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• Fetching Partition Information

  - by Mike Femenella

  For a recent SSIS package at work I needed to determine the distinct values in a partition, the number of rows in each partition and the file group name on which each partition resided in order to come up with a grouping mechanism. Of course sys.partitions comes to mind for some of that but there are a few other tables you need to link to in order to grab the information required. The table I’m working on contains 8.8 billion rows. Finding the distinct partition keys from this table was not a fast operation. My original solution was to create  a temporary table, grab the distinct values for the partitioned column, then update via sys.partitions for the rows and the $partition function for the partitionid and finally look back to the sys.filegroups table for the filegroup names. It wasn’t pretty, it could take up to 15 minutes to return the results. The primary issue is pulling distinct values from the table. Queries for distinct against 8.8 billion rows don’t go quickly. A few beers into a conversation with a friend and we ended up talking about work which led to a conversation about the task described above. The solution was already built in SQL Server, just needed to pull it together. The first table I needed was sys.partition_range_values. This contains one row for each range boundary value for a partition function. In my case I have a partition function which uses dayid values. For example July 4th would be represented as an int, 20130704. This table lists out all of the dayid values which were defined in the function. This eliminated the need to query my source table for distinct dayid values, everything I needed was already built in here for me. The only caveat was that in my SSIS package I needed to create a bucket for any dayid values that were out of bounds for my function. For example if my function handled 20130501 through 20130704 and I had day values of 20130401 or 20130705 in my table, these would not be listed in sys.partition_range_values. I just created an “everything else” bucket in my ssis package just in case I had any dayid values unaccounted for. To get the number of rows for a partition is very easy. The sys.partitions table contains values for each partition. Easy enough to achieve by querying for the object_id and index value of 1 (the clustered index) The final piece of information was the filegroup name. There are 2 options available to get the filegroup name, sys.data_spaces or sys.filegroups. For my query I chose sys.filegroups but really it’s a matter of preference and data needs. In order to bridge between sys.partitions table and either sys.data_spaces or sys.filegroups you need to get the container_id. This can be done by joining sys.allocation_units.container_id to the sys.partitions.hobt_id. sys.allocation_units contains the field data_space_id which then lets you join in either sys.data_spaces or sys.file_groups. The end result is the query below, which typically executes for me in under 1 second. I’ve included the join to sys.filegroups and to sys.dataspaces, and I’ve  just commented out the join sys.filegroups. As I mentioned above, this shaves a good 10-15 minutes off of my original ssis package and is a really easy tweak to get a boost in my ETL time. Enjoy.

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• How do I organize a GUI application for passing around events and for setting up reads from a shared resource

  - by Savanni D'Gerinel

  My tools involved here are GTK and Haskell. My questions are probably pretty trivial for anyone who has done significant GUI work, but I've been off in the equivalent of CGI applications for my whole career. I'm building an application that displays tabular data, displays the same data in a graph form, and has an edit field for both entering new data and for editing existing data. After asking about sharing resources, I decided that all of the data involved will be stored in an MVar so that every component can just read the current state from the MVar. All of that works, but now it is time for me to rearrange the application so that it can be interactive. With that in mind, I have three widgets: a TextView (for editing), a TreeView (for displaying the data), and a DrawingArea (for displaying the data as a graph). I THINK I need to do two things, and the core of my question is, are these the right things, or is there a better way. Thing the first: All event handlers, those functions that will be called any time a redisplay is needed, need to be written at a high level and then passed into the function that actually constructs the widget to begin with. For instance: drawStatData :: DrawingArea -> MVar Core.ST -> (Core.ST -> SetRepWorkout.WorkoutStore) -> IO () createStatView :: (DrawingArea -> IO ()) -> IO VBox createUI :: MVar Core.ST -> (Core.ST -> SetRepWorkout.WorkoutStore) -> IO HBox createUI storeMVar field = do graphs <- createStatView (\area -> drawStatData area storeMVar field) hbox <- hBoxNew False 10 boxPackStart hbox graphs PackNatural 0 return hbox In this case, createStatView builds up a VBox that contains a DrawingArea to graph the data and potentially other widgets. It attaches drawStatData to the realize and exposeEvent events for the DrawingArea. I would do something similar for the TreeView, but I am not completely sure what since I have not yet done it and what I am thinking of would involve replacing the TreeModel every time the TreeView needs to be updated. My alternative to the above would be... drawStatData :: DrawingArea -> MVar Core.ST -> (Core.ST -> SetRepWorkout.WorkoutStore) -> IO () createStatView :: IO (VBox, DrawingArea) ... but in this case, I would arrange createUI like so: createUI :: MVar Core.ST -> (Core.ST -> SetRepWorkout.WorkoutStore) -> IO HBox createUI storeMVar field = do (graphbox, graph) <- createStatView (\area -> drawStatData area storeMVar field) hbox <- hBoxNew False 10 boxPackStart hbox graphs PackNatural 0 on graph realize (drawStatData graph storeMVar field) on graph exposeEvent (do liftIO $ drawStatData graph storeMVar field return ()) return hbox I'm not sure which is better, but that does lead me to... Thing the second: it will be necessary for me to rig up an event system so that various events can send signals all the way to my widgets. I'm going to need a mediator of some kind to pass events around and to translate application-semantic events to the actual events that my widgets respond to. Is it better for me to pass my addressable widgets up the call stack to the level where the mediator lives, or to pass the mediator down the call stack and have the widgets register directly with it? So, in summary, my two questions: 1) pass widgets up the call stack to a global mediator, or pass the global mediator down and have the widgets register themselves to it? 2) pass my redraw functions to the builders and have the builders attach the redraw functions to the constructed widgets, or pass the constructed widgets back and have a higher level attach the redraw functions (and potentially link some widgets together)? Okay, and... 3) Books or wikis about GUI application architecture, preferably coherent architectures where people aren't arguing about minute details? The application in its current form (displays data but does not write data or allow for much interaction) is available at https://bitbucket.org/savannidgerinel/fitness . You can run the application by going to the root directory and typing runhaskell -isrc src/Main.hs data/ or... cabal build dist/build/fitness/fitness data/ You may need to install libraries, but cabal should tell you which ones.

