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What's so bad about building XML with string concatenation?

- by wsanville

In the thread What’s your favorite “programmer ignorance” pet peeve?, the following answer appears, with a large amount of upvotes: Programmers who build XML using string concatenation. My question is, why is building XML via string concatenation (such as a StringBuilder in C#) bad? I've done this several times in the past, as it's sometimes the quickest way for me to get from point A to point B when to comes to the data structures/objects I'm working with. So far, I have come up with a few reasons why this isn't the greatest approach, but is there something I'm overlooking? Why should this be avoided? Probably the biggest reason I can think of is you need to escape your strings manually, and most programmers will forget this. It will work great for them when they test it, but then "randomly" their apps will fail when someone throws an & symbol in their input somewhere. Ok, I'll buy this, but it's really easy to prevent the problem (SecurityElement.Escape to name one). When I do this, I usually omit the XML declaration (i.e. <?xml version="1.0"?>). Is this harmful? Performance penalties? If you stick with proper string concatenation (i.e. StringBuilder), is this anything to be concerned about? Presumably, a class like XmlWriter will also need to do a bit of string manipulation... There are more elegant ways of generating XML, such as using XmlSerializer to automatically serialize/deserialize your classes. Ok sure, I agree. C# has a ton of useful classes for this, but sometimes I don't want to make a class for something really quick, like writing out a log file or something. Is this just me being lazy? If I am doing something "real" this is my preferred approach for dealing w/ XML.

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ASP.NET: Page HTML head rendering

- by Fabian

I've been trying to figure out the best way to custom render the <head> element of a pag to get rid of the extra line breaks which is caused by <head runat="server">, so its properly formatted. So far the only thing i've found which works is the following: protected override void Render(HtmlTextWriter writer) { StringWriter stringWriter = new StringWriter(); HtmlTextWriter htmlTextWriter = new HtmlTextWriter(stringWriter); base.Render(htmlTextWriter); htmlTextWriter.Close(); string html = stringWriter.ToString(); string newHTML = html.Replace("\r\n\r\n<!DOCTYPE", "<!DOCTYPE") .Replace("\r\n<html", "<html") .Replace("<title>\r\n\t", "<title>") .Replace("\r\n</title>", "</title>") .Replace("</head>", "\n</head>"); writer.Write(newHTML); } I define my had tag like Now i have 2 questions: How does the above code affect the performance (so is this viable in an production environment)? Is there a better way to do this, for example a method which i can override to just custom render the <head>? Oh yeah ASP.NET MVC is not an option.

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Is there an efficient way in LINQ to use a contains match if and only if there is no exact match?

- by Peter

I have an application where I am taking a large number of 'product names' input by a user and retrieving some information about each product. The problem is, the user may input a partial name or even a wrong name, so I want to return the closest matches for further selection. Essentially if product name A exactly matches a record, return that, otherwise return any contains matches. Otherwise return null. I have done this with three separate statements, and I was wondering if there was a more efficient way to do this. I am using LINQ to EF, but I materialize the products to a list first for performance reasons. productNames is a List of product names (input by the user). products is a List of product 'records' var directMatches = (from s in productNames join p in products on s.ToLower() equals p.name.ToLower() into result from r in result.DefaultIfEmpty() select new {Key = s, Product = r}); var containsMatches = (from d in directMatches from p in products where d.Product == null && p.name.ToLower().Contains(d.Key) select new { d.Key, Product = p }); var matches = from d in directMatches join c in containsMatches on d.Key equals c.Key into result from r in result.DefaultIfEmpty() select new {d.Key, Product = d.Product ?? (r != null ? r.Product: null) };

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Is locking on the requested object a bad idea?

- by Quick Joe Smith

Most advice on thread safety involves some variation of the following pattern: public class Thing { private static readonly object padlock = new object(); private string stuff, andNonsense; public string Stuff { get { lock (Thing.padlock) { if (this.stuff == null) this.stuff = "Threadsafe!"; } return this.stuff; } } public string AndNonsense { get { lock (Thing.padlock) { if (this.andNonsense == null) this.andNonsense = "Also threadsafe!"; } return this.andNonsense; } } // Rest of class... } In cases where the get operations are expensive and unrelated, a single locking object is unsuitable because a call to Stuff would block all calls to AndNonsense, degrading performance. And rather than create a lock object for each call, wouldn't it be better to acquire the lock on the member itself (assuming it is not something that implements SyncRoot or somesuch for that purpose? For example: public string Stuff { get { lock (this.stuff) { // Pretend that this is a very expensive operation. if (this.stuff == null) this.stuff = "Still threadsafe and good?"; } return this.stuff; } } Strangely, I have never seen this approach recommended or warned against. Am I missing something obvious?

