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• Understanding sql queries formulation methodoloy. How do you think while formulating Sql Queries

  - by Shantanu Gupta

  I have been working on sql server and front end coding and have usually faced problem formulating queries. I do understand most of the concepts of sql that are needed in formulating queries but whenever some new functionality comes into the picture that can be dont using sql query, i do usually fails resolving them. I am very comfortable with select queries using joins and all such things but when it comes to DML operation i usually fails For every query that i never done before I usually finds uncomfortable with that while creating them. Whenever I goes for an interview I usually faces this problem. Is it their some concept behind approaching on formulating sql queries. Eg. I need to create an sql query such that A table contain single column having duplicate record. I need to remove duplicate records. I know i can find the solution to this query very easily on Googling, but I want to know how everyone comes to the desired result. Is it something like Practice Makes Man Perfect i.e. once you did it, next time you will be able to formulate or their is some logic or concept behind.

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• How can I display multiple django modelformset forms together?

  - by JT

  I have a problem with needing to provide multiple model backed forms on the same page. I understand how to do this with single forms, i.e. just create both the forms call them something different then use the appropriate names in the template. Now how exactly do you expand that solution to work with modelformsets? The wrinkle, of course, is that each 'form' must be rendered together in the appropriate fieldset. For example I want my template to produce something like this: <fieldset> <label for="id_base-0-desc">Home Base Description:</label> <input id="id_base-0-desc" type="text" name="base-0-desc" maxlength="100" /> <label for="id_likes-0-icecream">Want ice cream?</label> <input type="checkbox" name="likes-0-icecream" id="id_likes-0-icecream" /> </fieldset> <fieldset> <label for="id_base-1-desc">Home Base Description:</label> <input id="id_base-1-desc" type="text" name="base-1-desc" maxlength="100" /> <label for="id_likes-1-icecream">Want ice cream?</label> <input type="checkbox" name="likes-1-icecream" id="id_likes-1-icecream" /> </fieldset> I am using a loop like this to process the results for base_form, likes_form in map(None, base_forms, likes_forms): which works as I'd expect (I'm using map because the # of forms can be different). The problem is that I can't figure out a way to do the same thing with the templating engine. The system does work if I layout all the base models together then all the likes models after wards, but it doesn't meet the layout requirements.

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• Comprehending the Semantic web and it's methods, syntax, vocabularies and languages

  - by DreamCodeR

  Hi. I have just been introduced to the semantic web and it's family of functions but I have a hard time understanding some of it, which I was hoping someone could explain to me. As far as I've understood, RDF can be written in several syntaxes. RDF/XML, Turtle, etc. Now, I understand XML. How it is presented and how it can be parsed. However, some people write in the turtle syntax, but how do they parse that information? I can't seem to find a single library for any language to "extract" the information written in a turtle syntax into another form. The same goes for N3. How can it be used? Executed or else? I seem to be able to understand RDFa. That it is a way to implement RDF into XHTML. For me that is a way to implement RDF into "something". But how can I compare that to turtle, N3, or the like? Thanks in advance.

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• How much effort do you have to put in to get gains from using SSE?

  - by John

  Case One Say you have a little class: class Point3D { private: float x,y,z; public: operator+=() ...etc }; Point3D &Point3D::operator+=(Point3D &other) { this->x += other.x; this->y += other.y; this->z += other.z; } A naive use of SSE would simply replace these function bodies with using a few intrinsics. But would we expect this to make much difference? MMX used to involve costly state cahnges IIRC, does SSE or are they just like other instructions? And even if there's no direct "use SSE" overhead, would moving the values into SSE registers and back out again really make it any faster? Case Two Instead, you're working with a less OO-based code base. Rather than an array/vector of Point3D objects, you simply have a big array of floats: float coordinateData[NUM_POINTS*3]; void add(int i,int j) //yes it's unsafe, no overlap check... example only { for (int x=0;x<3;++x) { coordinateData[i*3+x] += coordinateData[j*3+x]; } } What about use of SSE here? Any better? In conclusion Is trying to optimise single vector operations using SSE actually worthwhile, or is it really only valuable when doing bulk operations?

