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  • Schliemann's method of programming language learning

    - by DVK
    Background: 19th-century German archeologist Heinrich Schliemann was of course famous for his successful quest to find and excavate the city of Troy (an actual archeological site for the Troy of Homer's Iliad). However, he is just as famous for being an astonishing learner of languages - within the space of two years, he taught himself fluent Dutch, English, French, Spanish, Italian and Portuguese, and later went on to learn seven more, including both modern and ancient Greek. One of the methods he famously used was comparison of a known text, e.g. take a book in a language one is fluent in, take a good translation of a book in a language you wish to learn, and go over them in parallel. (various sources cited the book used by Schliemann to be the Bible, or, as the link above states, a novel). Now, for the actual question. Has anyone used (or heard of) an equivalent of Schliemann's method for learning a new programming language? E.g. instead of basing the leaning on references and tutorials, take a somewhat comprehensive set of programs known to have high-quality code in both languages implementing similar/identical algorithms and learn by comparing them? I'm curious about either personal experiences of applying such an approach, or references to something published, or existance of codebases which could be used for such an approach? What got me thinking about the idea was Project Euler and some code snippets I saw on SO, in C++, Perl and Lisp.

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  • Slow XML-RPC in Windows 7 with XML-RPC.NET

    - by Emre Sahin
    I'm considering to use XML-RPC.NET to communicate with a Linux XML-RPC server written in Python. I have tried a sample application (MathApp) from Cook Computing's XML-RPC.NET but it took 30 seconds for the app to add two numbers within the same LAN with server. I have also tried to run a simple client written in Python on Windows 7 to call the same server and it responded in 5 seconds. The machine has 4 GB of RAM with comparable processing power so this is not an issue. Then I tried to call the server from a Windows XP system with Java and PHP. Both responses were pretty fast, almost instantly. The server was responding quickly on localhost too, so I don't think the latency arise from server. My googling returned me some problems regarding Windows' use of IPv6 but our call to server does include IPv4 address (not hostname) in the same subnet. Anyways I turned off IPv6 but nothing changed. Are there any more ways to check for possible causes of latency?

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  • Best ways to teach a beginner to program?

    - by Justin Standard
    Original Question I am currently engaged in teaching my brother to program. He is a total beginner, but very smart. (And he actually wants to learn). I've noticed that some of our sessions have gotten bogged down in minor details, and I don't feel I've been very organized. (But the answers to this post have helped a lot.) What can I do better to teach him effectively? Is there a logical order that I can use to run through concept by concept? Are there complexities I should avoid till later? The language we are working with is Python, but advice in any language is welcome. How to Help If you have good ones please add the following in your answer: Beginner Exercises and Project Ideas Resources for teaching beginners Screencasts / blog posts / free e-books Print books that are good for beginners Please describe the resource with a link to it so I can take a look. I want everyone to know that I have definitely been using some of these ideas. Your submissions will be aggregated in this post. Online Resources for teaching beginners: A Gentle Introduction to Programming Using Python How to Think Like a Computer Scientist Alice: a 3d program for beginners Scratch (A system to develop programming skills) How To Design Programs Structure and Interpretation of Computer Programs Learn To Program Robert Read's How To Be a Programmer Microsoft XNA Spawning the Next Generation of Hackers COMP1917 Higher Computing lectures by Richard Buckland (requires iTunes) Dive into Python Python Wikibook Project Euler - sample problems (mostly mathematical) pygame - an easy python library for creating games Create Your Own Games With Python ebook Foundations of Programming for a next step beyond basics. Squeak by Example Recommended Print Books for teaching beginners Accelerated C++ Python Programming for the Absolute Beginner Code by Charles Petzold

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  • Reverse engineering and patching a DirectX game?

    - by yodaj007
    Background I am playing Imperishable Night, one of the Touhou series of games. The shoot button is 'z', moving slower is 'shift', and the arrow keys move. Unfortunately for me, using shift-z ghosts my right arrow key, so I can't move to the right while shooting. This ghosting happens in all applications, and switching keyboards fixes it. Goal I want to locate in the disassembled code the directx function that gets the keyboard input and compares it against the 'z' key, and change that key to 'a'. I'm considering this a fun project. Assuming the size of the scan codes are the same, this should be fairly simple. And because the executable is only 400k, maybe this will provide a unique opportunity for me to explore the dark side of the computing underworld (kidding). Relevant experience I have some experience with coding in assembly, but not in the disassembly of such. I have no experience with the DirectX apis. Question I need some guidance. I've found a listing of directx keyboard scan codes, and a program called PEExplorer that looks like it will do what I need. Is there a means by which I can turn some of the assembly with C function calls so it's more easily read? I will need to locate where the game retrieves the currently pressed keys, compares those against a list, and it's that list I need to modify. Any input would be greatly appreciated.

