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  • The Krewe App Post-Mortem

    - by Chris Gardner
    Originally posted on: http://geekswithblogs.net/freestylecoding/archive/2014/05/23/the-krewe-app-post-mortem.aspxNow that teched has come and gone, I thought I would use this opportunity to do a little post-mortem on The Krewe app. It is one thing to test the app at home. It is a completely different animal to see how it responds in the environment TechEd creates. At a future time, I will list all the things that I would like to change with the app. At this point, I will find some good way to get community feedback. I want to break all this down screen by screen. We'll start with the screen I got right. The first of these is the events calendar. This is the one screen that, to you guys, just worked. However, there was an issue here. When I wrote v1 for last year, I was lazy and placed everything in CST. This caused problems with the achievements, which I will explain later. Furthermore, the event locations were not check-in locations. This created another problem with the achievements. Next, we get to the Twitter page. For what this page does, it works great. For those that don't know, I have an Azure Worker Role that polls Twitter pretty close to the rate limit. I cache these results in my database, and serve them upon request. This gives me great control over the content. I just have to remember to flush past tweets after a period, to save database growth. The next screen is the check-in screen. This screen has been the bane of my existence since I first created the thing. Last year, I used a background task to check people out of locations after they traveled. This year, I removed the background task in favor of a foursquare model. You are checked out after 3 hours or when you check-in to some other location. This seemed to work well, until those pesky achievements came into the mix. Again, more on this later. Next, I want to address the Connect and Connections screens together. I wanted to use some of the capabilities of the phone, and NFC seemed a natural choice. From this, I came up with the gamification aspects of the app. Since we are, fundamentally, a networking organization, I wanted to encourage people to actually network. Users could make and share a profile, similar to a virtual business card. I just had to figure out how to get people to use the feature. Why not just give someone a business card? Thus, the achievements were born. This was such a good idea. It would have been a great idea, if I have come up with it about two months earlier... When I came up with these ideas, I had about 2 weeks to implement them. Version 1 of the app was, basically, a pure consumption app. We provided data and centralized it. With version 2, the app became a much more interactive experience. The API was not ready for this change in such a short period of time. Most of this became apparent when I started implementing the achievements. The achievements based on count and specific person when fairly easy. The problem came with tying them to locations and events. This took some true SQL kung fu. This also showed me the rookie mistake of putting CST, not UTC, in the database. Once I got all of that cleaned up, I had to find a way to get the achievement system to talk to the phone. I knew I needed to be able to dynamically add achievements. I wouldn't know the precise location of some things until I got to Houston. I wanted the server to approve the achievements. This, unfortunately, required a decent data connection. Some achievements required GPS levels of location accuracy in areas of network triangulation. All of this became a huge nightmare. My flagship feature was based on some silly assumptions. Still, I managed to get 31 people to get the first achievement (Make 1 Connection.) Quite a few of those managed to get to the higher levels. Soon, I will post a list of the feature and changes that need to happen to the API. This includes things like proper objects for communication, geo-fencing, and caching. However, that is for another day.

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  • Tool to identify potential reviewers for a proposed change

    - by Lorin Hochstein
    Is there a tool that takes as input a proposed patch and a git repository, and identifies the developers are the best candidates for reviewing the patch? It would use the git history to identify the authors that have the most experience with the files / sections of code that are being changed. Edit: The use case is a large open source project (OpenStack Compute), where merge proposals come in, and I see a merge proposal on a chunk of code I'm not familiar with, and I want to add somebody else's name to the list of suggested reviewers so that person gets a notification to look at the merge proposal.

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  • 301 redirect bulk aspx URLs on IIS

    - by tiki16
    We recently relaunched an old ASPX site as a new Drupal site on the same domain. No 301 redirect was implemented. I have outputted a list of 1000 URLs that need to be 301 redirected. Most of the URLs are the results of search queries that were committed on the website. I.E.: http://www.mysite.com/electronics/CommunityDetails.aspx?FirstLetter=%&ID=444 We are running a Drupal site on IIS using a PHP plugin. Is there a way I can wild card a redirect of all ASPX pages? I know I can do it with .htaccess but that doesn't apply here. Any suggestions appreciated.

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  • MySQL Connector/Net 6.5.5 Maintenance Release has been released