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• Calculate the digital root of a number

  - by Gregory Higley

  A digital root, according to Wikipedia, is "the number obtained by adding all the digits, then adding the digits of that number, and then continuing until a single-digit number is reached." For instance, the digital root of 99 is 9, because 9 + 9 = 18 and 1 + 8 = 9. My Haskell solution -- and I'm no expert -- is as follows. digitalRoot n | n < 10 = n | otherwise = digitalRoot . sum . map (\c -> read [c]) . show $ n As a language junky, I'm interested in seeing solutions in as many languages as possible, both to learn about those languages and possibly to learn new ways of using languages I already know. (And I know at least a bit of quite a few.) I'm particularly interested in the tightest, most elegant solutions in Haskell and REBOL, my two principal "hobby" languages, but any ol' language will do. (I pay the bills with unrelated projects in Objective C and C#.) Here's my (verbose) REBOL solution: digital-root: func [n [integer!] /local added expanded] [ either n < 10 [ n ][ expanded: copy [] foreach c to-string n [ append expanded to-integer to-string c ] added: 0 foreach e expanded [ added: added + e ] digital-root added ] ] EDIT: As some have pointed out either directly or indirectly, there's a quick one-line expression that can calculate this. You can find it in several of the answers below and in the linked Wikipedia page. (I've awarded Varun the answer, as the first to point it out.) Wish I'd known about that before, but we can still bend our brains with this question by avoiding solutions that involve that expression, if you're so inclined. If not, Crackoverflow has no shortage of questions to answer. :)

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• Should you declare methods using overloads or optional parameters in C# 4.0?

  - by Greg Beech

  I was watching Anders' talk about C# 4.0 and sneak preview of C# 5.0, and it got me thinking about when optional parameters are available in C# what is going to be the recommended way to declare methods that do not need all parameters specified? For example something like the FileStream class has about fifteen different constructors which can be divided into logical 'families' e.g. the ones below from a string, the ones from an IntPtr and the ones from a SafeFileHandle. FileStream(string,FileMode); FileStream(string,FileMode,FileAccess); FileStream(string,FileMode,FileAccess,FileShare); FileStream(string,FileMode,FileAccess,FileShare,int); FileStream(string,FileMode,FileAccess,FileShare,int,bool); It seems to me that this type of pattern could be simplified by having three constructors instead, and using optional parameters for the ones that can be defaulted, which would make the different families of constructors more distinct [note: I know this change will not be made in the BCL, I'm talking hypothetically for this type of situation]. What do you think? From C# 4.0 will it make more sense to make closely related groups of constructors and methods a single method with optional parameters, or is there a good reason to stick with the traditional many-overload mechanism?

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• Timer Service in ejb 3.1 - schedule calling timeout problem

  - by Greg

  Hi Guys, I have created simple example with @Singleton, @Schedule and @Timeout annotations to try if they would solve my problem. The scenario is this: EJB calls 'check' function every 5 secconds, and if certain conditions are met it will create single action timer that would invoke some long running process in asynchronous fashion. (it's sort of queue implementation type of thing). It then continues to check, but as long as long running process is there it won't start another one. Below is the code I came up with, but this solution does not work, because it looks like asynchronous call I'm making is in fact blocking my @Schedule method. @Singleton @Startup public class GenerationQueue { private Logger logger = Logger.getLogger(GenerationQueue.class.getName()); private List<String> queue = new ArrayList<String>(); private boolean available = true; @Resource TimerService timerService; @Schedule(persistent=true, minute="*", second="*/5", hour="*") public void checkQueueState() { logger.log(Level.INFO,"Queue state check: "+available+" size: "+queue.size()+", "+new Date()); if (available) { timerService.createSingleActionTimer(new Date(), new TimerConfig(null, false)); } } @Timeout private void generateReport(Timer timer) { logger.info("!!--timeout invoked here "+new Date()); available = false; try { Thread.sleep(1000*60*2); // something that lasts for a bit } catch (Exception e) {} available = true; logger.info("New report generation complete"); } What am I missing here or should I try different aproach? Any ideas most welcome :) Testing with Glassfish 3.0.1 latest build - forgot to mention

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• Can I copy an entire Magento application to a new server?

