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• Simulate 'Shock absorbtion' with tire rubber in PhysX (2.8.x)

  - by Mungoid

  This is a kinda tricky question and I fear there is no easy enough solution, but I figured I'd hit SE up before giving up on it and just doing what I can. A machine I am working on has no suspension or shocks or springs of any sort in the real machine, so you would think that when it drives over bumps, it would shake like crazy but because its tires (6 of them) are quite large they seem to absorb a lot of shock from the bumps. Part of this is because the machine is around 30k lbs and it just smashes/compresses any bumps in the ground down (This is another issue im still working on) and the other part is that the tires seem to have a lot of flex to them with a lot of air as well. So my current task is to simulate shock absorption in physx without visibly separating the tires from the spindle/axle.. I have been messing with all kinds of NxMaterial, NxSpring, Joints, etc. and have had no luck getting this to work. The main problem is that the spindle attached to the tire is directly in the center and the axle is basically solidly attached to the chassis, so if i give it any spring or suspension travel, that spindle on the tires will move upwards or downwards, looking very odd because now its not any longer in the center of the tire. I tried giving it a higher restitution but that just makes it bouncy without any shock absorption. Another avenue I am messing with is to actively smooth the terrain in front of the tires so that before it hits a bumpy patch, that patch is smoothed and it doesn't bounce. The only issue with this is that it is pretty expensive to do with 6 tires, high tesselation of the terrain and other complex things going on at the same time in this simulation. I am still working on this but I am hoping to mix and match a few different aspects to get the best possible outcome. This is a bit of a complex issue so I'm not expecting anyone to have a definitive answer, just hoping someone may think of something I haven't =-) -Side note: Yes i know PhysX 2.8.x is quite outdated but we have to stick with it for this implementation. We are in the process of going to another physics engine but it is out of scope to apply that engine to this project.

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• WHERE x = @x OR @x IS NULL

  - by steveh99999

  Every SQL DBA and developer should read the blog of MVP Erland Sommarskog – but particularly  his article on dynamic search conditions in T-SQL. I’ve linked above to his SQL 2005 article but his 2008 version is also a must-read. I seem to regularly come across uses of the SQL in the title above… Erland’s article explains in detail why this is inefficient, but I came across a nice example recently… A stored procedure contained the following code :- WHERE @Name is null or [Name] like @Name as a nonclustered index exists on the Name column, you might assume this would be handled efficiently by SQL Server. However, I got the following output from SET STATISTICS IO Table 'xxxxx'. Scan count 15, logical reads 47760, physical reads 9, read-ahead reads 13872, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0. Note the high number of logical reads… After a bit of investigation, we found that @Name could never actually be set to NULL in this particular example. ie the @x IS NULL was spurious… So, we changed the call to WHERE  [Name] like @Name Now, how much more efficient is this code ? Table 'xxxxx'. Scan count 3, logical reads 24, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0 A nice easy win in this case…… a full index scan has been replaced by a significantly more efficient index seek. I managed to recreate the same behaviour on Adventureworks – here’s a quick query to demonstrate :- USE adventureworks SET STATISTICS IO ON DECLARE @id INT = 51721 SELECT * FROM Sales.SalesOrderDetail WHERE @id IS NULL OR salesorderid = @id SELECT * FROM Sales.SalesOrderDetail WHERE salesorderid = @id Take a look at the STATISTICS IO output and compare the actual query plans used to prove the impact of  WHERE @id IS NULL. And just to follow some of Erland’s advice – here’s how you could get similar performance if it was possible that @id could actually sometimes contain NULL. DECLARE @sql NVARCHAR(4000), @parameterlist NVARCHAR(4000) DECLARE @id INT = 51721 – or change to NULL to prove query is functionally correct SET @sql = 'SELECT * FROM Sales.SalesOrderDetail WHERE 1 = 1' IF @id IS NOT NULL SET @sql = @sql + ' AND salesorderid = @id' IF @id IS NULL SET @sql = @sql + ' AND salesorderid IS NULL' SET @parameterlist = '@id INT' EXEC sp_executesql @sql, @parameterlist,@id Sometimes I think we focus too much on hardware and SQL Server configuration – when really the answer is focus on writing efficient SQL.

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• Operation times out trying to SSH outside LAN i.e. from internet to LAN no connection is established

  - by Pelle L

  I run Ubuntu 12.04 and have no success connecting with SSH from "Internet". The router is a TL-MR3420 which is set up to forward requests to one of the NIC's on ubuntu machine (which has in total 3 NICs). I can SSH from a client on the "local" network/LAN. The forward mechanism in the router seems to work. If I stop SSH service on the Ubuntu machine and instead start one on the windows machine - it works like a charm. I do not use the Std port 22 but that shouldn't be an issue as far as I understand - sine it works on the same port on the win machine. Since my public IS isn't static I use a dynDNS service but as said earlier the same setup works from the win machine. The router is located on 192.168.0.1 The Ubuntu NICs has the following IP: eth2 192.168.0.100 , eth1 192.168.0.101 , eth0 192.168.0.102 and I have forwarded the "outside" request to 192.168.0.100 In regards for firewall settings on the Ubuntu machine I have disabled the ufw and the command ufw status give status: inactive. I don't now it this is relevant information but teh command iptables --list give: Chain INPUT (policy ACCEPT) target prot opt source destination Chain FORWARD (policy ACCEPT) target prot opt source destination Chain OUTPUT (policy ACCEPT) target prot opt source destination I have tried to catch traffic with help of wireshark (a tool I'm not too used to use) and it seems as a few (3?) "requests" actually reaches the NIC but ... nothing happens. The syslog does not show any entries during these attempts. Perhaps it could be some routing issues but I have reached my level of competence and are stuck ... all help and support to get this sorted out is much appreciated. I'm new to Linux so please do not assume I have a configuration that is correct - but as I wrote earlier - if the client that initiate SSH is on the LAN it all works. PS:I have also tried to get VPN (PPP) working from Internet with no success - once again VPN works on the windows machine ... so my best guess is that this is related to how the ubuntu machine handles (IP) traffic and not the TL-MR3420 router or other network issues.