    - by fernando
    MySQL Connector/Net 6.5.5, a new maintenance release of our 6.5 series, has been released.  This release is GA quality and is appropriate for use in production environments.  Please note that 6.6 is our latest driver series and is the recommended product for development. It is now available in source and binary form from http://dev.mysql.com/downloads/connector/net/#downloads and mirror sites (note that not all mirror sites may be up to date at this point-if you can't find this version on some mirror, please try again later or choose another download site.) The 6.5.5 version of MySQL Connector/Net brings the following fixes: - Fix for ArgumentNull exception when using Take().Count() in a LINQ to Entities query (bug MySql #64749, Oracle bug #13913047). - Fix for type varchar changed to bit when saving in Table Designer (Oracle bug #13916560). - Fix for error when trying to change the name of an Index on the Indexes/Keys editor; along with this fix now users can change the Index type of a new Index which could not be done   in previous versions, and when changing the Index name the change is reflected on the list view at the left side of the Index/Keys editor (Oracle bug #13613801). - Fix for stored procedure call using only its name with EF code first (MySql bug #64999, Oracle bug #14008699). - Fix for List.Contains generates a bunch of ORs instead of more efficient IN clause in   LINQ to Entities (Oracle bug #14016344, MySql bug #64934). - Fix for performance issue in generated EF query: .NET StartsWith/Contains/EndsWith produces MySql's locate instead of Like (MySql bug #64935, Oracle bug #14009363). - Fix for script generated for code first contains wrong alter table and wrong declaration for byte[] (MySql bug #64216, Oracle bug #13900091). - Fix and code contribution for bug Timed out sessions are removed without notification which allow to enable the Expired CallBack when Session Provider times out any session (bug MySql #62266 Oracle bug # 13354935) - Fix for Exception thrown when using cascade delete in an EDM Model-First in Entity Framework (Oracle bug #14008752, MySql bug #64779). - Fix for Session locking issue with MySqlSessionStateStore (MySql bug #63997, Oracble bug #13733054). - Fixed deleting a user profile using Profile provider (MySQL bug #64470, Oracle bug #13790123) - Fix for bug Cannot Create an Entity with a Key of Type String (MySQL bug #65289, Oracle bug #14540202). This fix checks if the type has a FixedLength facet set in order to create a char otherwise should create varchar, mediumtext or longtext types when using a String CLR type in Code First or Model First also tested in Database First. Unit tests added for Code First and ProviderManifest. - Fix for bug "CacheServerProperties can cause 'Packet too large' error". The issue was due to a missing reading of Max_allowed_packet server property when CacheServerProperties is in true, since the value was read only in the first connection but the following pooled connections had a wrong value causing a Packet too large error. Including also a unit test for this scenario. All unit test passed. MySQL Bug #66578 Orabug #14593547. - Fix for handling unnamed parameter in MySQLCommand. This fix allows the mysqlcommand to handle parameters without requiring naming (e.g. INSERT INTO Test (id,name) VALUES (?, ?) ) (MySQL Bug #66060, Oracle bug #14499549). - Fixed inheritance on Entity Framework Code First scenarios. Discriminator column is created using its correct type as varchar(128) (MySql bug #63920 and Oracle bug #13582335). - Fixed "Trying to customize column precision in Code First does not work" (MySql bug #65001, Oracle bug #14469048). - Fixed bug ASP.NET Membership database fails on MySql database UTF32 (MySQL bug #65144, Oracle bug #14495292). - Fix for MySqlCommand.LastInsertedId holding only 32 bit values (MySql bug #65452, Oracle bug #14171960) by changing   several internal declaration of lastinsertid from int to long. - Fixed "Decimal type should have digits at right of decimal point", now default is 2, but user's changes in   EDM designer are recognized (MySql bug #65127, Oracle bug #14474342). - Fix for NullReferenceException when saving an uninitialized row in Entity Framework (MySql bug #66066, Oracle bug #14479715). - Fix for error when calling RoleProvider.RemoveUserFromRole(): causes an exception due to a wrong table being used (MySql bug #65805, Oracle bug #14405338). - Fix for "Memory Leak on MySql.Data.MySqlClient.MySqlCommand", too many MemoryStream's instances created (MySql bug #65696, Oracle bug #14468204). - Added ANTLR attribution notice (Oracle bug #14379162). - Fixed Entity Framework + mysql connector/net in partial trust throws exceptions (MySql bug #65036, Oracle bug #14668820). - Added support in Parser for Datetime and Time types with precision when using Server 5.6 (No bug Number). - Small improvement on MySqlPoolManager CleanIdleConnections for better mysqlpoolmanager idlecleanuptimer at startup (MySql bug #66472 and Oracle bug #14652624). - Fix for bug TIMESTAMP values are mistakenly represented as DateTime with Kind = Local (Mysql bug #66964, Oracle bug #14740705). - Fix for bug Keyword not supported. Parameter name: AttachDbFilename (Mysql bug #66880, Oracle bug #14733472). - Added support to MySql script file to retrieve data when using "SHOW" statements. - Fix for Package Load Failure in Visual Studio 2005 (MySql bug #63073, Oracle bug #13491674). - Fix for bug "Unable to connect using IPv6 connections" (MySQL bug #67253, Oracle bug #14835718). - Added auto-generated values for Guid identity columns (MySql bug #67450, Oracle bug #15834176). - Fix for method FirstOrDefault not supported in some LINQ to Entities queries (MySql bug #67377, Oracle bug #15856964). The release is available to download at http://dev.mysql.com/downloads/connector/net/6.5.html Documentation ------------------------------------- You can view current Connector/Net documentation at http://dev.mysql.com/doc/refman/5.5/en/connector-net.html You can find our team blog at http://blogs.oracle.com/MySQLOnWindows. You can also post questions on our forums at http://forums.mysql.com/. Enjoy and thanks for the support! 

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  • Oracle presentations at the CIPS ICE Conference, November 5 - 7, Edmonton, Alberta, Canada

    - by Darin Pendergraft
    Oracle will be presenting at the CIPS ICE conference the last week of October in Calgary and the first week of November in Edmonton. Here is a list of the presentations for Edmonton: SHAW Conference Centre • Session Title: Identity and Access Management Integrated; Analyzing the Platform vs Point Solution Approach • Speaker: Darin Pendergraft • Monday, November 5th @ 10:45 AM - 12:00 PM • Session Title: Is Your IT Security Strategy Putting Your Institution at Risk? • Speaker: Spiros Angelopoulos • Monday, November 5th @ 1:45 PM - 3:00 PM Three sessions under the TRAIN: Practical Knowledge Track • Monday, November 5th @ 10:45 AM, 1:45 PM, 3:30 PM • Title: What's new in the Java Platform   Presenter: Donald Smith • Title: Java Enterprise Edition 6   Presenter: Shaun Smith • Title: The Road Ahead for Java SE, JavaFX and Java EE    Presenters: Donald Smith and Shaun Smith To learn more about the conference, and to see the other sessions go to the conference website.

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  • RTS Voxel Engine using LWJGL - Textures glitching