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do the Python libraries have a natural dependence on the global namespace?

- by msw

I first ran into this when trying to determine the relative performance of two generators: t = timeit.repeat('g.get()', setup='g = my_generator()') So I dug into the timeit module and found that the setup and statement are evaluated with their own private, initially empty namespaces so naturally the binding of g never becomes accessible to the g.get() statement. The obvious solution is to wrap them into a class, thus adding to the global namespace. I bumped into this again when attempting, in another project, to use the multiprocessing module to divide a task among workers. I even bundled everything nicely into a class but unfortunately the call pool.apply_async(runmc, arg) fails with a PicklingError because buried inside the work object that runmc instantiates is (effectively) an assignment: self.predicate = lambda x, y: x > y so the whole object can't be (understandably) pickled and whereas: def foo(x, y): return x > y pickle.dumps(foo) is fine, the sequence bar = lambda x, y: x > y yields True from callable(bar) and from type(bar), but it Can't pickle <function <lambda> at 0xb759b764>: it's not found as __main__.<lambda>. I've given only code fragments because I can easily fix these cases by merely pulling them out into module or object level defs. The bug here appears to be in my understanding of the semantics of namespace use in general. If the nature of the language requires that I create more def statements I'll happily do so; I fear that I'm missing an essential concept though. Why is there such a strong reliance on the global namespace? Or, what am I failing to understand? Namespaces are one honking great idea -- let's do more of those!

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The correct usage of nested #pragma omp for directives

- by GoldenLee

The following code runs like a charm before OpenMP parallelization was applied. In fact, the following code was in a state of endless loop! I'm sure that's result from my incorrect use to the OpenMP directives. Would you please show me the correct way? Thank you very much. #pragma omp parallel for for (int nY = nYTop; nY <= nYBottom; nY++) { for (int nX = nXLeft; nX <= nXRight; nX++) { // Use look-up table for performance dLon = theApp.m_LonLatLUT.LonGrid()[nY][nX] + m_FavoriteSVISSRParams.m_dNadirLon; dLat = theApp.m_LonLatLUT.LatGrid()[nY][nX]; // If you don't want to use longitude/latitude look-up table, uncomment the following line //NOMGeoLocate.XYToGEO(dLon, dLat, nX, nY); if (dLon > 180 || dLat > 180) { continue; } if (Navigation.GeoToXY(dX, dY, dLon, dLat, 0) > 0) { continue; } // Skip void data scanline dY = dY - nScanlineOffset; // Compute coefficients as well as its four neighboring points' values nX1 = int(dX); nX2 = nX1 + 1; nY1 = int(dY); nY2 = nY1 + 1; dCx = dX - nX1; dCy = dY - nY1; dP1 = pIRChannelData->operator [](nY1)[nX1]; dP2 = pIRChannelData->operator [](nY1)[nX2]; dP3 = pIRChannelData->operator [](nY2)[nX1]; dP4 = pIRChannelData->operator [](nY2)[nX2]; // Bilinear interpolation usNomDataBlock[nY][nX] = (unsigned short)BilinearInterpolation(dCx, dCy, dP1, dP2, dP3, dP4); } }

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How to get a debug flow of execution in C++

- by Rich

Hi, I work on a global trading system which supports many users. Each user can book,amend,edit,delete trades. The system is regulated by a central deal capture service. The deal capture service informs all the user of any updates that occur. The problem comes when we have crashes, as the production environment is impossible to re-create on a test system, I have to rely on crash dumps and log files. However this doesn't tell me what the user has been doing. I'd like a system that would (at the time of crashing) dump out a history of what the user has been doing. Anything that I add has to go into the live environment so it can't impact performance too much. Ideas wise I was thinking of a MACRO at the top of each function which acted like a stack trace (only I could supply additional user information, like trade id's, user dialog choices, etc ..) The system would record stack traces (on a per thread basis) and keep a history in a cyclic buffer (varying in size, depending on how much history you wanted to capture). Then on crash, I could dump this history stack. I'd really like to hear if anyone has a better solution, or if anyone knows of an existing framework? Thanks Rich