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• Upgrades from Beta or CTP SQL Server Software is NOT Supported

  - by BuckWoody

  As of this writing, SQL Server 2008 R2 has released, and just like every release, I get e-mails and calls from folks with this question: “Can I upgrade from Customer Technical Preview (CTP) x or Beta #x or Release Candidate (RC) to the “Released to Manufacturing” (RTM) version?” No. Right up until the last minute, things are changing in the code – and you want that to happen. Our internal testing runs right up until the second we lock down for release, and we watch the CTP/RC/Beta reports to make sure there are no show-stoppers, and fix what we find. And it’s not just “big” changes you need to worry about – a simple change in one line of code can have a massive effect. I know, I know – you’ve possibly upgraded an RC or CTP to the RTM version and it worked “just fine”. But hear this tale: I’ve dealt with someone who faced this exact situation in SQL Server 2008. They upgraded (which is clearly prohibited in the documentation) from a CTP to the RTM version over a year ago. Everything was working fine. But then…one day they had an issue. Couldn’t fix it themselves, we took a look, days went by, and we finally had to call in the big guns for support. Turns out, the upgrade was the problem. So we had to come up with some elaborate schemes to get the system migrated over while they were in production. This was painful for everyone involved. So the answer is still no. Just don’t do it. There is one caveat to this story – if you are a “TAP” customer (you’ll know if you are), we help you move from the CTP products to RTM, but that’s a special case that we track carefully and send along special instructions and tools to help you along. That level of effort isn’t possible on a large scale, so it’s not just a magic tool that we run to upgrade from CTP to RTM. So again, unless you’re a TAP customer, it’s a no-no. Share this post: email it! | bookmark it! | digg it! | reddit! | kick it! | live it!

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• Spotlight on an office - Moscow

  - by Maria Sandu

  Probably the most famous place in Moscow, after Red Square, is the centre of Moscow. Here you can find beautiful buildings that seem to touch the sky, located on the banks of the river. In one of these high towers you can find the Oracle offices, friendly and modern. The stunning view will keep capture your attention for a couple of minutes and then you can enjoy a delicious coffee and take a seat at your desk, starting a new day. My name is Dmitry and I can tell you that we’re enjoying every minute spent in the office and that’s because of the pleasant atmosphere. As soon as you enter the offices, the friendly environment will make you feel more relaxed. Even though the space is split between the different departments, we interact and communicate a lot. We take our cup of coffee or tea together and discuss our achievements and all sort of subjects in the kitchen or in the open space. One of my favorite parts are the festive events when we celebrate with cakes and goodies. Any birthday or new arrival is a good reason for a tea party! We have some work-related traditions that help us as employees. One of them is the monthly Tech Hour when Experts from the Pre-sales team discuss technical topics and about the most recent innovations within the company. Lunch is another good opportunity to interact and chat. We have a variety of options, such as the two kitchens or the vast number of restaurants where you can serve up anything you want. As we are right in the centre of Moscow, you can choose between Sushi, Italian Pasta and all sorts of food. We usually go with our colleagues to have lunch. If you care about your health, I have very good news for you as nearby there are two first-class fitness centres with swimming pools, yoga and various sport classes that you can attend. My suggestion would be to either start or end your day with a visit to the swimming pool for a well-deserved hour of relaxation. As I mentioned before, we’re right in the heart of Moscow, so after work you can spend some time in the large shopping centers where you can choose between many different entertainment options. We often go to bowling or to the cinema. I hope I have given you a glimpse into working life at the Oracle offices in Moscow, a really great and pleasant place to work in, so follow us on http://campus.oracle.com for our latest vacancies and internships.

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• Finding Tools Guidance in OUM

  - by user716869

  OUM is not tool – specific. However, it does include tool guidance.  Tool guidance in OUM includes: a mention of a tool that could be used to complete a specific task(s) templates created with a specific tool example work products in a specific tool links to tool resources Tool Supplemental Guides So how do you find all this helpful tool information? Start at the lowest level first – the Task Overview.  Even though the task overviews are written tool-agnostic, they sometimes mention suggestions, or examples of a tool that might be used to complete the task.  More specific tool information can be found in the Task Overview, Templates and Tools section.  In some cases, the tool used to create the template (for example, Microsoft Word, Powerpoint, Project and Visio) is useful. The Templates and Tools section also provides more specific tool guidance, such as links to: White Papers Viewlets Example Work Products Additional Resources Tool Supplemental Guides If you’re more interested in seeing what tools might be helpful in general for your project or to see if there is any tool guidance for a specific tool that your project is committed to using, go to the Supplemental Guidance page in OUM.  This page is available from the Method Navigation pull down located in the header of almost every OUM page. When you open the Supplemental Guidance page, the first thing you see is a table index of everything that is included on the page.  At the top of the right column are all the Tool Supplemental Guides available in OUM.  Use the index to navigate to any of the guides. Next in the right column is Discipline/Industry/View Resources and Samples.  Use the index to navigate to any of these topics and see what’s available and more specifically, if there is any tool guidance available.  For example, if you navigate to the Cloud Resources, you will find a link to the IT Strategies from Oracle page that provides information for Cloud Practitioner Guides, Cloud Reference Architectures and Cloud White Papers, including the Cloud Candidate Selection Tool and Cloud Computing Maturity Model. The section for Method Tool and Technique Cross References can take you to the Task to Tool Cross Reference.  This page provides a task listing with possible helpful tools and links to more information regarding the tools.  By no means is this tool guidance all inclusive.  You can use other tools not mentioned in OUM to complete an OUM task. The Method Tool and Technique Cross References can also take you to the various Technique pages (Index and Cross References).  While techniques are not necessarily “tools,” they can certainly provide valuable assistance in completing tasks. In the Other Resources section of the Supplemental Guidance page, you find links to the viewlets and white papers that are included within OUM.

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• ETPM Forms Accelerator

  - by MHundal

  The ETPM Forms Accelerator provides a template that can be used to enter data related to Registration and Tax Forms.  The Forms Accelerator includes a worksheet for each portion related to forms development (Form Type, Form Section, Form Lines and Form Rules).  The Forms Accelerator provides the details that must be defined in ETPM.  This allows for taking an existing form and translating the details of that form into the spreadsheet.  The spreadsheet can then be used to define the details in the system.  In addition, each of the items to be defined is explained it detail - what the field expects and based on the input, how it impacts the field and form definition.   This is a living document - as there is feedback provided, the document will be updated.  The goal of this accelerator is to be an aide in the Forms Development process.  We encourage feedback to help improve the document.  The document is for ETPM 2.3.1.  Implementations using older version of ETPM will find that some of the field definition options may not exist their current system.   The spreadsheet attached contains the following Worksheets: Instructions:  High-level overview for the different worksheets provided. Form Type:  The fields to be populated when defining the Form Type for a Registration or Tax Form Form Section:  The fields to be populated when creating a Form Section.  The number of sections will differ based on the the form being implemented. Form Lines:  The fields to be populated when creating different Form Lines. The number of lines per section will differ based on the form being implemented. Form Rules:  Based on the form, allows for documenting the Form Rules to be configured based on form instructions and Form Lines. Right click on the link and select the "Save Link As" option.  ETPM Forms Accelerator.xls Please provide feedback to [email protected]. You feedback is encouraged and appreciated.  

