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• MySQL table organization and optimization (Rails)

  - by aguynamedloren

  I've been learning Ruby on Rails over the past few months with no prior programming experience. Lately, I've been thinking about database optimization and table organization. I know there are great books on the subject, but I typically learn by example / as I go. Here's a hypothetical situation: Let's say I am building a social network for a niche community with 250,000 members (users). The users have the ability to attend events. Let's say there are 50,000 past/present/future events. Much like Facebook events, a user can attend any number of events and an event can have any number of attendees. In the database, there would be a table for users and a table for events. Somehow I would have to create an association between the users and events. I could create an "events" column in the users table such that each user row would contain a hash of event IDs, or I could create an "attendees" column in the events table such that each event row would contain a hash of user IDs. Neither of these solutions seem ideal, however. On a users profile page, I want to display the list of events they are associated with, which would require scanning the 50,000 event rows for the user ID of said user if I include an "attendees" column in the events table. Likewise, on an event page, I want to display a list of attendees for the event, which would require scanning the 250,000 user rows for the event ID of said event if I include an "events" column in the users table. Option 3 would be to create a third table that contains the attendee information for each and every event - but I don't see how this would solve any problems. Are these non-issues? Rails makes accessing all of this information easy, but I guess I'm worried about scale. It is entirely possible that I am under-estimating the speed and processing power of modern databases / servers / etc. How long would it take to scan 250,000 user rows for specific event IDs - 10ms? 100ms? 1,000ms? I guess that's not that bad. Am I just over-thinking this?

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• chaining array of tasks with continuation

  - by Andrei Cristof

  I have a Task structure that is a little bit complex(for me at least). The structure is: (where T = Task) T1, T2, T3... Tn. There's an array (a list of files), and the T's represent tasks created for each file. Each T has always two subtasks that it must complete or fail: Tn.1, Tn.2 - download and install. For each download (Tn.1) there are always two subtasks to try, download from two paths(Tn.1.1, Tn.1.2). Execution would be: First, download file: Tn1.1. If Tn.1.1 fails, then Tn.1.2 executes. If either from download tasks returns OK - execute Tn.2. If Tn.2 executed or failed - go to next Tn. I figured the first thing to do, was to write all this structure with jagged arrays: private void CreateTasks() { //main array Task<int>[][][] mainTask = new Task<int>[_queuedApps.Count][][]; for (int i = 0; i < mainTask.Length; i++) { Task<int>[][] arr = GenerateOperationTasks(); mainTask[i] = arr; } } private Task<int>[][] GenerateOperationTasks() { //two download tasks Task<int>[] downloadTasks = new Task<int>[2]; downloadTasks[0] = new Task<int>(() => { return 0; }); downloadTasks[1] = new Task<int>(() => { return 0; }); //one installation task Task<int>[] installTask = new Task<int>[1] { new Task<int>(() => { return 0; }) }; //operations Task is jagged - keeps tasks above Task<int>[][] operationTasks = new Task<int>[2][]; operationTasks[0] = downloadTasks; operationTasks[1] = installTask; return operationTasks; } So now I got my mainTask array of tasks, containing nicely ordered tasks just as described above. However after reading the docs on ContinuationTasks, I realise this does not help me since I must call e.g. Task.ContinueWith(Task2). I'm stumped about doing this on my mainTask array. I can't write mainTask[0].ContinueWith(mainTask[1]) because I dont know the size of the array. If I could somehow reference the next task in the array (but without knowing its index), but cant figure out how. Any ideas? Thank you very much for your help. Regards,

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• Reading Source Code Aloud

  - by Jon Purdy

  After seeing this question, I got to thinking about the various challenges that blind programmers face, and how some of them are applicable even to sighted programmers. Particularly, the problem of reading source code aloud gives me pause. I have been programming for most of my life, and I frequently tutor fellow students in programming, most often in C++ or Java. It is uniquely aggravating to try to verbally convey the essential syntax of a C++ expression. The speaker must give either an idiomatic translation into English, or a full specification of the code in verbal longhand, using explicit yet slow terms such as "opening parenthesis", "bitwise and", et cetera. Neither of these solutions is optimal. On the one hand, an idiomatic translation is only useful to a programmer who can de-translate back into the relevant programming code—which is not usually the case when tutoring a student. In turn, education (or simply getting someone up to speed on a project) is the most common situation in which source is read aloud, and there is a very small margin for error. On the other hand, a literal specification is aggravatingly slow. It takes far far longer to say "pound, include, left angle bracket, iostream, right angle bracket, newline" than it does to simply type #include <iostream>. Indeed, most experienced C++ programmers would read this merely as "include iostream", but again, inexperienced programmers abound and literal specifications are sometimes necessary. So I've had an idea for a potential solution to this problem. In C++, there is a finite set of keywords—63—and operators—54, discounting named operators and treating compound assignment operators and prefix versus postfix auto-increment and decrement as distinct. There are just a few types of literal, a similar number of grouping symbols, and the semicolon. Unless I'm utterly mistaken, that's about it. So would it not then be feasible to simply ascribe a concise, unique pronunciation to each of these distinct concepts (including one for whitespace, where it is required) and go from there? Programming languages are far more regular than natural languages, so the pronunciation could be standardised. Speakers of any language would be able to verbally convey C++ code, and due to the regularity and fixity of the language, speech-to-text software could be optimised to accept C++ speech with a high degree of accuracy. So my question is twofold: first, is my solution feasible; and second, does anyone else have other potential solutions? I intend to take suggestions from here and use them to produce a formal paper with an example implementation of my solution.

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• how to implement a "soft barrier" in multithreaded c++

  - by Jason

  I have some multithreaded c++ code with the following structure: do_thread_specific_work(); update_shared_variables(); //checkpoint A do_thread_specific_work_not_modifying_shared_variables(); //checkpoint B do_thread_specific_work_requiring_all_threads_have_updated_shared_variables(); What follows checkpoint B is work that could have started if all threads have reached only checkpoint A, hence my notion of a "soft barrier". Typically multithreading libraries only provide "hard barriers" in which all threads must reach some point before any can continue. Obviously a hard barrier could be used at checkpoint B. Using a soft barrier can lead to better execution time, especially since the work between checkpoints A and B may not be load-balanced between the threads (i.e. 1 slow thread who has reached checkpoint A but not B could be causing all the others to wait at the barrier just before checkpoint B). I've tried using atomics to synchronize things and I know with 100% certainty that is it NOT guaranteed to work. For example using openmp syntax, before the parallel section start with: shared_thread_counter = num_threads; //known at compile time #pragma omp flush Then at checkpoint A: #pragma omp atomic shared_thread_counter--; Then at checkpoint B (using polling): #pragma omp flush while (shared_thread_counter > 0) { usleep(1); //can be removed, but better to limit memory bandwidth #pragma omp flush } I've designed some experiments in which I use an atomic to indicate that some operation before it is finished. The experiment would work with 2 threads most of the time but consistently fail when I have lots of threads (like 20 or 30). I suspect this is because of the caching structure of modern CPUs. Even if one thread updates some other value before doing the atomic decrement, it is not guaranteed to be read by another thread in that order. Consider the case when the other value is a cache miss and the atomic decrement is a cache hit. So back to my question, how to CORRECTLY implement this "soft barrier"? Is there any built-in feature that guarantees such functionality? I'd prefer openmp but I'm familiar with most of the other common multithreading libraries. As a workaround right now, I'm using a hard barrier at checkpoint B and I've restructured my code to make the work between checkpoint A and B automatically load-balancing between the threads (which has been rather difficult at times). Thanks for any advice/insight :)

