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• Choosing a distributed shared memory solution

  - by mindas

  I have a task to build a prototype for a massively scalable distributed shared memory (DSM) app. The prototype would only serve as a proof-of-concept, but I want to spend my time most effectively by picking the components which would be used in the real solution later on. The aim of this solution is to take data input from an external source, churn it and make the result available for a number of frontends. Those "frontends" would just take the data from the cache and serve it without extra processing. The amount of frontend hits on this data can literally be millions per second. The data itself is very volatile; it can (and does) change quite rapidly. However the frontends should see "old" data until the newest has been processed and cached. The processing and writing is done by a single (redundant) node while other nodes only read the data. In other words: no read-through behaviour. I was looking into solutions like memcached however this particular one doesn't fulfil all our requirements which are listed below: The solution must at least have Java client API which is reasonably well maintained as the rest of app is written in Java and we are seasoned Java developers; The solution must be totally elastic: it should be possible to add new nodes without restarting other nodes in the cluster; The solution must be able to handle failover. Yes, I realize this means some overhead, but the overall served data size isn't big (1G max) so this shouldn't be a problem. By "failover" I mean seamless execution without hardcoding/changing server IP address(es) like in memcached clients when a node goes down; Ideally it should be possible to specify the degree of data overlapping (e.g. how many copies of the same data should be stored in the DSM cluster); There is no need to permanently store all the data but there might be a need of post-processing of some of the data (e.g. serialization to the DB). Price. Obviously we prefer free/open source but we're happy to pay a reasonable amount if a solution is worth it. In any way, paid 24hr/day support contract is a must. The whole thing has to be hosted in our data centers so SaaS offerings like Amazon SimpleDB are out of scope. We would only consider this if no other options would be available. Ideally the solution would be strictly consistent (as in CAP); however, eventual consistence can be considered as an option. Thanks in advance for any ideas.

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• JPA entity design / cannot delete entity

  - by timaschew

  I though its simple what I want, but I cannot find any solution for my problem. I'm using playframework 1.2.3 and it's using Hibernate as JPA. So I think playframework has nothing to do with the problem. I have some classes (I omit the nonrelevant fields) public class User { ... } public class Task { public DataContainer dataContainer; } public class DataContainer { public Session session; public User user; } public class Session { ... } So I have association from Task to DataContainer and from DataContainer to Sesssion and the DataContainer belongs to a User. The DataContainers can have always the same User, but the Session have to be different for each instance. And the DataContainer of a Task have also to be different in each instance. A DataContainer can have a Sesesion or not (it's optinal). I use only unidirectional assoc. It should be sufficient. In other words: Every Task must has one DataContainer. Every DataContainer must has one/the same User and can have one Session. To create a DB schema I use JPA annotations: @Entity public class User extends Model { ... } @Entity public class Task extends Model { @OneToOne(optional = false, cascade = CascadeType.ALL) public DataContainer dataContainer; } @Entity public class DataContainer extends Model { @OneToOne(optional = true, cascade = CascadeType.ALL) public Session session; @ManyToOne(optional = false, cascade = CascadeType.ALL) public User user; } @Entity public class Session extends Model { ... } BTW: Model is a play class and provides the primary id as long type. When I create some for each entity a object and 'connect them', I mean the associations, it works fine. But when I try to delete a Session, I get a constraint violation exception, because a DataContainer still refers to the Session I want to delete. I want that the Session (field) of the DataContainer will be set to null respectively the foreign key (session_id) should be unset in the database. This will be okay, because its optional. I don't know, I think I have multiple problems. Am I using the right annotation @OneToOne ? I found on the internet some additional annotation and attributes: @JoinColumn and a mappedBy attribute for the inverse relationship. But I don't have it, because its not bidirectional. Or is a bidirectional assoc. essentially? Another try was to use @OnDelete(action = OnDeleteAction.CASCADE) the the contraint changed from NO ACTIONs when update or delete to: ADD CONSTRAINT fk4745c17e6a46a56 FOREIGN KEY (session_id) REFERENCES annotation_session (id) MATCH SIMPLE ON UPDATE NO ACTION ON DELETE CASCADE; But in this case, when I delete a session, the DataContainer and User is deleted. That's wrong for me. EDIT: I'm using postgresql 9, the jdbc stuff is included in play, my only db config is db=postgres://app:app@localhost:5432/app

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• Recommended textbook for machine-level programming?

  - by Norman Ramsey

  I'm looking at textbooks for an undergraduate course in machine-level programming. If the perfect book existed, this is what it would look like: Uses examples written in C or assembly language, or both. Covers machine-level operations such as two's-complement integer arithmetic, bitwise operations, and floating-point arithmetic. Explains how caches work and how they affect performance. Explains machine instructions or assembly instructions. Bonus if the example assembly language includes x86; triple bonus if it includes x86-64 (aka AMD64). Explains how C values and data structures are represented using hardware registers and memory. Explains how C control structures are translated into assembly language using conditional and unconditional branch instructions. Explains something about procedure calling conventions and how procedure calls are implemented at the machine level. Books I might be interested in would probably have the words "machine organization" or "computer architecture" in the title. Here are some books I'm considering but am not quite happy with: Computer Systems: A Programmer's Perspective by Randy Bryant and Dave O'Hallaron. This is quite a nice book, but it's a book for a broad, shallow course in systems programming, and it contains a great deal of material my students don't need. Also, it is just out in a second edition, which will make it expensive. Computer Organization and Design: The Hardware/Software Interface by Dave Patterson and John Hennessy. This is also a very nice book, but it contains way more information about how the hardware works than my students need. Also, the exercises look boring. Finally, it has a show-stopping bug: it is based very heavily on MIPS hardware and the use of a MIPS simulator. My students need to learn how to use DDD, and I can't see getting this to work on a simulator. Not to mention that I can't see them cross-compiling their code for the simulator, and so on and so forth. Another flaw is that the book mentions the x86 architecture only to sneer at it. I am entirely sympathetic to this point of view, but news flash! You guys lost! Write Great Code Vol I: Understanding the Machine by Randall Hyde. I haven't evaluated this book as thoroughly as the other two. It has a lot of what I need, but the translation from high-level language to assembler is deferred to Volume Two, which has mixed reviews. My students will be annoyed if I make them buy a two-volume series, even if the price of those two volumes is smaller than the price of other books. I would really welcome other suggestions of books that would help students in a class where they are to learn how C-language data structures and code are translated to machine-level data structures and code and where they learn how to think about performance, with an emphasis on the cache.