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• Are there any good Java/JVM libraries for my Expression Tree architecture?

  - by Snuggy

  My team and I are developing an enterprise-level application and I have devised an architecture for it that's best described as an "Expression Tree". The basic idea is that the leaf nodes of the tree are very simple expressions (perhaps simple values or strings). Nodes closer to the trunk will get more and more complex, taking the simpler nodes as their inputs and returning more complex results for their parents. Looking at it the other way, the application performs some task, and for this it creates a root expression. The root expression divides its input into smaller units and creates child expressions, which when evaluated it can use to build it's own result. The subdividing process continues until the simplest leaf nodes. There are two very important aspects of this architecture: It must be possible to manipulate nodes of the tree after it is built. The nodes may be given new input values to work with and any change in result for that node needs to be propagated back up the tree to the root node. The application must make best use of available processors and ultimately be scalable to other computers in a grid or in the cloud. Nodes in the tree will often be updating concurrently and notifying other interested nodes in the tree when they get a new value. Unfortunately, I'm not at liberty to discuss my actual application, but to aid understanding a little bit, you might imagine a kind of spreadsheet application being implemented with a similar architecture, where changes to cells in the table are propagated all over the place to other cells that need the result. The spreadsheet could get so massive that applying multi-core multi-computer distributed system to solve it would be of benefit. I've got my prototype "Expression Engine" working nicely on a single multi-core PC but I've started to run into a few concurrency issues (as expected because I haven't been taking too much care so far) so it's now time to start thinking about migrating the Engine to a more robust library, and that leads to a number of related questions: Is there any precedent for my "Expression Tree" architecture that I could research? What programming concepts should I consider. I realise this approach has many similarities to a functional programming style, and I'm already aware of the concepts of using futures and actors. Are there any others? Are there any languages or libraries that I should study? This question is inspired by my accidental discovery of Scala and the Akka library (which has good support for Actors, Futures, Distributed workloads etc.) and I'm wondering if there is anything else I should be looking at as well?

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• Is this a pattern? Should it be?

  - by Arkadiy

  The following is more of a statement than a question - it describes something that may be a pattern. The question is: is this a known pattern? Or, if it's not, should it be? I've had a situation where I had to iterate over two dissimilar multi-layer data structures and copy information from one to the other. Depending on particular use case, I had around eight different kinds of layers, combined in about eight different combinations: A-B-C B-C A-C D-E A-D-E and so on After a few unsuccessful attempts to factor out the repetition of per-layer iteration code, I realized that the key difficulty in this refactoring was the fact that the bottom level needed access to data gathered at higher levels. To explicitly accommodate this requirement, I introduced IterationContext class with a number of get() and set() methods for accumulating the necessary information. In the end, I had the following class structure: class Iterator { virtual void iterateOver(const Structure &dataStructure1, IterationContext &ctx) const = 0; }; class RecursingIterator : public Iterator { RecursingIterator(const Iterator &below); }; class IterateOverA : public RecursingIterator { virtual void iterateOver(const Structure &dataStructure1, IterationContext &ctx) const { // Iterate over members in dataStructure1 // locate corresponding item in dataStructure2 (passed via context) // and set it in the context // invoke the sub-iterator }; class IterateOverB : public RecursingIterator { virtual void iterateOver(const Structure &dataStructure1, IterationContext &ctx) const { // iterate over members dataStructure2 (form context) // set dataStructure2's item in the context // locate corresponding item in dataStructure2 (passed via context) // invoke the sub-iterator }; void main() { class FinalCopy : public Iterator { virtual void iterateOver(const Structure &dataStructure1, IterationContext &ctx) const { // copy data from structure 1 to structure 2 in the context, // using some data from higher levels as needed } } IterationContext ctx(dateStructure2); IterateOverA(IterateOverB(FinalCopy())).iterate(dataStructure1, ctx); } It so happens that dataStructure1 is a uniform data structure, similar to XML DOM in that respect, while dataStructure2 is a legacy data structure made of various structs and arrays. This allows me to pass dataStructure1 outside of the context for convenience. In general, either side of the iteration or both sides may be passed via context, as convenient. The key situation points are: complicated code that needs to be invoked in "layers", with multiple combinations of layer types possible at the bottom layer, the information from top layers needs to be visible. The key implementation points are: use of context class to access the data from all levels of iteration complicated iteration code encapsulated in implementation of pure virtual function two interfaces - one aware of underlying iterator, one not aware of it. use of const & to simplify the usage syntax.

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• Organization &amp; Architecture UNISA Studies &ndash; Chap 13

  - by MarkPearl

  Learning Outcomes Explain the advantages of using a large number of registers Discuss the way in which compilers optimize register usage Discuss the evolution of CISC machines Describe the characteristics of RISC architecture Discuss the RISC vs. CISC controversy Describe the way in which RISC and CISC design principles can be combined Instruction Execution Characteristics To understand the the line of reasoning of RISC advocates, we need a brief overview of instruction execution characteristics. These include… Operations Operands Procedure Calls These three sections can be studied in depth in the textbook at pages 503 - 505 A number of groups have come up with the conclusion that the attempt to make the instruction set architecture closer to HLLs (High Level Languages) is not the most effective design strategy. Rather HLL’s can be best supported by optimizing performance of the most time-consuming features of typical HLL programs. Generally 3 main characteristics came up to improve performance… Use a large number of registers or use a compiler to optimize register usage Careful attention needs to be paid to the design of instruction pipelines A simplified (reduced) instruction set is indicated The use of a large register optimization One of the most important design principles of RISC machines is the use of a large number of registers. The concept of register windows and the use of a large register file versus the use of cache memory are discussed. On the face of it, the use of a large set of registers should decrease the need to access memory. The design task is to organize the registers in such a fashion that this goal is realized. Read page 507 – 510 for a detailed explanation. Compiler-based register optimization   Reduced Instructions Set Architecture There are two advantages to smaller programs… Because the program takes up less memory, there is a savings in that resource (this was more compelling when memory was more expensive) Smaller programs should improve performance, and this will happen in two ways – fewer instructions means fewer instruction bytes to be fetched and in a paging environment smaller programs occupy fewer pages, reducing page faults. Certain characteristics are common to RISC processors… One instruction per cycle Register-to-register operations Simple addressing modes Simple instruction formats RISC vs. CISC After initial enthusiasm for RISC machines, there has been a growing realization that RISC designs may benefit from the inclusion of some CISC features CISC designs may benefit from the inclusion of some RISC features

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• is a factory pattern to prevent multuple instances for same object (instance that is Equal) good design?