  - by Gapton

  I am quite new to Magento and I have a case where a client has a running ecommerce website built with Magento and is running on Amazon AWS EC2 server. If I can locate the web root (/var/www/) and download everything from it (say via FTP), I should be able to boot up my virtual machine with LAMP installed, put every single files in there and it should run, right? So I did just that, and Magento is giving me an error. I am guessing there are configs somewhere that needs to be changed in order to make it work, or even a lot of paths need to be changed etc. Also databases to be replicated. What are the typical things I should get right? Database is one, and the EC2 instance uses nginx while I use plain Apache, I guess that won't work straight out of the box, and I probably will have to install nginx and a lot of other stuffs. But basically, if I setup the environment right, it should run. Is my assumption correct? Thanks for answering!

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• How to format the Facebook news feed description of grouped app posts?

  - by JcFx

  I have an app which posts a message like this to a user's Facebook timeline: This is working fine, but if I post a few times, my posts get grouped on my news feed, and I get this: What settings should I use to control the way this news report appears? Instead of 'All about periods' and the page link in the box at the top, I'd like 'Body iQ Quiz' and the app description. Where would I set these values? And is it possible to make the grouped report say 'Jay cee Effex shared a link via Body iQ Quiz', the way the original post does? I'm posting from the Facebook AS3 API, and my post code looks like this: var auth:FacebookAuthResponse = Facebook.getAuthResponse(); var token:String = auth.accessToken; var user:String = auth.uid; var values:Object = { access_token: token, name: "Body iQ Quiz", picture: "http://a7.sphotos.ak.fbcdn.net/hphotos-ak-snc6/282950_427728213914009_630526316_n.jpg", link:"http://www.lil-lets.co.uk/en-GB/Wellbeing", description: "Women, how well do we know our bodies? Click here to find out what your Body iQ is.", message: result.FacebookBody + " " + result.FacebookTitle }; Facebook.api("/" + user + "/feed", handleSubmitFeed, values, URLRequestMethod.POST); ... but I'm not sure if this is something I can fix in code, or if the app configuration needs tweaking? NOTE: Some users report getting the latter format in their news feed even with a single post (I can't reproduce this), so perhaps grouping is a red herring, and the real question is how to format the news feed report of a timeline post?

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• Design for a Debate club assignment application

  - by Amir Rachum

  Hi all, For my university's debate club, I was asked to create an application to assign debate sessions and I'm having some difficulties as to come up with a good design for it. I will do it in Java. Here's what's needed: What you need to know about BP debates: There are four teams of 2 debaters each and a judge. The four groups are assigned a specific position: gov1, gov2, op1, op2. There is no significance to the order within a team. The goal of the application is to get as input the debaters who are present (for example, if there are 20 people, we will hold 2 debates) and assign them to teams and roles with regards to the history of each debater so that: Each debater should debate with (be on the same team) as many people as possible. Each debater should uniformly debate in different positions. The debate should be fair - debaters have different levels of experience and this should be as even as possible - i.e., there shouldn't be a team of two very experienced debaters and a team of junior debaters. There should be an option for the user to restrict the assignment in various ways, such as: Specifying that two people should debate together, in a specific position or not. Specifying that a single debater should be in a specific position, regardless of the partner. etc... If anyone can try to give me some pointers for a design for this application, I'll be so thankful! Also, I've never implemented a GUI before, so I'd appreciate some pointers on that as well, but it's not the major issue right now.