    - by Dieter Hubau
    I'm currently working on an RTS game engine using voxels. I have implemented a basic chunk manager using an Octree of Octrees which contains my voxels (simple square blocks, as in Minecraft). I'm using a Voronoi-based terrain generation to get a simplistic yet relatively realistic heightmap. I have no problem showing a 256*256*256 grid of voxels with a decent framerate (250), because of frustum culling, face culling and only rendering visible blocks. For example, in a random voxel grid of 256*256*256 I generally only render 100k-120k faces, not counting frustum culling. Frustum culling is only called every 100ms, since calling it every frame seemed a bit overkill. Now I have reached the stage of texturing and I'm experiencing some problems: Some experienced people might already see the problem, but if we zoom in, you can see the glitches more clearly: All the seams between my blocks are glitching and kind of 'overlapping' or something. It's much more visible when you're moving around. I'm using a single, simple texture map to draw on my cubes, where each texture is 16*16 pixels big: I have added black edges around the textures to get a kind of cellshaded look, I think it's cool. The texture map has 256 textures of each 16*16 pixels, meaning the total size of my texture map is 256*256 pixels. The code to update the ChunkManager: public void update(ChunkManager chunkManager) { for (Octree<Cube> chunk : chunks) { if (chunk.getId() < 0) { // generate an id for the chunk to be able to call it later chunk.setId(glGenLists(1)); } glNewList(chunk.getId(), GL_COMPILE); glBegin(GL_QUADS); faces += renderChunk(chunk); glEnd(); glEndList(); } } Where my renderChunk method is: private int renderChunk(Octree<Cube> node) { // keep track of the number of visible faces in this chunk int faces = 0; if (!node.isEmpty()) { if (node.isLeaf()) { faces += renderItem(node); } List<Octree<Cube>> children = node.getChildren(); if (children != null && !children.isEmpty()) { for (Octree<Cube> child : children) { faces += renderChunk(child); } } return faces; } Where my renderItem method is the following: private int renderItem(Octree<Cube> node) { Cube cube = node.getItem(-1, -1, -1); int faces = 0; float x = node.getPosition().x; float y = node.getPosition().y; float z = node.getPosition().z; float size = cube.getSize(); Vector3f point1 = new Vector3f(-size + x, -size + y, size + z); Vector3f point2 = new Vector3f(-size + x, size + y, size + z); Vector3f point3 = new Vector3f(size + x, size + y, size + z); Vector3f point4 = new Vector3f(size + x, -size + y, size + z); Vector3f point5 = new Vector3f(-size + x, -size + y, -size + z); Vector3f point6 = new Vector3f(-size + x, size + y, -size + z); Vector3f point7 = new Vector3f(size + x, size + y, -size + z); Vector3f point8 = new Vector3f(size + x, -size + y, -size + z); TextureCoordinates tc = textureManager.getTextureCoordinates(cube.getCubeType()); // front face if (cube.isVisible(CubeSide.FRONT)) { faces++; glTexCoord2f(TEXTURE_U_COORDINATES[tc.u], TEXTURE_V_COORDINATES[tc.v]); glVertex3f(point1.x, point1.y, point1.z); glTexCoord2f(TEXTURE_U_COORDINATES[tc.u + 1], TEXTURE_V_COORDINATES[tc.v]); glVertex3f(point4.x, point4.y, point4.z); glTexCoord2f(TEXTURE_U_COORDINATES[tc.u + 1], TEXTURE_V_COORDINATES[tc.v + 1]); glVertex3f(point3.x, point3.y, point3.z); glTexCoord2f(TEXTURE_U_COORDINATES[tc.u], TEXTURE_V_COORDINATES[tc.v + 1]); glVertex3f(point2.x, point2.y, point2.z); } // back face if (cube.isVisible(CubeSide.BACK)) { faces++; glTexCoord2f(TEXTURE_U_COORDINATES[tc.u + 1], TEXTURE_V_COORDINATES[tc.v]); glVertex3f(point5.x, point5.y, point5.z); glTexCoord2f(TEXTURE_U_COORDINATES[tc.u + 1], TEXTURE_V_COORDINATES[tc.v + 1]); glVertex3f(point6.x, point6.y, point6.z); glTexCoord2f(TEXTURE_U_COORDINATES[tc.u], TEXTURE_V_COORDINATES[tc.v + 1]); glVertex3f(point7.x, point7.y, point7.z); glTexCoord2f(TEXTURE_U_COORDINATES[tc.u], TEXTURE_V_COORDINATES[tc.v]); glVertex3f(point8.x, point8.y, point8.z); } // left face if (cube.isVisible(CubeSide.SIDE_LEFT)) { faces++; glTexCoord2f(TEXTURE_U_COORDINATES[tc.u], TEXTURE_V_COORDINATES[tc.v]); glVertex3f(point5.x, point5.y, point5.z); glTexCoord2f(TEXTURE_U_COORDINATES[tc.u + 1], TEXTURE_V_COORDINATES[tc.v]); glVertex3f(point1.x, point1.y, point1.z); glTexCoord2f(TEXTURE_U_COORDINATES[tc.u + 1], TEXTURE_V_COORDINATES[tc.v + 1]); glVertex3f(point2.x, point2.y, point2.z); glTexCoord2f(TEXTURE_U_COORDINATES[tc.u], TEXTURE_V_COORDINATES[tc.v + 1]); glVertex3f(point6.x, point6.y, point6.z); } // ETC ETC return faces; } When all this is done, I simply render my lists every frame, like this: public void render(ChunkManager chunkManager) { glBindTexture(GL_TEXTURE_2D, textureManager.getCubeTextureId()); // load all chunks from the tree List<Octree<Cube>> chunks = chunkManager.getTree().getAllItems(); for (Octree<Cube> chunk : chunks) { if (frustum.cubeInFrustum(chunk.getPosition(), chunk.getSize() / 2)) { glCallList(chunk.getId()); } } } I don't know if anyone is willing to go through all of this code or maybe you can spot the problem right away, but that is basically the problem, and I can't find a solution :-) Thanks for reading and any help is appreciated!

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  • Please Help with ATI Radeon 4250 and Xinerama

    - by Luis Enrique
    I am using ubuntu 11.10 fresh install and I am having problems making the second screen to work, I remember before I was able to do it by extending the desktop to a larger number like 3840 X 1080 but since I am new I completely forgot how to do it, Now I have a philips 230 E monitor full 1920 X 1080 and a Toshiba tv HDMI and I want to activate the second monitor to be able to use Xinerama but I don't know how to go about this, I want to keep the Phillips as a primary monitor since it's the smaller one and use the TV from time to time to play videos movies and presentations. I installed all the additional drivers and don't know what else to do. I would prefer if I can use a list of exact commands to copy and paste onto the terminal since that is all I know how to use LOL . Thank you so much for your help. If you need more details of my mother board or video card or cpu just ask thank you. Luis

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  • Access Control Service: Passive/Active Transition Sample

    - by Your DisplayName here!
    Here you can find my updated ACS2 sample. In addition to the existing front ends (web [WS-Federation], console [SOAP & REST], Silverlight [REST]) and error handling, it now also includes a WPF client that shows the passive/active transition with a SOAP service as illustrated here. All the ACS interaction is encapsulated in a WPF user control that: retrieves the JSON feed displays a list of supported identity providers triggers the sign in via a browser control retrieves the token response packages the token as a GenericXmlSecurityToken (to be used directly with the WIF ChannelFactory extensions methods) All you need to supply is the ACS namespace and the realm. Have fun!

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  • Five Reasons to Attend PLM Summit 2013: The Conference Formerly Known as AGILITY

    - by Terri Hiskey
    As we approach the end of 2012, we are also closing in on the last couple of weeks that Agile customers and prospects can register for the upcoming PLM Summit 2013 for the bargain early bird rate of $195. Register now to secure your spot! The Conference Formerly Known as AGILITY... Long-time Agile customers may remember AGILITY, which was Agile's PLM customer conference that was held on an annual basis prior to Oracle's acquisiton of Agile in 2007. In February 2012, due to feedback we received from our Agile PLM community, we successfully resurrected the AGILITY conference and renamed it the PLM Summit. The PLM Summit was so well received and well-attended, that we are doing it again in 2013. This upcoming PLM Summit is being co-located in San Francisco under the overarching banner of the Oracle Value Chain Summit, and will be held alongside several other Oracle customer conferences that cover a range of value chain solutions, including Value Chain Planning, Value Chain Execution, Procurement, Maintenance and Manufacturing. This setup offers PLM attendees the best of all worlds--the opportunity to participate and learn about PLM in smaller, focused sessions by product and by industry, while also giving attendees the chance to see how PLM works together with other critical enterprise applications that address other important aspects of the value chain. Top Five Reasons to Attend the PLM Summit 2013 In the spirit of all of the end-of-the-year lists that are currently popping up, here is a list of the top five reasons to attend the PLM Summit for anyone out there needs a little extra encouragement to register: 1. The Best Opportunities for Customer Networking   The PLM Summit offers attendees numerous opportunities to learn and network with fellow Agile users. Customer stories are featured in keynote and breakout presentations and the schedule allows for plenty of networking time during breakfasts, lunches, breaks and dinners. Customer networking is the number one reason that Agile users attend the PLM Summit. Read what attendees thought of the most recent PLM Summit: "Hearing about the implementation of Agile products from a customers’ perspective is invaluable." - Director of Quality Assurance & Regulatory Affairs, leading medical device manufacturer "Understanding the scope of other companies’ projects and the lessons learned made attending this event well worth my time." - Director of Test Engineering, global industrial manufacturer "The most beneficial thing about attending this event is the opportunity to network with other customers with similar experiences." - Director of Business Process Improvement, leading high technology company Come to the PLM Summit and play an active role within the PLM community: swap war stories and business cards, connect on LinkedIn and Facebook, share your stories and discuss the sessions from each day. Register now! 2. It's Educational! The PLM Summit is the premier educational event for anyone in the Agile PLM community. There are nearly 40 PLM-focused in-depth educational sessions led by Agile PLM experts, customers and partners that will cover a range of specific product and industry-focused topics. Keynotes will give attendees a broad overview of the entire Agile PLM footprint, while sessions will delve deeply into specific product functionality and customer case studies. There is truly something for everyone. Check out the latest agenda for view of all the sessions. 3. Visit with the PLM Partner Community Our partners play a significant and important role within the Agile PLM community. At the PLM Summit, attendees will be able to meet and mingle with several of the top Oracle Agile PLM partners including: Deloitte, Domain, GoEngineer, Hitachi Consulting, IBM, Kalypso, KPIT Cummins (CPG Solutions), Perception Software, Verdant, Xavor and ZeroWaitState. Go here for a complete list of all the Value Chain Summit sponsors. 4. See Agile PLM in Action at our Dedicated PLM Demo Pods At the PLM Summit, attendees will have the chance to see Agile PLM in action at dedicated PLM demo pods, manned by expert members of our Agile PLM team. If you would like to see up close specific Agile PLM functionality, or if you have a question on how to extend the scope of your current implemention or if you want a better understanding of how to leverage Agile PLM to address specific use-cases, stop by one of the Agile PLM demo pods and engage the Agile PLM experts on hand at the PLM Summit. 5. Spend Some Time in Lovely San Francisco Still on the fence about the upcoming PLM Summit? Remember that it is being held in San Francisco, which is a fantastic city for a getaway. After spending time learning and networking about PLM, take an extra day or two to escape the dreary winter and enjoy the beautiful scenery and the unique actitivies offered only by the City by the Bay. You will walk away from the conference not only with renewed excitement about Agile PLM, but feeling rejuvenated in general.