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  • Code Golf: Leibniz formula for Pi

    - by Greg Beech
    I recently posted one of my favourite interview whiteboard coding questions in "What's your more controversial programming opinion", which is to write a function that computes Pi using the Leibniz formula. It can be approached in a number of different ways, and the exit condition takes a bit of thought, so I thought it might make an interesting code golf question. Shortest code wins! Given that Pi can be estimated using the function 4 * (1 - 1/3 + 1/5 - 1/7 + ...) with more terms giving greater accuracy, write a function that calculates Pi to within 0.00001. Edit: 3 Jan 2008 As suggested in the comments I changed the exit condition to be within 0.00001 as that's what I really meant (an accuracy 5 decimal places is much harder due to rounding and so I wouldn't want to ask that in an interview, whereas within 0.00001 is an easier to understand and implement exit condition). Also, to answer the comments, I guess my intention was that the solution should compute the number of iterations, or check when it had done enough, but there's nothing to prevent you from pre-computing the number of iterations and using that number. I really asked the question out of interest to see what people would come up with.

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  • Navigating through a sea of hype

    - by wouldLikeACrystalBall
    This is a vague, open question, so if you have no interest in these, please leave now. A few years ago it seemed everyone thought the death of desktop software was imminent. Web applications were the future. Everyone would move to cloud-based software-as-a-service systems, and developing applications for specific end-user platforms like Windows would soon become something of a ghetto. Joel's "How Microsoft Lost the API War" was but one of many such pieces sounding the death knell for this way of software development. Flash-forward to 2010, and the hype is all around mobile devices, particularly the iPhone. Software-as-a-Service vendors--even small ones such as YCombinator startups--go out of their way to build custom applications for the iPhone and other smart phone devices; applications that can be quite sophisticated, that run only on specific hardware and software architectures and are thus inherently incompatible. Now some of you are probably thinking, "Well, only the decline of desktop software was predicted; mobile devices aren't desktops." But the term was used by those predicting its demise to mean laptops also, and really any platform capable of running a browser. What was promised was a world where HTML and related standards would supplant native applications and their inherent difficulties. We would all code to the browser, not the OS. But here we are in 2010 with the AppStore bulging and development for the iPad just revving up. A few days ago, I saw someone on Hacker News claim that the future of computing was entirely in small, portable devices. Apparently the future is underpowered, requires dexterous thumbs and induces near-sightedness. How do those who so vehemently asserted one thing now assert the opposite with equal vehemence, without making even the slightest admission of error? And further, how are we as developers supposed to sift through all of this? I bought into the whole web-standards utopianism that was in vogue back in '06-'07 and now feel like it was a mistake. Is there some formula one can apply rather than a mere appeal to experience?

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  • MacPorts - Installing Port, Dependencies Failed

    - by Louis
    I am attempting to install xulrunner on OSX 10.6.3 using the following: sudo port install xulrunner However, I am receiving the following error: nat-10-200-136-126:phoneyc-new $ sudo port install xulrunner ---> Computing dependencies for xulrunner ---> Activating zlib @1.2.5_0 Error: The following dependencies failed to build: gconf dbus-glib glib2 zlib gtk-doc docbook-xml docbook-xml-4.1.2 xmlcatmgr docbook-xml-4.2 docbook-xml-4.3 docbook-xml-4.4 docbook-xml-4.5 docbook-xml-5.0 docbook-xsl gnome-doc-utils iso-codes libxslt libxml2 p5-xml-parser py26-libxml2 python26 bzip2 db46 gdbm openssl readline sqlite3 tk Xft2 fontconfig freetype xrender xorg-libX11 xorg-bigreqsproto xorg-inputproto xorg-kbproto xorg-libXau xorg-xproto xorg-libXdmcp xorg-util-macros xorg-xcmiscproto xorg-xextproto xorg-xf86bigfontproto xorg-xtrans xorg-renderproto tcl xorg-libXScrnSaver xorg-libXext xorg-scrnsaverproto rarian getopt intltool gnome-common p5-getopt-long p5-pathtools p5-scalar-list-utils gtk2 atk cairo libpixman libpng jasper jpeg pango shared-mime-info tiff xorg-libXcomposite xorg-compositeproto xorg-libXfixes xorg-fixesproto xorg-libXcursor xorg-libXdamage xorg-damageproto xorg-libXi xorg-libXinerama xorg-xineramaproto xorg-libXrandr xorg-randrproto orbit2 libidl policykit heimdal lcms libcanberra gstreamer bison flex gzip texinfo lzmautils libvorbis libogg libnotify nss xorg-libXt xorg-libsm xorg-libice Error: Status 1 encountered during processing. Before reporting a bug, first run the command again with the -d flag to get complete output. nat-10-200-136-126:phoneyc-new$ I am unsure how to correct this issue, so any help would be much appreciated!