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• What common interface would be appropriate for these game object classes?

  - by Jefffrey

  Question A component based system's goal is to solve the problems that derives from inheritance: for example the fact that some parts of the code (that are called components) are reused by very different classes that, hypothetically, would lie in a very different branch of the inheritance tree. That's a very nice concept, but I've found out that CBS is often hard to accomplish without using ugly hacks. Implementations of this system are often far from clean. But I don't want to discuss this any further. My question is: how can I solve the same problems a CBS try to solve with a very clean interface? (possibly with examples, there are a lot of abstract talks about the "perfect" design already). Context Here's an example I was going for before realizing I was just reinventing inheritance again: class Human { public: Position position; Movement movement; Sprite sprite; // other human specific components }; class Zombie { Position position; Movement movement; Sprite sprite; // other zombie specific components }; After writing that I realized I needed an interface, otherwise I would have needed N containers for N different types of objects (or to use boost::variant to gather them all together). So I've thought of polymorphism (move what systems do in a CBS design into class specific functions): class Entity { public: virtual void on_event(Event) {} // not pure virtual on purpose virtual void on_update(World) {} virtual void on_draw(Window) {} }; class Human : public Entity { private: Position position; Movement movement; Sprite sprite; public: virtual void on_event(Event) { ... } virtual void on_update(World) { ... } virtual void on_draw(Window) { ... } }; class Zombie : public Entity { private: Position position; Movement movement; Sprite sprite; public: virtual void on_event(Event) { ... } virtual void on_update(World) { ... } virtual void on_draw(Window) { ... } }; Which was nice, except for the fact that now the outside world would not even be able to know where a Human is positioned (it does not have access to its position member). That would be useful to track the player position for collision detection or if on_update the Zombie would want to track down its nearest human to move towards him. So I added const Position& get_position() const; to both the Zombie and Human classes. And then I realized that both functionality were shared, so it should have gone to the common base class: Entity. Do you notice anything? Yes, with that methodology I would have a god Entity class full of common functionality (which is the thing I was trying to avoid in the first place). Meaning of "hacks" in the implementation I'm referring to I'm talking about the implementations that defines Entities as simple IDs to which components are dynamically attached. Their implementation can vary from C-stylish: int last_id; Position* positions[MAX_ENTITIES]; Movement* movements[MAX_ENTITIES]; Where positions[i], movements[i], component[i], ... make up the entity. Or to more C++-style: int last_id; std::map<int, Position> positions; std::map<int, Movement> movements; From which systems can detect if an entity/id can have attached components.

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• PHP-FPM stops responding and dies [migrated]