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Memory Leak in returning NSMutableArray from class

- by Structurer

Hi I am quite new to Objective C for the iPhone, so I hope you wont kill me for asking a simple question. I have made an App that works fine, except that Instruments reports memory leaks from the class below. I use it to store settings from one class and then retrieve them from another class. These settings are stored on a file so they can be retrieved every time the App is ran. What can I do do release the "setting" and is there anything that can be done to call (use) the class in a smarter way? Thanks ----- Below is Settings.m ----- import "Settings.h" @implementation Settings @synthesize settings; -(NSString *)dataFilePath // Return path for settingfile, including filename { NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES); NSString *documentsDirectory = [paths objectAtIndex:0]; return [documentsDirectory stringByAppendingPathComponent:kUserSettingsFileName]; } -(NSMutableArray *)getParameters // Return settings from disk after checking if file exist (if not create with default values) { NSString *filePath = [self dataFilePath]; if ([[NSFileManager defaultManager] fileExistsAtPath:filePath]) // Getting data from file { settings = [[NSMutableArray alloc] initWithContentsOfFile:filePath]; } else // Creating default settings { settings = [[NSMutableArray alloc] initWithObjects: [NSNumber numberWithInteger:50], [NSNumber numberWithInteger:50], nil]; [settings writeToFile:[self dataFilePath] atomically:YES]; } return settings; } ----- Below is my other class from where I call my Settings class ----- // Get settings from file Settings *aSetting = [[Settings alloc] init]; mySettings = [aSetting getParameters]; [aSetting release];

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Grouping Categorized Data In WPF.

- by VoidDweller

Here is what I am trying to do. Dynamic Category: Columns can be 0 or more. Must contain 1 or more Type Columns. Will only be displayed if any row contains Type Column data associated with it. Data Rows: Will be added Asynchronously. Will be grouped by a Common Category column. Will add a Dynamic Category if it does not yet exist. Will add a Type Column if it does not yet exist within its appropriate Dynamic Category. Platform Info: WPF .Net 3.5 sp1 C# MVVM I have a few partially functional prototypes, but each has it's own major set of problems. Can any of you give me some guidance on this? Envision this nicely styled. :-) -------------------------------------------------------------------------- |[ Common Category ]|[ Dynamic Category 0 ]|[ Dynamic Category N ]| -------------------------------------------------------------------------- |[Header 1]|[Header 2]|[ Type 0 ]|[ Type N ]|[ Type 0 ]|[ Type N ]| -------------------------------------------------------------------------- |[Data 2 Group] | -------------------------------------------------------------------------- | Data A | Data 2 || Null | Data 1 || Data 0 | Data 1 || | Data B | Data 2 || Data 0 | Null || Data 0 | Data 1 || -------------------------------------------------------------------------- |[Data 1 Group] | -------------------------------------------------------------------------- | Data C | Data 1 || Null | Data 1 || Data 0 | Data 1 || | Data D | Data 1 || Null | Null || Data 0 | Null || -------------------------------------------------------------------------- Edit: Sorting and Paging is not necessary. I have looked at nested ListViews and DataGrids, dynamically building a Grid. Dynamically building a Grid and leveraging the SharedSizeGroup property seems the most promising strategy, but I am concerned about performance. Would a better approach be to consider this a dynamic report? If so, what should I be looking at? Thanks for your help.

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Gradual memory leak and slowdown in loop

- by Benji XVI

I have a simple foundation tool that exports every frame of a movie as a .tiff file. Here is the relevant code: NSString* movieLoc = [NSString stringWithCString:argv[1]]; QTMovie *sourceMovie = [QTMovie movieWithFile:movieLoc error:nil]; int i=0; while (QTTimeCompare([sourceMovie currentTime], [sourceMovie duration]) != NSOrderedSame) { // save image of movie to disk NSAutoreleasePool *arp = [[NSAutoreleasePool alloc] init]; NSString *filePath = [NSString stringWithFormat:@"/somelocation_%d.tiff", i++]; NSData *currentImageData = [[sourceMovie currentFrameImage] TIFFRepresentation]; [currentImageData writeToFile:filePath atomically:NO]; NSLog(@"%@", filePath); [sourceMovie stepForward]; [arp release]; } [pool drain]; return 0; As you can see, in order to prevent very large memory buildups with the various transparently-autoreleased variables in the loop, we create, and flush, an autoreleasepool with every run through the loop. However, over the course of stepping through a movie, the amount of memory used by the program still gradually increases, and the speed at which frames are processed drops precipitously. (From ~0.5 seconds per frame at the start, to ~2 seconds per frame by the 250th frame.) The only thing I can think can be causing the gradual memory leak is a buildup of the NSAutoreleasePool objects themselves. Am I right in thinking they will only be deallocated when the outer pool is released? If so, is there a better memory management solution here? Creating a pool every run through the loop seems a little hacky. And if not, what is causing the slow memory leak? (It is not NSStrings, and much too slow to be NSImages or NSDatas.) And what could be causing the slowdown?