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  • Arrrg! MovieClip object refuses to moved in any rational way in as3?

    - by Aaron H.
    I have a MovieClip object, which is exported for actionscript (AS3) in an .swc file. When I place an instance of the clip on the stage without any modifications, it appears in the upper left corner, about half off stage (i.e. only the lower right quadrant of the object is visible). I understand that this is because the clip has a registration point which is not the upper left corner. If you call getBounds() on the movieclip you can get the bounds of the clip (presumably from the "point" that it's aligned on) which looks something like (left: -303, top: -100, right: 303, bottom: 100), you can subtract the left and top values from the clip x and y: clip.x -= bounds.left; clip.y -= bounds.top; This seems to properly align the clip fully on stage with the top left of the clip squarely in the corner of the stage. But! Following that logic doesn't seem to work when aligning it on the center of the stage! clip.x = (stage.stageWidth / 2); etc... This creates the crazy parallel universe where the clip is now down in the lower right corner of the stage. The only clue I have is that looking at: clip.transform.matrix and clip.transform.concatenatedMatrix matrix has a tx value of 748 (half of stage height) ty value of 426 (Half of stage height) concatenatedMatrix has a tx value of 1699.5 and ty value of 967.75 That's also obviously where the movieclip is getting positioned, but why? Where is this additional translation coming from?

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  • JVM CMS Garbage Collecting Issues

    - by jlintz
    I'm seeing the following symptoms on an application's GC log file with the Concurrent Mark-Sweep collector: 4031.248: [CMS-concurrent-preclean-start] 4031.250: [CMS-concurrent-preclean: 0.002/0.002 secs] [Times: user=0.00 sys=0.00, real=0.00 secs] 4031.250: [CMS-concurrent-abortable-preclean-start] CMS: abort preclean due to time 4036.346: [CMS-concurrent-abortable-preclean: 0.159/5.096 secs] [Times: user=0.00 sys=0.01, real=5.09 secs] 4036.346: [GC[YG occupancy: 55964 K (118016 K)]4036.347: [Rescan (parallel) , 0.0641200 secs]4036.411: [weak refs processing, 0.0001300 secs]4036.411: [class unloading, 0.0041590 secs]4036.415: [scrub symbol & string tables, 0.0053220 secs] [1 CMS-remark: 16015K(393216K)] 71979K(511232K), 0.0746640 secs] [Times: user=0.08 sys=0.00, real=0.08 secs] The preclean process keeps aborting continously. I've tried adjusting CMSMaxAbortablePrecleanTime to 15 seconds, from the default of 5, but that has not helped. The current JVM options are as follows... Djava.awt.headless=true -Xms512m -Xmx512m -Xmn128m -XX:MaxPermSize=128m -XX:+HeapDumpOnOutOfMemoryError -XX:+UseParNewGC -XX:+UseConcMarkSweepGC -XX:BiasedLockingStartupDelay=0 -XX:+DoEscapeAnalysis -XX:+UseBiasedLocking -XX:+EliminateLocks -XX:+CMSParallelRemarkEnabled -verbose:gc -XX:+PrintGCTimeStamps -XX:+PrintGCDetails -XX:+PrintHeapAtGC -Xloggc:gc.log -XX:+CMSClassUnloadingEnabled -XX:+CMSPermGenPrecleaningEnabled -XX:CMSInitiatingOccupancyFraction=50 -XX:ReservedCodeCacheSize=64m -Dnetworkaddress.cache.ttl=30 -Xss128k It appears the concurrent-abortable-preclean never gets a chance to run. I read through http://blogs.sun.com/jonthecollector/entry/did_you_know which had a suggestion of enabling CMSScavengeBeforeRemark, but the side effects of pausing did not seem ideal. Could anyone offer up any suggestions? Also I was wondering if anyone had a good reference for grokking the CMS GC logs, in particular this line: [1 CMS-remark: 16015K(393216K)] 71979K(511232K), 0.0746640 secs] Not clear on what memory regions those numbers are referring to.