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• Testing for existence using SELECT WHERE HAVING and NOT HAVING in a grouped subset

  - by IanC

  I have data on which I need to count +1 if a particular condition exists or another condition doesn't exist. I'm using SQL Server 2008. I shred the following simplified sample XML into a temp table and validate it: <product type="1"> <param type="1"> <item mode="0" weight="1" /> </param> <param type="2"> <item mode="1" weight="1" /> <item mode="0" weight="0.1" /> </param> <param type="3"> <item mode="1" weight="0.75" /> <item mode="1" weight="0.25" /> </param> </product> The validation in concern is the following rule: For each product type, for each param type, mode may be 0 & (1 || 2). In other words, there may be a 0(s), but then 1s or 2s are required, or there may be only 1(s) or 2(s). There cannot be only 0s, and there cannot be 1s and 2s. The only part I haven't figured out is how to detect if there are only 0s. This seems like a "not having" problem. The validation code (for this part): WITH t1 AS ( SELECT SUM(t.ParamWeight) AS S, COUNT(1) AS C, t.ProductTypeID, t.ParamTypeID, t.Mode FROM @t AS t GROUP BY t.ProductTypeID, t.ParamTypeID, t.Mode ), ... UNION ALL SELECT TOP (1) 1 -- only mode 0 & (1 || 2) is allowed FROM t1 WHERE t1.Mode IN (1, 2) GROUP BY t1.ProductTypeID, t1.ParamTypeID HAVING COUNT(1) > 1 UNION ALL ... ) SELECT @C = COUNT(1) FROM t2 This will show if any mode 1s & 2s are mixed, but not if the group contains only a 0. I'm sure there is a simple solution, but it's evading me right now. EDIT: I thought of a "cheat" that works perfectly. I added the following to the above: SELECT TOP (1) 1 -- only mode 0 & (null || 1 || 2) is allowed FROM t1 GROUP BY t1.ProductTypeID, t1.ParamTypeID HAVING SUM(t1.Mode) = 0 However, I'd still like to know how to do this without cheating.

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• Difference in DocumentBuilder.parse when using JRE 1.5 and JDK 1.6

  - by dhiller

  Recently at last we have switched our projects to Java 1.6. When executing the tests I found out that using 1.6 a SAXParseException is not thrown which has been thrown using 1.5. Below is my test code to demonstrate the problem. import java.io.StringReader; import javax.xml.parsers.DocumentBuilder; import javax.xml.parsers.DocumentBuilderFactory; import javax.xml.transform.stream.StreamSource; import javax.xml.validation.SchemaFactory; import org.junit.Test; import org.xml.sax.InputSource; import org.xml.sax.SAXParseException; /** * Test class to demonstrate the difference between JDK 1.5 to JDK 1.6. * * Seen on Linux: * * <pre> * #java version "1.6.0_18" * Java(TM) SE Runtime Environment (build 1.6.0_18-b07) * Java HotSpot(TM) Server VM (build 16.0-b13, mixed mode) * </pre> * * Seen on OSX: * * <pre> * java version "1.6.0_17" * Java(TM) SE Runtime Environment (build 1.6.0_17-b04-248-10M3025) * Java HotSpot(TM) 64-Bit Server VM (build 14.3-b01-101, mixed mode) * </pre> * * @author dhiller (creator) * @author $Author$ (last editor) * @version $Revision$ * @since 12.03.2010 11:32:31 */ public class TestXMLValidation { /** * Tests the schema validation of an XML against a simple schema. * * @throws Exception * Falls ein Fehler auftritt * @throws junit.framework.AssertionFailedError * Falls eine Unit-Test-Pruefung fehlschlaegt */ @Test(expected = SAXParseException.class) public void testValidate() throws Exception { final StreamSource schema = new StreamSource( new StringReader( "<?xml version=\"1.0\" encoding=\"UTF-8\"?>" + "<xs:schema xmlns:xs=\"http://www.w3.org/2001/XMLSchema\" " + "elementFormDefault=\"qualified\" xmlns:xsd=\"undefined\">" + "<xs:element name=\"Test\"/>" + "</xs:schema>" ) ); final String xml = "<Test42/>"; final DocumentBuilderFactory newFactory = DocumentBuilderFactory.newInstance(); newFactory.setSchema( SchemaFactory.newInstance( "http://www.w3.org/2001/XMLSchema" ).newSchema( schema ) ); final DocumentBuilder documentBuilder = newFactory.newDocumentBuilder(); documentBuilder.parse( new InputSource( new StringReader( xml ) ) ); } } When using a JVM 1.5 the test passes, on 1.6 it fails with "Expected exception SAXParseException". The Javadoc of the DocumentBuilderFactory.setSchema(Schema) Method says: When errors are found by the validator, the parser is responsible to report them to the user-specified ErrorHandler (or if the error handler is not set, ignore them or throw them), just like any other errors found by the parser itself. In other words, if the user-specified ErrorHandler is set, it must receive those errors, and if not, they must be treated according to the implementation specific default error handling rules. The Javadoc of the DocumentBuilder.parse(InputSource) method says: BTW: I tried setting an error handler via setErrorHandler, but there still is no exception. Now my question: What has changed to 1.6 that prevents the schema validation to throw a SAXParseException? Is it related to the schema or to the xml that I tried to parse?

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• Are there known problems with >= and <= and the eval function in JS?

  - by Augier

  I am currently writing a JS rules engine which at one point needs to evaluate boolean expressions using the eval() function. Firstly I construct an equation as such: var equation = "relation.relatedTrigger.previousValue" + " " + relation.operator + " " + "relation.value"; relation.relatedTrigger.previousValue is the value I want to compare. relation.operator is the operator (either "==", "!=", <=, "<", "", ="). relation.value is the value I want to compare with. I then simply pass this string to the eval function and it returns true or false as such: return eval(equation); This works absolutely fine (with words and numbers) or all of the operators except for = and <=. E.g. When evaluating the equation: relation.relatedTrigger.previousValue <= 100 It returns true when previousValue = 0,1,10,100 & all negative numbers but false for everything in between. I would greatly appreciate the help of anyone to either answer my question or to help me find an alternative solution. Regards, Augier. P.S. I don't need a speech on the insecurities of the eval() function. Any value given to relation.relatedTrigger.previousValue is predefined. edit: Here is the full function: function evaluateRelation(relation) { console.log("Evaluating relation") var currentValue; //if multiple values if(relation.value.indexOf(";") != -1) { var values = relation.value.split(";"); for (x in values) { var equation = "relation.relatedTrigger.previousValue" + " " + relation.operator + " " + "values[x]"; currentValue = eval(equation); if (currentValue) return true; } return false; } //if single value else { //Evaluate the relation and get boolean var equation = "relation.relatedTrigger.previousValue" + " " + relation.operator + " " + "relation.value"; console.log("relation.relatedTrigger.previousValue " + relation.relatedTrigger.previousValue); console.log(equation); return eval(equation); } } Answer: Provided by KennyTM below. A string comparison doesn't work. Converting to a numerical was needed.