  - by user12361

  I'm running Drupal 6 with Nginx 1.5.1 and PHP-FPM (PHP 5.3.26) on a 1GB single core VPS with 3GB of swap space on SSD storage. I just switched from shared hosting to this unmanaged VPS because my site was getting too heavy, so I'm still learning the ropes. I have moderately high traffic, I don't really monitor it closely but Google Adsense usually record close to 30K page views/day. I usually have 50 to 80 authenticated users logged in and a few hundred more anonymous users hitting the Boost static HTML cache at any given moment. The problem I'm having is that PHP-FPM frequently stops responding, resulting in Nginx 502 or 504 errors. I swear I have read every page on the internet about this issue, which seems fairly common, and I've tried endless combinations of configurations, and I can't find a good solution. After restarting Nginx and PHP-FPM, the site runs really fast for a while, and then without warning it simply stops responding. I get a white screen while the browser waits on the server, and after about 30 seconds to a minute it throws an Nginx 502 or 504 error. Sometimes it runs well for 2 minutes, sometimes 5 minutes, sometimes 5 hours, but it always ends up hanging. When I find the server in this state, there is still plenty of free memory (500MB or more) and no major CPU usage, the control and worker PHP-FPM processes are still present, and the server is still pingable and usable via SSH. A reload of PHP-FPM via the init script revives it again. The hangups don't seem to correspond to the amount of traffic, because I observed this behavior consistently when I was testing this configuration on a development VPS with no traffic at all. I've been constantly tweaking the settings, but I can't definitively eliminate the problem. I set Nginx workers to just 1. In the PHP-FPM config I have tried all three of the process managers. "Dynamic" is definitely the least reliable, consistently hanging up after only a few minutes. "Static" also has been unreliable and unpredictable. The least buggy has been "ondemand", but even that is failing me, sometimes after as much as 12 to 24 hours. But I can't leave the server unattended because PHP-FPM dies and never comes back on its own. I tried adjusting the pm.max_children value from as low as 3 to as high as 50, doesn't make a lot of difference, but I currently have it at 10. Same thing for the spare servers values. I also have set pm.max_requests anywhere from 30 to unlimited, and it doesn't seem to make a difference. According to the logs, the PHP-FPM processes are not exiting with SIGSEGV or SIGBUS, but rather with SIGTERM. I get a lot of lines like: WARNING: [pool www] child 3739, script '/var/www/drupal6/index.php' (request: "GET /index.php") execution timed out (38.739494 sec), terminating and: WARNING: [pool www] child 3738 exited on signal 15 (SIGTERM) after 50.004380 seconds from start I actually found several articles that recommend doing a graceful reload of PHP-FPM via cron every few minutes or hours to circumvent this issue. So that's what I did, "/etc/init.d/php-fpm reload" every 5 minutes. So far, it's keeping the lights on. But it feels like a dreadful hack. Is PHP-FPM really that unreliable? Is there anything else I can do? Thanks a lot!

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• Concurrent Affairs

  - by Tony Davis

  I once wrote an editorial, multi-core mania, on the conundrum of ever-increasing numbers of processor cores, but without the concurrent programming techniques to get anywhere near exploiting their performance potential. I came to the.controversial.conclusion that, while the problem loomed for all procedural languages, it was not a big issue for the vast majority of programmers. Two years later, I still think most programmers don't concern themselves overly with this issue, but I do think that's a bigger problem than I originally implied. Firstly, is the performance boost from writing code that can fully exploit all available cores worth the cost of the additional programming complexity? Right now, with quad-core processors that, at best, can make our programs four times faster, the answer is still no for many applications. But what happens in a few years, as the number of cores grows to 100 or even 1000? At this point, it becomes very hard to ignore the potential gains from exploiting concurrency. Possibly, I was optimistic to assume that, by the time we have 100-core processors, and most applications really needed to exploit them, some technology would be around to allow us to do so with relative ease. The ideal solution would be one that allows programmers to forget about the problem, in much the same way that garbage collection removed the need to worry too much about memory allocation. From all I can find on the topic, though, there is only a remote likelihood that we'll ever have a compiler that takes a program written in a single-threaded style and "auto-magically" converts it into an efficient, correct, multi-threaded program. At the same time, it seems clear that what is currently the most common solution, multi-threaded programming with shared memory, is unsustainable. As soon as a piece of state can be changed by a different thread of execution, the potential number of execution paths through your program grows exponentially with the number of threads. If you have two threads, each executing n instructions, then there are 2^n possible "interleavings" of those instructions. Of course, many of those interleavings will have identical behavior, but several won't. Not only does this make understanding how a program works an order of magnitude harder, but it will also result in irreproducible, non-deterministic, bugs. And of course, the problem will be many times worse when you have a hundred or a thousand threads. So what is the answer? All of the possible alternatives require a change in the way we write programs and, currently, seem to be plagued by performance issues. Software transactional memory (STM) applies the ideas of database transactions, and optimistic concurrency control, to memory. However, working out how to break down your program into sufficiently small transactions, so as to avoid contention issues, isn't easy. Another approach is concurrency with actors, where instead of having threads share memory, each thread runs in complete isolation, and communicates with others by passing messages. It simplifies concurrent programs but still has performance issues, if the threads need to operate on the same large piece of data. There are doubtless other possible solutions that I haven't mentioned, and I would love to know to what extent you, as a developer, are considering the problem of multi-core concurrency, what solution you currently favor, and why. Cheers, Tony.

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• The new direction of the gaming industry