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  • Disco/MapReduce: Using results of previous iteration as input to new iteration

    - by muckabout
    Currently am implementing PageRank on Disco. As an iterative algorithm, the results of one iteration are used as input to the next iteration. I have a large file which represents all the links, with each row representing a page and the values in the row representing the pages to which it links. For Disco, I break this file into N chunks, then run MapReduce for one round. As a result, I get a set of (page, rank) tuples. I'd like to feed this rank to the next iteration. However, now my mapper needs two inputs: the graph file, and the pageranks. I would like to "zip" together the graph file and the page ranks, such that each line represents a page, it's rank, and it's out links. Since this graph file is separated into N chunks, I need to split the pagerank vector into N parallel chunks, and zip the regions of the pagerank vectors to the graph chunks This all seems more complicated than necessary, and as a pretty straightforward operation (with the quintessential mapreduce algorithm), it seems I'm missing something about Disco that could really simplify the approach. Any thoughts?

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  • Excel export displaying '#####...'

    - by Cypher
    I'm trying to export an Excel database into .txt (Tab Delimited), but some of my cells are quite large. When I export into a txt some of the cells are exported as '#######....' which is surprisingly useless. Has this happened to anyone else? Do you know an easy fix? Data from one cell of my column: Accounting, African Studies, Agricultural/Bioresource Engineering, Agricultural Economics, Agricultural Science, Anatomy/Cell Biology, Animal Biology, Animal Science, Anthropology, Applied Zoology, Architecture, Art History, Atmospheric/Oceanic Science, Biochemistry, Biology, Botanical Sciences, Canadian Studies, Chemical Engineering, Chemistry/Bio-Organic/Environmental/Materials,ChurchMusicPerformance, Civil Engineering/Applied Mechanics, Classics, Composition, Computer Engineering,ComputerScience, ContemporaryGerman Studies, Dietetics, Early Music Performance, Earth/Planetary Sciences, East Asian Studies, Economics, Electrical Engineering, English Literature/ Drama/Theatre/Cultural Studies, Entrepreneurship, Environment, Environmental Biology, Finance, Food Science, Foundations of Computing, French Language/Linguistics/Literature/Translation, Geography, Geography/ Urban Systems, German, German Language/Literature/Culture, Hispanic Languages/Literature/Culture,History,Humanistic Studies, Industrial Relations, Information Systems, International Business, International Development Studies, Italian Studies/Medieval/Renaissance, Jazz Performance, Jewish Studies, Keyboard Studies, Kindergarten/Elementary Education, Kindergarten/Elementary Education/Jewish Studies,Kinesiology, Labor/Management Relations, Latin American/Caribbean Studies, Linguistics, Literature/Translation, Management Science, Marketing, Materials Engineering,Mathematics,Mathematics/Statistics,Mechanical Engineering, Microbiology, Microbiology/Immunology, Middle Eastern Studies, Mining Engineering, Music, Music Education, MusicHistory,Music Technology,Music Theory,North American Studies, Nutrition,OperationsManagement,OrganizationalBehavior/Human Resources Management, Performing Arts, Philosophy, Physical Education, Physics, Physiology, Plant Sciences, Political Science, Psychology, Quebec Studies, Religious Studies/Scriptures/Interpretations/World Religions,ResourceConservation,Russian, Science for Teachers,Secondary Education, Secondary Education/Music, Secondary Education/Science, SocialWork, Sociology, Software Engineering, Soil Science, Strategic Management, Teaching of French/English as a Second Language, Theology, Wildlife Biology, Wildlife Resources, Women’s Studies.