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• File Output using Gforth

  - by sheepez

  As a first project I have been writing a short program to render the Mandelbrot fractal. I have got to the point of trying to output my results to a file ( e.g. .bmp or .ppm ) and got stuck. I have not really found any examples of exactly what I am trying to do, but I have found two examples of code to copy from one file to another. The examples in the Gforth documentation ( Section 3.27 ) did not work for me ( winXP ) in fact they seemed to open and create files but not write to files properly. This is the Gforth documentation example that copies the contents of one file to another: 0 Value fd-in 0 Value fd-out : open-input ( addr u -- ) r/o open-file throw to fd-in ; : open-output ( addr u -- ) w/o create-file throw to fd-out ; s" foo.in" open-input s" foo.out" open-output : copy-file ( -- ) begin line-buffer max-line fd-in read-line throw while line-buffer swap fd-out write-line throw repeat ; I found this example ( http://rosettacode.org/wiki/File_IO#Forth ) which does work. The main problem is that I can't isolate the part that writes to a file and have it still work. The main confusion is that r doesn't seem to consume TOS as I might expect. : copy-file2 ( a1 n1 a2 n2 -- ) r/o open-file throw >r w/o create-file throw r> begin pad maxstring 2 pick read-file throw ?dup while pad swap 3 pick write-file throw repeat close-file throw close-file throw ; \ Invoke it like this: s" output.txt" s" input.txt" copy-file I would be very grateful if someone could explain exactly how the open, create read and write -file words actually work, as my investigation keeps resulting in somewhat bizarre stacks. Any clues as to why the Gforth examples do not work might help too. In summary, I want to output from Gforth to a file and so far have been thwarted. Can anyone offer any help? Thank you Vijay, I think that I understand the example that you gave. However when I try to use something like this ( which I think is similar ): 0 value test-file : write-test s" testfile.out" w/o create-file throw to test-file s" test text" test-file write-line ; I get ok but nothing is put into the file, have I made a mistake? It seems that the problem was due to not flushing the relevant buffers or explicitly closing the file. Adding something like test-file flush-file throw or test-file close-file throw between write-line and ; makes it work. Thanks again Vijay for helping.

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• Java app makes screen display unresponsive after 10 minutes of user idle time

  - by Ross

  I've written a Java app that allows users to script mouse/keyboard input (JMacro, link not important, only for the curious). I personally use the application to automate character actions in an online game overnight while I sleep. Unfortunately, I keep coming back to the computer in the morning to find it unresponsive. Upon further testing, I'm finding that my application causes the computer to become unresponsive after about 10 minutes of user idle time (even if the application itself it simulating user activity). I can't seem to pin-point the issue, so I'm hoping somebody else might have a suggestion of where to look or what might be causing the issue. The relevant symptoms and characteristics: Unresponsiveness occurs after user is idle for 10 minutes User can still move the mouse pointer around the screen Everything but the mouse appears frozen... mouse clicks have no effect and no applications update their displays, including the Windows 7 desktop I left the task manager up along the with the app overnight so I could see the last task manager image before the screen freezes... the Java app is at normal CPU/Memory usage and total CPU usage is only ~1% After moving the mouse (in other words, the user comes back from being idle), the screen image starts updating again within 30 minutes (this is very hit and miss... sometimes 10 minutes, sometimes no results after two hours) User can CTRL-ALT-DEL to get to Windows 7's CTRL-ALT-DEL screen (after a 30 second pause). User is still able to move mouse pointer, but clicking any of the button options causes the screen to appear to freeze again On some very rare occasions, the system never freezes, and I come back to it in the morning with full responsiveness The Java app automatically stops input scripting in the middle of the night, so Windows 7 detects "real" idleness and turns the monitors into Standby mode... which they successfully come out of upon manually moving the mouse in the morning when I wake up, even though the desktop display still appears frozen Given the symptoms and characteristics of the issue, it's as if the Java app is causing the desktop display of the logged in user to stop updating, including any running applications. Programming concepts and Java packages used: Multi-threading Standard out and err are rerouted to a javax.swing.JTextArea The application uses a Swing GUI awt.Robot (very heavily used) awt.PointerInfo awt.MouseInfo System Specs: Windows 7 Professional Java 1.6.0 u17 In conclusion, I should stress that I'm not looking for any specific solutions, as I'm not asking a very specific question. I'm just wondering if anybody has run into a similar problem when using the Java libraries that I'm using. I would also gladly appreciate any suggestions for things to try to attempt to further pinpoint what is causing my problem. Thanks! Ross PS, I'll post an update/answer if I manage to stumble across anything else while I continue to debug this.

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• using '.each' method: how do I get the indexes of multiple ordered lists to each begin at [0]?