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  • Empathy chat limits the number of contacts displayed?

    - by Ka7anax
    I'm using Empathy Chat with these accounts: GTalk & Facebook. I just noticed now that from my GTalk friends only 6 appear online (including me) and in reality online are 14 (checked on GMail). And from Facebook it displays 44. So is Empathy Chat limited to display only 50 contacts? I looked through the settings and didn't see anything like this :| The worst part is that I have 1 GTalk contact as Favorite and it's not in the list... Is it a bug? PS: I'm using Ubuntu 10.10

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  • New games for 2011

    - by Oli
    I know there have been other questions like "What native games are available?" and they often have issues because they turn into a never-ending list of every game ever released for Linux. But I'd like to know what's coming out this year. Good answers can include: A game that's coming out in 2011 A Linux port being released for games that might be older (eg Trine) As much information and as many screenshots and links as possible Few old games unless they're doing a major update that changes the game very significantly. One game per answer, add as much information as possible and work with each other to build a catalogue of awesome things to look forward to this year.

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  • How do I know I'm using kubuntu?

    - by Adobe
    I installed Kubuntu image long time ago, and did several release upgrades since that. I have package kubuntu-full installed, and boot into KDE. Currently it looks like I'm using ubuntu: ~: lsb_release -a No LSB modules are available. Distributor ID: Ubuntu Description: Ubuntu 13.10 Release: 13.10 Codename: saucy There's not a single kubuntu word in my /etc/apt/sources.list, or is it Kubuntu = Ubuntu - Unity + KDE now? For example there's a Pre-Alpha Ubuntu Thar already, but no Kubuntu one. Would I get Kubuntu Thar, by installing Ubuntu Thar in the way mentioned above? Probably Kubuntu team now are the guys responsible for KDE working in Ubuntu.

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  • TechDays 2010: What’s New On C# 4.0

    - by Paulo Morgado
    I would like to thank those that attended my session at TechDays 2010 and I hope that I was able to pass the message of what’s new on C#. For those that didn’t attend (or did and want to review it), the presentation can be downloaded from here. Code samples can be downlaoded from here. Here’s a list of resources mentioned on the session: The evolution of C# The Evolution Of C# Covariance and contravariance  C# 4.0: Covariance And Contravariance In Generics Covariance And Contravariance In Generics Made Easy Covarince and Contravariance in Generics Exact rules for variance validity Events get a little overhaul in C# 4, Afterward: Effective Events Named and optional arguments  Named And Optional Arguments Alternative To Optional Arguments Named and Optional Arguments (C# Programming Guide) Dynamic programming  Dynamic Programming C# Proposal: Compile Time Static Checking Of Dynamic Objects Using Type dynamic (C# Programming Guide) Dynamic Language Runtime Overview COM Interop Improvements COM Interop Improvements Type Equivalence and Embedded Interop Types Conclusion Visual C# Developer Center Visual C# 2010 Samples C# Language Specification 4.0 .NET Reflector LINQPad

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  • Thunderbird uses the wrong browser

    - by Aaron Digulla
    I'm unable to make Thunderbird open the default browser. In the browser preferences, Chromium is selected as the default browser. It's also selected in "Default Applications" in System Settings. In Thunderbird, I read "Chrome (Default)" which is wrong on all levels: Chrome itself complains that it's not the default browser when I click a link inside Thunderbird. In all other places, that I could find, Chromium is the default Here is what I tried: I used update-alternatives --config x-www-browser to select chromium-browser as well (see How do I change the default browser?). And even when I select a different browser from the list in the Thunderbird preferences, it still opens Chrome. My current solution is to create a link from /usr/bin/google-chrome to chromium-browser. How can I force Thunderbird to use the browser I want??? EDIT I also updated gnome-www-browser (update-alternatives --config gnome-www-browser) after feedback from roadmr but that didn't help. At least sensible-browser opens Chromium, now, but Thunderbird is stubborn.

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  • How to UEFI install Ubuntu 12.10?