  - by raccoon_tim

  Just recently I read a great blog post by David Darling, the founder of Codemasters: http://www.develop-online.net/blog/347/Jurassic-consoles-could-become-extinct. In the blog post he talks about how traditional retail games are experiencing a downfall thanks to the increasing popularity of digital distribution. I personally think of retail games as being relics of the past. It does not really make much sense to still keep distributing boxed games when the same game can be elegantly downloaded and updated over the air through a digital distribution channel. The world is not all rainbows, however. One big issue with mixing digital distribution with boxed retail games is that resellers will not condone you selling your game for 10€ digitally while their selling the same game for 70€. The only way to get around this issue is to move to full digital distribution. This has the added benefit of minimizing piracy as the game can be tightly bound to the service you downloaded the game from. Many players are, however, complaining about not being able to play the games offline. Having games tightly bound to the internet is a problem when games are bought from a retailer as we tend to expect that once we have the product we can use it anywhere because we physically own it. The truth is that we don’t actually own the product. Instead, the typical EULA actually states that we only have a license to use the product. We’re not, for instance, allowed to disassemble the product, which the owner is indeed permitted to do. Digital distribution allows us to provide games as services, instead of selling them as standalone products. This means that for a service to work you have to be connected to the internet but you still have the same rights to use the product. It’s really straightforward; if you downloaded a client from the internet you are expected to have an internet connection so you’re able to connect to the server. A game distributed digitally that is built using a client-server architecture has the added benefit of allowing you to play anywhere as long as you have the client installed and you are able to log in with your user information. Your save games can be backed up and your game can continue anywhere. Another development we’re seeing in the gaming industry is the increasing popularity of free-to-play games. These are games that let you play for free but allow you to boost your gaming experience with real world money. The nature of these games is that players are constantly rewarded with new content and the game can evolve according to their way of playing and their wishes can be incorporated into the product. Free-to-play games can quickly gain a large player basis and monetization is done by providing players valuable things to buy making their gaming experience more fun. I am personally very excited about free-to-play games as it’s possible to start building the game together with your players and there is no need to work on the game for 5 years from start to finish and only then see if it’s actually something the players like. This is a typical problem with big movie-like retail games and recent news about Radical Entertainment practically closing its doors paints a clear picture of what can happen when the risk does not pay off: http://news.teamxbox.com/xbox/25874/Prototype-Developer-Radical-Entertainment-Closes/.

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• Multithreading recommendation based on program description

  - by user260197

  I would like to describe some specifics of my program and get feedback on what the best multithreading model to use would be most applicable. I've spent a lot of time now reading on ThreadPool, Threads, Producer/Consumer, etc. and have yet to come to solid conclusions. I have a list of files (all the same format) but with different contents. I have to perform work on each file. The work consists of reading the file, some processing that takes about 1-2 minutes of straight number crunching, and then writing large output files at the end. I would like the UI interface to still be responsive after I initiate the work on the specified files. Some questions: What model/mechanisms should I use? Producer/Consumer, WorkPool, etc. Should I use a BackgroundWorker in the UI for responsiveness or can I launch the threading from within the Form as long as I leave the UI thread alone to continue responding to user input? How could I take results or status of each individual work on each file and report it to the UI in a thread safe way to give user feedback as the work progresses (there can be close to 1000 files to process) Update: Great feedback so far, very helpful. I'm adding some more details that are asked below: Output is to multiple independent files. One set of output files per "work item" that then themselves gets read and processed by another process before the "work item" is complete The work items/threads do not share any resources. The work items are processed in part using a unmanaged static library that makes use of boost libraries.

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• Using a Mac for cross platform development?

  - by mdec

  Who uses Macs for cross-platform development? By cross platform I essentially mean you can compile to target Windows or Unix (not necessarily both at the same time). I understand that this also has a lot to do with writing portable code, but I am more interested in people's experience with Mac OS X to develop software. I understand that there are a range of IDEs to choose from, I would probably use Eclipse (I like the GCC toolchain) however Xcode seems to be quite popular. Could it be used as described above? At a pinch I could always virtualise with VirtualBox or VMware Player or parallels to use Visual Studio (or dual boot for that matter). Having said that I am open to any other suggested compilers (with preferably an IDE that uses GCC.) Also with the range of Macs available, which one would you recommend? I would prefer a laptop (as I already have a desktop) but am unsure of reasonable specifications. If you are currently using a Mac to do development, I would love to hear what you develop on your Mac and what you like and don't like about it. I would primarily be developing in C/C++/Java. I am also looking to experiment with Boost and Qt, so I'm interested in hearing about any (potential) compatibility issues. If you have any other tips I'd love you hear what you have to say.

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• How do you keep all your languages straight?

  - by Chris Blackwell

  I think I'm going a little crazy. Right now, I'm working with the following languages (I was just doing a mental inventory): C++ - our game engine Assembler - low level debugging and a few co-processor specific routines Lua - our game engine scripting language HLSL - for shaders Python - our build system and utility tools Objective C/C++ - game engine platform code for Mac and iPhone C# - A few tools developed in our overseas office ExtendScript - Photoshop exporting tools ActionScript - UI scripting VBScript - some spreadsheet related stuff PHP - some web related stuff SQL - some web and tool related stuff On top of this are the plethora of API's that often have many different ways of doing the same thing: std library, boost, .NET, wxWidgets, Cocoa, Carbon, native script libraries for Python, Lua, etc, OpenGL, Direct3d, GDI, Aqua, augh! I find myself inadvertently conflating languages and api's, not realizing what I'm doing until I get syntax errors. I feel like I can't possibly keep up with it, and I can't possibly be proficient in all of these areas. Especially outside the realm of C++ and Python, I find myself programming more by looking at manuals that from memory. Do you have a similar problem? Ideas for compartmentalizing so you're more efficient? Deciding where you want to stay proficient? Organizational tips? Good ways to remember when you switch from Lua to C++ you need to start using semi-colons again? Rants on how complicated we programmers have made things for ourselves? Any ideas welcome!

