively. We used a variation of PTLQueue for message passing in our recent OPODIS 2013 paper. ul { list-style:none; padding-left:0; padding:0; margin:0; margin-left:0; } ul#myTagID { padding: 0px; margin: 0px; list-style:none; margin-left:0;} -- -- There's quite a bit of related literature in this area. I'll call out a few relevant references: Wilson's NYU Courant Institute UltraComputer dissertation from 1988 is classic and the canonical starting point : Operating System Data Structures for Shared-Memory MIMD Machines with Fetch-and-Add. Regarding provenance and priority, I think PTLQueue or queues effectively equivalent to PTLQueue have been independently rediscovered a number of times. See CB-Queue and BNPBV, below, for instance. But Wilson's dissertation anticipates the basic idea and seems to predate all the others. Gottlieb et al : Basic Techniques for the Efficient Coordination of Very Large Numbers of Cooperating Sequential Processors Orozco et al : CB-Queue in Toward high-throughput algorithms on many-core architectures which appeared in TACO 2012. Meneghin et al : BNPVB family in Performance evaluation of inter-thread communication mechanisms on multicore/multithreaded architecture Dmitry Vyukov : bounded MPMC queue (highly recommended) Alex Otenko : US8607249 (highly related). John Mellor-Crummey : Concurrent queues: Practical fetch-and-phi algorithms. Technical Report 229, Department of Computer Science, University of Rochester Thomasson : FIFO Distributed Bakery Algorithm (very similar to PTLQueue). Scott and Scherer : Dual Data Structures I'll propose an optimization left as an exercise for the reader. Say we wanted to reduce memory usage by eliminating inter-slot padding. Such padding is usually "dark" memory and otherwise unused and wasted. But eliminating the padding leaves us at risk of increased false sharing. Furthermore lets say it was usually the case that the PutCursor and TakeCursor were numerically close to each other. (That's true in some use cases). We might still reduce false sharing by incrementing the cursors by some value other than 1 that is not trivially small and is coprime with the number of slots. Alternatively, we might increment the cursor by one and mask as usual, resulting in a logical index. We then use that logical index value to index into a permutation table, yielding an effective index for use in the slot array. The permutation table would be constructed so that nearby logical indices would map to more distant effective indices. (Open question: what should that permutation look like? Possibly some perversion of a Gray code or De Bruijn sequence might be suitable). As an aside, say we need to busy-wait for some condition as follows : "while C == 0 : Pause". Lets say that C is usually non-zero, so we typically don't wait. But when C happens to be 0 we'll have to spin for some period, possibly brief. We can arrange for the code to be more machine-friendly with respect to the branch predictors by transforming the loop into : "if C == 0 : for { Pause; if C != 0 : break; }". Critically, we want to restructure the loop so there's one branch that controls entry and another that controls loop exit. A concern is that your compiler or JIT might be clever enough to transform this back to "while C == 0 : Pause". You can sometimes avoid this by inserting a call to a some type of very cheap "opaque" method that the compiler can't elide or reorder. On Solaris, for instance, you could use :"if C == 0 : { gethrtime(); for { Pause; if C != 0 : break; }}". It's worth noting the obvious duality between locks and queues. If you have strict FIFO lock implementation with local spinning and succession by direct handoff such as MCS or CLH,then you can usually transform that lock into a queue. Hidden commentary and annotations - invisible : * And of course there's a well-known duality between queues and locks, but I'll leave that topic for another blog post. * Compare and contrast : PTLQ vs PTL and MultiLane * Equivalent : Turn; seq; sequence; pos; position; ticket * Put = Lock; Deposit Take = identify and reserve slot; wait; extract & clear; unlock * conceptualize : Distinct PutLock and TakeLock implemented as ticket lock or PTL Distinct arrival cursors but share per-slot "Turn" variable provides exclusive role-based access to slot's mailbox field put() acquires exclusive access to a slot for purposes of "deposit" assigns slot round-robin and then acquires deposit access rights/perms to that slot take() acquires exclusive access to slot for purposes of "withdrawal" assigns slot round-robin and then acquires withdrawal access rights/perms to that slot At any given time, only one thread can have withdrawal access to a slot at any given time, only one thread can have deposit access to a slot Permissible for T1 to have deposit access and T2 to simultaneously have withdrawal access * round-robin for the purposes of; role-based; access mode; access role mailslot; mailbox; allocate/assign/identify slot rights; permission; license; access permission; * PTL/Ticket hybrid Asymmetric usage ; owner oblivious lock-unlock pairing K-exclusion add Grant cursor pass message m from lock to unlock via Slots[] array Cursor performs 2 functions : + PTL ticket + Assigns request to slot in round-robin fashion Deconstruct protocol : explication put() : allocate slot in round-robin fashion acquire PTL for "put" access store message into slot associated with PTL index take() : Acquire PTL for "take" access // doorway step seq = fetchAdd (&Grant, 1) s = &Slots[seq & Mask] // waiting phase while s-Turn != seq : pause Extract : wait for s-mailbox to be full v = s-mailbox s-mailbox = null Release PTL for both "put" and "take" access s-Turn = seq + Mask + 1 * Slot round-robin assignment and lock "doorway" protocol leverage the same cursor and FetchAdd operation on that cursor FetchAdd (&Cursor,1) + round-robin slot assignment and dispersal + PTL/ticket lock "doorway" step waiting phase is via "Turn" field in slot * PTLQueue uses 2 cursors -- put and take. Acquire "put" access to slot via PTL-like lock Acquire "take" access to slot via PTL-like lock 2 locks : put and take -- at most one thread can access slot's mailbox Both locks use same "turn" field Like multilane : 2 cursors : put and take slot is simple 1-capacity mailbox instead of queue Borrow per-slot turn/grant from PTL Provides strict FIFO Lock slot : put-vs-put take-vs-take at most one put accesses slot at any one time at most one put accesses take at any one time reduction to 1-vs-1 instead of N-vs-M concurrency Per slot locks for put/take Release put/take by advancing turn * is instrumental in ... * P-V Semaphore vs lock vs K-exclusion * See also : FastQueues-excerpt.java dice-etc/queue-mpmc-bounded-blocking-circular-xadd/ * PTLQueue is the same as PTLQB - identical * Expedient return; ASAP; prompt; immediately * Lamport's Bakery algorithm : doorway step then waiting phase Threads arriving at doorway obtain a unique ticket number Threads enter in ticket order * In the terminology of Reed and Kanodia a ticket lock corresponds to the busy-wait implementation of a semaphore using an eventcount and a sequencer It can also be thought of as an optimization of Lamport's bakery lock was designed for fault-tolerance rather than performance Instead of spinning on the release counter, processors using a bakery lock repeatedly examine the tickets of their peers --