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Get the first and last posts in a thread

- by Grampa

I am trying to code a forum website and I want to display a list of threads. Each thread should be accompanied by info about the first post (the "head" of the thread) as well as the last. My current database structure is the following: threads table: id - int, PK, not NULL, auto-increment name - varchar(255) posts table: id - int, PK, not NULL, auto-increment thread_id - FK for threads The tables have other fields as well, but they are not relevant for the query. I am interested in querying threads and somehow JOINing with posts so that I obtain both the first and last post for each thread in a single query (with no subqueries). So far I am able to do it using multiple queries, and I have defined the first post as being: SELECT * FROM threads t LEFT JOIN posts p ON t.id = p.thread_id ORDER BY p.id LIMIT 0, 1 The last post is pretty much the same except for ORDER BY id DESC. Now, I could select multiple threads with their first or last posts, by doing: SELECT * FROM threads t LEFT JOIN posts p ON t.id = p.thread_id ORDER BY p.id GROUP BY t.id But of course I can't get both at once, since I would need to sort both ASC and DESC at the same time. What is the solution here? Is it even possible to use a single query? Is there any way I could change the structure of my tables to facilitate this? If this is not doable, then what tips could you give me to improve the query performance in this particular situation?

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Obfuscator for .NET assembly (Maybe just a C++ obfuscator?)

- by Pirate for Profit

The software company I work for is using a ton of open source LGPL/BSD/MIT C++ code that we have written wrappers around to port "helper classes" into a .NET assembly, via C++/CLI. These libraries have wrapped old cryptic APIs into easy-to-use ones based on common sense, and will be very helpful for a lot of different tasks will be included in many future client's applications, and we might even license it to other software companies in the same field. So naturally we are tasked with looking into solutions for securing the code from prying eyes. What we're trying to do is stop the casual observer from seeing what's going on. Now I have hacked some crazy shit in EverQuest and other video games in my day so I know with enough tireless effort anything can be done. But we don't want to make it easy for whomever. To the point, besides the Visual Studio compiler's optimizations, is there's a C++ obfuscator or .NET assembly obfuscator (after it's been built o.O) or something that would scramble everything up, re-arrange data structures, string constants, etc. idk? And if such a thing exists, we'd be curious to know how that would impact performance, as some sections of code are time critical (funny saying that using a managed M$ framework).

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Approach for caching data from data logger

- by filip-fku

Greetings, I've been working on a C#.NET app that interacts with a data logger. The user can query and obtain logs for a specified time period, and view plots of the data. Typically a new data log is created every minute and stores a measurement for a few parameters. To get meaningful information out of the logger, a reasonable number of logs need to be acquired - data for at least a few days. The hardware interface is a UART to USB module on the device, which restricts transfers to a maximum of about 30 logs/second. This becomes quite slow when reading in the data acquired over a number of days/weeks. What I would like to do is improve the perceived performance for the user. I realize that with the hardware speed limitation the user will have to wait for the full download cycle at least the first time they acquire a larger set of data. My goal is to cache all data seen by the app, so that it can be obtained faster if ever requested again. The approach I have been considering is to use a light database, like SqlServerCe, that can store the data logs as they are received. I am then hoping to first search the cache prior to querying a device for logs. The cache would be updated with any logs obtained by the request that were not already cached. Finally my question - would you consider this to be a good approach? Are there any better alternatives you can think of? I've tried to search SO and Google for reinforcement of the idea, but I mostly run into discussions of web request/content caching. Thanks for any feedback!