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• C++ smart pointers: sharing pointers vs. sharing data

  - by Eli Bendersky

  In this insightful article, one of the Qt programmers tries to explain the different kinds of smart pointers Qt implements. In the beginning, he makes a distinction between sharing data and sharing the pointers themselves: First, let’s get one thing straight: there’s a difference between sharing pointers and sharing data. When you share pointers, the value of the pointer and its lifetime is protected by the smart pointer class. In other words, the pointer is the invariant. However, the object that the pointer is pointing to is completely outside its control. We don’t know if the object is copiable or not, if it’s assignable or not. Now, sharing of data involves the smart pointer class knowing something about the data being shared. In fact, the whole point is that the data is being shared and we don’t care how. The fact that pointers are being used to share the data is irrelevant at this point. For example, you don’t really care how Qt tool classes are implicitly shared, do you? What matters to you is that they are shared (thus reducing memory consumption) and that they work as if they weren’t. Frankly, I just don't undersand this explanation. There was a clarification plea in the article comments, but I didn't find the author's explanation sufficient. If you do understand this, please explain. What is this distinction, and how are other shared pointer classes (i.e. from boost or the new C++ standards) fit into this taxonomy? Thanks in advance

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• Lucene - querying with long strings

  - by Mikos

  I have an index, with a field "Affiliation", some example values are: "Stanford University School of Medicine, Palo Alto, CA USA", "Institute of Neurobiology, School of Medicine, Stanford University, Palo Alto, CA", "School of Medicine, Harvard University, Boston MA", "Brigham & Women's, Harvard University School of Medicine, Boston, MA" "Harvard University, Cambridge MA" and so on... (the bottom-line being the affiliations are written in multiple ways with no apparent consistency) I query the index on the affiliation field using say "School of Medicine, Stanford University, Palo Alto, CA" (with QueryParser) to find all Stanford related documents, I get a lot of false +ves, presumably because of the presence of School of Medicine etc. etc. (note: I cannot use Phrase query because of variability in the way affiliation is constructed) I have tried the following: Use a SpanNearQuery by splitting the search phrase with a whitespace (here I get no results!) Tried boosting (using ^) by splitting with the comma and boosting the last parts such as "Palo Alto CA" with a much higher boost than the initial phrases. Here I still get lots of false +ves. Any suggestions on how to approach this? If SpanNearQuery the way to go, Any ideas on why I get 0 results?

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• C++ design question on traversing binary trees

  - by user231536

  I have a binary tree T which I would like to copy to another tree. Suppose I have a visit method that gets evaluated at every node: struct visit { virtual void operator() (node* n)=0; }; and I have a visitor algorithm void visitor(node* t, visit& v) { //do a preorder traversal using stack or recursion if (!t) return; v(t); visitor(t->left, v); visitor(t->right, v); } I have 2 questions: I settled on using the functor based approach because I see that boost graph does this (vertex visitors). Also I tend to repeat the same code to traverse the tree and do different things at each node. Is this a good design to get rid of duplicated code? What other alternative designs are there? How do I use this to create a new binary tree from an existing one? I can keep a stack on the visit functor if I want, but it gets tied to the algorithm in visitor. How would I incorporate postorder traversals here ? Another functor class?

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• Will fixed-point arithmetic be worth my trouble?

  - by Thomas

  I'm working on a fluid dynamics Navier-Stokes solver that should run in real time. Hence, performance is important. Right now, I'm looking at a number of tight loops that each account for a significant fraction of the execution time: there is no single bottleneck. Most of these loops do some floating-point arithmetic, but there's a lot of branching in between. The floating-point operations are mostly limited to additions, subtractions, multiplications, divisions and comparisons. All this is done using 32-bit floats. My target platform is x86 with at least SSE1 instructions. (I've verified in the assembler output that the compiler indeed generates SSE instructions.) Most of the floating-point values that I'm working with have a reasonably small upper bound, and precision for near-zero values isn't very important. So the thought occurred to me: maybe switching to fixed-point arithmetic could speed things up? I know the only way to be really sure is to measure it, that might take days, so I'd like to know the odds of success beforehand. Fixed-point was all the rage back in the days of Doom, but I'm not sure where it stands anno 2010. Considering how much silicon is nowadays pumped into floating-point performance, is there a chance that fixed-point arithmetic will still give me a significant speed boost? Does anyone have any real-world experience that may apply to my situation?

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• C++ thread safety - exchange data between worker and controller