  - by dsollen

  I have a number of objects storing state. There are essentially two types of fields. The ones that uniquly define what the object is (what node, what edge etc), and the oens that store state describing how these things are connected (this node is connected to these edges, this edge is part of these paths) etc. My model is updating the state variables using package methdos, so these objects all act as immutable to anyone not in Model scope. All Objects extend one base type. I've toyed with the idea of a Factory approch which accepts a Builder object and construct the applicable object. However, if an instance of the object already exists (ie would return true if I created the object defined by the builder and passed it to the equal method for the existing instance) the factory returns the current object instead of creating a new instance. Because the Equal method would only compare what uniquly defines the type of object (this is node A nto node B) but won't check the dynamic state stuff (node A is currently connected to nodes C and E) this would be a way of ensuring anyone that wants my Node A automatically knows it's state connections. More importantly it would prevent aliasing nightmares of someone trying to pass an instance of node A with different state then the node A in my model has. I've never heard of this pattern before, and it's a bit odd. I would have to do some overiding of serlization methods to make it work (ensure when I read in a serilized object I add it to my facotry list of known instances, and/or return an existing factory in it's place), as well as using a weakHashMap as if it was a weakHashSet to know rather an instance exists without worrying about a quasi-memory leak occuring. I don't know if this is too confusing or prone to it's own obscure bugs. One thing I know is that plugins interface with lowest level hardware. The plugins have to be able to return state taht is different then my memory; to tell my memory when it's own state is inconsistent. I believe this is possible despit their fetching objects that exist in my memory; we allow building of objects without checking their consistency with the model until the addToModel is called anyways; and the existing plugins design was written before all this extra state existed and worked fine without ever being aware of it. Should I just be using some other design to avoid this crazyness? (I have another question to that affect I'm posting).

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• Developing web sites that imitate desktop apps. How to fight that paradigm? [closed]

  - by user1598390

  Supposse there's a company where web sites/apps are designed to resemble desktop apps. They struggle to add: Splash screens Drop-down menus Tab-pages Pages that don't grow downward with content, context is inside scrollable area so page is of a fixed size, as if resembling the one-screen limitation of desktop apps. Modal windows, pop-ups, etc. Tree views Absolutely no access to content unless you login-first, even with non-sensitive content. After splash screen desapears, you are presented with a login screen. No links - just simulated buttons. Fixed page-size. Cannot open a linked in other tab Print button that prints directly ( not showing printable page so the user can't print via the browser's print command ) Progress bars for loading content even when the browser indicates it with its own animation Fonts and color amulate a desktop app made with Visual Basic, PowerBuilder etc. Every app seems almost as if were made in Visual Basic. They reject this elements: Breadcrumbs Good old underlined links Generated/dynamic navigation, usage-based suggestions Ability to open links in multiple tabs Pagination Printable pages Ability to produce a URL you can save or share that links to an item, like when you send someone the link to an especific StackExchange question. The only URL is the main one. Back button To achieve this, tons of javascript code is needed. Lots and lots of Javascript and Ajax code for things not related with the business but with the necessity to hide/show that button, refresh this listbox, grey-out that label, etc. The coplexity generated by forcing one paradigm into another means most lines of code are dedicated to maintain the illusion of a desktop app. What is the best way to change this mindset, and make them embrace the web, and start producing modern, web apps instead of desktop imitations ? EDIT: These sites are intranet sites. Users hate these apps. They constantly whine about them, but they have to use them to do their daily work. These sites are in-house solutions, the end-users have no choice but to use them. They are a "captive audience". Also, substitution will not happen because of high costs. But at least if that mindset is changed, new developments would be more web-like.

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• Can Anything be Done to Make Improv (a 1993 Win 3.1 App) handle larger Files?

  - by user75185

  My very favorite spradsheet is Improv, a 1993 Windows 3.1 application. It still puts Excel to shame for building spreadsheets and writing formulas. The only problem is because Improv was written when 1 Meg of RAM was state of the art, it becomes unstable when working with larger spreadsheets and often crashes and/or corrupts the data file. I am working on a project that greatly exceeds Improv's limits. Although it will ultimately require more robust databasing capability, I could save a lot of critical time if I could delay that headache and continue working in Improv for now. To that end, I moved to the only product I could find that comes close, Quantrix, which is nothing more than Improv updated to handle large spreadsheets and utilize today's technologies. The problems with Quantrix are its speed (significantly slower than Improv) and its $1000 price (which I cannot afford). I have already had 3 15 day extensions after the initial 30 day trial, so my time to use Quantrix as a bridge is at its end. Searches for Improv over the years have gotten me nowhere and, not surprisingly after reading some posts on this site, I got nothing for the money and time invested to find a programmer to write code to "fix" this problem. Improv is freely available as "abandonware" at http://vetusware.com/download/LotusImprov2.1/?id=5797 , and the best background info can be found on Wikipedia and at "Moose's Greatest Software Products of All Time - Lotus Improv" http://moosevalley.fhost.com.au/mooses_review_page_lotus_improv.html It is critically urgent for me to focus on analyzing the data asap. Working in a stable Improv would, without question, be the fastest route. To that end, I am looking for answers to the following questions and anything else that might be helpful: 1) Is it lawful to hire someone to fix Improv for my own use? If so, 2) About how much should it cost? 3) About how long should it take? 4) What skills should I be looking for &/or how should a post be worded? 5) Is there a niche site where it should it be posted? 6) What questions can I ask to quickly screen candidates? Since I am not a programmer, I need questions the answers to which leave no room to confuse me, whether intentional or not. For example, what tools or players should someone with an acceptable competency level have knowledge of?

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• The difference

  So with the CTP tools available, weve been building a few apps, just to get a feel for the tools and whats supported in the framework.  Whats been great is that everything is fairly familiar and consistent, largely to do with the .net framework and Microsofts focus on providing good tools.  Weve produced mobile applications, mostly in concept form, for Windows Phone Classic, iPhone and Android but never so quickly and not of such high quality and visual impression.  I attribute some of this obviously to our familiarity to the Microsoft platform and tools.  Though when you look at the designs our team has produced, it becomes clear that this is not just another mobile application container.                                                            The Metro design language implores content prominence with fluid motion and transitions, with a crisp font and easily organized features and services placement.  In addition to a purposeful right edge tease, where the intent is for users to discover new premium content and services.   The concept that enables this is called hubs, building application with hubs changes your thinking from a single mobile application task, to thinking creatively about a mobile experience. Its engaging to think of the other brands and industry verticals that will take advantage of this core feature.  Combine this with Windows Phone 7 live tiles, more on that later, and you have a recipe for a solid mobile services platform.                                                              This so much more fun and liberating than my icon on a gridDid you know that DotNetSlackers also publishes .net articles written by top known .net Authors? We already have over 80 articles in several categories including Silverlight. Take a look: here.