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Hibernate: fetching multiple bags efficiently

- by Jens Jansson

Hi! I'm developing a multilingual application. For this reason many objects have in their name and description fields collections of something I call LocalizedStrings instead of plain strings. Every LocalizedString is basically a pair of a locale and a string localized to that locale. Let's take an example an entity, let's say a book -object. public class Book{ @OneToMany private List<LocalizedString> names; @OneToMany private List<LocalizedString> description; //and so on... } When a user asks for a list of books, it does a query to get all the books, fetches the name and description of every book in the locale the user has selected to run the app in, and displays it back to the user. This works but it is a major performance issue. For the moment hibernate makes one query to fetch all the books, and after that it goes through every single object and asks hibernate for the localized strings for that specific object, resulting in a "n+1 select problem". Fetching a list of 50 entities produces about 6000 rows of sql commands in my server log. I tried making the collections eager but that lead me to the "cannot simultaneously fetch multiple bags"-issue. Then I tried setting the fetch strategy on the collections to subselect, hoping that it would do one query for all books, and after that do one query that fetches all LocalizedStrings for all the books. Subselects didn't work in this case how i would have hoped and it basically just did exactly the same as my first case. I'm starting to run out of ideas on how to optimize this. So in short, what fetching strategy alternatives are there when you are fetching a collection and every element in that collection has one or multiple collections in itself, which has to be fetch simultaneously.

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best web database solution for scala for a high traffic site?

- by egervari

I am in charge of a rebuilding a website that gets about 250,000 visitors a day. We'd like to use Scala, but it does not work very well with Spring (in some minor cases) and Hibernate (there is a major and very annoying mismatch here if you want to use scala collections, which we do). The application itself is going to have about 40-50 tables. Other than Hibernate, is there an ORM that works awesome with Scala and is as performant and reliable as Hibernate? Does it also have the same capabilities, or are we going to run into leaky-abstractions if we don't use Hibernate? It would be a big risk for us to go with a framework that is newer and doesn't seem to have a lot of industry backing... and at the same time, Hibernate is a real pain to program against when using Scala. 1) The Java Collection <- Scala Collection is absolutely painful. There is a lot more boilerplate and crap to write. 2) The IDE doesn't import JavaConversions and java interfaces automatically... so we this needs to be done manually. Optimizing Imports in IDEA is going to destroy all the manual work. 3) There is also a performance cost to converting back and forth all the time in your domain objects and your dao classes. 4) Not to mention there needs to be a lot of casting, which produces code ugly as sin. I actually would love to write my own orm that is 100% tailored to scala, but obviously this is really outside of the scope of our project for now. So what is the best approach?

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Dealing with image upload on server

- by user1073320

I have got a the following problem: I have got multi-step form where in one step user upload image to server and then few steps further supplies other information, when this information is invalid no data should be commited - also the image should be deleted. I was thinking about PHP session, but I've read here PHP - Store Images in SESSION data? that it is inefficient way. Every time you proceed step in the form the image is reloaded (in the session) and as somebody mentioned "You will want it to only be as big as it needs to be and you need to delete it as soon as you don't need it because large pieces of information in the session will slow down the session startup." - here i got a question: will it slow down the stratup the session of user who upload file or sessions of all users? I have to mention that I'm looking for solution that doesn't rely on operating system scripts (cron or etc) - I have no permission to run such scripts. The perfect solution for me would be: saving image on disk (for example in some folder named after session id) then after the latest step of form move this image or delete depending on form validation. If user unexpectedly destroy the session (for example closing the browser) of course the folder with image should be deleted. In nutshell I need somethig like callback to event "destroying session".

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Move to php in windows? Concern, hints, "please don't do!"?

- by Daniel

I am considering to move frome Microsoft languages to PHP (just for web dev) which has quite an interesting syntax, a perlish look (but a wider programmer base) and it allows me to reuse the web without reinventing it. I have some concerns too. I would be more than happy to gather some wisdom from stackoverflow community, (challenge to my opinions warmly welcome). Here are my doubts. Efficiency. Cgi are slow, what I am supposed to use? Fastcgi? Or what else? Efficiency + stability. Is PHP on windows really stable and a good choice in terms of performances? Database. I use very often MSSQL (I regret, i like it). Could I widely and efficiently interface PHP with MSSQL (using smartly stored pro, for example). XSLT + XML performance. I work quite a lot with XML and XSLT and I really find the MS xml parser a great software component. Are parser used in PHP fast, reliable and efficient (I am interested mainly in DOM, not SAX)? Objects. Is the PHP object programming model valid end efficient? 6 Regex. How efficient is PHP processing regexp? Many thanks for your advices.