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• Powerpoint displays a "can't start the application" error when an Excel Chart object is embedded in

  - by A9S6

  This is a very common problem when Excel Worksheet or Chart is embedded into Word or Powerpoint. I am seeing this problem in both Word and Powerpoint and the reason it seems is the COM addin attached to Excel. The COM addin is written in C# (.NET). See the attached images for error dialogs. I debugged the addin and found a very strange behavior. The OnConnection(...), OnDisConnection(...) etc methods in the COM addin works fine until I add an event handler to the code. i.e. handle the Worksheet_SheetChange, SelectionChange or any similar event available in Excel. As soon as I add even a single event handler (though my code has several), Word and Powerpoint start complaining and do not Activate the embedded object. On some of the posts on the internet, people have been asked to remove the anti-virus addins for office (none in my case) so this makes me believe that the problem is somewhat related to COM addins which are loaded when the host app activates the object. Does anyone have any idea of whats happening here?

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• Loading Native library to external Package in Eclipse not working. is it a Bug?

  - by TacB0sS

  I was about to report a but to Eclipse, but I was thinking to give this a chance here first: If I add an external package, the application cannot find the referenced native library, except in the case specified at the below: If my workspace consists of a single project, and I import an external package 'EX_package.jar' from a folder outside of the project folder, I can assign a folder to the native library location via: mouse over package - right click - properties - Native Library - Enter your folder. This does not work. In runtime the application does not load the library, System.mapLibraryName(Path) also does not work. Further more, if I create a User Library, and add the package to it and define a folder for the native library it still does not. If it works for you then I have a major bug since it does not work on my computer I test this in any combination I could think of, including adding the path to the windows PATH parameter, and so many other ways I can't even start to remember, nothing worked, I played with this for hours and had a colleague try to assist me, but we both came up empty. Further more, if I have a main project that is dependent on few other projects in my workspace, and they all need to use the same 'EX_package.jar' I MUST supply a HARD COPY INTO EACH OF THEM, it will ONLY (I can't stress the ONLYNESS, I got freaked out by this) work if I have a hard copy of the package in ALL of the project folders that the main project has a dependency on, and ONLY if I configure the Native path in each of them!! This also didn't do the trick. please tell me there is a solution to this, this drives me nuts... Thanks, Adam Zehavi.

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• MalformedURLException with file URI

  - by Paul Reiners

  While executing the following code: doc = builder.parse(file); where doc is an instance of org.w3c.dom.Document and builder is an instance of javax.xml.parsers.DocumentBuilder, I'm getting the following exception: Exception in thread "main" java.net.MalformedURLException: unknown protocol: c at java.net.URL.<init>(Unknown Source) at java.net.URL.<init>(Unknown Source) at java.net.URL.<init>(Unknown Source) at com.sun.org.apache.xerces.internal.impl.XMLEntityManager.setupCurrentEntity(Unknown Source) at com.sun.org.apache.xerces.internal.impl.XMLEntityManager.startEntity(Unknown Source) at com.sun.org.apache.xerces.internal.impl.XMLEntityManager.startDTDEntity(Unknown Source) at com.sun.org.apache.xerces.internal.impl.XMLDTDScannerImpl.setInputSource(Unknown Source) at com.sun.org.apache.xerces.internal.impl.XMLDocumentScannerImpl$DTDDriver.dispatch(Unknown Source) at com.sun.org.apache.xerces.internal.impl.XMLDocumentScannerImpl$DTDDriver.next(Unknown Source) at com.sun.org.apache.xerces.internal.impl.XMLDocumentScannerImpl$PrologDriver.next(Unknown Source) at com.sun.org.apache.xerces.internal.impl.XMLDocumentScannerImpl.next(Unknown Source) at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl.scanDocument(Unknown Source) at com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(Unknown Source) at com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(Unknown Source) at com.sun.org.apache.xerces.internal.parsers.XMLParser.parse(Unknown Source) at com.sun.org.apache.xerces.internal.parsers.DOMParser.parse(Unknown Source) at com.sun.org.apache.xerces.internal.jaxp.DocumentBuilderImpl.parse(Unknown Source) at javax.xml.parsers.DocumentBuilder.parse(Unknown Source) at com.acme.ItemToThetaValues.createFiles(ItemToThetaValues.java:47) It's choking on this line of the file: <!DOCTYPE questestinterop SYSTEM "C:\Program Files\Acme\parsers\acme_full.dtd"> I am not getting this error on my machine, while a user is getting it on his machine. We are both using version 6 of the Sun JRE. This error also occurs when he's uses double backslashes in the path instead of single backslashes and when he uses forward slashes instead of backslashes. First of all, is the XML correct? Is the path expressed correctly? Second of all, why is this error occurring on one computer but not on another?