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  • Online Password Security Tactics

    - by BuckWoody
    Recently two more large databases were attacked and compromised, one at the popular Gawker Media sites and the other at McDonald’s. Every time this kind of thing happens (which is FAR too often) it should remind the technical professional to ensure that they secure their systems correctly. If you write software that stores passwords, it should be heavily encrypted, and not human-readable in any storage. I advocate a different store for the login and password, so that if one is compromised, the other is not. I also advocate that you set a bit flag when a user changes their password, and send out a reminder to change passwords if that bit isn’t changed every three or six months.    But this post is about the *other* side – what to do to secure your own passwords, especially those you use online, either in a cloud service or at a provider. While you’re not in control of these breaches, there are some things you can do to help protect yourself. Most of these are obvious, but they contain a few little twists that make the process easier.   Use Complex Passwords This is easily stated, and probably one of the most un-heeded piece of advice. There are three main concepts here: ·         Don’t use a dictionary-based word ·         Use mixed case ·         Use punctuation, special characters and so on   So this: password Isn’t nearly as safe as this: P@ssw03d   Of course, this only helps if the site that stores your password encrypts it. Gawker does, so theoretically if you had the second password you’re in better shape, at least, than the first. Dictionary words are quickly broken, regardless of the encryption, so the more unusual characters you use, and the farther away from the dictionary words you get, the better.   Of course, this doesn’t help, not even a little, if the site stores the passwords in clear text, or the key to their encryption is broken. In that case…   Use a Different Password at Every Site What? I have hundreds of sites! Are you kidding me? Nope – I’m not. If you use the same password at every site, when a site gets attacked, the attacker will store your name and password value for attacks at other sites. So the only safe thing to do is to use different names or passwords (or both) at each site. Of course, most sites use your e-mail as a username, so you’re kind of hosed there. So even though you have hundreds of sites you visit, you need to have at least a different password at each site.   But it’s easier than you think – if you use an algorithm.   What I’m describing is to pick a “root” password, and then modify that based on the site or purpose. That way, if the site is compromised, you can still use that root password for the other sites.   Let’s take that second password: P@ssw03d   And now you can append, prepend or intersperse that password with other characters to make it unique to the site. That way you can easily remember the root password, but make it unique to the site. For instance, perhaps you read a lot of information on Gawker – how about these:   P@ssw03dRead ReadP@ssw03d PR@esasdw03d   If you have lots of sites, tracking even this can be difficult, so I recommend you use password software such as Password Safe or some other tool to have a secure database of your passwords at each site. DO NOT store this on the web. DO NOT use an Office document (Microsoft or otherwise) that is “encrypted” – the encryption office automation packages use is very trivial, and easily broken. A quick web search for tools to do that should show you how bad a choice this is.   Change Your Password on a Schedule I know. It’s a real pain. And it doesn’t seem worth it…until your account gets hacked. A quick note here – whenever a site gets hacked (and I find out about it) I change the password at that site immediately (or quit doing business with them) and then change the root password on every site, as quickly as I can.   If you follow the tip above, it’s not as hard. Just add another number, year, month, day, something like that into the mix. It’s not unlike making a Primary Key in an RDBMS.   P@ssw03dRead10242010   Change the site, and then update your password database. I do this about once a month, on the first or last day, during staff meetings. (J)   If you have other tips, post them here. We can all learn from each other on this.