  - by peterchen

  I still feel a bit unsafe about the topic and hope you folks can help me - For passing data (configuration or results) between a worker thread polling something and a controlling thread interested in the most recent data, I've ended up using more or less the following pattern repeatedly: Mutex m; tData * stage; // temporary, accessed concurrently // send data, gives up ownership, receives old stage if any tData * Send(tData * newData) { ScopedLock lock(m); swap(newData, stage); return newData; } // receiving thread fetches latest data here tData * Fetch(tData * prev) { ScopedLock lock(m); if (stage != 0) { // ... release prev prev = stage; stage = 0; } return prev; // now current } Note: This is not supposed to be a full producer-consumer queue, only the msot recent data is relevant. Also, I've skimmed ressource management somewhat here. When necessary I'm using two such stages: one to send config changes to the worker, and for sending back results. Now, my questions assuming that ScopedLock implements a full memory barrier: do stage and/or workerData need to be volatile? is volatile necessary for tData members? can I use smart pointers instead of the raw pointers - say boost::shared_ptr? Anything else that can go wrong? I am basically trying to avoid "volatile infection" spreading into tData, and minimize lock contention (a lock free implementation seems possible, too). However, I'm not sure if this is the easiest solution. ScopedLock acts as a full memory barrier. Since all this is more or less platform dependent, let's say Visual C++ x86 or x64, though differences/notes for other platforms are welcome, too. (a prelimenary "thanks but" for recommending libraries such as Intel TBB - I am trying to understand the platform issues here)

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• ajax delay load UserControl asp.net

  - by user196202

  regarding ajax delay load of usercontrols (or any controls) on Post at Encosia.com : http://encosia.com/2008/02/05/boost-aspnet-performance-with-deferred-content-loading/ I tried to implement it , but I noticed that it can be done only for simple controls or UserControls that Have simple asp.net controls (or html tags) . But when it involved with advanced dynamic ajax control (like ajaxControlToolkit or Telerik controls) that have javascripts inside them This method of injecting the html code to the .InnerHtml property of div tag (for example) IS NOT WORKING , and I red about it that The browser need to load the script on load and after that it won't iterperate the scripts injectd via .InnerHtml. So I attached here example of delay load project (from encosia.com by dave ward) with my modification (look at DefaultPopup.aspx and beforePopup.aspx and AfterPopup.aspx) Which I modified the RssReader to show listview with popup items (which is implemented via ACT HoverMenuExtender ) So in the regular way the popup items are shown right , but on the delay load which is done by creating virtual page for rendering the html and injecting it to .InnerHtml property – This ISN'T WORKING. So my question is : is there a way to do delay loading for controls which include scripts lik ACT and Telerik and others? And for the ajax templates – if I need to inject advanced control to the page – how I do it with your approach? Thanks very much (I can't attach here files so everyone please ask me by mail ([email protected]) and i'll send it to him. ) Zahi Kramer

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• Build System with Recursive Dependency Aggregation

  - by radman

  Hi, I recently began setting up my own library and projects using a cross platform build system (generates make files, visual studio solutions/projects etc on demand) and I have run into a problem that has likely been solved already. The issue that I have run into is this: When an application has a dependency that also has dependencies then the application being linked must link the dependency and also all of its sub-dependencies. This proceeds in a recursive fashion e.g. (For arguments sake lets assume that we are dealing exclusively with static libraries.) TopLevelApp.exe dependency_A dependency_A-1 dependency_A-2 dependency_B dependency_B-1 dependency_B-2 So in this example TopLevelApp will need to link dependency_A, dependency_A-1, dependency_A-2 etc and the same for B. I think the responsibility of remembering all of these manually in the target application is pretty sub optimal. There is also the issue of ensuring the same version of the dependency is used across all targets (assuming that some targets depend on the same things, e.g. boost). Now linking all of the libraries is required and there is no way of getting around it. What I am looking for is a build system that manages this for you. So all you have to do is specify that you depend on something and the appropriate dependencies of that library will be pulled in automatically. The build system I have been looking at is premake premake4 which doesn't handle this (as far as I can determine). Does anyone know of a build system that does handle this? and if there isn't then why not?

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• Ways std::stringstream can set fail/bad bit?

  - by Evan Teran

  A common piece of code I use for simple string splitting looks like this: inline std::vector<std::string> split(const std::string &s, char delim) { std::vector<std::string> elems; std::stringstream ss(s); std::string item; while(std::getline(ss, item, delim)) { elems.push_back(item); } return elems; } Someone mentioned that this will silently "swallow" errors occurring in std::getline. And of course I agree that's the case. But it occurred to me, what could possibly go wrong here in practice that I would need to worry about. basically it all boils down to this: inline std::vector<std::string> split(const std::string &s, char delim) { std::vector<std::string> elems; std::stringstream ss(s); std::string item; while(std::getline(ss, item, delim)) { elems.push_back(item); } if(ss.fail()) { // *** How did we get here!? *** } return elems; } A stringstream is backed by a string, so we don't have to worry about any of the issues associated with reading from a file. There is no type conversion going on here since getline simply reads until it sees a newline or EOF. So we can't get any of the errors that something like boost::lexical_cast has to worry about. I simply can't think of something besides failing to allocate enough memory that could go wrong, but that'll just throw a std::bad_alloc well before the std::getline even takes place. What am I missing?