    - by Geezanansa
    Running a newer FM1 motherboard which is using an AMD 3870k APU with a new 1TB HDD. Following the advice in the motherboard manual and https://help.ubuntu.com/community/UEFI have now got to grub option screen for UEFI install. see http://imgur.com/VW5vz The dvd.iso being used is Ubuntu 12.10 desktop amd64 from ubuntu .com. The hdd has had a gpt partition table made for, by using gparted when in a live desktop session when booted in bios mode. (*edit/update: Although the old cd updates on running it is an old kernel and it did make a gpt but that version of gparted uses fdisk whereas gdisk is required to make gpt. Think am going to have to spend more time here http://www.dedoimedo.com/computers/gparted.html lol Using the gparted from 12.10 live session to make partitions; following the guidance regarding this at https://help.ubuntu.com/community/UEFI#Creating_an_EFI_partition, but can only boot to grub option screen http://imgur.com/VW5vz when 12.10 options to "try ubuntu" or "install ubuntu" are selected they give errors as described below*) but after making the gpt decided to leave it unformatted/unallocated space with the intention of using installer to set up partitions. update-originally but gparted now sees hdd as http://imgur.com/hFIvm as described above. *Booting live dvd in EFI mode gives "Secure Boot not installed" just before grub kernel option list with the option to "install ubuntu" but get "can not read cd/0" and "the kernel must be loaded first" errors; when that option is selected. Any pointers on how to get installer going for UEFI install would be good. Thanks in advance. update: Hopefully these screenshots can help better highlight where i am going wrong or if there is something else going on http://imgur.com/g30RB, http://imgur.com/VW5vz, http://imgur.com/31E0q, http://imgur.com/bnuaG, http://imgur.com/y4KGu, http://imgur.com/3u2QE, http://imgur.com/n9lN3, http://imgur.com/FEKvz, http://imgur.com/hFIvm, update: Thank you fernando garcia for pointing me in the right direction to start the process of elimantion. What i have done since asking question is a little home work starting here http://askubuntu.com/faq#bounty and here http://askubuntu.com/questions/how-to-ask. Looking at other similar questions was good fun and found this 12.10 UEFI Secure Boot install the most relative in helping getting ubuntu to uefi install on my system. In response to wolverine's question this article was referred to http://web.dodds.net/~vorlon/wiki/blog/SecureBoot_in_Ubuntu_12.10/ This article in the first sentence gives a link to http://www.ubuntu.com/download which is where i downloaded the 12.10 desktop amd64 .iso(and others) but have been unable to do a efi install of ubuntu on this system and as this is a new system have ended up just going with bios installer running which at least puts my mind at ease that i have not bricked my new mobo.(had to do a clrcmos and flash to latest bios version) So it possibly could be the bios settings or the bios version being used that is problem. To try and eliminate bios version i can not get to post screen in order to id bios version being used. Pressing tab to show post instead of logo and trying to pausebreak to catch post is proving difficult. If logo screen in bios is disabled just get black screen no post shown and pressing tab does not show post. Appreciate using appropriate bios settings and latest 12.10 release should simply get uefi installer running when selected from the grub list (nice graphic details in Identifying if computer boots the cd in efi mode section at https://help.ubuntu.com/community/UEFI#Identifying_if_the_computer_boots_the_CD_in_EFI_mode) And to confirm the hdd is booting in efi mode https://help.ubuntu.com/community/UEFI#Identifying_if_the_computer_boots_the_HDD_in_EFI_mode running the command [ -d /sys/firmware/efi ] && echo "EFI boot on HDD" || echo "Legacy boot on HDD" gave Legacy boot on HDD This is as expected because i allowed the bios installer (which was 12.04 desktop amd64 after trying 12.10 desktop amd64 in efi mode) to run to get a working installation. Which is not what was intended or wished for but wanted to get a working os to bench test new mobo i.e. prove it is working. There are other options as in installing other bootmanagers/loaders but do not wish to do so as shim should get grub2 going that is after secure boot has been signed.(Now got rough idea what should happen just it aint happening. Is it possible ahci drivers are required?) Will post boot info script url of the updated config/setup. The original question asked seems irrelevant to what is being said in this update but as the problem is not resolved will keep on trying efi installing! i.e the problem is same as when question asked just trying to update. Have tried to edit and update the best i can!

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  • [GEEK SCHOOL] Network Security 3: Windows Defender and a Malware-Free System

    - by Ciprian Rusen
    In this second lesson we are going to talk about one of the most confusing security products that are bundled with Windows: Windows Defender. In the past, this product has had a bad reputation and for good reason – it was very limited in its capacity to protect your computer from real-world malware. However, the latest version included in Windows 8.x operating systems is much different than in the past and it provides real protection to its users. The nice thing about Windows Defender in its current incarnation, is that it protects your system from the start, so there are never gaps in coverage. We will start this lesson by explaining what Windows Defender is in Windows 7 and Vista versus what it is in Windows 8, and what product to use if you are using an earlier version. We next will explore how to use Windows Defender, how to improve its default settings, and how to deal with the alerts that it displays. As you will see, Windows Defender will have you using its list of quarantined items a lot more often than other security products. This is why we will explain in detail how to work with it and remove malware for good or restore those items that are only false alarms. Lastly, you will learn how to turn off Windows Defender if you no longer want to use it and you prefer a third-party security product in its place and then how to enable it back, if you have changed your mind about using it. Upon completion, you should have a thorough understanding of your system’s default anti-malware options, or how to protect your system expeditiously. What is Windows Defender? Unfortunately there is no one clear answer to this question because of the confusing way Microsoft has chosen to name its security products. Windows Defender is a different product, depending on the Windows operating system you are using. If you use Windows Vista or Windows 7, then Windows Defender is a security tool that protects your computer from spyware. This but one form of malware made out of tools and applications that monitor your movements on the Internet or the activities you make on your computer. Spyware tends to send the information that is collected to a remote server and it is later used in all kinds of malicious purposes, from displaying advertising you don’t want, to using your personal data, etc. However, there are many other types of malware on the Internet and this version of Windows Defender is not able to protect users from any of them. That’s why, if you are using Windows 7 or earlier, we strongly recommend that you disable Windows Defender and install a more complete security product like Microsoft Security Essentials, or third-party security products from specialized security vendors. If you use Windows 8.x operating systems, then Windows Defender is the same thing as Microsoft Security Essentials: a decent security product that protects your computer in-real time from viruses and spyware. The fact that this product protects your computer also from viruses, not just from spyware, makes a huge difference. If you don’t want to pay for security products, Windows Defender in Windows 8.x and Microsoft Security Essentials (in Windows 7 or earlier) are good alternatives. Windows Defender in Windows 8.x and Microsoft Security Essentials are the same product, only their name is different. In this lesson, we will use the Windows Defender version from Windows 8.x but our instructions apply also to Microsoft Security Essentials (MSE) in Windows 7 and Windows Vista. If you want to download Microsoft Security Essentials and try it out, we recommend you to use this page: Download Microsoft Security Essentials. There you will find both 32-bit and 64-bit editions of this product as well versions in multiple languages. How to Use and Configure Windows Defender Using Windows Defender (MSE) is very easy to use. To start, search for “defender” on the Windows 8.x Start screen and click or tap the “Windows Defender” search result. In Windows 7, search for “security” in the Start Menu search box and click “Microsoft Security Essentials”. Windows Defender has four tabs which give you access to the following tools and options: Home – here you can view the security status of your system. If everything is alright, then it will be colored in green. If there are some warnings to consider, then it will be colored in yellow, and if there are threats that must be dealt with, everything will be colored in red. On the right side of the “Home” tab you will find options for scanning your computer for viruses and spyware. On the bottom of the tab you will find information about when the last scan was performed and what type of scan it was. Update – here you will find information on whether this product is up-to-date. You will learn when it was last updated and the versions of the definitions it is using. You can also trigger a manual update. History – here you can access quarantined items, see which items you’ve allowed to run on your PC even if they were identified as malware by Windows Defender, and view a complete list with all the malicious items Windows Defender has detected on your PC. In order to access all these lists and work with them, you need to be signed in as an administrator. Settings – this is the tab where you can turn on the real-time protection service, exclude files, file types, processes, and locations from its scans as well as access a couple of more advanced settings. The only difference between Windows Defender in Windows 8.x and Microsoft Security Essentials (in Windows 7 or earlier) is that, in the “Settings” tab, Microsoft Security Essentials allows you to set when to run scheduled scans while Windows Defender lacks this option.