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  • frame lock networking

    - by kochol
    I'm developing an RTS game and I want to add multiplayer support to my game. I picked the easiest technique to implement for start frame locking technique. I used server client networking architecture (I think it's my first mistake I think using peer to peer is a better one for this) On game update every clients send their commands and maybe receive some command then render the frame and wait for all clients to send their update complete message then all of them can go for the next frame. I send commands and all logic is calculated on the clients based on commands but the clients can go out of sync easily. Every AI controlled units make different decisions on each clients What I have to do to sync my game? Do you suggest me a better network architecture or technique?

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  • Create .deb form gambas2 project

    - by Mauricio Andrés
    I have been working with Gambas 2 (the one in the software center), Actially I took the source code of other program and create a new program basen on that. But now that I finished, I can't create .deb files, gambas show me this error: La creación del paquete ha fallado. Package.MakeDebPackage.368: File or directory does not exist So I dont know what to do now, I really need this program. I tried with Gambas 3, but is too much work to do that the program based in Gmabas 2 works in Gambas 3, also I tried creating a .deb package and gambas get frozen. Please some help

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  • Unlock the full potential of Oracle Retail with Oracle Retail Consulting

    - by user801960
    In this video, Maria Porretta, Engagement Director, introduces Oracle Retail Consulting which supports Oracle Retail customers by unlocking the potential of the software solutions they are utilising. Oracle Retail Consulting comprises of a global team of over 300 consultants, 70 of which are EMEA based. 90% of the team have a retail background in either IT or business, ensuring true industry expertise and maximum business benefit. Oracle Retail Consulting offers two primary streams of service; design authority which looks at analysis and design to ensure a guided process through to implementation, and delivery ownership which runs throughout the implementation process. Further information is available on our website regarding Oracle Retail Consulting.

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  • Is Google Closure a true compiler?

    - by James Allardice
    This question is inspired by the debate in the comments on this Stack Overflow question. The Google Closure Compiler documentation states the following (emphasis added): The Closure Compiler is a tool for making JavaScript download and run faster. It is a true compiler for JavaScript. Instead of compiling from a source language to machine code, it compiles from JavaScript to better JavaScript. However, Wikipedia gives the following definition of a "compiler": A compiler is a computer program (or set of programs) that transforms source code written in a programming language (the source language) into another computer language... A language rewriter is usually a program that translates the form of expressions without a change of language. Based on that, I would say that Google Closure is not a compiler. But the fact that Google explicitly state that it is in fact a "true compiler" makes me wonder if there's more to it. Is Google Closure really a JavaScript compiler?

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  • Announcement Oracle Solaris Cluster 4.1 Availability!

    - by uwes
    On 26th of October Oracle announced the availability of Oracle Solaris Cluster 4.1. Highlights include: New Oracle Solaris 10 Zone Clusters: customers can now consolidate mission critical Oracle Solaris 10 applications on Oracle Solaris 11 virtualized systems in a virtual cluster Expanded disaster recovery operations: Oracle Solaris Cluster now offers managed switchover and disaster-recovery takeover of applications and data using ZFS Storage Appliance replication services in a multi-site, multi-custer configuration Faster application recovery with improved storage failure detection and resource dependencies management New labeled security environment for mission-critical deployments in Oracle Solaris Zone Clusters with Oracle Solaris 11 Trusted Extensions Learn more about Oracle Solaris Cluster 4.1: What's New in Oracle Solaris 4.1 Oracle Solaris Cluster 4.1 FAQ Oracle.com Oracle Solaris Cluster page Oracle Technology Network Oracle Solaris Cluster page Resouces for downloading: Oracle Solaris Cluster 4.1 download or order a media kit Existing Oracle Solaris Cluster 4.0 customers can quickly and simply update by using the network based repository.   Note: This repository requires keys and certificates which can be obtained here.

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  • When does a game idea cross the line between homage/parody to ripoff?

    - by Daniel T.
    I'm not sure where this question belongs, but as it pertains to the development of a game idea, I figured I'd try to post it here. Recently I've been inspired to create a game based on another game I've played. However, the idea that I have is very similar to the original game. I was wondering, when does a game idea cross from being a homage or parody into the realm of being a ripoff? Are there any hard or fast rules or does this cross into a gray area?

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