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• WiFi on Ubuntu 12.04 custom: downloading unbearably slow

  - by Mark

  iwconfig reports 11 Mbps, yet I've seen as low as <1 KBps. This is the latest in my laundry list of Ubuntu problems in a dual-boot machine (cyberpowerpc custom, intel i7-3820, nvidia gtx 570). I received it two days ago, Windows 7 running fine, still having problems with Ubuntu. The browsing is intermittent but unacceptable. e.g. I could get to this site last night but I couldn't post this question. The downloading is unbearably slow, I can't download anything or install any packages because the speed is so slow. e.g. I am trying to install vim which is inexplicably missing from my 12.04 install (add another one to the problems list) and my download speed reported in the terminal was 241 B/s. Yes, bytes. iwconfig reports 11 Mbps, which further adds to the confusion. User@ubuntu:~$ iwconfig lo no wireless extensions. wlan0 IEEE 802.11bgn ESSID:"linksys" Mode:Managed Frequency:2.437 GHz Access Point: 00:18:39:76:2C:A1 Bit Rate=11 Mb/s Tx-Power=20 dBm Retry long limit:7 RTS thr:off Fragment thr:off Power Management:off Link Quality=36/70 Signal level=-74 dBm Rx invalid nwid:0 Rx invalid crypt:0 Rx invalid frag:0 Tx excessive retries:54 Invalid misc:18 Missed beacon:0 eth0 no wireless extensions. Any ideas? I see this is a problem a lot of people, but none of the on line solutions have worked for me so far. e.g. one site recommends editing the ath9k.conf file in /etc/modprobe.d, yet this file isn't even in the folder: User@ubuntu:/$ cd etc/modprobe.d User@ubuntu:/etc/modprobe.d$ ls alsa-base.conf blacklist-oss.conf blacklist-ath_pci.conf blacklist-rare-network.conf blacklist.conf blacklist-watchdog.conf blacklist-firewire.conf dkms.conf blacklist-framebuffer.conf nvidia-current_hybrid.conf blacklist-modem.conf nvidia-graphics-drivers.conf I think the nvidia gpu might be mucking things up. I had the "blinking cursor" problem when installing in the first place, and then I had the monitor out of range problem as well. I have my faithful Asus laptop, which is running Ubuntu 12.04 just fine. The only difference is executing host -t SOA local in the terminal gives User@ubuntu:~$ host -t SOA local local has SOA record local. nobody.localhost. 42 86400 43200 604800 10800 in my new machine, and the command reports Host local. not found in the laptop. Help would be most welcome, as I am in danger of reverting back to Windows. I'm seriously considering it. Sorry for the length, trying to show my effort in resolving the issue and include terminal snippets that might be helpful.

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• Send raw data to USB parallel port after upgrading to 11.10 oneiric

  - by zaphod

  I have a laser cutter connected via a generic USB to parallel adapter. The laser cutter speaks HPGL, as it happens, but since this is a laser cutter and not a plotter, I usually want to generate the HPGL myself, since I care about the ordering, speed, and direction of cuts and so on. In previous versions of Ubuntu, I was able to print to the cutter by copying an HPGL file directly to the corresponding USB "lp" device. For example: cp foo.plt /dev/usblp1 Well, I just upgraded to Ubuntu 11.10 oneiric, and I can't find any "lp" devices in /dev anymore. D'oh! What's the preferred way to send raw data to a parallel port in Ubuntu? I've tried System Settings Printing + Add, hoping that I might be able to associate my device with some kind of "raw printer" driver and print to it with a command like lp -d LaserCutter foo.plt But my USB to parallel adapter doesn't seem to show up in the list. What I do see are my HP Color LaserJet, two USB-to-serial adapters, "Enter URI", and "Network Printer". Meanwhile, over in /dev, I do see /dev/ttyUSB0 and /dev/ttyUSB1 devices for the 2 USB-to-serial adapters. I don't see anything obvious corresponding to the HP printer (which was /dev/usblp0 prior to the upgrade), except for generic USB stuff. For example, sudo find /dev | grep lp produces no output. I do seem to be able to print to the HP printer just fine, though. The printer setup GUI gives it a device URI starting with "hp:" which isn't much help for the parallel adapter. The CUPS administrator's guide makes it sound like I might need to feed it a device URI of the form parallel:/dev/SOMETHING, but of course if I had a /dev/SOMETHING I'd probably just go on writing to it directly. Here's what dmesg says after I disconnect and reconnect the device from the USB port: [ 924.722906] usb 1-1.1.4: USB disconnect, device number 7 [ 959.993002] usb 1-1.1.4: new full speed USB device number 8 using ehci_hcd And here's how it shows up in lsusb -v: Bus 001 Device 008: ID 1a86:7584 QinHeng Electronics CH340S Device Descriptor: bLength 18 bDescriptorType 1 bcdUSB 1.10 bDeviceClass 0 (Defined at Interface level) bDeviceSubClass 0 bDeviceProtocol 0 bMaxPacketSize0 8 idVendor 0x1a86 QinHeng Electronics idProduct 0x7584 CH340S bcdDevice 2.52 iManufacturer 0 iProduct 2 USB2.0-Print iSerial 0 bNumConfigurations 1 Configuration Descriptor: bLength 9 bDescriptorType 2 wTotalLength 32 bNumInterfaces 1 bConfigurationValue 1 iConfiguration 0 bmAttributes 0x80 (Bus Powered) MaxPower 96mA Interface Descriptor: bLength 9 bDescriptorType 4 bInterfaceNumber 0 bAlternateSetting 0 bNumEndpoints 2 bInterfaceClass 7 Printer bInterfaceSubClass 1 Printer bInterfaceProtocol 2 Bidirectional iInterface 0 Endpoint Descriptor: bLength 7 bDescriptorType 5 bEndpointAddress 0x82 EP 2 IN bmAttributes 2 Transfer Type Bulk Synch Type None Usage Type Data wMaxPacketSize 0x0020 1x 32 bytes bInterval 0 Endpoint Descriptor: bLength 7 bDescriptorType 5 bEndpointAddress 0x02 EP 2 OUT bmAttributes 2 Transfer Type Bulk Synch Type None Usage Type Data wMaxPacketSize 0x0020 1x 32 bytes bInterval 0 Device Status: 0x0000 (Bus Powered)

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• SharePoint 2010 HierarchicalConfig Caching Problem