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  • Disable automount in Nautilus

    - by jimmybondy
    I have added my mount devices in /etc/fstab and they get correctly mounted (2nd partition with ntfs and nas-share with nfs). I have also disabled automount in Nautilus preferences by using dconf-editor (following this post): user@server:~$ gsettings list-recursively org.gnome.desktop.media-handling org.gnome.desktop.media-handling automount false org.gnome.desktop.media-handling automount-open false org.gnome.desktop.media-handling autorun-never false Now i see every mount device twice in Nautilus (the entry in fstab already mounted). When clicking on the other entry i get the eligible message mount.nfs: /media/nas_share is busy or already mounted How i can i disable the appearente of those devices in Nautilus? EDIT Regarding automount: I have only one line in /etc/auto.master: +auto.master

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  • Invalid Opcode 0000

    - by Mr47
    At random times (usually when watching a movie in XBMC), the computer locks up. I can still sometimes SSH in and get the 'dmesg' output before that locks up too. A hard reboot is usually required to get things going again. I have cut out the date/time/server columns for easier reading, please do ask if these seem relevant omissions... System: Ubuntu 11.04 (2.6.38-8-server) x64 X11 installed with IceWm (and XBMC) Core 2 Duo E8400 @ 3.00GHz 8 GB RAM Asus P5Q premium motherboard Primary harddrive: OCZ Vertex 2 60 GB (SSD) Other harddrives: various 750GB, 1TB, 1.5TB & 2TB (WD & samsung) Any important information I am not supplying is purely a sign of my incompetence in these matters, so please do ask and excuse me for my inabilities... invalid opcode: 0000 [#1] SMP last sysfs file: /sys/devices/system/cpu/cpu1/cache/index2/shared_cpu_map CPU 0 Modules linked in: parport_pc ppdev vesafb snd_hda_codec_analog tuner_simple tuner_types wm8775 tda9887 tda8290 tea5767 tuner cx25840 ir_lirc_codec lirc_dev snd_hda_intel snd_hda_codec snd_hwdep snd_pcm ir_sony_decoder snd_seq_midi snd_rawmidi snd_seq_midi_event snd_seq rc_rc6_mce ivtv ir_jvc_decoder cx2341x i2c_algo_bit v4l2_common mceusb videodev ir_rc6_decoder ir_rc5_decoder snd_timer ir_nec_decoder nvidia(P) btusb bluetooth rc_core v4l2_compat_ioctl32 tveeprom snd_seq_device pata_marvell psmouse shpchp serio_raw snd asus_atk0110 soundcore snd_page_alloc lp parport firewire_ohci firewire_core crc_itu_t r8169 sky2 ahci libahci Pid: 4597, comm: xbmc.bin Tainted: P 2.6.38-8-server #42-Ubuntu System manufacturer P5Q Premium/P5Q Premium RIP: 0010:[<ffffffff8119bc4a>] [<ffffffff8119bc4a>] do_mpage_readpage+0x9a/0x510 RSP: 0018:ffff88021f5a59d8 EFLAGS: 00210246 RAX: 0000000000000020 RBX: ffff88021f5a5ac8 RCX: 0000000000000000 RDX: 0000000000000001 RSI: 0000000015e36fe0 RDI: 0000000000000000 RBP: ffff88021f5a5a98 R08: ffff88021f5a5ac8 R09: ffff88021f5a5b38 R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000 R13: 000000000000b148 R14: 0000000000000001 R15: ffff8802067034b8 FS: 00007f3f34eb1700(0000) GS:ffff8800cfc00000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007feb8d515000 CR3: 000000021d744000 CR4: 00000000000406f0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400 Process xbmc.bin (pid: 4597, threadinfo ffff88021f5a4000, task ffff88021f63db80) Stack: ffff88021f5a5a28 ffffffff8116019d ffff88021f5a5b40 0000002000000003 ffff88021f5a5b38 ffff880206703370 ffffea0006d800f8 0000000000000000 ffffea0006d800f8 0000000c811270b5 ffff88021f5a5a68 ffffffff8110bdba Call Trace: [<ffffffff8116019d>] ? mem_cgroup_cache_charge+0xed/0x130 [<ffffffff8110bdba>] ? add_to_page_cache_locked+0xea/0x160 [<ffffffff8119c232>] mpage_readpages+0x102/0x150 [<ffffffff812063e0>] ? ext4_get_block+0x0/0x20 [<ffffffff812063e0>] ? ext4_get_block+0x0/0x20 [<ffffffff81149475>] ? alloc_pages_current+0xa5/0x110 [<ffffffff8120157d>] ext4_readpages+0x1d/0x20 [<ffffffff81116a9b>] __do_page_cache_readahead+0x14b/0x220 [<ffffffff81116ed1>] ra_submit+0x21/0x30 [<ffffffff81116ff5>] ondemand_readahead+0x115/0x230 [<ffffffff811171a0>] page_cache_async_readahead+0x90/0xc0 [<ffffffff8110b184>] ? file_read_actor+0xd4/0x170 [<ffffffff812de72e>] ? radix_tree_lookup_slot+0xe/0x10 [<ffffffff8110c521>] do_generic_file_read.clone.23+0x271/0x450 [<ffffffff8110d1ba>] generic_file_aio_read+0x1ca/0x240 [<ffffffff8100a82e>] ? __switch_to+0x20e/0x2f0 [<ffffffff81164c82>] do_sync_read+0xd2/0x110 [<ffffffff8108b61c>] ? hrtimer_try_to_cancel+0x4c/0xe0 [<ffffffff81279083>] ? security_file_permission+0x93/0xb0 [<ffffffff81164fa1>] ? rw_verify_area+0x61/0xf0 [<ffffffff81165463>] vfs_read+0xc3/0x180 [<ffffffff81165571>] sys_read+0x51/0x90 [<ffffffff8100bfc2>] system_call_fastpath+0x16/0x1b Code: ff ff 48 c7 85 78 ff ff ff 00 00 00 00 49 d3 ee b9 0c 00 00 00 2b 4d 8c 48 8b b2 c8 00 00 00 ba 01 00 00 00 41 0f af c6 49 d3 e5 <0f> 36 4d 8c 4c 01 e8 d3 e2 4c 8d 44 16 ff 48 8b 53 20 49 d3 f8 RIP [<ffffffff8119bc4a>] do_mpage_readpage+0x9a/0x510 RSP <ffff88021f5a59d8> ---[ end trace ac6cd2f4692205a3 ]--- Please note that the error is ALWAYS occuring at do_mpage_readpage+0x9a/0x510 with the same numbers after it. I've tried to come up with the possible meaning of these, but couldn't get any further. I've also noticed that the top block from the call trace is always the following with the exact same numbers: [<ffffffff8116019d>] ? mem_cgroup_cache_charge+0xed/0x130 [<ffffffff8110bdba>] ? add_to_page_cache_locked+0xea/0x160 [<ffffffff8119c232>] mpage_readpages+0x102/0x150 [<ffffffff812063e0>] ? ext4_get_block+0x0/0x20 [<ffffffff812063e0>] ? ext4_get_block+0x0/0x20 Could this indicate a hard drive issue, a RAM issue or something else entirely?