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• Maven mercurial extension constantly fails

  - by TheLQ

  After 2+ hours I was able to get the maven-scm-provider-hg extension (for pushing to mercurial repos from Maven) semi working, meaning that it was executing commands instead of just giving errors. However I think I've run into a wall with this error [INFO] [deploy:deploy {execution: default-deploy}] [INFO] Retrieving previous build number from pircbotx.googlecode.com [INFO] Removing C:\DOCUME~1\Owner\LOCALS~1\Temp\wagon-scm1210107000.checkout\pir cbotx\pircbotx\1.3-SNAPSHOT [INFO] EXECUTING: cmd.exe /X /C "hg clone -r tip https://*SNIP*@site.pircbotx.googlecode.com/hg/maven2/snapshots/pircbotx/pircbotx/1.3-SNAPSHOT C:\DOCUME~1\Owner\LOCALS~1\Temp\wagon-scm1210107000.checkout\pircbotx\pircbotx\1.3-SNAPSHOT" [INFO] EXECUTING: cmd.exe /X /C "hg locate" [INFO] repository metadata for: 'snapshot pircbotx:pircbotx:1.3-SNAPSHOT' could not be found on repository: pircbotx.googlecode.com, so will be created Uploading: scm:hg:https://site.pircbotx.googlecode.com/hg/maven2/snapshots/pircbotx/pircbotx/1.3-SNAPSHOT/pircbotx-1.3-SNAPSHOT.jar [INFO] ------------------------------------------------------------------------ [ERROR] BUILD ERROR [INFO] ------------------------------------------------------------------------ [INFO] Error deploying artifact: Error listing repository: No such command 'list'. What on earth would cause that error? I'm on a Windows box, so any commands that aren't commands give "'list' is not recognized as an internal or external command...", not "No such command 'list'." POM <build> <extensions> <extension> <groupId>org.apache.maven.scm</groupId> <artifactId>maven-scm-provider-hg</artifactId> <version>1.4</version> </extension> <extension> <groupId>org.apache.maven.wagon</groupId> <artifactId>wagon-scm</artifactId> <version>1.0-beta-7</version> </extension> </extensions> ... <distributionManagement> <snapshotRepository> <id>pircbotx.googlecode.com</id> <name>PircBotX Site</name> <url>scm:hg:https://site.pircbotx.googlecode.com/hg/maven2/snapshots</url> <uniqueVersion>false</uniqueVersion> </snapshotRepository> </distributionManagement> Mercurial version W:\programming\pircbot-hg>hg version Mercurial Distributed SCM (version 1.7.2) Any suggestions?

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• Spring AOP pointcut that matches annotation on interface

  - by seanizer

  Hello, this is my first post here, so I apologize in advance for any stupidity on my side. I have a service class implemented in Java 6 / Spring 3 that needs an annotation to restrict access by role. I have defined an annotation called RequiredPermission that has as its value attribute one or more values from an enum called OperationType: public @interface RequiredPermission { /** * One or more {@link OperationType}s that map to the permissions required * to execute this method. * * @return */ OperationType[] value();} public enum OperationType { TYPE1, TYPE2; } package com.mycompany.myservice; public interface MyService{ @RequiredPermission(OperationType.TYPE1) void myMethod( MyParameterObject obj ); } package com.mycompany.myserviceimpl; public class MyServiceImpl implements MyService{ public myMethod( MyParameterObject obj ){ // do stuff here } } I also have the following aspect definition: /** * Security advice around methods that are annotated with * {@link RequiredPermission}. * * @param pjp * @param param * @param requiredPermission * @return * @throws Throwable */ @Around(value = "execution(public *" + " com.mycompany.myserviceimpl.*(..))" + " && args(param)" + // parameter object " && @annotation( requiredPermission )" // permission annotation , argNames = "param,requiredPermission") public Object processRequest(final ProceedingJoinPoint pjp, final MyParameterObject param, final RequiredPermission requiredPermission) throws Throwable { if(userService.userHasRoles(param.getUsername(),requiredPermission.values()){ return pjp.proceed(); }else{ throw new SorryButYouAreNotAllowedToDoThatException( param.getUsername(),requiredPermission.value()); } } The parameter object contains a user name and I want to look up the required role for the user before allowing access to the method. When I put the annotation on the method in MyServiceImpl, everything works just fine, the pointcut is matched and the aspect kicks in. However, I believe the annotation is part of the service contract and should be published with the interface in a separate API package. And obviously, I would not like to put the annotation on both service definition and implementation (DRY). I know there are cases in Spring AOP where aspects are triggered by annotations one interface methods (e.g. Transactional). Is there a special syntax here or is it just plain impossible out of the box. PS: I have not posted my spring config, as it seems to be working just fine. And no, those are neither my original class nor method names. Thanks in advance, Sean PPS: Actually, here is the relevant part of my spring config: <aop:aspectj-autoproxy proxy-target-class="false" /> <bean class="com.mycompany.aspect.MyAspect"> <property name="userService" ref="userService" /> </bean>

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• PERL newbie : get a proper minimal debug_mode solution

  - by Michael Mao

  Hi all: I am learning PERL in a "head-first" manner. I am absolutely a newbie in this language: I am trying to have a debug_mode switch from CLI which can be used to control how my script works, by switching certain subroutines "on and off". And below is what I've got so far: #!/usr/bin/perl -s -w # purpose : make subroutine execution optional, # which is depending on a CLI switch flag use strict; use warnings; use constant DEBUG_VERBOSE => "v"; use constant DEBUG_SUPPRESS_ERROR_MSGS => "s"; use constant DEBUG_IGNORE_VALIDATION => "i"; use constant DEBUG_SETPPING_COMPUTATION => "c"; our ($debug_mode); mainMethod(); sub mainMethod # () { if(!$debug_mode) { print "debug_mode is OFF\n"; } elsif($debug_mode) { print "debug_mode is ON\n"; } else { print "OMG!\n"; exit -1; } checkArgv(); printErrorMsg("Error_Code_123", "Parsing Error at..."); verbose(); } sub checkArgv #() { print ("Number of ARGV : ".(1 + $#ARGV)."\n"); } sub printErrorMsg # ($error_code, $error_msg, ..) { if(defined($debug_mode) && !($debug_mode =~ DEBUG_SUPPRESS_ERROR_MSGS)) { print "You can only see me if -debug_mode is NOT set". " to DEBUG_SUPPRESS_ERROR_MSGS\n"; die("terminated prematurely...\n") and exit -1; } } sub verbose # () { if(defined($debug_mode) && ($debug_mode =~ DEBUG_VERBOSE)) { print "Blah blah blah...\n"; } } So far as I can tell, at least it works...: the -debug_mode switch doesn't interfere with normal ARGV the following commandlines work: ./optional.pl ./optional.pl -debug_mode ./optional.pl -debug_mode=v ./optional.pl -debug_mode=s However, I am puzzled when multiple debug_modes are "mixed", such as: ./optional.pl -debug_mode=sv ./optional.pl -debug_mode=vs I don't understand why the above lines of code "magically works". I see both of the "DEBUG_VERBOS" and "DEBUG_SUPPRESS_ERROR_MSGS" apply to the script, which is fine in this case. However, if there are some "conflicting" debug modes, I am not sure how to set the "precedence of debue_modes"? Also, I am not certain if my approach is good enough to Perlists and I hope I am getting my feet in the right direction. One biggest problem is that I now put if statements inside most of my subroutines for controlling their behavior under different modes. Is this okay? Is there a more elegant way? I know there must be a debug module from CPAN or elsewhere, but I wanna a real minimal solution that doesn't depend on any other module than the "default" And I cannot have any control on the environment where this script will be executed... Many thanks to the suggestions in advance.