  - by shecky

  I've got multiple divs, each with an ordered list (various lengths). I'm using jquery to add a class to each list item according to its index (for the purpose of columnizing portions of each list). What I have so far ... <script type="text/javascript"> /* Objective: columnize list items from a single ul or ol in a pre-determined number of columns 1. get the index of each list item 2. assign column class according to li's index */ $(document).ready(function() { $('ol li').each(function(index){ // assign class according to li's index ... index = li number -1: 1-6 = 0-5; 7-12 = 6-11, etc. if ( index <= 5 ) { $(this).addClass('column-1'); } if ( index > 5 && index < 12 ) { $(this).addClass('column-2'); } if ( index > 11 ) { $(this).addClass('column-3'); } // add another class to the first list item in each column $('ol li').filter(function(index) { return index != 0 && index % 6 == 0; }).addClass('reset'); }); // closes li .each func }); // closes doc.ready.func </script> ... succeeds if there's only one list; when there are additional lists, the last column class ('column-3') is added to all remaining list items on the page. In other words, the script is presently indexing continuously through all subsequent lists/list items, rather than being re-set to [0] for each ordered list. Can someone please show me the proper method/syntax to correct/amend this, so that the script addresses/indexes each ordered list anew? many thanks in advance. shecky p.s. the markup is pretty straight-up: <div class="tertiary"> <h1>header</h1> <ol> <li><a href="#" title="a link">a link</a></li> <li><a href="#" title="a link">a link</a></li> <li><a href="#" title="a link">a link</a></li> </ol> </div><!-- END div class="tertiary" -->

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• Implementing a logging library in .NET with a database as the storage medium

  - by Dave

  I'm just starting to work on a logging library that everyone can use to keep track of any sort of system information while the user is running our application. The simplest example so far is to track Info, Warnings, and Errors. I want all plugins to be able to use this feature, but since each developer might have a different idea of what's important to report, I want to keep this as generic as possible. In the C++ world, I would normally use something like a stl::pair<string,string> to act as a key value pair structure, and have a stl::list of these to act as a "row" in the log. The log cache would then be a list<list<pair<string,string>>> (ugh!). This way, the developers can use a const string key like INFO, WARNING, ERROR to have a consistent naming for a column in the database (for SELECTing specific types of information). I'd like the database to be able to deal with any number of distinct column names. For example, John might have an INFO row with a column called USER, and Bill might have an INFO row with a column called FILENAME. I want the log viewer to be able to display all information, and if one report doesn't have a value for INFO / FILENAME, those fields should just appear blank. So one option is to use List<List<KeyValuePair<String,String>>, and the another is to have the log library consumer somehow "register" its schema, and then have the database do an ALTER TABLE to handle this situation. Yet another idea is to have a table that's just for key value pairs, with a foreign key that maps the key value pairs back to the original log entry. I obviously don't want logging to bog down the system, so I only lock the log cache to make a copy of the data (and remove the already-copied data), then a background thread will dump the information to the database. My specific questions regarding this are: Do you see any performance issues? In other words, have you ever tried something like this and found that certain things just don't work well in practice? Is there a more .NETish way to implement the key value pairs, other than List<List<KeyValuePair<String,String>>>? Even if there is a way to do #2 better, is the ALTER TABLE idea I proposed above a Bad Thing? Would you recommend multiple databases over a single one? I don't yet have an idea of how frequently the log would get written to, but we ideally would like to have lots of low level information. Perhaps there should be a DB with a fixed schema only for the low level stuff, and then another DB that's more flexible for reporting information back to users.

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• why this sql code dont work

  - by magy

  <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"> <head> <meta http-equiv="Content-Type" content="text/html; charset=windows-1256"> <title>??? ?????? ???? ????</title> </head> <body> <table width="100%" border="1"> <tr> <td>name</td> <td>number</td> <td>math</td> <td>arab</td> <td>history</td> <td>geo</td> </tr> <?php require_once "conf.php"; $sql2=("SELECT * FROM student WHERE snum = $ss"); $rs2 = mysql_query($sql2) or die(mysql_error()); $num = mysql_num_rows($rs2); $ss= $_POST["ss"]; if (empty($ss)) { echo "please write your search words";} else if ($num < 1 ) { echo "not found any like "; }else { $sql=("SELECT * FROM student WHERE snum = $ss "); $rs = mysql_query($sql) or die(mysql_error()); while($data=mysql_fetch_array($rs)){ $name=$data["sname"]; $number=$data["snum"]; $math=$data["math"]; $arab=$data["arab"]; $history=$data["history"]; $geo=$data["geo"]; echo" <tr> <td>$name</td> <td>$number</td> <td>$math</td> <td>$arab</td> <td>$history</td> <td>$geo</td> </tr> "; } }; ?> </table> </body> </html>

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• Gradual memory leak in loop over contents of QTMovie

  - by Benji XVI

  I have a simple foundation tool that exports every frame of a movie as a .tiff file. Here is the relevant code: NSString* movieLoc = [NSString stringWithCString:argv[1]]; QTMovie *sourceMovie = [QTMovie movieWithFile:movieLoc error:nil]; int i=0; while (QTTimeCompare([sourceMovie currentTime], [sourceMovie duration]) != NSOrderedSame) { // save image of movie to disk NSAutoreleasePool *arp = [[NSAutoreleasePool alloc] init]; NSString *filePath = [NSString stringWithFormat:@"/somelocation_%d.tiff", i++]; NSData *currentImageData = [[sourceMovie currentFrameImage] TIFFRepresentation]; [currentImageData writeToFile:filePath atomically:NO]; NSLog(@"%@", filePath); [sourceMovie stepForward]; [arp release]; } [pool drain]; return 0; As you can see, in order to prevent very large memory buildups with the various transparently-autoreleased variables in the loop, we create, and flush, an autoreleasepool with every run through the loop. However, over the course of stepping through a movie, the amount of memory used by the program still gradually increases. Instruments is not detecting any memory leaks per se, but the object trace shows certain General Data blocks to be increasing in size. [Edited out reference to slowdown as it doesn't seem to be as much of a problem as I thought.] Edit: let's knock out some parts of the code inside the loop & see what we find out... Test 1 while (banana) { NSAutoreleasePool *arp = [[NSAutoreleasePool alloc] init]; NSString *filePath = [NSString stringWithFormat:@"/somelocation_%d.tiff", i++]; NSLog(@"%@", filePath); [sourceMovie stepForward]; [arp release]; } Here we simply loop over the whole movie, creating the filename and logging it. Memory characteristics: remains at 15MB usage for the duration. Test 2 while (banana) { NSAutoreleasePool *arp = [[NSAutoreleasePool alloc] init]; NSImage *image = [sourceMovie currentFrameImage]; [sourceMovie stepForward]; [arp release]; } Here we add back in the creation of the NSImage from the current frame. Memory characteristics: gradually increasing memory usage. RSIZE is at 60MB by frame 200; 75MB by f300. Test 3 while (banana) { NSAutoreleasePool *arp = [[NSAutoreleasePool alloc] init]; NSImage *image = [sourceMovie currentFrameImage]; NSData *imageData = [image TIFFRepresentation]; [sourceMovie stepForward]; [arp release]; } We've added back in the creation of an NSData object from the NSImage. Memory characteristics: Memory usage is again increasing: 62MB at f200; 75MB at f300. In other words, largely identical. It looks like a memory leak in the underlying system QTMovie uses to do currentFrameImage, to me.