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• Start-job to call script from main

  - by Naveen

  I have three script , from main - 1-script , I am calling other two scripts. so that I can execute both scripts parallely because it's taking too much time in sequential order. Only variables are different in the script. How can I merge script 2 & 3 in a single script so that I can call from the main script and it will run as parallel. 1 CompareCtrlM... Completed False localhost ######################... 3 CompareCtrlM... Completed True localhost ######################... Main -1 Script Start-Job -Name "LoopComparectrlMasterModel" -filepath D:\tmp\naveen\Script\CompareCtrlMasterCtrlModel.ps1 Start-Job -Name "LoopCompareProdMasterModel" -filepath D:\idv\CA\rcm_data\tmp\work\CompareCtrlMasterProdModel.ps1 Wait-Job -Name "LoopComparectrlMasterModel" Receive-Job "LoopComparectrlMasterModel" Wait-Job -Name "LoopCompareProdMasterModel" Receive-Job "LoopCompareProdMasterModel" =============================================== Script 2- for ($i = 1 ; $i -lt 3; $i++){ $jobName = 'CompareCtrlMasterProdModelESS$i' echolog $THISSCRIPT $RCM_UPDATE_LOG_FILE $LLINFO ("Starting Ctrl Master-Prod Model comparison #" + $i + ", create SBT") $rc = CreateSbtFile $sbtCompareCtrlMasterProdModel[$i-1] $cfgProdModel $cfgCtrlMaster "" "" $SBT_MODE_COMPARE_CFGS_FULL $workDir Start-Job -Name "$jobName" -filepath $ExecuteSbtWithRcmClientTool -ArgumentList $sbtCompareCtrlMasterProdModel[$i-1],"",$true,$false | Out-Null Wait-Job -Name "$jobName" $results = Receive-Job -Name $jobName } ========================================================================== Script 3- for ($i = 1 ; $i -lt 3; $i++){ $jobName = 'CompareCtrlMasterCtrlModelESS$i' echolog $THISSCRIPT $RCM_UPDATE_LOG_FILE $LLINFO ("Starting Ctrl Master-Ctrl Model comparison #" + $i + ", create SBT") $rc = CreateSbtFile $sbtCompareCtrlMasterCtrlModel[$i-1] $cfgCtrlModel $cfgCtrlMaster "" "" $SBT_MODE_COMPARE_CFGS_FULL $workDir Start-Job -Name "$jobName" -filepath $ExecuteSbtWithRcmClientTool -ArgumentList $sbtCompareCtrlMasterCtrlModel[$i-1],"",$true,$false | Out-Null Wait-Job -Name "$jobName" $results = Receive-Job -Name $jobName } write-output $results Thanks a lot for help Regards Naven

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• Associating an object with another object for GC clearup

  - by thecoop

  Is there any way of associating an object instance (object A) with a second object (object B) in a generalised way, so that when B gets collected A becomes eligable for collection? The same behaviour that would happen if B had an instance variable pointing to A, but without explicitly changing the class definition of B, and being able to do this in a dynamic way? The same sort of effect could be done by using the Component.Disposed event in a funky way, but I don't want to make B disposable EDIT I'm basically creating a cache of objects that are associated with a single 'root' object, and I don't want the cache to be static, as there can be lots of root objects using different caches, so lots of memory will be used up when a root object is no longer used but the cached objects are still around. So, I want a collection of cached objects to be associated with each 'root' object, without changing the root object definition. Sort of like metadata of an extra object reference attached to each root object instance. That way, each collection will get collected when the root object is collected, and not hang around like they would if a static cache was used.