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• while creating archetype getting following error

  - by munna

  D:\Training\workspace\vppsourcemvn archetype:generate -B -DarchetypeGroupId=org .appfuse.archetypes -DarchetypeArtifactId=appfuse-modular-struts-archetype -Darc hetypeVersion=2.1.0-M1 -DgroupId=com.vmware -DartifactId=vpp [INFO] Scanning for projects... [INFO] Searching repository for plugin with prefix: 'archetype'. [INFO] ------------------------------------------------------------------------ [INFO] Building Maven Default Project [INFO] task-segment: [archetype:generate] (aggregator-style) [INFO] ------------------------------------------------------------------------ [INFO] Preparing archetype:generate [INFO] No goals needed for project - skipping [INFO] [archetype:generate {execution: default-cli}] [INFO] Generating project in Batch mode [WARNING] Error reading archetype catalog http://repo1.maven.org/maven2 org.apache.maven.wagon.TransferFailedException: Error transferring file: Connect ion timed out: connect at org.apache.maven.wagon.providers.http.LightweightHttpWagon.fillInputD ata(LightweightHttpWagon.java:143) at org.apache.maven.wagon.StreamWagon.getInputStream(StreamWagon.java:11 6) at org.apache.maven.wagon.StreamWagon.getIfNewer(StreamWagon.java:88) at org.apache.maven.wagon.StreamWagon.get(StreamWagon.java:61) at org.apache.maven.archetype.source.RemoteCatalogArchetypeDataSource.ge tArchetypeCatalog(RemoteCatalogArchetypeDataSource.java:97) at org.apache.maven.archetype.DefaultArchetypeManager.getRemoteCatalog(D efaultArchetypeManager.java:195) at org.apache.maven.archetype.DefaultArchetypeManager.getRemoteCatalog(D efaultArchetypeManager.java:184) at org.apache.maven.archetype.ui.DefaultArchetypeSelector.getArchetypesB yCatalog(DefaultArchetypeSelector.java:278) at org.apache.maven.archetype.ui.DefaultArchetypeSelector.selectArchetyp e(DefaultArchetypeSelector.java:69) at org.apache.maven.archetype.mojos.CreateProjectFromArchetypeMojo.execu te(CreateProjectFromArchetypeMojo.java:186) at org.apache.maven.plugin.DefaultPluginManager.executeMojo(DefaultPlugi nManager.java:490) at org.apache.maven.lifecycle.DefaultLifecycleExecutor.executeGoals(Defa ultLifecycleExecutor.java:694) at org.apache.maven.lifecycle.DefaultLifecycleExecutor.executeStandalone Goal(DefaultLifecycleExecutor.java:569) at org.apache.maven.lifecycle.DefaultLifecycleExecutor.executeGoal(Defau ltLifecycleExecutor.java:539) at org.apache.maven.lifecycle.DefaultLifecycleExecutor.executeGoalAndHan dleFailures(DefaultLifecycleExecutor.java:387) at org.apache.maven.lifecycle.DefaultLifecycleExecutor.executeTaskSegmen ts(DefaultLifecycleExecutor.java:284) at org.apache.maven.lifecycle.DefaultLifecycleExecutor.execute(DefaultLi fecycleExecutor.java:180) at org.apache.maven.DefaultMaven.doExecute(DefaultMaven.java:328) at org.apache.maven.DefaultMaven.execute(DefaultMaven.java:138) at org.apache.maven.cli.MavenCli.main(MavenCli.java:362) at org.apache.maven.cli.compat.CompatibleMain.main(CompatibleMain.java:6 0) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl. java:39) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAcces sorImpl.java:25) at java.lang.reflect.Method.invoke(Method.java:597) at org.codehaus.classworlds.Launcher.launchEnhanced(Launcher.java:315) at org.codehaus.classworlds.Launcher.launch(Launcher.java:255) at org.codehaus.classworlds.Launcher.mainWithExitCode(Launcher.java:430) at org.codehaus.classworlds.Launcher.main(Launcher.java:375) Caused by: java.net.ConnectException: Connection timed out: connect at java.net.PlainSocketImpl.socketConnect(Native Method) at java.net.PlainSocketImpl.doConnect(PlainSocketImpl.java:333) at java.net.PlainSocketImpl.connectToAddress(PlainSocketImpl.java:195) at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:182) at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:366) at java.net.Socket.connect(Socket.java:529) at java.net.Socket.connect(Socket.java:478) at sun.net.NetworkClient.doConnect(NetworkClient.java:163) at sun.net.www.http.HttpClient.openServer(HttpClient.java:394) at sun.net.www.http.HttpClient.openServer(HttpClient.java:529) at sun.net.www.http.HttpClient.(HttpClient.java:233) at sun.net.www.http.HttpClient.New(HttpClient.java:306) at sun.net.www.http.HttpClient.New(HttpClient.java:323) at sun.net.www.protocol.http.HttpURLConnection.getNewHttpClient(HttpURLC onnection.java:860) at sun.net.www.protocol.http.HttpURLConnection.plainConnect(HttpURLConne ction.java:801) at sun.net.www.protocol.http.HttpURLConnection.connect(HttpURLConnection .java:726) at sun.net.www.protocol.http.HttpURLConnection.getInputStream(HttpURLCon nection.java:1049) at java.net.HttpURLConnection.getResponseCode(HttpURLConnection.java:373 ) at org.apache.maven.wagon.providers.http.LightweightHttpWagon.fillInputD ata(LightweightHttpWagon.java:115) ... 28 more [WARNING] No archetype found in Remote catalog. Defaulting to internal Catalog [INFO] ------------------------------------------------------------------------ [ERROR] BUILD FAILURE [INFO] ------------------------------------------------------------------------ [INFO] [INFO] ------------------------------------------------------------------------ [INFO] For more information, run Maven with the -e switch [INFO] ------------------------------------------------------------------------ [INFO] Total time: 46 seconds [INFO] Finished at: Wed Jun 09 16:11:07 IST 2010 [INFO] Final Memory: 11M/28M [INFO] ------------------------------------------------------------------------

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• architecture python question

  - by tom smith

  hi. creating a distributed crawling python app. it consists of a master server, and associated client apps that will run on client servers. the purpose of the client app is to run across a targeted site, to extract specific data. the clients need to go "deep" within the site, behind multiple levels of forms, so each client is specifically geared towards a given site. each client app looks something like main: parse initial url call function level1 (data1) function level1 (data) parse the url, for data1 use the required xpath to get the dom elements call the next function call level2 (data) function level2 (data2) parse the url, for data2 use the required xpath to get the dom elements call the next function call level3 function level3 (dat3) parse the url, for data3 use the required xpath to get the dom elements call the next function call level4 function level4 (data) parse the url, for data4 use the required xpath to get the dom elements at the final function.. --all the data output, and eventually returned to the server --at this point the data has elements from each function... my question: given that the number of calls that is made to the child function by the current function varies, i'm trying to figure out the best approach. each function essentialy fetches a page of content, and then parses the page using a number of different XPath expressions, combined with different regex expressions depending on the site/page. if i run a client on a single box, as a sequential process, it'll take awhile, but the load on the box is rather small. i've thought of attempting to implement the child functions as threads from the current function, but that could be a nightmare, as well as quickly bring the "box" to its knees! i've thought of breaking the app up in a manner that would allow the master to essentially pass packets to the client boxes, in a way to allow each client/function to be run directly from the master. this process requires a bit of rewrite, but it has a number of advantages. a bunch of redundancy, and speed. it would detect if a section of the process was crashing and restart from that point. but not sure if it would be any faster... i'm writing the parsing scripts in python.. so... any thoughts/comments would be appreciated... i can get into a great deal more detail, but didn't want to bore anyone!! thanks! tom

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• How can i use a duration setting on .animate if it is inside the callback from a .fadeOut effect?