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• Need a fast programming language that can drive two printers

  - by Pete

  I have a rather unusual application that isn't working the way I need, and I hope someone here will have some suggestions or at least a direction to investigate. We have a museum exhibit that has a computer at the entrance driving two small receipt printers. There are two buttons on a console, wired to the left and right buttons of a disemboweled mouse. The two printers and associated buttons are for girls and boys, each button does a random selection from a database of names and prints a small ticket on the appropriate printer with a graphic image, a few words about the exhibit and the randomly chosen name. Conceptually all is well, but it hangs quite often. I got the project at the last minute, because the original designer got bogged down and couldn't deliver, so the exhibit's author asked me the day before opening, whether I could write something that would work. I did it in Word, since I am an experienced VBA programmer. Several other avenues I attempted first all lead to dead ends - one couldn't do graphics, another couldn't handle two printers, yet another couldn't change fonts and so on. The problem is that it simply isn't fast enough - Word can only drive one printer at a time and changing the active printer takes a long time. Not by office standards, where a second or two of delay before a printer starts working on your document is not an issue, but here I need more or less instant response. If kids press a button and nothing happens, they press it over and over until something does happen, resulting in maybe half a dozen commands being sent before the printer starts reacting. Sometimes it jams the program completely, since boys and girls will be pressing the two buttons simultaneously and Word locks up, and even when it doesn't jam, the printers then spit out a stream of tickets, making a mess. The kids start squabbling over which ticket is whose, pulling them out of the printers, snarling the paper tape, jamming the printer and generally making a mess of the whole affair, often necessitating the exhibit caretakers having to restart the computer and clear torn bits of paper out the printers. What I need is some sort of fast programming language that can drive two printers *-simultaneously-*, not the MSOffice claptrap of having to switch the active printer, that can react to both left and right mouse button click events, can print a small graphic image and can print in different font sizes and styles and. I don't need many, but it's not all in one typeface. Can anyone suggest what I might use for this? I don't even know if it's possible at all under Windows, whether the "single active printer" garbage is an Office artifact, or a Windows restriction. My little Commodore-64 twenty-five years ago had two printers attached to it and drove both simultaneously with no difficulties - it doesn't seem to me it should be such an impossible requirement today.

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• Parallel programming in C#

  - by Alxandr

  I'm interested in learning about parallel programming in C#.NET (not like everything there is to know, but the basics and maybe some good-practices), therefore I've decided to reprogram an old program of mine which is called ImageSyncer. ImageSyncer is a really simple program, all it does is to scan trough a folder and find all files ending with .jpg, then it calculates the new position of the files based on the date they were taken (parsing of xif-data, or whatever it's called). After a location has been generated the program checks for any existing files at that location, and if one exist it looks at the last write-time of both the file to copy, and the file "in its way". If those are equal the file is skipped. If not a md5 checksum of both files is created and matched. If there is no match the file to be copied is given a new location to be copied to (for instance, if it was to be copied to "C:\test.jpg" it's copied to "C:\test(1).jpg" instead). The result of this operation is populated into a queue of a struct-type that contains two strings, the original file and the position to copy it to. Then that queue is iterated over untill it is empty and the files are copied. In other words there are 4 operations: 1. Scan directory for jpegs 2. Parse files for xif and generate copy-location 3. Check for file existence and if needed generate new path 4. Copy files And so I want to rewrite this program to make it paralell and be able to perform several of the operations at the same time, and I was wondering what the best way to achieve that would be. I've came up with two different models I can think of, but neither one of them might be any good at all. The first one is to parallelize the 4 steps of the old program, so that when step one is to be executed it's done on several threads, and when the entire of step 1 is finished step 2 is began. The other one (which I find more interesting because I have no idea of how to do that) is to create a sort of worker and consumer model, so when a thread is finished with step 1 another one takes over and performs step 2 at that object (or something like that). But as said, I don't know if any of these are any good solutions. Also, I don't know much about parallel programming at all. I know how to make a thread, and how to make it perform a function taking in an object as its only parameter, and I've also used the BackgroundWorker-class on one occasion, but I'm not that familiar with any of them. Any input would be appreciated.

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• How to overwrite an array of char pointers with a larger list of char pointers?

  - by Casey

  My function is being passed a struct containing, among other things, a NULL terminated array of pointers to words making up a command with arguments. I'm performing a glob match on the list of arguments, to expand them into a full list of files, then I want to replace the passed argument array with the new expanded one. The globbing is working fine, that is, g.gl_pathv is populated with the list of expected files. However, I am having trouble copying this array into the struct I was given. #include <glob.h> struct command { char **argv; // other fields... } void myFunction( struct command * cmd ) { char **p = cmd->argv; char* program = *p++; // save the program name (e.g 'ls', and increment to the first argument glob_t g; memset(&g, 0, sizeof(g)); g.gl_offs = 1; int res = glob(*p++, GLOB_DOOFFS, NULL, &g); glob_handle_res(res); while (*p) { res = glob(*p, GLOB_DOOFFS | GLOB_APPEND, NULL, &g); glob_handle_res(res); } if( g.gl_pathc <= 0 ) { globfree(&g); } cmd->argv = malloc((g.gl_pathc + g.gl_offs) * sizeof *cmd->argv); if (cmd->argv == NULL) { sys_fatal_error("pattern_expand: malloc failed\n");} // copy over the arguments size_t i = g.gl_offs; for (; i < g.gl_pathc + g.gl_offs; ++i) cmd->argv[i] = strdup(g.gl_pathv[i]); // insert the original program name cmd->argv[0] = strdup(program); ** cmd->argv[g.gl_pathc + g.gl_offs] = 0; ** globfree(&g); } void command_free(struct esh_command * cmd) { char ** p = cmd->argv; while (*p) { free(*p++); // Segfaults here, was it already freed? } free(cmd->argv); free(cmd); } Edit 1: Also, I realized I need to stick program back in there as cmd-argv[0] Edit 2: Added call to calloc Edit 3: Edit mem management with tips from Alok Edit 4: More tips from alok Edit 5: Almost working.. the app segfaults when freeing the command struct Finally: Seems like I was missing the terminating NULL, so adding the line: cmd->argv[g.gl_pathc + g.gl_offs] = 0; seemed to make it work.