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• Maximum page fetch with maximum bandwith

  - by Ehsan

  Hi I want to create an application like a spider I've implement fetching page as the following code in multi-thread application but there is two problem 1) I want to use my maximum bandwidth to send/receive request, how should I config my request to do so (Like Download Accelerator application and the like) cause I heard the normal application will use 66% of the available bandwidth. 2) I don't know what exactly HttpWebRequest.KeepAlive do, but as its name implies I think i can create a connection to a website and without closing the connection sending another request to that web site using existing connection. does it boost performance or Im wrong ?? public PageFetchResult Fetch() { PageFetchResult fetchResult = new PageFetchResult(); try { HttpWebRequest req = (HttpWebRequest)HttpWebRequest.Create(URLAddress); HttpWebResponse resp = (HttpWebResponse)req.GetResponse(); Uri requestedURI = new Uri(URLAddress); Uri responseURI = resp.ResponseUri; string resultHTML = ""; byte[] reqHTML = ResponseAsBytes(resp); if (!string.IsNullOrEmpty(FetchingEncoding)) resultHTML = Encoding.GetEncoding(FetchingEncoding).GetString(reqHTML); else if (!string.IsNullOrEmpty(resp.CharacterSet)) resultHTML = Encoding.GetEncoding(resp.CharacterSet).GetString(reqHTML); req.Abort(); resp.Close(); fetchResult.IsOK = true; fetchResult.ResultHTML = resultHTML; } catch (Exception ex) { fetchResult.IsOK = false; fetchResult.ErrorMessage = ex.Message; } return fetchResult; }

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• Is Annotation in Javascript? If not, how to switch between debug/productive modes in declarative way

  - by Michael Mao

  Hi all: This is but a curious question. I cannot find any useful links from Google so it might be better to ask the gurus here. The point is: is there a way to make "annotation" in javascript source code so that all code snippets for testing purpose can be 'filtered out' when project is deployed from test field into the real environment? I know in Java, C# or some other languages, you can assign an annotation just above the function name, such as : // it is good to remove the annoying warning messages @SuppressWarnings("unchecked") public class Tester extends TestingPackage { ... } Basically I've got a lot of testing code that prints out something into FireBug console. I don't wanna manually "comment out" them because the guy that is going to maintain the code might not be aware of all the testing functions, so he/she might just miss one function and the whole thing can be brought down to its knees. One other thing, we might use a minimizer to "shrink" the source code into "human unreadable" code and boost up performance (just like jQuery.min), so trying to match testing section out of the mess is not possible for plain human eyes in the future. Any suggestion is much appreciated.

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• Passenger error message I can't figure out

  - by Sam Kong

  Hi, I am testing Rails 3 on DreamHost which just installed Rails 3. I created a simple controller and it failed. Browser shows 500 error (Internal Server Error) and the log shows the following message. Could not find i18n-0.5.0 in any of the sources Try running `bundle install`. *** Exception EOFError in spawn manager (Unexpected end-of-file detected.) (process 17951): from /dh/passenger/lib/phusion_passenger/utils.rb:306:in `unmarshal_and_raise_errors' from /dh/passenger/lib/phusion_passenger/rack/application_spawner.rb:71:in `spawn_application' from /dh/passenger/lib/phusion_passenger/rack/application_spawner.rb:41:in `spawn_application' from /dh/passenger/lib/phusion_passenger/spawn_manager.rb:159:in `spawn_application' from /dh/passenger/lib/phusion_passenger/spawn_manager.rb:287:in `handle_spawn_application' from /dh/passenger/lib/phusion_passenger/abstract_server.rb:352:in `__send__' from /dh/passenger/lib/phusion_passenger/abstract_server.rb:352:in `main_loop' from /dh/passenger/lib/phusion_passenger/abstract_server.rb:196:in `start_synchronously' from /dh/passenger/bin/passenger-spawn-server:61 [ pid=13245 file=ext/apache2/Hooks.cpp:727 time=2010-12-24 12:13:38.287 ]: Unexpected error in mod_passenger: Cannot spawn application '/home/cp_rails3/sites/rails3.codepremise.com': The spawn server has exited unexpectedly. Backtrace: in 'virtual boost::shared_ptr<Passenger::Application::Session> Passenger::ApplicationPoolServer::Client::get(const Passenger::PoolOptions&)' (ApplicationPoolServer.h:471) in 'int Hooks::handleRequest(request_rec*)' (Hooks.cpp:523) It runs fine in console (app.get "url") and also ok with "rails server". What's wrong? Thanks. Sam

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• Why This Maintainability Index Increase?

  - by Timothy

  I would be appreciative if someone could explain to me the difference between the following two pieces of code in terms of Visual Studio's Code Metrics rules. Why does the Maintainability Index increase slightly if I don't encapsulate everything within using ( )? Sample 1 (MI score of 71) public static String Sha1(String plainText) { using (SHA1Managed sha1 = new SHA1Managed()) { Byte[] text = Encoding.Unicode.GetBytes(plainText); Byte[] hashBytes = sha1.ComputeHash(text); return Convert.ToBase64String(hashBytes); } } Sample 2 (MI score of 73) public static String Sha1(String plainText) { Byte[] text, hashBytes; using (SHA1Managed sha1 = new SHA1Managed()) { text = Encoding.Unicode.GetBytes(plainText); hashBytes = sha1.ComputeHash(text); } return Convert.ToBase64String(hashBytes); } I understand metrics are meaningless outside of a broader context and understanding, and programmers should exercise discretion. While I could boost the score up to 76 with return Convert.ToBase64String(sha1.ComputeHash(Encoding.Unicode.GetBytes(plainText))), I shouldn't. I would clearly be just playing with numbers and it isn't truly any more readable or maintainable at that point. I am curious though as to what the logic might be behind the increase in this case. It's obviously not line-count.