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  • Making an Ubuntu installation disc UEFI bootable

    - by skytreader
    I'm trying to install Ubuntu 12.04 on a machine with UEFI (Windows 8). Following Rod Books, I managed to get my system to boot using rEFInd. However rEFInd does not offer me any options to boot from my Ubuntu installer disc. Another thing...after following Rod Books' instructions, my machine greeted me with something along the lines of "The bootloader is not trusted" (my usage of the term "bootloader" is possibly wrong; I'm not well-acquainted with these terms) I got to work around this by setting up some passwords in the BIOS and putting the renamed .efi of rEFInd to the trusted list. While in this screen, it showed me the drives with a possible .efi (among them, the drive S in Rod Books' guide) and one of the drives it showed was my optical drive with an Ubuntu installer. I tried browsing for an .efi in the Ubuntu installer but found none. True enough, at Windows, I searched the drive for an .efi but found none. So how do I make my Ubuntu installer UEFI bootable?

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  • Is using MultiMaps code smell? If so what alternative data structures fit my needs?

    - by Pureferret
    I'm trying to model nWoD characters for a roleplaying game in a character builder program. The crux is I want to support saving too and loading from yaml documents. One aspect of the character's is their set of skills. Skills are split between exactly three 'types': Mental, Physical, and Social. Each type has a list of skills under if. My Yaml looks like this: PHYSICAL: Athletics: 0 Brawl: 3 MENTAL: Academics: 2 Computers My initial thought was to use a Multimap of some sort, and have the skill type as an Enum, and key to my map. Each Skill is an element in the collection that backs the multimap. However, I've been struggling to get the yaml to work. On explaining this to a colleague outside of work they said this was probably a sign of code smell, and he's never seen it used 'well'. Are multiMaps really code smell? If so what alternate data structures would suit my goals?

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  • .NET Security Part 2

    - by Simon Cooper
    So, how do you create partial-trust appdomains? Where do you come across them? There are two main situations in which your assembly runs as partially-trusted using the Microsoft .NET stack: Creating a CLR assembly in SQL Server with anything other than the UNSAFE permission set. The permissions available in each permission set are given here. Loading an assembly in ASP.NET in any trust level other than Full. Information on ASP.NET trust levels can be found here. You can configure the specific permissions available to assemblies using ASP.NET policy files. Alternatively, you can create your own partially-trusted appdomain in code and directly control the permissions and the full-trust API available to the assemblies you load into the appdomain. This is the scenario I’ll be concentrating on in this post. Creating a partially-trusted appdomain There is a single overload of AppDomain.CreateDomain that allows you to specify the permissions granted to assemblies in that appdomain – this one. This is the only call that allows you to specify a PermissionSet for the domain. All the other calls simply use the permissions of the calling code. If the permissions are restricted, then the resulting appdomain is referred to as a sandboxed domain. There are three things you need to create a sandboxed domain: The specific permissions granted to all assemblies in the domain. The application base (aka working directory) of the domain. The list of assemblies that have full-trust if they are loaded into the sandboxed domain. The third item is what allows us to have a fully-trusted API that is callable by partially-trusted code. I’ll be looking at the details of this in a later post. Granting permissions to the appdomain Firstly, the permissions granted to the appdomain. This is encapsulated in a PermissionSet object, initialized either with no permissions or full-trust permissions. For sandboxed appdomains, the PermissionSet is initialized with no permissions, then you add permissions you want assemblies loaded into that appdomain to have by default: PermissionSet restrictedPerms = new PermissionSet(PermissionState.None); // all assemblies need Execution permission to run at all restrictedPerms.AddPermission( new SecurityPermission(SecurityPermissionFlag.Execution)); // grant general read access to C:\config.xml restrictedPerms.AddPermission( new FileIOPermission(FileIOPermissionAccess.Read, @"C:\config.xml")); // grant permission to perform DNS lookups restrictedPerms.AddPermission( new DnsPermission(PermissionState.Unrestricted)); It’s important to point out that the permissions granted to an appdomain, and so to all assemblies loaded into that appdomain, are usable without needing to go through any SafeCritical code (see my last post if you’re unsure what SafeCritical code is). That is, partially-trusted code loaded into an appdomain with the above permissions (and so running under the Transparent security level) is able to create and manipulate a FileStream object to read from C:\config.xml directly. It is only for operations requiring permissions that are not granted to the appdomain that partially-trusted code is required to call a SafeCritical method that then asserts the missing permissions and performs the operation safely on behalf of the partially-trusted code. The application base of the domain This is simply set as a property on an AppDomainSetup object, and is used as the default directory assemblies are loaded from: AppDomainSetup appDomainSetup = new AppDomainSetup { ApplicationBase = @"C:\temp\sandbox", }; If you’ve read the documentation around sandboxed appdomains, you’ll notice that it mentions a security hole if this parameter is set correctly. I’ll be looking at this, and other pitfalls, that will break the sandbox when using sandboxed appdomains, in a later post. Full-trust assemblies in the appdomain Finally, we need the strong names of the assemblies that, when loaded into the appdomain, will be run as full-trust, irregardless of the permissions specified on the appdomain. These assemblies will contain methods and classes decorated with SafeCritical and Critical attributes. I’ll be covering the details of creating full-trust APIs for partial-trust appdomains in a later post. This is how you get the strongnames of an assembly to be executed as full-trust in the sandbox: // get the Assembly object for the assembly Assembly assemblyWithApi = ... // get the StrongName from the assembly's collection of evidence StrongName apiStrongName = assemblyWithApi.Evidence.GetHostEvidence<StrongName>(); Creating the sandboxed appdomain So, putting these three together, you create the appdomain like so: AppDomain sandbox = AppDomain.CreateDomain( "Sandbox", null, appDomainSetup, restrictedPerms, apiStrongName); You can then load and execute assemblies in this appdomain like any other. For example, to load an assembly into the appdomain and get an instance of the Sandboxed.Entrypoint class, implementing IEntrypoint, you do this: IEntrypoint o = (IEntrypoint)sandbox.CreateInstanceFromAndUnwrap( "C:\temp\sandbox\SandboxedAssembly.dll", "Sandboxed.Entrypoint"); // call method the Execute method on this object within the sandbox o.Execute(); The second parameter to CreateDomain is for security evidence used in the appdomain. This was a feature of the .NET 2 security model, and has been (mostly) obsoleted in the .NET 4 model. Unless the evidence is needed elsewhere (eg. isolated storage), you can pass in null for this parameter. Conclusion That’s the basics of sandboxed appdomains. The most important object is the PermissionSet that defines the permissions available to assemblies running in the appdomain; it is this object that defines the appdomain as full or partial-trust. The appdomain also needs a default directory used for assembly lookups as the ApplicationBase parameter, and you can specify an optional list of the strongnames of assemblies that will be given full-trust permissions if they are loaded into the sandboxed appdomain. Next time, I’ll be looking closer at full-trust assemblies running in a sandboxed appdomain, and what you need to do to make an API available to partial-trust code.