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• HTML: Include, or exclude, optional closing tags?

  - by Ian Boyd

  Some HTML1 closing tags are optional, i.e.: </HTML> </HEAD> </BODY> </P> </DT> </DD> </LI> </OPTION> </THEAD> </TH> </TBODY> </TR> </TD> </TFOOT> </COLGROUP> Note: Not to be confused with closing tags that are forbidden to be included, i.e.: </IMG> </INPUT> </BR> </HR> </FRAME> </AREA> </BASE> </BASEFONT> </COL> </ISINDEX> </LINK> </META> </PARAM> Note: xhtml is different from HTML. xhtml is a form of xml, which requires every element have a closing tag. A closing tag can be forbidden in html, yet mandatory in xhtml. Are the optional closing tags ideally included, but we'll accept them if you forgot them, or ideally not included, but we'll accept them if you put them in In other words, should i include them, or should i not include them? The HTML 4.01 spec talks about closing element tags being optional, but doesn't say if it's preferable to include them, or preferable to not include them. On the other hand, a random article on DevGuru says: The ending tag is optional. However, it is recommended that it be included. The reason i ask is because you just know it's optional for compatibility reasons; and they would have made them (mandatory | forbidden) if they could have. Put it another way: What did HTML 1, 2, 3 do with regards to these, now optional, closing tags. What does HTML 5 do? And what should i do? Footnotes 1HTML 4.01

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• Calling cdecl Functions That Have Different Number of Arguments

  - by KlaxSmashing

  I have functions that I wish to call based on some input. Each function has different number of arguments. In other words, if (strcmp(str, "funcA") == 0) funcA(a, b, c); else if (strcmp(str, "funcB") == 0) funcB(d); else if (strcmp(str, "funcC") == 0) funcC(f, g); This is a bit bulky and hard to maintain. Ideally, these are variadic functions (e.g., printf-style) and can use varargs. But they are not. So exploiting the cdecl calling convention, I am stuffing the stack via a struct full of parameters. I'm wondering if there's a better way to do it. Note that this is strictly for in-house (e.g., simple tools, unit tests, etc.) and will not be used for any production code that might be subjected to malicious attacks. Example: #include <stdio.h> typedef struct __params { unsigned char* a; unsigned char* b; unsigned char* c; } params; int funcA(int a, int b) { printf("a = %d, b = %d\n", a, b); return a; } int funcB(int a, int b, const char* c) { printf("a = %d, b = %d, c = %s\n", a, b, c); return b; } int funcC(int* a) { printf("a = %d\n", *a); *a *= 2; return 0; } typedef int (*f)(params); int main(int argc, char**argv) { int val; int tmp; params myParams; f myFuncA = (f)funcA; f myFuncB = (f)funcB; f myFuncC = (f)funcC; myParams.a = (unsigned char*)100; myParams.b = (unsigned char*)200; val = myFuncA(myParams); printf("val = %d\n", val); myParams.c = (unsigned char*)"This is a test"; val = myFuncB(myParams); printf("val = %d\n", val); tmp = 300; myParams.a = (unsigned char*)&tmp; val = myFuncC(myParams); printf("a = %d, val = %d\n", tmp, val); return 0; } Output: gcc -o func func.c ./func a = 100, b = 200 val = 100 a = 100, b = 200, c = This is a test val = 200 a = 300 a = 600, val = 0

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• Rails send mail with GMail

  - by Danny McClelland

  Hi Everyone, I am on rails 2.3.5 and have the latest Ruby installed and my application is running well, except, GMail emails. I am trying to setup my gmail imap connection which has worked previously but now doesnt want to know. This is my code: # Be sure to restart your server when you modify this file # Uncomment below to force Rails into production mode when # you don't control web/app server and can't set it the proper way # ENV['RAILS_ENV'] ||= 'production' # Specifies gem version of Rails to use when vendor/rails is not present RAILS_GEM_VERSION = '2.3.5' unless defined? RAILS_GEM_VERSION # Bootstrap the Rails environment, frameworks, and default configuration require File.join(File.dirname(__FILE__), 'boot') Rails::Initializer.run do |config| # Gems config.gem "capistrano-ext", :lib => "capistrano" config.gem "configatron" # Make Time.zone default to the specified zone, and make Active Record store time values # in the database in UTC, and return them converted to the specified local zone. config.time_zone = "London" # The internationalization framework can be changed to have another default locale (standard is :en) or more load paths. # All files from config/locales/*.rb,yml are added automatically. # config.i18n.load_path << Dir[File.join(RAILS_ROOT, 'my', 'locales', '*.{rb,yml}')] #config.i18n.default_locale = :de # Your secret key for verifying cookie session data integrity. # If you change this key, all old sessions will become invalid! # Make sure the secret is at least 30 characters and all random, # no regular words or you'll be exposed to dictionary attacks. config.action_controller.session = { :session_key => '_base_session', :secret => '7389ea9180b15f1495a5e73a69a893311f859ccff1ffd0fa2d7ea25fdf1fa324f280e6ba06e3e5ba612e71298d8fbe7f15fd7da2929c45a9c87fe226d2f77347' } config.active_record.observers = :user_observer end ActiveSupport::CoreExtensions::Date::Conversions::DATE_FORMATS.merge!(:default => '%d/%m/%Y') ActiveSupport::CoreExtensions::Time::Conversions::DATE_FORMATS.merge!(:default => '%d/%m/%Y') require "will_paginate" ActionMailer::Base.delivery_method = :smtp ActionMailer::Base.smtp_settings = { :enable_starttls_auto => true, :address => "smtp.gmail.com", :port => 587, :domain => "XXXXXXXX.XXX", :authentication => :plain, :user_name => "XXXXXXXXXX.XXXXXXXXXX.XXX", :password => "XXXXX" } But the above just results in an SMTP auth error in the production log. I have read varied reports of this not working in Rails 2.2.2 but nothing for 2.3.5, anyone got any ideas? Thanks, Danny

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• How does the event dispatch thread work?