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Keep the images downloaded in the listview during scrolling

- by Paveliko

I'm developing my first app and have been reading a LOT here. I've been trying to find a solution for the following issue for over a week with no luck. I have an Adapter that extends ArrayAdapter to show image and 3 lines of text in each row. Inside the getView I assign relevant information for the TextViews and use ImageLoader class to download image and assign it to the ImageView. Everything works great! I have 4.5 rows visible on my screen (out of total of 20). When I scroll down for the first time the images continue to download and be assigned in right order to the list. BUT when I scroll back the list looses all the images and start redrawing them again (0.5-1 sec per image) in correct order. From what I've been reading it's the standard list performance but I want to change it. I want that, once the image was downloaded, it will be "sticked" to the list for the whole session of the current window. Just like in Contacts list or in the Market. It is only 20 images (6-9kb each). Hope I managed to explain myself.

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How to do "map chunks", like terraria or minecraft maps?

- by O'poil

Due to performance issues, I have to cut my maps into chunks. I manage the maps in this way: listMap[x][y] = new Tile (x,y); I tried in vain to cut this list for several "chunk" to avoid loading all the map because the fps are not very high with large map. And yet, when I update or Draw I do it with a little tile range. Here is how I proceed: foreach (List<Tile> list in listMap) { foreach (Tile leTile in list) { if ((leTile.Position.X < screenWidth + hero.Pos.X) && (leTile.Position.X > hero.Pos.X - tileSize) && (leTile.Position.Y < screenHeight + hero.Pos.Y) && (leTile.Position.Y > hero.Pos.Y - tileSize) ) { leTile.Draw(spriteBatch, gameTime); } } } (and the same thing, for the update method). So I try to learn with games like minecraft or terraria, and any two manages maps much larger than mine, without the slightest drop of fps. And apparently, they load "chunks". What I would like to understand is how to cut my list in Chunk, and how to display depending on the position of my character. I try many things without success. Thank you in advance for putting me on the right track! Ps : Again, sorry for my English :'( Pps : I'm not an experimented developer ;)

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Problem with incomplete input when using Attoparsec

- by Dan Dyer

I am converting some functioning Haskell code that uses Parsec to instead use Attoparsec in the hope of getting better performance. I have made the changes and everything compiles but my parser does not work correctly. I am parsing a file that consists of various record types, one per line. Each of my individual functions for parsing a record or comment works correctly but when I try to write a function to compile a sequence of records the parser always returns a partial result because it is expecting more input. These are the two main variations that I've tried. Both have the same problem. items :: Parser [Item] items = sepBy (comment <|> recordType1 <|> recordType2) endOfLine For this second one I changed the record/comment parsers to consume the end-of-line characters. items :: Parser [Item] items = manyTill (comment <|> recordType1 <|> recordType2) endOfInput Is there anything wrong with my approach? Is there some other way to achieve what I am attempting?

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C++ BigInt multiplication conceptual problem

- by Kapo

I'm building a small BigInt library in C++ for use in my programming language. The structure is like the following: short digits[ 1000 ]; int len; I have a function that converts a string into a bigint by splitting it up into single chars and putting them into digits. The numbers in digits are all reversed, so the number 123 would look like the following: digits[0]=3 digits[1]=3 digits[2]=1 I have already managed to code the adding function, which works perfectly. It works somewhat like this: overflow = 0 for i ++ until length of both numbers exceeded: add numberA[ i ] to numberB[ i ] add overflow to the result set overflow to 0 if the result is bigger than 10: substract 10 from the result overflow = 1 put the result into numberReturn[ i ] (Overflow is in this case what happens when I add 1 to 9: Substract 10 from 10, add 1 to overflow, overflow gets added to the next digit) So think of how two numbers are stored, like those: 0 | 1 | 2 --------- A 2 - - B 0 0 1 The above represents the digits of the bigints 2 (A) and 100 (B). - means uninitialized digits, they aren't accessed. So adding the above number works fine: start at 0, add 2 + 0, go to 1, add 0, go to 2, add 1 But: When I want to do multiplication with the above structure, my program ends up doing the following: Start at 0, multiply 2 with 0 (eek), go to 1, ... So it is obvious that, for multiplication, I have to get an order like this: 0 | 1 | 2 --------- A - - 2 B 0 0 1 Then, everything would be clear: Start at 0, multiply 0 with 0, go to 1, multiply 0 with 0, go to 2, multiply 1 with 2 How can I manage to get digits into the correct form for multiplication? I don't want to do any array moving/flipping - I need performance!