  - by Jannis

  I am trying to just fade the content of section#secondary out and once the content has been faded out, the parent (section#secondary) should animate 'shut' in a slider animation. All this is working however the durations are not and I cannot figure out why. Here is my code: HTML <section id="secondary"> <a href="#" class="slide_button">&laquo;</a> <!-- slide in/back button --> <article> <h1>photos</h1> <div class="album_nav"><a href="#">photo 1 of 6</a> | <a href="#">create an album</a></div> <div class="bar"> <p class="section_title">current image title</p> </div> <section class="image"> <div class="links"> <a class="_back album_link" href="#">« from the album: james new toy</a> <nav> <a href="#" class="_back small_button">back</a> <a href="#" class="_next small_button">next</a> </nav> </div> <img src="http://localhost/~jannis/3781_doggie_wonderland/www/preview/static/images/sample-image-enlarged.jpg" width="418" height="280" alt="" /> </section> </article> <footer> <embed src="http://localhost/~jannis/3781_doggie_wonderland/www/preview/static/flash/secondary-footer.swf" wmode="transparent" width="495" height="115" type="application/x-shockwave-flash" /> </footer> </section> <!-- close secondary --> jQuery // ============================= // = Close button (slide away) = // ============================= $('a.slide_button').click(function() { $(this).closest('section#secondary').children('*').fadeOut('slow', function() { $('section#secondary').animate({'width':'0'}, 3000); }); }); Because the content of section#secondary is variable I use the * selector. What happens is that the fadeOut uses the appropriate slow speed but as soon as the callback fires (once the content is faded out) the section#secondary animates to width: 0 within a couple of milliseconds and not the 3000 ms ( 3 sec ) I set the animation duration to. Any ideas would be appreciated. PS: I cannot post an example at this point but since this is more a matter of theory of jQuery I don't think an example is necessary here. Correct me if I am wrong..

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• Getting problem in Java OpenCV code.

  - by Chetan

  I had successfully compile my java code in Eclipse with name FaceDetection.java... I am getting an Exception in thread "main" java.lang.NoSuchMethodError: main.... Please help me to remove this Exception.. Here is the code import java.awt.; import java.awt.event.; import java.awt.image.MemoryImageSource; import hypermedia.video.OpenCV; @SuppressWarnings("serial") public class FaceDetection extends Frame implements Runnable { /** * Main method. * @param String[] a list of user's arguments passed from the console to this program */ public static void main( String[] args ) { System.out.println( "\nOpenCV face detection sample\n" ); new FaceDetection(); } // program execution frame rate (millisecond) final int FRAME_RATE = 1000/30; OpenCV cv = null; // OpenCV Object Thread t = null; // the sample thread // the input video stream image Image frame = null; // list of all face detected area Rectangle[] squares = new Rectangle[0]; /** * Setup Frame and Object(s). */ FaceDetection() { super( "Face Detection Sample" ); // OpenCV setup cv = new OpenCV(); cv.capture( 320, 240 ); cv.cascade( OpenCV.CASCADE_FRONTALFACE_ALT ); // frame setup this.setBounds( 100, 100, cv.width, cv.height ); this.setBackground( Color.BLACK ); this.setVisible( true ); this.addKeyListener( new KeyAdapter() { public void keyReleased( KeyEvent e ) { if ( e.getKeyCode()==KeyEvent.VK_ESCAPE ) { // ESC : release OpenCV resources cv.dispose(); System.exit(0); } } } ); // start running program t = new Thread( this ); t.start(); } /** * Draw video frame and each detected faces area. */ public void paint( Graphics g ) { // draw image g.drawImage( frame, 0, 0, null ); // draw squares g.setColor( Color.RED ); for( Rectangle rect : squares ) g.drawRect( rect.x, rect.y, rect.width, rect.height ); } /** * Execute this sample. */ @SuppressWarnings("static-access") public void run() { while( t!=null && cv!=null ) { try { t.sleep( FRAME_RATE ); // grab image from video stream cv.read(); // create a new image from cv pixels data MemoryImageSource mis = new MemoryImageSource( cv.width, cv.height, cv.pixels(), 0, cv.width ); frame = createImage( mis ); // detect faces squares = cv.detect( 1.2f, 2, OpenCV.HAAR_DO_CANNY_PRUNING, 20, 20 ); // of course, repaint repaint(); } catch( InterruptedException e ) {;} } } }

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• Variable sized packet structs with vectors

  - by Rev316

  Lately I've been diving into network programming, and I'm having some difficulty constructing a packet with a variable "data" property. Several prior questions have helped tremendously, but I'm still lacking some implementation details. I'm trying to avoid using variable sized arrays, and just use a vector. But I can't get it to be transmitted correctly, and I believe it's somewhere during serialization. Now for some code. Packet Header class Packet { public: void* Serialize(); bool Deserialize(void *message); unsigned int sender_id; unsigned int sequence_number; std::vector<char> data; }; Packet ImpL typedef struct { unsigned int sender_id; unsigned int sequence_number; std::vector<char> data; } Packet; void* Packet::Serialize(int size) { Packet* p = (Packet *) malloc(8 + 30); p->sender_id = htonl(this->sender_id); p->sequence_number = htonl(this->sequence_number); p->data.assign(size,'&'); //just for testing purposes } bool Packet::Deserialize(void *message) { Packet *s = (Packet*)message; this->sender_id = ntohl(s->sender_id); this->sequence_number = ntohl(s->sequence_number); this->data = s->data; } During execution, I simply create a packet, assign it's members, and send/receive accordingly. The above methods are only responsible for serialization. Unfortunately, the data never gets transferred. Couple of things to point out here. I'm guessing the malloc is wrong, but I'm not sure how else to compute it (i.e. what other value it would be). Other than that, I'm unsure of the proper way to use a vector in this fashion, and would love for someone to show me how (code examples please!) :) Edit: I've awarded the question to the most comprehensive answer regarding the implementation with a vector data property. Appreciate all the responses!

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• Unit finalization order for application, compiled with run-time packages?