  - by Damon

  We've started using the Application Foundations for SharePoint 2010 in some of our projects at work, and I came across a nasty issue with the hierarchical configuration settings.  I have some settings that I am storing at the Farm level, and as I was testing my code it seemed like the settings were not being saved - at least that is what it appeared was the case at first.  However, I happened to reset IIS and the settings suddenly appeared.  Immediately, I figured that it must be a caching issue and dug into the code base.  I found that there was a 10 second caching mechanism in the SPFarmPropertyBag and the SPWebAppPropertyBag classes.  So I ran another test where I waited 10 seconds to make sure that enough time had passed to force the caching mechanism to reset the data.  After 10 minutes the cache had still not cleared.  After digging a bit further, I found a double lock check that looked a bit off in the GetSettingsStore() method of the SPFarmPropertyBag class: if (_settingStore == null || (DateTime.Now.Subtract(lastLoad).TotalSeconds) > cacheInterval)) { //Need to exist so don't deadlock. rrLock.EnterWriteLock(); try { //make sure first another thread didn't already load... if (_settingStore == null) { _settingStore = WebAppSettingStore.Load(this.webApplication); lastLoad = DateTime.Now; } } finally { rrLock.ExitWriteLock(); } } What ends up happening here is the outer check determines if the _settingStore is null or the cache has expired, but the inner check is just checking if the _settingStore is null (which is never the case after the first time it's been loaded).  Ergo, the cached settings are never reset.  The fix is really easy, just add the cache checking back into the inner if statement. //make sure first another thread didn't already load... if (_settingStore == null || (DateTime.Now.Subtract(lastLoad).TotalSeconds) > cacheInterval) { _settingStore = WebAppSettingStore.Load(this.webApplication); lastLoad = DateTime.Now; } And then it starts working just fine. as long as you wait at least 10 seconds for the cache to clear.

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• AS3 - At exactly 23 empty alpha channels, images below stop drawing

  - by user46851

  I noticed, while trying to draw large numbers of circles, that occasionally, there would be some kind of visual bug where some circles wouldn't draw properly. Well, I narrowed it down, and have noticed that if there is 23 or more objects with 00 for an alpha value on the same spot, then the objects below don't draw. It appears to be on a pixel-by-pixel basis, since parts of the image still draw. Originally, this problem was noticed with a class that inherited Sprite. It was confirmed to also be a problem with Sprites, and now Bitmaps, too. If anyone can find a lower-level class than Bitmap which doesn't have this problem, please speak up so we can try to find the origin of the problem. I prepared a small test class that demonstrates what I mean. You can change the integer value at line 20 in order to see the three tests I came up with to clearly show the problem. Is there any kind of workaround, or is this just a limit that I have to work with? Has anyone experienced this before? Is it possible I'm doing something wrong, despite the bare-bones implementation? package { import flash.display.Sprite; import flash.events.Event; import flash.display.Bitmap; import flash.display.BitmapData; public class Main extends Sprite { public function Main():void { if (stage) init(); else addEventListener(Event.ADDED_TO_STAGE, init); } private function init(e:Event = null):void { removeEventListener(Event.ADDED_TO_STAGE, init); // entry point Test(3); } private function Test(testInt:int):void { if(testInt==1){ addChild(new Bitmap(new BitmapData(200, 200, true, 0xFFFF0000))); for (var i:int = 0; i < 22; i++) { addChild(new Bitmap(new BitmapData(100, 100, true, 0x00000000))); } } if(testInt==2){ addChild(new Bitmap(new BitmapData(200, 200, true, 0xFFFF0000))); for (var j:int = 0; j < 23; j++) { addChild(new Bitmap(new BitmapData(100, 100, true, 0x00000000))); } } if(testInt==3){ addChild(new Bitmap(new BitmapData(200, 200, true, 0xFFFF0000))); for (var k:int = 0; k < 22; k++) { addChild(new Bitmap(new BitmapData(100, 100, true, 0x00000000))); } var M:Bitmap = new Bitmap(new BitmapData(100, 100, true, 0x00000000)); M.x += 50; M.y += 50; addChild(M); } } } }

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• Application stuck in TCP retransmit

  - by SandeepJ

  I am running Linux kernel 3.13 (Ubuntu 14.04) on two Virtual Machines each of which operates inside two different servers running ESXi 5.1. There is a zeromq client-server application running between the two VMs. After running for about 10-30 minutes, this application consistently hangs due to inability to retransmit a lost packet. When I run the same setup over Ubuntu 12.04 (Linux 3.11), the application never fails If you notice below, "ss" (socket statistics) shows 1 packet lost, sk_wmem_queued of 14110 (i.e. w14110) and a high rto (120000). State Recv-Q Send-Q Local Address:Port Peer Address:Port ESTAB 0 12350 192.168.2.122:41808 192.168.2.172:55550 timer:(on,16sec,10) uid:1000 ino:35042 sk:ffff880035bcb100 <- skmem:(r0,rb648720,t0,tb1164800,f2274,w14110,o0,bl0) ts sack cubic wscale:7,7 rto:120000 rtt:7.5/3 ato:40 mss:8948 cwnd:1 ssthresh:21 send 9.5Mbps unacked:1 retrans:1/10 lost:1 rcv_rtt:1476 rcv_space:37621 Since this has happened so consistently, I was able to capture the TCP log in wireshark. I found that the packet which is lost does get retransmitted and even acknowledged by the TCP in the other OS (the sequence number is seen in the ACK), but the sender doesn't seem to understand this ACK and continues retransmitting. MTU is 9000 on both virtual machines and througout the route. The packets being sent are large in size. As I said earlier, this does not happen on Ubuntu 12.04 (kernel 3.11). So I did a diff on the TCP config options (seen via "sysctl -a |grep tcp ") between 14.04 and 12.04 and found the following differences. I also noticed that net.ipv4.tcp_mtu_probing=0 in both configurations. Left side is 3.11, right side is 3.13 <<net.ipv4.tcp_abc = 0 <<net.ipv4.tcp_cookie_size = 0 <<net.ipv4.tcp_dma_copybreak = 4096 14c11 << net.ipv4.tcp_early_retrans = 2 --- >> net.ipv4.tcp_early_retrans = 3 17c14 << net.ipv4.tcp_fastopen = 0 >> net.ipv4.tcp_fastopen = 1 20d16 << net.ipv4.tcp_frto_response = 0 26,27c22 << net.ipv4.tcp_max_orphans = 16384 << net.ipv4.tcp_max_ssthresh = 0 >> net.ipv4.tcp_max_orphans = 4096 29,30c24,25 << net.ipv4.tcp_max_tw_buckets = 16384 << net.ipv4.tcp_mem = 94377 125837 188754 >> net.ipv4.tcp_max_tw_buckets = 4096 >> net.ipv4.tcp_mem = 23352 31138 46704 34a30 >> net.ipv4.tcp_notsent_lowat = -1 My question to the networking experts on this forum : Are there any other debugging tools or options I can install/enable to dig further into why this TCP retransmit failure is occurring so consistently ? Are there any configuration changes which might account for this weird behaviour.