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• What is the general feeling about reflection extensions in std::type_info?

  - by Evan Teran

  I've noticed that reflection is one feature that developers from other languages find very lacking in c++. For certain applications I can really see why! It is so much easier to write things like an IDE's auto-complete if you had reflection. And certainly serialization APIs would be a world easier if we had it. On the other side, one of the main tenets of c++ is don't pay for what you don't use. Which makes complete sense. That's something I love about c++. But it occurred to me there could be a compromise. Why don't compilers add extensions to the std::type_info structure? There would be no runtime overhead. The binary could end up being larger, but this could be a simple compiler switch to enable/disable and to be honest, if you are really concerned about the space savings, you'll likely disable exceptions and RTTI anyway. Some people cite issues with templates, but the compiler happily generates std::type_info structures for template types already. I can imagine a g++ switch like -fenable-typeinfo-reflection which could become very popular (and mainstream libs like boost/Qt/etc could easily have a check to generate code which uses it if there, in which case the end user would benefit with no more cost than flipping a switch). I don't find this unreasonable since large portable libraries like this already depend on compiler extensions. So why isn't this more common? I imagine that I'm missing something, what are the technical issues with this?

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• Find all cycles in graph, redux

  - by Shadow

  Hi, I know there are a quite some answers existing on this question. However, I found none of them really bringing it to the point. Some argue that a cycle is (almost) the same as a strongly connected components (s. http://stackoverflow.com/questions/546655/finding-all-cycles-in-graph/549402#549402) , so one could use algorithms designed for that goal. Some argue that finding a cycle can be done via DFS and checking for back-edges (s. boost graph documentation on file dependencies). I now would like to have some suggestions on whether all cycles in a graph can be detected via DFS and checking for back-edges? My opinion is that it indeed could work that way as DFS-VISIT (s. pseudocode of DFS) freshly enters each node that was not yet visited. In that sense, each vertex exhibits a potential start of a cycle. Additionally, as DFS visits each edge once, each edge leading to the starting point of a cycle is also covered. Thus, by using DFS and back-edge checking it should indeed be possible to detect all cycles in a graph. Note that, if cycles with different numbers of participant nodes exist (e.g. triangles, rectangles etc.), additional work has to be done to discriminate the acutal "shape" of each cycle.

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• SQL with Regular Expressions vs Indexes with Logical Merging Functions

  - by geeko

  Hello Lads, I am trying to develop a complex textual search engine. I have thousands of textual pages from many books. I need to search pages that contain specified complex logical criterias. These criterias can contain virtually any compination of the following: A: Full words. B: Word roots (semilar to stems; i.e. all words with certain key letters). C: Word templates (in some languages are filled in certain templates to form various part of speech such as adjactives, past/present verbs...). D: Logical connectives: AND/OR/XOR/NOT/IF/IFF and parentheses to state priorities. Now, would it be faster to have the pages' full text in database (not indexed) and search though them all using SQL and Regular Expressions ? Or would it be better to construct indexes of word/root/template-page-location tuples. Hence, we can boost searching for individual words/roots/templates. However, it gets tricky as we interdouce logical connectives into our query. I thought of doing the following steps in such cases: 1: Seperately search for each individual words/roots/templates in the specified query. 2: On priority bases, we merge two result lists (from step 1) at a time depedning on the logical connective For example, if we are searching for "he AND (is OR was)": 1: We shall search for "he", "is" and "was" seperately and get result lists for each word. 2: Merge the result lists of "is" and "was" using the merging function OR-MERGE 3: Merge the merged result list from the OR-MERGE function with the one of "he" using the merging function AND-MERGE The result of step 3 is then returned as the result of the specified query. What do you think gurues ? Which is faster ? Any better ideas ? Thank you all in advance.

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• Thread safe lazy contruction of a singleton in C++

  - by pauldoo

  Is there a way to implement a singleton object in C++ that is: Lazily constructed in a thread safe manner (two threads might simultaneously be the first user of the singleton - it should still only be constructed once). Doesn't rely on static variables being constructed beforehand (so the singleton object is itself safe to use during the construction of static variables). (I don't know my C++ well enough, but is it the case that integral and constant static variables are initialized before any code is executed (ie, even before static constructors are executed - their values may already be "initialized" in the program image)? If so - perhaps this can be exploited to implement a singleton mutex - which can in turn be used to guard the creation of the real singleton..) Excellent, it seems that I have a couple of good answers now (shame I can't mark 2 or 3 as being the answer). There appears to be two broad solutions: Use static initialisation (as opposed to dynamic initialisation) of a POD static varible, and implementing my own mutex with that using the builtin atomic instructions. This was the type of solution I was hinting at in my question, and I believe I knew already. Use some other library function like pthread_once or boost::call_once. These I certainly didn't know about - and am very grateful for the answers posted.

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