  - by Alexander

  I need to execute my code after finalization of SysUtils unit. I've placed my code in separate unit and included it first in uses clause of dpr-file, like this: project Project1; uses MyUnit, // <- my separate unit SysUtils, Classes, SomeOtherUnits; procedure Test; begin // end; begin SetProc(Test); end. MyUnit looks like this: unit MyUnit; interface procedure SetProc(AProc: TProcedure); implementation var Test: TProcedure; procedure SetProc(AProc: TProcedure); begin Test := AProc; end; initialization finalization Test; end. Note that MyUnit doesn't have any uses. This is usual Windows exe, no console, without forms and compiled with default run-time packages. MyUnit is not part of any package (but I've tried to use it from package too). I expect that finalization section of MyUnit will be executed after finalization section of SysUtils. This is what Delphi's help tells me. However, this is not always the case. I have 2 test apps, which differs a bit by code in Test routine/dpr-file and units, listed in uses. MyUnit, however, is listed first in all cases. One application is run as expected: Halt0 - FinalizeUnits - ...other units... - SysUtils's finalization - MyUnit's finalization - ...other units... But the second is not. MyUnit's finalization is invoked before SysUtils's finalization. The actual call chain looks like this: Halt0 - FinalizeUnits - ...other units... - SysUtils's finalization (skipped) - MyUnit's finalization - ...other units... - SysUtils's finalization (executed) Both projects have very similar settings. I tried a lot to remove/minimize their differences, but I still do not see a reason for this behaviour. I've tried to debug this and found out that: it seems that every unit have some kind of reference counting. And it seems that InitTable contains multiply references to the same unit. When SysUtils's finalization section is called first time - it change reference counter and do nothing. Then MyUnit's finalization is executed. And then SysUtils is called again, but this time ref-count reaches zero and finalization section is executed: Finalization: // SysUtils' finalization 5003B3F0 55 push ebp // here and below is some form of stub 5003B3F1 8BEC mov ebp,esp 5003B3F3 33C0 xor eax,eax 5003B3F5 55 push ebp 5003B3F6 688EB50350 push $5003b58e 5003B3FB 64FF30 push dword ptr fs:[eax] 5003B3FE 648920 mov fs:[eax],esp 5003B401 FF05DCAD1150 inc dword ptr [$5011addc] // here: some sort of reference counter 5003B407 0F8573010000 jnz $5003b580 // <- this jump skips execution of finalization for first call 5003B40D B8CC4D0350 mov eax,$50034dcc // here and below is actual SysUtils' finalization section ... Can anyone can shred light on this issue? Am I missing something?

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• Can't connect in C# and google spreadsheet api

  - by RockySanders99

  Trying to access google spreadsheets using their api. following their example, the code doesnt work, and its not obvious why. All I'm trying to do is to connect, and I keep getting back the same error. This is with their code set as of 4/15/10. Can anyone offer any suggestion on what I'm doing wrong? CodE: using System; using Google.GData.Client; using Google.GData.Extensions; using Google.GData.Spreadsheets; namespace google_spreadsheet { class Program { static void Main(string[] args) { SpreadsheetsService myService = new SpreadsheetsService("MySpreadsheet" ); myService.setUserCredentials("[email protected]", "xxxxxxx"); string token1 = myService.QueryClientLoginToken(); Console.WriteLine("token is {0}", token1); Console.ReadLine(); SpreadsheetQuery query = new SpreadsheetQuery(); SpreadsheetFeed feed = myService.Query(query); Console.WriteLine("list"); foreach (SpreadsheetEntry entry in feed.Entries) { Console.WriteLine("Value: {0}", entry.Title.Text); When I run this, it keeps erroring out at the myService.Query statement, with the following error: Google.GData.Client.GDataRequestException was unhandled Message=Execution of request failed: http://spreadsheets.google.com/feeds/spreadsheets/private/full Source=Google.GData.Client ResponseString=<HTML> <HEAD> <TITLE>Not Found</TITLE> </HEAD> <BODY BGCOLOR="#FFFFFF" TEXT="#000000"> <H1>Not Found</H1> <H2>Error 404</H2> </BODY> </HTML> StackTrace: at Google.GData.Client.GDataRequest.Execute() at Google.GData.Client.GDataGAuthRequest.Execute(Int32 retryCounter) at Google.GData.Client.GDataGAuthRequest.Execute() at Google.GData.Client.Service.Query(Uri queryUri, DateTime ifModifiedSince, String etag, Int64& contentLength) at Google.GData.Client.Service.Query(Uri queryUri, DateTime ifModifiedSince) at Google.GData.Client.Service.Query(FeedQuery feedQuery) at Google.GData.Spreadsheets.SpreadsheetsService.Query(SpreadsheetQuery feedQuery) at google_spreadsheet.Program.Main(String[] args) in C:\Development Items\VS Projects\VS2008\google_spreadsheet\google_spreadsheet\Program.cs:line 21 at System.AppDomain._nExecuteAssembly(Assembly assembly, String[] args) at Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly() at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state) at System.Threading.ThreadHelper.ThreadStart() InnerException: System.Net.WebException Message=The remote server returned an error: (404) Not Found. Source=System StackTrace: at System.Net.HttpWebRequest.GetResponse() at Google.GData.Client.GDataRequest.Execute() InnerException: Yet, I can take the url http://spreadsheets.google.com/feeds/spreadsheets/private/full and manually type it in with my username/password, and it works fine. Any suggestions? thanks rocky sanders

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• Optimizing mathematics on arrays of floats in Ada 95 with GNAT

  - by mat_geek

  Consider the bellow code. This code is supposed to be processing data at a fixed rate, in one second batches, It is part of an overal system and can't take up too much time. When running over 100 lots of 1 seconds worth of data the program takes 35 seconds (or 35%), executing this function in a loop. The test loop is timed specifically with Ada.RealTime. The data is pregenerated so the majority of the execution time is definatetly in this loop. How do I improce the code to get the processing time down to a minimum? The code will be running on an Intel Pentium-M which is a P3 with SSE2. package FF is new Ada.Numerics.Generic_Elementary_Functions(Float); N : constant Integer := 820; type A is array(1 .. N) of Float; type A3 is array(1 .. 3) of A; procedure F(state : in out A3; result : out A3; l : in A; r : in A) is s : Float; t : Float; begin for i in 1 .. N loop t := l(i) + r(i); t := t / 2.0; state(1)(i) := t; state(2)(i) := t * 0.25 + state(2)(i) * 0.75; state(3)(i) := t * 1.0 /64.0 + state(2)(i) * 63.0 /64.0; for r in 1 .. 3 loop s := state(r)(i); t := FF."**"(s, 6.0) + 14.0; if t > MAX then t := MAX; elsif t < MIN then t := MIN; end if; result(r)(i) := FF.Log(t, 2.0); end loop; end loop; end; psuedocode for testing create two arrays of 80 random A3 arrays, called ls and rs; init the state and result A3 array record the realtime time now, called last for i in 1 .. 100 loop for j in 1 .. 80 loop F(state, result, ls(j), rs(j)); end loop; end loop; record the realtime time now, called curr output the duration between curr and last

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• Long Running Stored Proc - Report Progress Using BackgroundWorker & Timer