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• How can I tweak this A* search pathfinding algorithm to handle different terrain movement values?

  - by user422318

  I'm creating a 2D map-based action game with similar interaction design as Diablo II. In other words, the player clicks around a map to move their player. I just finished player movement and am moving on to pathfinding. In the game, enemies should charge the player's character. There are also five different terrain types that give different movement bonuses. I want the AI to take advantage of these terrain bonuses as they try to reach the player. I was told to check out the A* search algorithm (http://en.wikipedia.org/wiki/A*_search_algorithm). I'm doing this game in HTML5 and JavaScript, and found a version in JavaScript: http://www.briangrinstead.com/blog/astar-search-algorithm-in-javascript I'm trying to figure out how to tweak it though. Below are my ideas about what I need to change. What else do I need to worry about? When I create a graph, I will need to initialize the 2D array I pass in passed on with a traversal of a map that corresponds to the different terrain types. in graph.js: "GraphNodeType" definition needs to be modified to handle the 5 terrain types. There will be no walls. in astar.js: The g and h scoring will need to be modified. How should I do this? in astar.js: isWall() should probably be removed. My game doesn't have walls. in astar.js: I'm not sure what this is. I think it indicates a node that isn't valid to be processed. When would this happen, though? At a high level, how do I change this algorithm from "oh, is there a wall there?" to "will this terrain get me to the player faster than the terrain around me?" Because of time, I'm also debating reusing my Bresenham algorithm for the enemies. Unfortunately, the different terrain movement bonuses won't be used by the AI, which will make the game suck. :/ I'd really like to have this in for the prototype, but I'm not a developer by trade nor am I a computer scientist. :D If you know of any code that does what I'm looking for, please share! Sanity check tips for this are also appreciated.

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• iOS app with a lot of text

  - by rdurand

  I just asked a question on StackOverflow, but I'm thinking that a part of it belongs here, as questions about design pattern are welcomed by the faq. Here is my situation. I have developed almost completely a native iOS app. The last section I need to implement is all the rules of a sport, so that's a lot of text. It has one main level of sections, divided in subsections, containing a lot of structured text (paragraphs, a few pictures, bulleted/numbered lists, tables). I have absolutely no problem with coding, I'm just looking for advice to improve and make the best design pattern possible for my app. My first shot (the last one so far) was a UITableViewController containing the sections, sending the user to another UITableViewController with the subsections of the selected section, and then one strange last UITableViewController where the cells contain UITextViews, sections header help structure the content, etc. What I would like is your advice on how to improve the structure of this section. I'm perfectly ready to destroy/rebuild the whole thing, I'm really lost in my design here.. As I said on SO, I've began to implement a UIWebView in a UIViewController, showing a html page with JQuery Mobile to display the content, and it's fine. My question is more about the 2 views taking the user to that content. I used UITableViewControllers because that's what seemed the most appropriate for a structured hierarchy like this one. But that doesn't seem like the best solution in term of user experience.. What structure / "view-flow" / kind of presentation would you try to implement in my situation? As always, any help would be greatly appreciated! Just so you can understand better the hierarchy, with a simple example : -----> Section 1 -----> SubSection 1.1 -----> Content | -----> SubSection 1.2 -----> Content | -----> SubSection 1.3 -----> Content | | | UINavigationController -------> Section 2 -----> SubSection 2.1 -----> Content | -----> SubSection 2.2 -----> Content | -----> SubSection 2.3 -----> Content | -----> SubSection 2.4 -----> Content | -----> SubSection 2.5 -----> Content | -----> Section 3 -----> SubSection 3.1 -----> Content -----> SubSection 3.2 -----> Content |------------------| |--------------------| |-------------| 1 UITableViewController 3 UITableViewControllers 10 UIViewControllers (3 rows) (with different with a UIWebView number of rows)

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• Are we queueing and serializing properly?

  - by insta

  We process messages through a variety of services (one message will touch probably 9 services before it's done, each doing a specific IO-related function). Right now we have a combination of the worst-case (XML data contract serialization) and best-case (in-memory MSMQ) for performance. The nature of the message means that our serialized data ends up about 12-15 kilobytes, and we process about 4 million messages per week. Persistent messages in MSMQ were too slow for us, and as the data grows we are feeling the pressure from MSMQ's memory-mapped files. The server is at 16GB of memory usage and growing, just for queueing. Performance also suffers when the memory usage is high, as the machine starts swapping. We're already doing the MSMQ self-cleanup behavior. I feel like there's a part we're doing wrong here. I tried using RavenDB to persist the messages and just queueing an identifier, but the performance there was very slow (1000 messages per minute, at best). I'm not sure if that's a result of using the development version or what, but we definitely need a higher throughput[1]. The concept worked very well in theory but performance was not up to the task. The usage pattern has one service acting as a router, which does all reads. The other services will attach information based on their 3rd party hook, and forward back to the router. Most objects are touched 9-12 times, although about 10% are forced to loop around in this system for awhile until the 3rd parties respond appropriately. The services right now account for this and have appropriate sleeping behaviors, as we utilize the priority field of the message for this reason. So, my question, is what is an ideal stack for message passing between discrete-but-LAN'ed machines in a C#/Windows environment? I would normally start with BinaryFormatter instead of XML serialization, but that's a rabbit hole if a better way is to offload serialization to a document store. Hence, my question. [1]: The nature of our business means the sooner we process messages, the more money we make. We've empirically proven that processing a message later in the week means we are less likely to make that money. While performance of "1000 per minute" sounds plenty fast, we really need that number upwards of 10k/minute. Just because I'm giving numbers in messages per week doesn't mean we have a whole week to process those messages.

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• No Sound in 12.04 on Acer TimelineX 3830TG