  - by Roman

  With the help of people on stackoverflow I was able to get the following working code of the simples GUI countdown (it just displays a window counting down seconds). My main problem with this code is the invokeLater stuff. As far as I understand the invokeLater send a task to the event dispatching thread (EDT) and then the EDT execute this task whenever it "can" (whatever it means). Is it right? To my understanding the code works like that: In the main method we use invokeLater to show the window (showGUI method). In other words, the code displaying the window will be executed in the EDT. In the main method we also start the counter and the counter (by construction) is executed in another thread (so it is not in the event dispatching thread). Right? The counter is executed in a separate thread and periodically it calls updateGUI. The updateGUI is supposed to update GUI. And GUI is working in the EDT. So, updateGUI should also be executed in the EDT. It is why the code for the updateGUI is inclosed in the invokeLater. Is it right? What is not clear to me is why we call the counter from the EDT. Anyway it is not executed in the EDT. It starts immediately a new thread and the counter is executed there. So, why we cannot call the counter in the main method after the invokeLater block? import javax.swing.JFrame; import javax.swing.JLabel; import javax.swing.SwingUtilities; public class CountdownNew { static JLabel label; // Method which defines the appearance of the window. public static void showGUI() { JFrame frame = new JFrame("Simple Countdown"); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); label = new JLabel("Some Text"); frame.add(label); frame.pack(); frame.setVisible(true); } // Define a new thread in which the countdown is counting down. public static Thread counter = new Thread() { public void run() { for (int i=10; i>0; i=i-1) { updateGUI(i,label); try {Thread.sleep(1000);} catch(InterruptedException e) {}; } } }; // A method which updates GUI (sets a new value of JLabel). private static void updateGUI(final int i, final JLabel label) { SwingUtilities.invokeLater( new Runnable() { public void run() { label.setText("You have " + i + " seconds."); } } ); } public static void main(String[] args) { SwingUtilities.invokeLater(new Runnable() { public void run() { showGUI(); counter.start(); } }); } }

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• How do I update with a newly-created detached entity using NHibernate?

  - by Daniel T.

  Explanation: Let's say I have an object graph that's nested several levels deep and each entity has a bi-directional relationship with each other. A -> B -> C -> D -> E Or in other words, A has a collection of B and B has a reference back to A, and B has a collection of C and C has a reference back to B, etc... Now let's say I want to edit some data for an instance ofC. In Winforms, I would use something like this: var instanceOfC; using (var session = SessionFactory.OpenSession()) { // get the instance of C with Id = 3 instanceOfC = session.Linq<C>().Where(x => x.Id == 3); } SendToUIAndLetUserUpdateData(instanceOfC); using (var session = SessionFactory.OpenSession()) { // re-attach the detached entity and update it session.Update(instanceOfC); } In plain English, we grab a persistent instance out of the database, detach it, give it to the UI layer for editing, then re-attach it and save it back to the database. Problem: This works fine for Winform applications because we're using the same entity all throughout, the only difference being that it goes from persistent to detached to persistent again. The problem occurs when I'm using a web service and a browser, sending over JSON data. In this case, the data that comes back is no longer a detached entity, but rather a transient one that just happens to have the same ID as the persistent one. If I use this entity to update, it will wipe out the relationship to B and D unless I sent the entire object graph over to the UI and got it back in one piece. Question: My question is, how do I serialize detached entities over the web, receive them back, and save them, while preserving any relationships that I didn't explicitly change? I know about ISession.SaveOrUpdateCopy and ISession.Merge() (they seem to do the same thing?), but this will still wipe out the relationships if I don't explicitly set them. I could copy the fields from the transient entity to the persistent entity one by one, but this doesn't work too well when it comes to relationships and I'd have to handle version comparisons manually.

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• Poor performance / speed of regex with lookahead

  - by Hugo Zaragoza

  I have been observing extremely slow execution times with expressions with several lookaheads. I suppose that this is due to underlying data structures, but it seems pretty extreme and I wonder if I do something wrong or if there are known work-arounds. The problem is determining if a set of words are present in a string, in any order. For example we want to find out if two terms "term1" AND "term2" are somewhere in a string. I do this with the expresion: (?=.*\bterm1\b)(?=.*\bterm2\b) But what I observe is that this is an order of magnitude slower than checking first just \bterm1\b and just then \bterm2\b This seems to indicate that I should use an array of patterns instead of a single pattern with lookaheads... is this right? it seems wrong... Here is an example test code and resulting times: public static void speedLookAhead() { Matcher m, m1, m2; boolean find; int its = 1000000; // create long non-matching string char[] str = new char[2000]; for (int i = 0; i < str.length; i++) { str[i] = 'x'; } String test = str.toString(); // First method: use one expression with lookaheads m = Pattern.compile("(?=.*\\bterm1\\b)(?=.*\\bterm2\\b)").matcher(test); long time = System.currentTimeMillis(); ; for (int i = 0; i < its; i++) { m.reset(test); find = m.find(); } time = System.currentTimeMillis() - time; System.out.println(time); // Second method: use two expressions and AND the results m1 = Pattern.compile("\\bterm1\\b").matcher(test); m2 = Pattern.compile("\\bterm2\\b").matcher(test); time = System.currentTimeMillis(); ; for (int i = 0; i < its; i++) { m1.reset(test); m2.reset(test); find = m1.find() && m2.find(); } time = System.currentTimeMillis() - time; System.out.println(time); } This outputs in my computer: 1754 150

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• dynamic module creation

  - by intuited

  I'd like to dynamically create a module from a dictionary, and I'm wondering if adding an element to sys.modules is really the best way to do this. EG context = { a: 1, b: 2 } import types test_context_module = types.ModuleType('TestContext', 'Module created to provide a context for tests') test_context_module.__dict__.update(context) import sys sys.modules['TestContext'] = test_context_module My immediate goal in this regard is to be able to provide a context for timing test execution: import timeit timeit.Timer('a + b', 'from TestContext import *') It seems that there are other ways to do this, since the Timer constructor takes objects as well as strings. I'm still interested in learning how to do this though, since a) it has other potential applications; and b) I'm not sure exactly how to use objects with the Timer constructor; doing so may prove to be less appropriate than this approach in some circumstances. EDITS/REVELATIONS/PHOOEYS/EUREKAE: I've realized that the example code relating to running timing tests won't actually work, because import * only works at the module level, and the context in which that statement is executed is that of a function in the testit module. In other words, the globals dictionary used when executing that code is that of main, since that's where I was when I wrote the code in the interactive shell. So that rationale for figuring this out is a bit botched, but it's still a valid question. I've discovered that the code run in the first set of examples has the undesirable effect that the namespace in which the newly created module's code executes is that of the module in which it was declared, not its own module. This is like way weird, and could lead to all sorts of unexpected rattlesnakeic sketchiness. So I'm pretty sure that this is not how this sort of thing is meant to be done, if it is in fact something that the Guido doth shine upon. The similar-but-subtly-different case of dynamically loading a module from a file that is not in python's include path is quite easily accomplished using imp.load_source('NewModuleName', 'path/to/module/module_to_load.py'). This does load the module into sys.modules. However this doesn't really answer my question, because really, what if you're running python on an embedded platform with no filesystem? I'm battling a considerable case of information overload at the moment, so I could be mistaken, but there doesn't seem to be anything in the imp module that's capable of this. But the question, essentially, at this point is how to set the global (ie module) context for an object. Maybe I should ask that more specifically? And at a larger scope, how to get Python to do this while shoehorning objects into a given module?