  - by daveywc

  While a long running stored proc (RMR_Seek) is executing (called via a Linq-To-SQL data context) I am trying to call another stored proc (RMR_GetLatestModelMessage) to check a table for the latest status message. The long running stored proc updates the table in question with status messages as it executes. I want to display the status message on a message panel to advise the user of the status of the execution of Proc_A. For various reasons it is not possible to determine how long RMR_Seek will take to execute so a progress bar with percentage increments is not feasible. I thought I'd found the way to do it by calling the long running stored proc from in a BackgroundWorker process DoWork event handler. This worked fine and allowed me to update my message panel with some dummy status messages that were NOT obtained via Proc_B while Proc_A was running. However now that I have tried to implement this fully by calling Proc_B to obtain the status messages I am running into problems that seem to be related to the mix of the backgroundworker and my System.Windows.Forms.Timer. An extract of the code I am using is below. I have tried many different ways around this but each one seems to present its own set of problems. The code below is problematic in the bw_DoWork event. The RMR_Seek stored proc gets called but does not execute properly - it also seems to be inconsistent as to whether _IsCompleted gets set to true. I'm sure there is a better way to achieve what I am trying to do. private bool _IsCompleted; private void RunRevenueSeek() { if (_SelectedModel == null) { MessageBox.Show("Please select a model from the list and try again.", "Model Generation", MessageBoxButtons.OK, MessageBoxIcon.Information); } else { var bw = new BackgroundWorker(); bw.DoWork += new DoWorkEventHandler(bw_DoWork); ProgressPanelControl.Visible = true; _IsCompleted = false; MessageTimer.Start(); // Has an interval of 3000 bw.RunWorkerAsync(); ProgressLabelControl.Text = "Refreshing Data"; this.Update(); ...more code goes here } } private void bw_DoWork(object sender, DoWorkEventArgs e) { using (var dc = new RevMdlrDataClassesDataContext()) { dc.CommandTimeout = 300; dc.RMR_Seek(_SelectedModel.ModelSet_ID); _IsCompleted = true; } } private void MessageTimer_Tick(object sender, EventArgs e) { string message = ""; if (_IsCompleted) { MessageTimer.Stop(); } else { using (var dc = new RevMdlrDataClassesDataContext()) { dc.CommandTimeout = 300; dc.RMR_GetLatestModelMessage(_SelectedModel.ModelSet_ID, ref message); ProgressLabelControl.Text = message; this.Update(); } } }

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• WCF Troubleshooting from ASP.NET Client -- Help!

  - by Kobojunkie

  I am trying to call a method in my service that is as below, from an ASP.NET application. public bool ValidateUser(string username, string password) { try { // String CurrentLoggedInWindowsUserName = WindowsIdentity.GetCurrent().Name; // //primary identity of the call // String CurrentServiceSecurityContextPrimaryIdentityName = // ServiceSecurityContext.Current.PrimaryIdentity.Name; // } catch (Exception ex) { FaultExceptionFactory fct = new FaultExceptionFactory(); throw new FaultException<CustomFaultException>(fct.CreateFaultException(ex)); } return false; } The Config for the client end of my service is as below <binding name="WSHttpBinding_IMembershipService" closeTimeout="00:01:00" openTimeout="00:01:00" receiveTimeout="00:10:00" sendTimeout="00:01:00" bypassProxyOnLocal="false" transactionFlow="false" hostNameComparisonMode="StrongWildcard" maxBufferPoolSize="524288" maxReceivedMessageSize="65536" messageEncoding="Text" textEncoding="utf-8" useDefaultWebProxy="false" allowCookies="false"> <readerQuotas maxDepth="32" maxStringContentLength="8192" maxArrayLength="16384" maxBytesPerRead="4096" maxNameTableCharCount="16384" /> <reliableSession ordered="true" inactivityTimeout="00:10:00" enabled="false" /> <security mode="Message"> <transport clientCredentialType="Windows" proxyCredentialType="None" realm="" /> <message clientCredentialType="Windows" negotiateServiceCredential="true" algorithmSuite="Default" establishSecurityContext="true" /> </security> </binding> Problem I keep having is when I call it; I get the following exception message. Server Error in '/' Application. The communication object, System.ServiceModel.Channels.ServiceChannel, cannot be used for communication because it is in the Faulted state. Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code. Exception Details: System.ServiceModel.CommunicationObjectFaultedException: The communication object, System.ServiceModel.Channels.ServiceChannel, cannot be used for communication because it is in the Faulted state. Stack Trace: [CommunicationObjectFaultedException: The communication object, System.ServiceModel.Channels.ServiceChannel, cannot be used for communication because it is in the Faulted state.] System.Runtime.Remoting.Proxies.RealProxy.HandleReturnMessage(IMessage reqMsg, IMessage retMsg) +7596735 System.Runtime.Remoting.Proxies.RealProxy.PrivateInvoke(MessageData& msgData, Int32 type) +275 System.ServiceModel.ICommunicationObject.Close(TimeSpan timeout) +0 System.ServiceModel.ClientBase`1.System.ServiceModel.ICommunicationObject. Close(TimeSpan timeout) +142 System.ServiceModel.ClientBase`1.Close() +38 System.ServiceModel.ClientBase`1.System.IDisposable.Dispose() +4 Controls.Membership.accountLogin.ValidateUserCredentials(String UserName, String Password) in C:\ Petition.WebClient\Controls\ Membership\accountLogin.ascx.cs:49 Controls.Membership.accountLogin.Login1_Authenticate(Object sender, AuthenticateEventArgs e) in C:\ WebClient\ Controls\Membership \accountLogin.ascx.cs:55 I am not entirely sure why I keep getting this. Just in case, here is how I call my service from the client private bool ValidateUserCredentials(string UserName, string Password) { bool boolReturnValue = false; using(Members.MembershipServiceClient client = new Controls.Members.MembershipServiceClient()) { try { boolReturnValue = client.ValidateUser(UserName, Password); } catch (FaultException<CustomFaultException> ex) { throw ex; } } return boolReturnValue; } Anyone have any idea what I need to do in this case?

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• Unable to disable generation of sources JAR with maven-release-plugin

  - by Chris Lieb

  I am trying to release a web project using Maven 2.2.1 and the maven-release-plugin 2.0-beta-9, but it always fails when doing release:perform on generating the sources jar for the EAR project, which makes sense since the EAR project doesn't have any source. [INFO] [INFO] [source:jar {execution: attach-sources}] [INFO] [INFO] ------------------------------------------------------------------------ [INFO] [ERROR] BUILD ERROR [INFO] [INFO] ------------------------------------------------------------------------ [INFO] [INFO] Error creating source archive: You must set at least one file. To try to disable the building of a sources JAR for the EAR project, I added the following to the POM for my EAR project (the version of the release plugin is set in a parent POM): <build> <plugins> ... <plugin> <groupId>org.apache.maven.plugins</groupId> <artifactId>maven-release-plugin</artifactId> <configuration> <useReleaseProfile>false</useReleaseProfile> </configuration> </plugin> </plugins> </build> Upon running the release again after checking in this change, I got the same error while generating the sources JAR for the EAR project, even though this should have been disabled by the previous POM snippet. What am I doing wrong? Why is the sources JAR still being built? Edit: I've tried to make the source plugin include my application.xml file so that this error doesn't occur by adding the following POM snippet: <build> <plugins> ... <plugin> <groupId>org.apache.maven.plugins</groupId> <artifactId>maven-source-plugin</artifactId> <configuration> <includes> <include>${basedir}/META-INF/**/*</include> </includes> <useDefaultExcludes>false</useDefaultExcludes> </configuration> </plugin> </plugins> </build> Unfortunately, this does not fix the problem either.

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• .NET: Avoidance of custom exceptions by utilising existing types, but which?