  - by Fawkes5

  When i first installed ubuntu 12.04 everything worked fine. All of a sudden my sound has stopped working!! This has happened before [like 2 days ago], however the next day it started working again. That may happen again...[I've already rebooted 5 times] My Sound Card is a HDA intel PCH My Sound Chip is Intel CougarPoint HDMI My machine is an Acer TimelineX 3830TG, heres my lcpci output 00:00.0 Host bridge: Intel Corporation 2nd Generation Core Processor Family DRAM Controller (rev 09) 00:01.0 PCI bridge: Intel Corporation Xeon E3-1200/2nd Generation Core Processor Family PCI Express Root Port (rev 09) 00:02.0 VGA compatible controller: Intel Corporation 2nd Generation Core Processor Family Integrated Graphics Controller (rev 09) 00:16.0 Communication controller: Intel Corporation 6 Series/C200 Series Chipset Family MEI Controller #1 (rev 04) 00:1a.0 USB controller: Intel Corporation 6 Series/C200 Series Chipset Family USB Enhanced Host Controller #2 (rev 04) 00:1b.0 Audio device: Intel Corporation 6 Series/C200 Series Chipset Family High Definition Audio Controller (rev 04) 00:1c.0 PCI bridge: Intel Corporation 6 Series/C200 Series Chipset Family PCI Express Root Port 1 (rev b4) 00:1c.1 PCI bridge: Intel Corporation 6 Series/C200 Series Chipset Family PCI Express Root Port 2 (rev b4) 00:1c.2 PCI bridge: Intel Corporation 6 Series/C200 Series Chipset Family PCI Express Root Port 3 (rev b4) 00:1c.3 PCI bridge: Intel Corporation 6 Series/C200 Series Chipset Family PCI Express Root Port 4 (rev b4) 00:1d.0 USB controller: Intel Corporation 6 Series/C200 Series Chipset Family USB Enhanced Host Controller #1 (rev 04) 00:1f.0 ISA bridge: Intel Corporation HM65 Express Chipset Family LPC Controller (rev 04) 00:1f.2 SATA controller: Intel Corporation 6 Series/C200 Series Chipset Family 6 port SATA AHCI Controller (rev 04) 00:1f.3 SMBus: Intel Corporation 6 Series/C200 Series Chipset Family SMBus Controller (rev 04) 01:00.0 VGA compatible controller: NVIDIA Corporation GF108 [GeForce GT 540M] (rev ff) 02:00.0 Ethernet controller: Atheros Communications Inc. AR8151 v2.0 Gigabit Ethernet (rev c0) 03:00.0 Network controller: Atheros Communications Inc. AR9287 Wireless Network Adapter (PCI-Express) (rev 01) 04:00.0 Unassigned class [ff00]: Realtek Semiconductor Co., Ltd. RTS5116 PCI Express Card Reader (rev 01) 05:00.0 USB controller: NEC Corporation uPD720200 USB 3.0 Host Controller (rev 04) I'm running a dual boot with Windows 7, sound always works there. I've tried loading earlier kernels [3.2.0 ] but that hasn't helped. I've tried playing with alsamixer, unmuting and raising volume, doesn't work I've tried playing with pauvcontrol, doesnt work. Althought, strangely, when i play a song, under output i can see a bar moving implying that something is working, just the sound isn't getting through my speakers. Thus it might be a hardware problem. I've tried unistalling and reinstalling pulsaudio annd alsamixer, doesn't work [maybe made it worse...]. I've heard reverting back to kernel 3.0... works, but i'm reluctant to try that[i dont know much about kernels]. Thank you. Please tell me what other information you need. EDIT: My audio has started working again after another reboot. However this time im not connected to my external audio on startup. I will see if this is the issue next time i'm at home Edit: Connecting to external audio is not the problem.

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• Strangling the life out of Software Testing

  - by MarkPearl

  I recently did a course at the local university on Software Engineering. At the beginning of the course I looked over the outline of the subject and there seemed to be some really good content. It covered traditional & agile project methodologies, some general communication and modelling chapters and finished off with testing. I was particularly excited to see the section on testing as this was something I learnt on my own and see great value in. The course has now just ended and I am very disappointed. I now know one of the reasons why so few people i.e. in my region do Test Driven Development, or perform even basic testing methodologies. The topic was to academic! Yes, you might be able to list 4 different types of black box test approaches vs. white box test approaches and describe the characteristics of Smoke Tests, but never during course did we see an example of an actual test or how it might be implemented! In fact, if I did not have personal experience of applying testing in actual projects, I wouldn’t even know what a unit test looked like. Now, what worries me is the following… It took us 6 months to cover the course material, other students more than likely came out of that course with little appreciation of the subject – in fact they now have a very complex view of what a test is – so complex that I think most of them will never attempt it again on their own. Secondly, imagine studying to be a dentist without ever actually seeing a tooth? Yes, you might be able to describe a tooth, and know what it is made out of – but nobody would want a dentist who has never seen a tooth to operate on them. Yet somehow we expect people studying software engineering to do the same? This is not right. Now, before I finish my rant let me say that I know this is not the same everywhere in the world, and that there needs to be a balance on practical implementation and academic understanding – I am just disappointed that this does not seem to be happening at the institution that I am currently studying at ;-( Please, if you happen to be a lecturer or teacher reading this post – a combination of theory and practical's goes a long way. We need to up the quality of software being produced and that starts at learner level!

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• A Simple Entity Tagger

  - by Elton Stoneman

  In the REST world, ETags are your gateway to performance boosts by letting clients cache responses. In the non-REST world, you may also want to add an ETag to an entity definition inside a traditional service contract – think of a scenario where a consumer persists its own representation of your entity, and wants to keep it in sync. Rather than load every entity by ID and check for changes, the consumer can send in a set of linked IDs and ETags, and you can return only the entities where the current ETag is different from the consumer’s version.  If your entity is a projection from various sources, you may not have a persistent ETag, so you need an efficient way to generate an ETag which is deterministic, so an entity with the same state always generates the same ETag. I have an implementation for a generic ETag generator on GitHub here: EntityTagger code sample. The essence is simple - we get the entity, serialize it and build a hash from the serialized value. Any changes to either the state or the structure of the entity will result in a different hash. To use it, just call SetETag, passing your populated object and a Func<> which acts as an accessor to the ETag property: EntityTagger.SetETag(user, x => x.ETag); The implementation is all in at 80 lines of code, which is all pretty straightforward: var eTagProperty = AsPropertyInfo(eTagPropertyAccessor); var originalETag = eTagProperty.GetValue(entity, null); try { ResetETag(entity, eTagPropertyAccessor); string json; var serializer = new DataContractJsonSerializer(entity.GetType()); using (var stream = new MemoryStream()) { serializer.WriteObject(stream, entity); json = Encoding.UTF8.GetString(stream.GetBuffer(), 0, (int)stream.Length); } var guid = GetDeterministicGuid(json); eTagProperty.SetValue(entity, guid.ToString(), null); //... There are a couple of helper methods to check if the object has changed since the ETag value was last set, and to reset the ETag. This implementation uses JSON to do the serializing rather than XML. Benefit - should be marginally more efficient as your hashing a much smaller serialized string; downside, JSON doesn't include namespaces or class names at the root level, so if you have two classes with the exact same structure but different names, then instances which have the same content will have the same ETag. You may want that behaviour, but change to use the XML DataContractSerializer if you think that will be an issue. If you can persist the ETag somewhere, it will save you server processing to load up the entity, but that will only apply to scenarios where you can reliably invalidate your ETag (e.g. if you control all the entry points where entity contents can be updated, then you can calculate and persist the new ETag with each update).

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