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What is the fastest way to get a DataTable into SQL Server?

- by John Gietzen

I have a DataTable in memory that I need to dump straight into a SQL Server temp table. After the data has been inserted, I transform it a little bit, and then insert a subset of those records into a permanent table. The most time consuming part of this operation is getting the data into the temp table. Now, I have to use temp tables, because more than one copy of this app is running at once, and I need a layer of isolation until the actual insert into the permanent table happens. What is the fastest way to do a bulk insert from a C# DataTable into a SQL Temp Table? I can't use any 3rd party tools for this, since I am transforming the data in memory. My current method is to create a parameterized SqlCommand: INSERT INTO #table (col1, col2, ... col200) VALUES (@col1, @col2, ... @col200) and then for each row, clear and set the parameters and execute. There has to be a more efficient way. I'm able to read and write the records on disk in a matter of seconds...

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How to model in J2EE / JEE?

- by Harry

Let's say, I have decided to go with J(2)EE stack for my enterprise application. Now, for domain modelling (or: for designing the M of MVC), which APIs can I safely assume and use, and which I should stay away from... say, via a layer of abstraction? For example, Should I go ahead and litter my Model with calls to Hibernate/JPA API? Or, should I build an abstraction... a persistence layer of my own to avoid hard-coding against these two specific persistence APIs? Why I ask this: Few years ago, there was this Kodo API which got superseded by Hibernate. If one had designed a persistence layer and coded the rest of the model against this layer (instead of littering the Model with calls to specific vendor API), it would have allowed one to (relatively) easily switch from Kodo to Hibernate to xyz. Is it recommended to make aggressive use of the *QL provided by your persistence vendor in your domain model? I'm not aware of any real-world issues (like performance, scalability, portability, etc) arising out of a heavy use of an HQL-like language. Why I ask this: I would like to avoid, as much as possible, writing custom code when the same could be accomplished via query language that is more portable than SQL. Sorry, but I'm a complete newbie to this area. Where could I find more info on this topic? Many thanks in advance. /HS

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What hash algorithms are parallelizable? Optimizing the hashing of large files utilizing on multi-co

- by DanO

I'm interested in optimizing the hashing of some large files (optimizing wall clock time). The I/O has been optimized well enough already and the I/O device (local SSD) is only tapped at about 25% of capacity, while one of the CPU cores is completely maxed-out. I have more cores available, and in the future will likely have even more cores. So far I've only been able to tap into more cores if I happen to need multiple hashes of the same file, say an MD5 AND a SHA256 at the same time. I can use the same I/O stream to feed two or more hash algorithms, and I get the faster algorithms done for free (as far as wall clock time). As I understand most hash algorithms, each new bit changes the entire result, and it is inherently challenging/impossible to do in parallel. Are any of the mainstream hash algorithms parallelizable? Are there any non-mainstream hashes that are parallelizable (and that have at least a sample implementation available)? As future CPUs will trend toward more cores and a leveling off in clock speed, is there any way to improve the performance of file hashing? (other than liquid nitrogen cooled overclocking?) or is it inherently non-parallelizable?

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Using Lucene to index private data, should I have a separate index for each user or a single index

- by Nathan Bayles

I am developing an Azure based website and I want to provide search capabilities using Lucene. (structured json objects would be indexed and stored in Lucene and other content such as Word documents, etc. would be indexed in lucene but stored in blob storage) I want the search to be secure, such that one user would never see a document belonging to another user. I want to allow ad-hoc searches as typed by the user. Lastly, I want to query programmatically to return predefined sets of data, such as "all notes for user X". I think I understand how to add properties to each document to achieve these 3 objectives. (I am listing them here so if anyone is kind enough to answer, they will have better idea of what I am trying to do) My questions revolve around performance and security. Can I improve document security by having a separate index for each user, or is including the user's ID as a parameter in each search sufficient? Can I improve indexing speed and total throughput of the system by having a separate index for each user? My thinking is that having separate indexes would allow me to scale the system by having multiple index writers (perhaps even on different server instances) working at the same time, each on their own index. Any insight would be greatly appreciated. Regards, Nate

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