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  • Resources related to data-mining and gaming on social networks

    - by darren
    Hi all I'm interested in the problem of patterning mining among players of social networking games. For example detecting cheaters of a game, given a company's user database. So far I have been following the usual recipe for a data mining project: construct a data warehouse that aggregates significant information select a classifier, and train it with a subsectio of records from the warehouse validate classifier with another test set lather, rinse, repeat Surprisingly, I've found very little in this area regarding literature, best practices, etc. I am hoping to crowdsource the information gathering problem here. Specifically what I'm looking for: What classifiers have worked will for this type of pattern mining (it seems highly temporal, users playing games, users receiving rewards, users transferring prizes etc). Are there any highly agreed upon attributes specific to social networking / gaming data? What is a practical amount of information that should be considered? One problem I've run into is data overload, where queries and data cleansing may take days to complete. Related to point above, what hardware resources are required to produce results? I've found it difficult to estimate the amount of computing power I will require for production use. It has become apparent that a white box in the corner does not have enough horse-power for such a project. Are companies generally resorting to cloud solutions? Are they buying clusters? Basically, any resources (theoretical, academic, or practical) about implementing a social networking / gaming pattern-mining program would be very much appreciated. Thanks.

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  • Segmentation fault while matrix multiplication using openMp?

    - by harshit
    My matrix multiplication code is int matMul(int ld, double** matrix) { //local variables initialize omp_set_num_threads(nthreads); #pragma omp parallel private(tid,diag,ld) shared(i,j,k,matrix) { /* Obtain and print thread id */ tid = omp_get_thread_num(); for ( k=0; k<ld; k++) { if (matrix[k][k] == 0.0) { error = 1; return error; } diag = 1.0 / matrix[k][k]; #pragma omp for for ( i=k+1; i < ld; i++) { matrix[i][k] = diag * matrix[i][k]; } for ( j=k+1; j<ld; j++) { for ( i=k+1; i<ld; i++) { matrix[i][j] = matrix[i][j] - matrix[i][k] * matrix[k][j]; } } } } return error; } I assume that it is because of matrix object only but why will it be null even though it is passed as a parameter..

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  • Which Computer Organization & Architecture book is good for me?

    - by claws
    I'm always interested in learning the inner working of things. I started with C programming and then learnt Operating systems (from stallings) and then linkers & loaders and then assembly language after reading these now I want to go into little more depth. Computer Architecture. I feel that makes everything clear. As per SO archives these are the two good books: Computer Architecture: A Quantitative Approach, 4th Edition Computer Organization and Design, Fourth Edition, ~ David A. Patterson, John L. Hennessy But I've browsed through the contents of these books and found that they don't exactly meet my needs. I want to learn more about caches, Memory Management Unit , mapping b/w virtual memory & physical memory I'm no way interested in other ISAs like MIPS etc.. I'm IA32 and X86-64 fan and I want to stick to it. I'm not a hardware developer I don't want to details like circuit diagrams or How is L1, L2 & L3 caches are implemented? I want to know the parallel processing technologies like HyperThreading at the architecture level but again I don't want to design them. I liked the table of Contents of - Computer Architecture: A Quantitative Approach, 4th Edition but Quantitave Approach? Seriously?? I want to know the details of current technologies and I dont want to spend reading 200 pages of outdated old technologies ( I experienced this while learning ASM}

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  • Computed width with decimal values in Firefox, but without decimals in Webkit

    - by jävi
    Hello one more time! I have a strange problem working with HTML,CSS in different browsers: Firefox 3.6 and Webkit browsers (Chrome & Safari). My HTML looks like this: <div class="ln-letters"> <a href="#" class="all">ALL</a> <a href="#" class="a">A</a> <a href="#" class="b">B</a> <a href="#" class="c">C</a> </div> And my CSS is... .ln-letters a { font-family: 'Lucida Grande'; font-size:14px; display:block; float:left; padding:0px 7px; border-left:1px solid silver; border-right:none; text-decoration:none; } So as you can guess, each anchor gets a different width depending on its inner text. For example the first element with the text 'ALL' will be bigger (more width) than the others. Now the problem is that in Firefox (using Firebug) I can see that the computed width for the first element is 26.5667px, while in Chrome (using Chrome's developer tools) the computed width for the same element is exactly 27px. Therefore the div.ln-letters ends with different widths in each browser and that is causing me some troubles. Question is: there is any workaround to avoid Firefox computing decimal values? Or the opposite: to force Chrome to compute decimal values? Thank you in advance!

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  • Can I avoid explicit 'self'?

    - by bguiz
    I am fairly new to Python and trying to pick it up, so please forgive if this question has a very obvious answer! I have been learning Python by following some pygame tutorials. Therein I found extensive use of the keyword self, and coming from a primarily Java background, I find that I keep forgetting to type self. For example, instead of self.rect.centerx I would type rect.centerx, because, to me, rect is already a member variable of the class. The Java parallel I can think of for this situation is having to prefix all references to member variables with this. Am I stuck prefixing all member variables with self, or is there a way to declare them that would allow me to avoid having to do so? Even if what I am suggesting isn't "pythonic", I'd still like to know if it is possible. I have taken a look at these related SO questions, but they don't quite answer what I am after: Python - why use “self” in a class? Why do you need explicitly have the “self” argument into a Python method?