  - by Mr. Disappointment

  Consider the following code (ASP.NET/C#): private void Application_Start(object sender, EventArgs e) { if (!SetupHelper.SetUp()) { throw new ShitHitFanException(); } } I've never been too hesitant to simply roll my own exception type, basically because I have found (bad practice, or not) that mostly a reasonable descriptive type name gives us enough as developers to go by in order to know what happened and why something might have happened. Sometimes the existing .NET exception types even accommodate these needs - regardless of the message. In this particular scenario, for demonstration purposes only, the application should die a horrible, disgraceful death should SetUp not complete properly (as dictated by its return value), but I can't find an already existing exception type in .NET which would seem to suffice; though, I'm sure one will be there and I simply don't know about it. Brad Abrams posted this article that lists some of the available exception types. I say some because the article is from 2005, and, although I try to keep up to date, it's a more than plausible assumption that more have been added to future framework versions that I am still unaware of. Of course, Visual Studio gives you a nicely formatted, scrollable list of exceptions via Intellisense - but even on analysing those, I find none which would seem to suffice for this situation... ApplicationException: ...when a non-fatal application error occurs The name seems reasonable, but the error is very definitely fatal - the app is dead. ExecutionEngineException: ...when there is an internal error in the execution engine of the CLR Again, sounds reasonable, superficially; but this has a very definite purpose and to help me out here certainly isn't it. HttpApplicationException: ...when there is an error processing an HTTP request Well, we're running an ASP.NET application! But we're also just pulling at straws here. InvalidOperationException: ...when a call is invalid for the current state of an instance This isn't right but I'm adding it to the list of 'possible should you put a gun to my head, yes'. OperationCanceledException: ...upon cancellation of an operation the thread was executing Maybe I wouldn't feel so bad using this one, but I'd still be hijacking the damn thing with little right. You might even ask why on earth I would want to raise an exception here but the idea is to find out that if I were to do so then do you know of an appropriate exception for such a scenario? And basically, to what extent can we piggy-back on .NET while keeping in line with rationality?

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• difference equations in MATLAB - why the need to switch signs?

  - by jefflovejapan

  Perhaps this is more of a math question than a MATLAB one, not really sure. I'm using MATLAB to compute an economic model - the New Hybrid ISLM model - and there's a confusing step where the author switches the sign of the solution. First, the author declares symbolic variables and sets up a system of difference equations. Note that the suffixes "a" and "2t" both mean "time t+1", "2a" means "time t+2" and "t" means "time t": %% --------------------------[2] MODEL proc-----------------------------%% % Define endogenous vars ('a' denotes t+1 values) syms y2a pi2a ya pia va y2t pi2t yt pit vt ; % Monetary policy rule ia = q1*ya+q2*pia; % ia = q1*(ya-yt)+q2*pia; %%option speed limit policy % Model equations IS = rho*y2a+(1-rho)yt-sigma(ia-pi2a)-ya; AS = beta*pi2a+(1-beta)*pit+alpha*ya-pia+va; dum1 = ya-y2t; dum2 = pia-pi2t; MPs = phi*vt-va; optcon = [IS ; AS ; dum1 ; dum2; MPs]; He then computes the matrix A: %% ------------------ [3] Linearization proc ------------------------%% % Differentiation xx = [y2a pi2a ya pia va y2t pi2t yt pit vt] ; % define vars jopt = jacobian(optcon,xx); % Define Linear Coefficients coef = eval(jopt); B = [ -coef(:,1:5) ] ; C = [ coef(:,6:10) ] ; % B[c(t+1) l(t+1) k(t+1) z(t+1)] = C[c(t) l(t) k(t) z(t)] A = inv(C)*B ; %(Linearized reduced form ) As far as I understand, this A is the solution to the system. It's the matrix that turns time t+1 and t+2 variables into t and t+1 variables (it's a forward-looking model). My question is essentially why is it necessary to reverse the signs of all the partial derivatives in B in order to get this solution? I'm talking about this step: B = [ -coef(:,1:5) ] ; Reversing the sign here obviously reverses the sign of every component of A, but I don't have a clear understanding of why it's necessary. My apologies if the question is unclear or if this isn't the best place to ask.

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• Managing multiple AJAX calls to PHP scripts

  - by relativelycoded

  I have a set of 5 HTML dropdowns that act as filters for narrowing results returned from a mySQL database. The three pertinent filters are for "Province", "Region", and "City" selection, respectively. I have three functions: findSchools(), which runs when any of the filters (marked with CSS class .filter) are changed, and fetches the results via AJAX from a PHP script. Once that is done, two other functions are called... changeRegionOptions(), which, upon changing the "Province" filter, and updates the available options using the same method as the first function, but posting to a different script. changeCityOptions(), which runs if the "Region" filter was changed, and updates options, again using the same method. The problem is that since I want these AJAX functions to run simultaneously, and they by nature run asynchronously, I've tried using $.when to control the execution of the functions, but it doesn't fix the problem. The functions run, but the Region and City filters return blank (no options); the FireBug report shows absolutely no output, even though the POST request went through. The posted parameter for filter_province gets sent normally, but the one for region gets cut off at the end -- it sends as filter_region=, with no value passed. So I'm presuming my logic is wrong somewhere. The code is below: // When any of the filters are changed, let's query the database... $("select.filter").change(function() { findSchools(); }); // First, we see if there are any results... function findSchools() { var sch_province = document.filterform.filter_province.value; var sch_region = document.filterform.filter_region.value; var sch_city = document.filterform.filter_city.value; var sch_cat = document.filterform.filter_category.value; var sch_type = document.filterform.filter_type.value; $.post("fetch_results.php", { filter_province : sch_province, filter_region : sch_region, filter_city : sch_city, filter_category : sch_cat, filter_type : sch_type }, function(data) { $("#results").html(""); $("#results").hide(); $("#results").html(data); $("#results").fadeIn(600); } ); // Once the results are fetched, we want to see if the filter they changed was the one for Province, and if so, update the Region and City options to match that selection... $("#filter_province").change(function() { $.when(findSchools()) .done(changeRegionOptions()); $.when(changeRegionOptions()) .done(changeCityOptions()); }); }; This is just one of the ways I've tried to solve it; I've tried using an IF statement, and tried calling the functions directly inside the general select.filter.change() function (after findSchools(); ), but they all return the same result. Any help with this would be great!

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• Running out of memory with UIImage creation on an offscreen Bitmap Context by NSOperation