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• Destroy process-less console windows left by Visual Studio debug sessions

  - by jon hanson

  A known bug with security update KB978037 can occur with Visual Studio 2003 (and 2008) where sometimes if you restart a debugging session on a console app then the console window doesn't get closed even though the owner process no longer exists. The problem is discussed further here: http://stackoverflow.com/questions/2402875/visual-studio-debug-console-sometimes-stays-open-and-is-impossible-to-close These zombie windows then can not be closed via the Taskbar or via the TaskManager, and typically require a power off/on to get rid of them. Over the period of even a single day you can accumulate quite a few of them, which clog up your TaskBar and are generally annoying. I thought I would knock up a simple C++ Win32 utility to attempt to call DestroyWindow() on these windows by passing the windows handle as a cmd-line argument and converting it to a HWND. I'm converting the handle from a string by parsing it as a DWORD then casting the DWORD to a HWND. This appears to be working as if I call GetWindowInfo() on the handle it succeeds. However calling DestroyWindow() on the handle fails with error 5 (access denied), presumably because the caller process (i.e. my app) doesn't own the window in question. Any ideas as to how I might get rid of the zombie windows, either via the above approach or any other alternative short of rebooting? I'm in a corporate environment so installing/uninstalling updates/service-packs etc isn't an option.

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• L10N: Trusted test data for Locale Specific Sorting

  - by Chris Betti

  I'm working on an internationalized database application that supports multiple locales in a single instance. When international users sort data in the applications built on top of the database, the database theoretically sorts the data using a collation appropriate to the locale associated with the data the user is viewing. I'm trying to find sorted lists of words that meet two criteria: the sorted order follows the collation rules for the locale the words listed will allow me to exercise most / all of the specific collation rules for the locale I'm having trouble finding such trusted test data. Are such sort-testing datasets currently available, and if so, what / where are they? "words.en.txt" is an example text file containing American English text: Andrew Brian Chris Zachary I am planning on loading the list of words into my database in randomized order, and checking to see if sorting the list conforms to the original input. Because I am not fluent in any language other than English, I do not know how to create sample datasets like the following sample one in French (call it "words.fr.txt"): cote côte coté côté The French prefer diacritical marks to be ordered right to left. If you sorted that using code-point order, it likely comes out like this (which is an incorrect collation): cote coté côte côté Thank you for the help, Chris

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• Does Android AsyncTaskQueue or similar exist?

  - by Ben L.

  I read somewhere (and have observed) that starting threads is slow. I always assumed that AsyncTask created and reused a single thread because it required being started inside the UI thread. The following (anonymized) code is called from a ListAdapter's getView method to load images asynchronously. It works well until the user moves the list quickly, and then it becomes "janky". final File imageFile = new File(getCacheDir().getPath() + "/img/" + p.image); image.setVisibility(View.GONE); view.findViewById(R.id.imageLoading).setVisibility(View.VISIBLE); (new AsyncTask<Void, Void, Bitmap>() { @Override protected Bitmap doInBackground(Void... params) { try { Bitmap image; if (!imageFile.exists() || imageFile.length() == 0) { image = BitmapFactory.decodeStream(new URL( "http://example.com/images/" + p.image).openStream()); image.compress(Bitmap.CompressFormat.JPEG, 85, new FileOutputStream(imageFile)); image.recycle(); } image = BitmapFactory.decodeFile(imageFile.getPath(), bitmapOptions); return image; } catch (MalformedURLException ex) { // TODO Auto-generated catch block ex.printStackTrace(); return null; } catch (IOException ex) { // TODO Auto-generated catch block ex.printStackTrace(); return null; } } @Override protected void onPostExecute(Bitmap image) { if (view.getTag() != p) // The view was recycled. return; view.findViewById(R.id.imageLoading).setVisibility( View.GONE); view.findViewById(R.id.image) .setVisibility(View.VISIBLE); ((ImageView) view.findViewById(R.id.image)) .setImageBitmap(image); } }).execute(); I'm thinking that a queue-based method would work better, but I'm wondering if there is one or if I should attempt to create my own implementation.