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  • Using Java Executor on AppEngine causes AccessControlException

    - by Drew
    How do you get java.util.concurrent.Executor or CompletionService to work on Google AppEngine? The classes are all officially white-listed, but I get a runtime security error when trying to submit asynchronous tasks. Code: // uses the async API but this factory makes it so that tasks really // happen sequentially Executor executor = java.util.concurrent.Executors.newSingleThreadExecutor(); // wrap Executor in CompletionService CompletionService<String> completionService = new ExecutorCompletionService<String>(executor); final SomeTask someTask = new SomeTask(); // this line throws exception completionService.submit(new Callable<String>(){ public String call() { return someTask.doNothing("blah"); } }); // alternately, send Runnable task directly to Executor, // which also throws an exception executor.execute(new Runnable(){ public void run() { someTask.doNothing("blah"); } }); } private class SomeTask{ public String doNothing(String message){ return message; } } Exception: java.security.AccessControlException: access denied (java.lang.RuntimePermission modifyThreadGroup) at java.security.AccessControlContext.checkPermission(AccessControlContext.java:323) at java.security.AccessController.checkPermission(AccessController.java:546) at java.lang.SecurityManager.checkPermission(SecurityManager.java:532) at com.google.appengine.tools.development.DevAppServerFactory$CustomSecurityManager.checkPermission(DevAppServerFactory.java:166) at com.google.appengine.tools.development.DevAppServerFactory$CustomSecurityManager.checkAccess(DevAppServerFactory.java:191) at java.lang.ThreadGroup.checkAccess(ThreadGroup.java:288) at java.lang.Thread.init(Thread.java:332) at java.lang.Thread.(Thread.java:565) at java.util.concurrent.Executors$DefaultThreadFactory.newThread(Executors.java:542) at java.util.concurrent.ThreadPoolExecutor.addThread(ThreadPoolExecutor.java:672) at java.util.concurrent.ThreadPoolExecutor.addIfUnderCorePoolSize(ThreadPoolExecutor.java:697) at java.util.concurrent.ThreadPoolExecutor.execute(ThreadPoolExecutor.java:652) at java.util.concurrent.Executors$DelegatedExecutorService.execute(Executors.java:590) at java.util.concurrent.ExecutorCompletionService.submit(ExecutorCompletionService.java:152) This code works fine when run on Tomcat or via command-line JVM. However, it chokes in the AppEngine SDK Jetty container (tried with Eclipse plugin and the maven-gae-plugin). AppEngine is likely designed to not allow potentially dangerous programs to run, so I could see them completely disabling thread creation. However, why would Google allow you to create a class, but not allow you to call methods on it? White-listing java.util.concurrent is misleading. Is there some other way to do parallel/simultaneous/concurrent tasks on GAE?

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  • Can't get any speedup from parallelizing Quicksort using Pthreads

    - by Murat Ayfer
    I'm using Pthreads to create a new tread for each partition after the list is split into the right and left halves (less than and greater than the pivot). I do this recursively until I reach the maximum number of allowed threads. When I use printfs to follow what goes on in the program, I clearly see that each thread is doing its delegated work in parallel. However using a single process is always the fastest. As soon as I try to use more threads, the time it takes to finish almost doubles, and keeps increasing with number of threads. I am allowed to use up to 16 processors on the server I am running it on. The algorithm goes like this: Split array into right and left by comparing the elements to the pivot. Start a new thread for the right and left, and wait until the threads join back. If there are more available threads, they can create more recursively. Each thread waits for its children to join. Everything makes sense to me, and sorting works perfectly well, but more threads makes it slow down immensely. I tried setting a minimum number of elements per partition for a thread to be started (e.g. 50000). I tried an approach where when a thread is done, it allows another thread to be started, which leads to hundreds of threads starting and finishing throughout. I think the overhead was way too much. So I got rid of that, and if a thread was done executing, no new thread was created. I got a little more speedup but still a lot slower than a single process. The code I used is below. http://pastebin.com/UaGsjcq2 Does anybody have any clue as to what I could be doing wrong?