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• Should I skip authorization, with CanCan, of an action that instantiates a resource?

  - by irkenInvader

  I am writing a web app to pick random lists of cards from larger, complete sets of cards. I have a Card model and a CardSet model. Both models have a full RESTful set of 7 actions (:index, :new, :show, etc). The CardSetsController has an extra action for creating random sets: :random. # app/models/card_set.rb class CardSet < ActiveRecord::Base belongs_to :creator, :class_name => "User" has_many :memberships has_many :cards, :through => :memberships # app/models/card.rb class Card < ActiveRecord::Base belongs_to :creator, :class_name => "User" has_many :memberships has_many :card_sets, :through => :memberships I have added Devise for authentication and CanCan for authorizations. I have users with an 'editor' role. Editors are allowed to create new CardSets. Guest users (Users who have not logged in) can only use the :index and :show actions. These authorizations are working as designed. Editors can currently use both the :random and the :new actions without any problems. Guest users, as expected, cannot. # app/controllers/card_sets_controller.rb class CardSetsController < ApplicationController before_filter :authenticate_user!, :except => [:show, :index] load_and_authorize_resource I want to allow guest users to use the :random action, but not the :new action. In other words, they can see new random sets, but not save them. The "Save" button on the :random action's view is hidden (as designed) from the guest users. The problem is, the first thing the :random action does is build a new instance of the CardSet model to fill out the view. When cancan tries to load_and_authorize_resource a new CardSet, it throws a CanCan::AccessDenied exception. Therefore, the view never loads and the guest user is served a "You need to sign in or sign up before continuing" message. # app/controllers/card_sets_controllers.rb def random @card_set = CardSet.new( :name => "New Set of 10", :set_type => "Set of 10" ) I realize that I can tell load_and_authorize_resource to skip the :random action by passing :except => :random to the call, but that just feels "wrong" for some reason. What's the "right" way to do this? Should I create the new random set without instantiating a new CardSet? Should I go ahead and add the exception?

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• Searching in Ruby on Rails - How do I search on each word entered and not the exact string?

  - by bgadoci

  I have built a blog application w/ ruby on rails and I am trying to implement a search feature. The blog application allows for users to tag posts. The tags are created in their own table and belong_to :post. When a tag is created, so is a record in the tag table where the name of the tag is tag_name and associated by post_id. Tags are strings. I am trying to allow a user to search for any word tag_name in any order. Here is what I mean. Lets say a particular post has a tag that is 'ruby code controller'. In my current search feature, that tag will be found if the user searches for 'ruby', 'ruby code', or 'ruby code controller'. It will not be found if the user types in 'ruby controller'. Essentially what I am saying is that I would like each word entered in the search to be searched for, not necessarily the 'string' that is entered into the search. I have been experimenting with providing multiple textfields to allow the user to type in multiple words, and also have been playing around with the code below, but can't seem to accomplish the above. I am new to ruby and rails so sorry if this is an obvious question and prior to installing a gem or plugin I thought I would check to see if there was a simple fix. Here is my code: View: /views/tags/index.html.erb <% form_tag tags_path, :method => 'get' do %> <p> <%= text_field_tag :search, params[:search], :class => "textfield-search" %> <%= submit_tag "Search", :name => nil, :class => "search-button" %> </p> <% end %> TagsController def index @tags = Tag.search(params[:search]).paginate :page => params[:page], :per_page => 5 @tagsearch = Tag.search(params[:search]) @tag_counts = Tag.count(:group => :tag_name, :order => 'count_all DESC', :limit => 100) respond_to do |format| format.html # index.html.erb format.xml { render :xml => @tags } end end Tag Model class Tag < ActiveRecord::Base belongs_to :post validates_length_of :tag_name, :maximum=>42 validates_presence_of :tag_name def self.search(search) if search find(:all, :order => "created_at DESC", :conditions => ['tag_name LIKE ?', "%#{search}%"]) else find(:all, :order => "created_at DESC") end end end

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• Converting C source to C++

  - by Barry Kelly

  How would you go about converting a reasonably large (300K), fairly mature C codebase to C++? The kind of C I have in mind is split into files roughly corresponding to modules (i.e. less granular than a typical OO class-based decomposition), using internal linkage in lieu private functions and data, and external linkage for public functions and data. Global variables are used extensively for communication between the modules. There is a very extensive integration test suite available, but no unit (i.e. module) level tests. I have in mind a general strategy: Compile everything in C++'s C subset and get that working. Convert modules into huge classes, so that all the cross-references are scoped by a class name, but leaving all functions and data as static members, and get that working. Convert huge classes into instances with appropriate constructors and initialized cross-references; replace static member accesses with indirect accesses as appropriate; and get that working. Now, approach the project as an ill-factored OO application, and write unit tests where dependencies are tractable, and decompose into separate classes where they are not; the goal here would be to move from one working program to another at each transformation. Obviously, this would be quite a bit of work. Are there any case studies / war stories out there on this kind of translation? Alternative strategies? Other useful advice? Note 1: the program is a compiler, and probably millions of other programs rely on its behaviour not changing, so wholesale rewriting is pretty much not an option. Note 2: the source is nearly 20 years old, and has perhaps 30% code churn (lines modified + added / previous total lines) per year. It is heavily maintained and extended, in other words. Thus, one of the goals would be to increase mantainability. [For the sake of the question, assume that translation into C++ is mandatory, and that leaving it in C is not an option. The point of adding this condition is to weed out the "leave it in C" answers.]

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