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• Technical choices in unmarshaling hash-consed data

  - by Pascal Cuoq

  There seems to be quite a bit of folklore knowledge floating about in restricted circles about the pitfalls of hash-consing combined with marshaling-unmarshaling of data. I am looking for citable references to these tidbits. For instance, someone once pointed me to library aterm and mentioned that the authors had clearly thought about this and that the representation on disk was bottom-up (children of a node come before the node itself in the data stream). This is indeed the right way to do things when you need to re-share each node (with a possible identical node already in memory). This re-sharing pass needs to be done bottom-up, so the unmarshaling itself might as well be, too, so that it's possible to do everything in a single pass. I am in the process of describing difficulties encountered in our own context, and the solutions we found. I would appreciate any citable reference to the kind of aforementioned folklore knowledge. Some people obviously have encountered the problems before (the aterm library is only one example). But I didn't find anything in writing. Even the little piece of information I have about aterm is hear-say. I am not worried it's not reliable (you can't make this up), but "personal communication" and "look how it's done in the source code" are considered poor form in citations. I have enough references on hash-consing alone. I am only interested in references where it interferes with other aspects of programming, such as marshaling or distribution.

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• What is a good way to assign order #s to ordered rows in a table in Sybase

  - by DVK

  I have a table T (structure below) which initially contains all-NULL values in an integer order column: col1 varchar(30), col2 varchar(30), order int NULL I also have a way to order the "colN" columns, e.g. SELECT * FROM T ORDER BY some_expression_involving_col1_and_col2 What's the best way to assign - IN SQL - numeric order values 1-N to the order table, so that the order values match the order of rows returned by the above ORDER BY? In other words, I would like a single query (Sybase SQL syntax so no Oracle's rowcount) which assigns order values so that SELECT * FROM T ORDER BY order returns 100% same order of rows as the query above. The query does NOT necessarily need to update the table T in place, I'm OK with creating a copy of the table T2 if that'll make the query simpler. NOTE1: A solution must be real query or a set of queries, not involving a loop or a cursor. NOTE2: Assume that the data is uniquely orderable according to the order by above - no need to worry about situation when 2 rows can be assigned the same order at random. NOTE3: I would prefer a generic solution, but if you wish a specific example of ordering expression, let's say: SELECT * FROM T ORDER BY CASE WHEN col1="" THEN "AAAAAA" ELSE col1 END, ISNULL(col2, "ZZZ")

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• Wait on multiple condition variables on Linux without unnecessary sleeps?

  - by Joseph Garvin

  I'm writing a latency sensitive app that in effect wants to wait on multiple condition variables at once. I've read before of several ways to get this functionality on Linux (apparently this is builtin on Windows), but none of them seem suitable for my app. The methods I know of are: Have one thread wait on each of the condition variables you want to wait on, which when woken will signal a single condition variable which you wait on instead. Cycling through multiple condition variables with a timed wait. Writing dummy bytes to files or pipes instead, and polling on those. #1 & #2 are unsuitable because they cause unnecessary sleeping. With #1, you have to wait for the dummy thread to wake up, then signal the real thread, then for the real thread to wake up, instead of the real thread just waking up to begin with -- the extra scheduler quantum spent on this actually matters for my app, and I'd prefer not to have to use a full fledged RTOS. #2 is even worse, you potentially spend N * timeout time asleep, or your timeout will be 0 in which case you never sleep (endlessly burning CPU and starving other threads is also bad). For #3, pipes are problematic because if the thread being 'signaled' is busy or even crashes (I'm in fact dealing with separate process rather than threads -- the mutexes and conditions would be stored in shared memory), then the writing thread will be stuck because the pipe's buffer will be full, as will any other clients. Files are problematic because you'd be growing it endlessly the longer the app ran. Is there a better way to do this? Curious for answers appropriate for Solaris as well.

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• Is there a way to get number of connections in Signalr hub group?