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  • Java exception handling in non sequential tasks (pattern/good practice)

    - by Hernán Eche
    There are some task that should't be done in parallel, (for example opening a file, reading, writing, and closing, there is an order on that...) But... Some task are more like a shoping list, I mean they could have a desirable order but it's not a must..example in communication or loading independient drivers etc.. For that kind of tasks, I would like to know a java best practice or pattern for manage exceptions.. The java simple way is: getUFO { try { loadSoundDriver(); loadUsbDriver(); loadAlienDetectorDriver(); loadKeyboardDriver(); } catch (loadSoundDriverFailed) { doSomethingA; } catch (loadUsbDriverFailed) { doSomethingB; } catch (loadAlienDetectorDriverFailed) { doSomethingC; } catch (loadKeyboardDriverFailed) { doSomethingD; } } But what about having an exception in one of the actions but wanting to try with the next ones?? I've thought this approach, but don't seem to be a good use for exceptions I don't know if it works, doesn't matter, it's really awful!! getUFO { Exception ex=null; try { try{ loadSoundDriver(); }catch (Exception e) { ex=e; } try{ loadUsbDriver(); }catch (Exception e) { ex=e; } try{ loadAlienDetectorDriver(); }catch (Exception e) { ex=e; } try{ loadKeyboardDriver() }catch (Exception e) { ex=e; } close the file; if(ex!=null) { throw ex; } } catch (loadSoundDriverFailed) { doSomethingA; } catch (loadUsbDriverFailed) { doSomethingB; } catch (loadAlienDetectorDriverFailed) { doSomethingC; } catch (loadKeyboardDriverFailed) { doSomethingD; } } seems not complicated to find a better practice for doing that.. I still didn't thanks for any advice

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  • Working around MySQL error "Deadlock found when trying to get lock; try restarting transaction"

    - by Anon Guy
    Hi all: I have a MySQL table with about 5,000,000 rows that are being constantly updated in small ways by parallel Perl processes connecting via DBI. The table has about 10 columns and several indexes. One fairly common operation gives rise to the following error sometimes: DBD::mysql::st execute failed: Deadlock found when trying to get lock; try restarting transaction at Db.pm line 276. The SQL statement that triggers the error is something like this: UPDATE file_table SET a_lock = 'process-1234' WHERE param1 = 'X' AND param2 = 'Y' AND param3 = 'Z' LIMIT 47 The error is triggered only sometimes. I'd estimate in 1% of calls or less. However, it never happened with a small table and has become more common as the database has grown. Note that I am using the a_lock field in file_table to ensure that the four near-identical processes I am running do not try and work on the same row. The limit is designed to break their work into small chunks. I haven't done much tuning on MySQL or DBD::mysql. MySQL is a standard Solaris deployment, and the database connection is set up as follows: my $dsn = "DBI:mysql:database=" . $DbConfig::database . ";host=${DbConfig::hostname};port=${DbConfig::port}"; my $dbh = DBI->connect($dsn, $DbConfig::username, $DbConfig::password, { RaiseError => 1, AutoCommit => 1 }) or die $DBI::errstr; I have seen online that several other people have reported similar errors and that this may be a genuine deadlock situation. I have two questions: What exactly about my situation is causing the error above? Is there a simple way to work around it or lessen its frequency? For example, how exactly do I go about "restarting transaction at Db.pm line 276"? Thanks in advance.

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  • Silverlight combobox performance issue

    - by Vinzz
    Hi, I'm facing a performance issue with a crowded combobox (5000 items). Rendering of the drop down list is really slow (as if it was computing all items before showing any). Do you have any trick to make this dropdown display lazy? Xaml code: <Grid x:Name="LayoutRoot"> <StackPanel Orientation="Horizontal" Width="200" Height="20"> <TextBlock>Test Combo </TextBlock> <ComboBox x:Name="fooCombo" Margin="5,0,0,0"></ComboBox> </StackPanel> </Grid> code behind: public MainPage() { InitializeComponent(); List<string> li = new List<string>(); int Max = 5000; for (int i = 0; i < Max; ++i) li.Add("Item - " + i); fooCombo.ItemsSource = li; }

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  • Duration of Excessive GC Time in "java.lang.OutOfMemoryError: GC overhead limit exceeded"