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  • Next generation Three MiFi unit - call for questions to put to Three

    - by Liam Westley
    I've been invited to a preview of the next generation Three mobile Mi-Fi unit in their London offices this week. If you've got feedback on the current MiFi unit; niggles, wish list items or general feedback, or you've got any questions about what the next generation MiFi unit might be, drop me an e-mail or post a comment with your question on this blog. I'll be taking any questions from my blog or my twitter account @westleyl to Three, and if I get an answer I can publish, I'll add to this blog post with the details. Thanks Liam

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  • Shared hosting with dedicated IP

    - by JP19
    Hi, Can you please mention here if you know any shared hosting providers who give option to get a dedicated IP? So far I know of one - Netfirms. Please list others if you know. Notes: 1) If mods feel enough people might be interested in this, we can make it community wiki. 2) The reason why someone would want shared hosting with dedicated IP is: i) In most shared hosting plans, you end up getting better CPU/burst RAM than a VPS provided you don't abuse. ii) Dedicated IP is good for SEO. For example, many times, you may get up getting an IP where some p*** sites are also hosted in shared hosting.

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  • Why lock-free data structures just aren't lock-free enough

    - by Alex.Davies
    Today's post will explore why the current ways to communicate between threads don't scale, and show you a possible way to build scalable parallel programming on top of shared memory. The problem with shared memory Soon, we will have dozens, hundreds and then millions of cores in our computers. It's inevitable, because individual cores just can't get much faster. At some point, that's going to mean that we have to rethink our architecture entirely, as millions of cores can't all access a shared memory space efficiently. But millions of cores are still a long way off, and in the meantime we'll see machines with dozens of cores, struggling with shared memory. Alex's tip: The best way for an application to make use of that increasing parallel power is to use a concurrency model like actors, that deals with synchronisation issues for you. Then, the maintainer of the actors framework can find the most efficient way to coordinate access to shared memory to allow your actors to pass messages to each other efficiently. At the moment, NAct uses the .NET thread pool and a few locks to marshal messages. It works well on dual and quad core machines, but it won't scale to more cores. Every time we use a lock, our core performs an atomic memory operation (eg. CAS) on a cell of memory representing the lock, so it's sure that no other core can possibly have that lock. This is very fast when the lock isn't contended, but we need to notify all the other cores, in case they held the cell of memory in a cache. As the number of cores increases, the total cost of a lock increases linearly. A lot of work has been done on "lock-free" data structures, which avoid locks by using atomic memory operations directly. These give fairly dramatic performance improvements, particularly on systems with a few (2 to 4) cores. The .NET 4 concurrent collections in System.Collections.Concurrent are mostly lock-free. However, lock-free data structures still don't scale indefinitely, because any use of an atomic memory operation still involves every core in the system. A sync-free data structure Some concurrent data structures are possible to write in a completely synchronization-free way, without using any atomic memory operations. One useful example is a single producer, single consumer (SPSC) queue. It's easy to write a sync-free fixed size SPSC queue using a circular buffer*. Slightly trickier is a queue that grows as needed. You can use a linked list to represent the queue, but if you leave the nodes to be garbage collected once you're done with them, the GC will need to involve all the cores in collecting the finished nodes. Instead, I've implemented a proof of concept inspired by this intel article which reuses the nodes by putting them in a second queue to send back to the producer. * In all these cases, you need to use memory barriers correctly, but these are local to a core, so don't have the same scalability problems as atomic memory operations. Performance tests I tried benchmarking my SPSC queue against the .NET ConcurrentQueue, and against a standard Queue protected by locks. In some ways, this isn't a fair comparison, because both of these support multiple producers and multiple consumers, but I'll come to that later. I started on my dual-core laptop, running a simple test that had one thread producing 64 bit integers, and another consuming them, to measure the pure overhead of the queue. So, nothing very interesting here. Both concurrent collections perform better than the lock-based one as expected, but there's not a lot to choose between the ConcurrentQueue and my SPSC queue. I was a little disappointed, but then, the .NET Framework team spent a lot longer optimising it than I did. So I dug out a more powerful machine that Red Gate's DBA tools team had been using for testing. It is a 6 core Intel i7 machine with hyperthreading, adding up to 12 logical cores. Now the results get more interesting. As I increased the number of producer-consumer pairs to 6 (to saturate all 12 logical cores), the locking approach was slow, and got even slower, as you'd expect. What I didn't expect to be so clear was the drop-off in performance of the lock-free ConcurrentQueue. I could see the machine only using about 20% of available CPU cycles when it should have been saturated. My interpretation is that as all the cores used atomic memory operations to safely access the queue, they ended up spending most of the time notifying each other about cache lines that need invalidating. The sync-free approach scaled perfectly, despite still working via shared memory, which after all, should still be a bottleneck. I can't quite believe that the results are so clear, so if you can think of any other effects that might cause them, please comment! Obviously, this benchmark isn't realistic because we're only measuring the overhead of the queue. Any real workload, even on a machine with 12 cores, would dwarf the overhead, and there'd be no point worrying about this effect. But would that be true on a machine with 100 cores? Still to be solved. The trouble is, you can't build many concurrent algorithms using only an SPSC queue to communicate. In particular, I can't see a way to build something as general purpose as actors on top of just SPSC queues. Fundamentally, an actor needs to be able to receive messages from multiple other actors, which seems to need an MPSC queue. I've been thinking about ways to build a sync-free MPSC queue out of multiple SPSC queues and some kind of sign-up mechanism. Hopefully I'll have something to tell you about soon, but leave a comment if you have any ideas.

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  • Using IP Restrictions with URL Rewrite-Week 25

    - by OWScott
    URL Rewrite offers tremendous flexibility for customizing rules to your environment. One area of functionality that is often desired for URL Rewrite is to allow a large list of approved or denied IP addresses and subnet ranges. IIS’s original IP Restrictions is helpful for fully blocking an IP address, but it doesn’t offer the flexibility that URL Rewrite does. An example where URL Rewrite is helpful is where you want to allow only authorized IPs to access staging.yoursite.com, but where staging.yoursite.com is part of the same site as www.yoursite.com. This requires conditional logic for the user’s IP. This lesson covers this unique situation while also introducing Rewrite Maps, server variables, and pairing rules to add more flexibility. This is week 25 of a 52 week series for the Web Pro. Past and future videos can be found here: http://dotnetslackers.com/projects/LearnIIS7/ You can find this week’s video here.

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