  - by pajo

  Here is my problem, I want to track if user is online or offline and notify other clients about it. I'm using hubs and implemented both IConnected and IDisconnect interfaces. My idea was to send notification to all clients when hub detects connect or disconnect. By default when user refreshes page he will get new connection id and eventually previous connection will call disconnect notifying other clients user is offline even though he's actually online. I tired to use my own ConnectionIdFactory returning username for connection id but with multiple tabs opened at some point it will detect user connectionid disconnected and after that client side hub will try to unsuccessfully connect to the hub in endless loop wasting memory and cpu making browser almost unusable. I needed to fix it fast so I removed my factory and now I add every new connection to the group using username, so I can easily notify single user on all connections, but then I have problem of detecting if user is online or offline as I don't know how many active connection user is having. So I'm wondering is there a way to get number of connections in one group? Or if anybody has some better idea how to track when user goes offline? I'm using Signalr 0.4

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• How to make active services highly available?

  - by Jader Dias

  I know that with Network Load Balancing and Failover Clusteringwe can make passive services highly available. But what about active apps? Example: One of my apps retrieves some content from a external resource in a fixed interval. I have imagined the following scenarios: Run it in a single machine. Problem: if this instance falls, the content won't be retrieved Run it in each machine of the cluster. Problem: the content will be retrieved multiple times Have it in each machine of the cluster, but run it only in one of them. Each instance will have to check some sort of common resource to decide whether it its turn to do the task or not. When I was thinking about the solution #3 I have wondered what should be the common resource. I have thought of creating a table in the database, where we could use it to get a global lock. Is this the best solution? How does people usually do this? By the way it's a C# .NET WCF app running on Windows Server 2008

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• C# ASP.NET Binding Controls via Generic Method

  - by OverTech

  I have a few web applications that I maintain and I find myself very often writing the same block of code over and over again to bind a GridView to a data source. I'm trying to create a Generic method to handle data binding but I'm having trouble getting it to work with Repeaters and DataLists. Here is the Generic method I have so far: public void BindControl<T>(T control, SqlCommand sql) where T : System.Web.UI.WebControls.BaseDataBoundControl { cmd = sql; cn.Open(); SqlDataReader dr = cmd.ExecuteReader(); if (dr.HasRows) { control.DataSource = dr; control.DataBind(); } dr.Close(); cn.Close(); } That way I can just define my CommandText then make a call to "BindControls(myGridView, cmd)" instead of retyping this same basic block of code every time I need to bind a grid. The problem is, this doesn't work with Repeaters or DataLists. Each of these controls inherit their respective "DataSource" and "DataBind" methods from different classes. Someone on another forum suggested that I implement an interface, but I'm not sure how to make that work either. The GridView, Datalist and Repeater get their respective "DataBind" methods from BaseDataBoundControl, BaseDataList, and Repeater classes. How would I go about creating a single interface to tie them all together? Or am I better off just using 3 overloads for this method? Dave

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• How to implement Horner's scheme for multivariate polynomials?

  - by gsreynolds

  Background I need to solve polynomials in multiple variables using Horner's scheme in Fortran90/95. The main reason for doing this is the increased efficiency and accuracy that occurs when using Horner's scheme to evaluate polynomials. I currently have an implementation of Horner's scheme for univariate/single variable polynomials. However, developing a function to evaluate multivariate polynomials using Horner's scheme is proving to be beyond me. An example bivariate polynomial would be: 12x^2y^2+8x^2y+6xy^2+4xy+2x+2y which would factorised to x(x(y(12y+8))+y(6y+4)+2)+2y and then evaluated for particular values of x & y. Research I've done my research and found a number of papers such as: staff.ustc.edu.cn/~xinmao/ISSAC05/pages/bulletins/articles/147/hornercorrected.pdf citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.40.8637&rep=rep1&type=pdf www.is.titech.ac.jp/~kojima/articles/B-433.pdf Problem However, I'm not a mathematician or computer scientist, so I'm having trouble with the mathematics used to convey the algorithms and ideas. As far as I can tell the basic strategy is to turn a multivariate polynomial into separate univariate polynomials and compute it that way. Can anyone help me? If anyone could help me turn the algorithms into pseudo-code that I can implement into Fortran myself, I would be very grateful.

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