    - by jilles de wit
    Occasionally, somewhere between once every 2 days to once every 2 weeks, my application crashes in a seemingly random location in the code with: java.lang.OutOfMemoryError: GC overhead limit exceeded. If I google this error I come to this SO question and that lead me to this piece of sun documentation which expains: The parallel collector will throw an OutOfMemoryError if too much time is being spent in garbage collection: if more than 98% of the total time is spent in garbage collection and less than 2% of the heap is recovered, an OutOfMemoryError will be thrown. This feature is designed to prevent applications from running for an extended period of time while making little or no progress because the heap is too small. If necessary, this feature can be disabled by adding the option -XX:-UseGCOverheadLimit to the command line. Which tells me that my application is apparently spending 98% of the total time in garbage collection to recover only 2% of the heap. But 98% of what time? 98% of the entire two weeks the application has been running? 98% of the last millisecond? I'm trying to determine a best approach to actually solving this issue rather than just using -XX:-UseGCOverheadLimit but I feel a need to better understand the issue I'm solving.

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  • Delphi dbExpress and Interbase: Unicode migration steps and risks?

    - by mjustin
    Currently, our database uses Win1252 as the only character encoding. We will have to support Unicode in the database tables soon, which means we have to perform this migration for four databases and around 80 Delphi applications which run in-house in a 24/7 environment. Are there recommendations for database migrations to UTF-8 (or UNICODE_FSS) for Delphi applications? Some questions listed below. Many thanks in advance for your answers! are there tools which help with the migration of the existing databases (sizes between 250 MB and 2 GB, no Blob fields), by dumping the data, recreating the database with UNICODE_FSS or UTF-8, and loading the data back? are there known problems with Delphi 2009, dbExpress and Interbase 7.5 related to Unicode character sets? would you recommend to upgrade the databases to Interbase 2009 first? (This upgrade is planned but does not have a high priority) can we simply migrate the database and Delphi will handle the Unicode character sets automatically, or will we have to change all character field types in every Datamodule (dfm and source code) too? which strategy would you recommend to work on the migration in parallel with the normal development and maintenance of the existing application? The application runs in-house so development and database administration is done internally. Update: one problem I found now is that there are two different persistent field types for Unicode and non Unicode character fields. For the existing database, dbExpress creates TStringField objects. For the Unicode database fields, dbExpress creates (or expects!) TWideStringField objects. So we can not just change the database and the connection code page to Unicode. We also have to modify all datamodules to use the new field type. The modified datamodule however will not be backwards compatible.

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  • Displaying shifts on a timetable/calendar using C#

    - by Dave Peters
    I am very much a beginner and have experience of SQL and a tiny amount of VBA. What I am looking to do is create a tool to pull shift times from a database and to display them on a timetable/calendar. It will be part of a desktop application that the (very tech illiterate) end users will use to view and amend shift patterns. In essence it will be a grid with days on one axis and people on the other (I would however like to have the blocks proportional to shift length). In my mind it would potentially be a simple Gantt chart. All computing stuff I’ve learnt has been through trial and error and I want to use this project to get a much better understanding of C# as well as to get to the end product. I have been reading around for ways to tackle the problem and my issue is creating the timetable framework to which I will bind the data. I am using Visual Studio 2010 and SQL Server 2008 R2. Do you know of good resources which will either start me on the road to designing my own interface or give a basic framework I can adapt? All the resources I’ve found so far have been in different languages or for web based applications. Thank you for your time.

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  • Recursively adding threads to a Java thread pool

    - by Leith
    I am working on a tutorial for my Java concurrency course. The objective is to use thread pools to compute prime numbers in parallel. The design is based on the Sieve of Eratosthenes. It has an array of n bools, where n is the largest integer you are checking, and each element in the array represents one integer. True is prime, false is non prime, and the array is initially all true. A thread pool is used with a fixed number of threads (we are supposed to experiment with the number of threads in the pool and observe the performance). A thread is given a integer multiple to process. The thread then finds the first true element in the array that is not a multiple of thread's integer. The thread then creates a new thread on the thread pool which is given the found number. After a new thread is formed, the existing thread then continues to set all multiples of it's integer in the array to false. The main program thread starts the first thread with the integer '2', and then waits for all spawned threads to finish. It then spits out the prime numbers and the time taken to compute. The issue I have is that the more threads there are in the thread pool, the slower it takes with 1 thread being the fastest. It should be getting faster not slower! All the stuff on the internet about Java thread pools create n worker threads the main thread then wait for all threads to finish. The method I use is recursive as a worker can spawn more worker threads. I would like to know what is going wrong, and if Java thread pools can be used recursively.

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