  - by sigsegv

  I have an app with multiple UIView subclasses that acts as pages for a UIScrollView. UIViews are moved back and forth to provide a seamless experience to the user. Since the content of the views is rather slow to draw, it's rendered on a single shared CGBitmapContext guarded by locks by NSOperation subclasses - executed one at once in an NSOperationQueue - wrapped up in an UIImage and then used by the main thread to update the content of the views. -(void)main { NSAutoreleasePool * pool = [[NSAutoreleasePool alloc]init]; if([self isCancelled]) { return; } if(nil == data) { return; } // Buffer is the shared instance of a CG Bitmap Context wrapper class // data is a dictionary CGImageRef img = [buffer imageCreateWithData:data]; UIImage * image = [[UIImage alloc]initWithCGImage:img]; CGImageRelease(img); if([self isCancelled]) { [image release]; return; } NSDictionary * result = [[NSDictionary alloc]initWithObjectsAndKeys:image,@"image",id,@"id",nil]; // target is the instance of the UIView subclass that will use // the image [target performSelectorOnMainThread:@selector(updateContentWithData:) withObject:result waitUntilDone:NO]; [result release]; [image release]; [pool release]; } The updateContentWithData: of the UIView subclass performed on the main thread is just as simple -(void)updateContentWithData:(NSDictionary *)someData { NSDictionary * data = [someData retain]; if([[data valueForKey:@"id"]isEqualToString:[self pendingRequestId]]) { UIImage * image = [data valueForKey:@"image"]; [self setCurrentImage:image]; [self setNeedsDisplay]; } // If the image has not been retained, it should be released together // with the dictionary retaining it [data release]; } The drawLayer:inContext: method of the subclass will just get the CGImage from the UIImage and use it to update the backing layer or part of it. No retain or release is involved in the process. The problem is that after a while I run out of memory. The number of the UIViews is static. CGImageRef and UIImage are created, retained and released correctly (or so it seems to me). Instruments does not show any leaks, just the free memory available dip constantly, rise a few times, and then dip even lower until the application is terminated. The app cycles through about 2-300 of the aforementioned pages before that, but I would expect to have the memory usage reach a more or less stable level of used memory after a bunch of pages have been already skimmed at fast speed or, since the images are up to 3MB in size, deplete way earlier. Any suggestion will be greatly appreciated.

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• Is it too early to start designing for Task Parallel Library?

  - by Joe Erickson

  I have been following the development of the .NET Task Parallel Library (TPL) with great interest since Microsoft first announced it. There is no doubt in my mind that we will eventually take advantage of TPL. What I am questioning is whether it makes sense to start taking advantage of TPL when Visual Studio 2010 and .NET 4.0 are released, or whether it makes sense to wait a while longer. Why Start Now? The .NET 4.0 Task Parallel Library appears to be well designed and some relatively simple tests demonstrate that it works well on today's multi-core CPUs. I have been very interested in the potential advantages of using multiple lightweight threads to speed up our software since buying my first quad processor Dell Poweredge 6400 about seven years ago. Experiments at that time indicated that it was not worth the effort, which I attributed largely to the overhead of moving data between each CPU's cache (there was no shared cache back then) and RAM. Competitive advantage - some of our customers can never get enough performance and there is no doubt that we can build a faster product using TPL today. It sounds fun. Yes, I realize that some developers would rather poke themselves in the eye with a sharp stick, but we really enjoy maximizing performance. Why Wait? Are today's Intel Nehalem CPUs representative of where we are going as multi-core support matures? You can purchase a Nehalem CPU with 4 cores which share a single level 3 cache today, and most likely a 6 core CPU sharing a single level 3 cache by the time Visual Studio 2010 / .NET 4.0 are released. Obviously, the number of cores will go up over time, but what about the architecture? As the number of cores goes up, will they still share a cache? One issue with Nehalem is the fact that, even though there is a very fast interconnect between the cores, they have non-uniform memory access (NUMA) which can lead to lower performance and less predictable results. Will future multi-core architectures be able to do away with NUMA? Similarly, will the .NET Task Parallel Library change as it matures, requiring modifications to code to fully take advantage of it? Limitations Our core engine is 100% C# and has to run without full trust, so we are limited to using .NET APIs.

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• Segmenting a double array of labels

  - by Ami

  The Problem: I have a large double array populated with various labels. Each element (cell) in the double array contains a set of labels and some elements in the double array may be empty. I need an algorithm to cluster elements in the double array into discrete segments. A segment is defined as a set of pixels that are adjacent within the double array and one label that all those pixels in the segment have in common. (Diagonal adjacency doesn't count and I'm not clustering empty cells). |-------|-------|------| | Jane | Joe | | | Jack | Jane | | |-------|-------|------| | Jane | Jane | | | | Joe | | |-------|-------|------| | | Jack | Jane | | | Joe | | |-------|-------|------| In the above arrangement of labels distributed over nine elements, the largest cluster is the “Jane” cluster occupying the four upper left cells. What I've Considered: I've considered iterating through every label of every cell in the double array and testing to see if the cell-label combination under inspection can be associated with a preexisting segment. If the element under inspection cannot be associated with a preexisting segment it becomes the first member of a new segment. If the label/cell combination can be associated with a preexisting segment it associates. Of course, to make this method reasonable I'd have to implement an elaborate hashing system. I'd have to keep track of all the cell-label combinations that stand adjacent to preexisting segments and are in the path of the incrementing indices that are iterating through the double array. This hash method would avoid having to iterate through every pixel in every preexisting segment to find an adjacency. Why I Don't Like it: As is, the above algorithm doesn't take into consideration the case where an element in the double array can be associated with two unique segments, one in the horizontal direction and one in the vertical direction. To handle these cases properly, I would need to implement a test for this specific case and then implement a method that will both associate the element under inspection with a segment and then concatenate the two adjacent identical segments. On the whole, this method and the intricate hashing system that it would require feels very inelegant. Additionally, I really only care about finding the large segments in the double array and I'm much more concerned with the speed of this algorithm than with the accuracy of the segmentation, so I'm looking for a better way. I assume there is some stochastic method for doing this that I haven't thought of. Any suggestions?

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• What is the Fastest Way to Check for a Keyword in a List of Keywords in Delphi?

  - by lkessler

  I have a small list of keywords. What I'd really like to do is akin to: case MyKeyword of 'CHIL': (code for CHIL); 'HUSB': (code for HUSB); 'WIFE': (code for WIFE); 'SEX': (code for SEX); else (code for everything else); end; Unfortunately the CASE statement can't be used like that for strings. I could use the straight IF THEN ELSE IF construct, e.g.: if MyKeyword = 'CHIL' then (code for CHIL) else if MyKeyword = 'HUSB' then (code for HUSB) else if MyKeyword = 'WIFE' then (code for WIFE) else if MyKeyword = 'SEX' then (code for SEX) else (code for everything else); but I've heard this is relatively inefficient. What I had been doing instead is: P := pos(' ' + MyKeyword + ' ', ' CHIL HUSB WIFE SEX '); case P of 1: (code for CHIL); 6: (code for HUSB); 11: (code for WIFE); 17: (code for SEX); else (code for everything else); end; This, of course is not the best programming style, but it works fine for me and up to now didn't make a difference. So what is the best way to rewrite this in Delphi so that it is both simple, understandable but also fast? (For reference, I am using Delphi 2009 with Unicode strings.) Followup: Toby recommended I simply use the If Then Else construct. Looking back at my examples that used a CASE statement, I can see how that is a viable answer. Unfortunately, my inclusion of the CASE inadvertently hid my real question. I actually don't care which keyword it is. That is just a bonus if the particular method can identify it like the POS method can. What I need is to know whether or not the keyword is in the set of keywords. So really I want to know if there is anything better than: if pos(' ' + MyKeyword + ' ', ' CHIL HUSB WIFE SEX ') > 0 then The If Then Else equivalent does not seem better in this case being: if (MyKeyword = 'CHIL') or (MyKeyword = 'HUSB') or (MyKeyword = 'WIFE') or (MyKeyword = 'SEX') then In Barry's comment to Kornel's question, he mentions the TDictionary Generic. I've not yet picked up on the new Generic collections and it looks like I should delve into them. My question here would be whether they are built for efficiency and how would using TDictionary compare in looks and in speed to the above two lines? In later profiling, I have found that the concatenation of strings as in: (' ' + MyKeyword + ' ') is VERY expensive time-wise and should be avoided whenever possible. Almost any other solution is better than doing this.

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