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• How to make a model instance read-only after saving it once?

  - by Ryszard Szopa

  One of the functionalities in a Django project I am writing is sending a newsletter. I have a model, Newsletter and a function, send_newsletter, which I have registered to listen to Newsletter's post_save signal. When the newsletter object is saved via the admin interface, send_newsletter checks if created is True, and if yes it actually sends the mail. However, it doesn't make much sense to edit a newsletter that has already been sent, for the obvious reasons. Is there a way of making the Newsletter object read-only once it has been saved? Edit: I know I can override the save method of the object to raise an error or do nothin if the object existed. However, I don't see the point of doing that. As for the former, I don't know where to catch that error and how to communicate the user the fact that the object wasn't saved. As for the latter, giving the user false feedback (the admin interface saying that the save succeded) doesn't seem like a Good Thing. What I really want is allow the user to use the Admin interface to write the newsletter and send it, and then browse the newsletters that have already been sent. I would like the admin interface to show the data for sent newsletters in an non-editable input box, without the "Save" button. Alternatively I would like the "Save" button to be inactive.

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• Implementing the ‘defer’ statement from Go in Objective-C?

  - by zoul

  Hello! Today I read about the defer statement in the Go language: A defer statement pushes a function call onto a list. The list of saved calls is executed after the surrounding function returns. Defer is commonly used to simplify functions that perform various clean-up actions. I thought it would be fun to implement something like this in Objective-C. Do you have some idea how to do it? I thought about dispatch finalizers, autoreleased objects and C++ destructors. Autoreleased objects: @interface Defer : NSObject {} + (id) withCode: (dispatch_block_t) block; @end @implementation Defer - (void) dealloc { block(); [super dealloc]; } @end #define defer(__x) [Defer withCode:^{__x}] - (void) function { defer(NSLog(@"Done")); … } Autoreleased objects seem like the only solution that would last at least to the end of the function, as the other solutions would trigger when the current scope ends. On the other hand they could stay in the memory much longer, which would be asking for trouble. Dispatch finalizers were my first thought, because blocks live on the stack and therefore I could easily make something execute when the stack unrolls. But after a peek in the documentation it doesn’t look like I can attach a simple “destructor” function to a block, can I? C++ destructors are about the same thing, I would create a stack-based object with a block to be executed when the destructor runs. This would have the ugly disadvantage of turning the plain .m files into Objective-C++? I don’t really think about using this stuff in production, I’m just interested in various solutions. Can you come up with something working, without obvious disadvantages? Both scope-based and function-based solutions would be interesting.

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• Using PHP to store results of a post request

  - by Paul M

  Im currently working with an API which requires we send our collection details in xml to their server using a post request. Nothing major there but its not working, so I want to output the sent xml to a txt file so I can look at actually whats being sent!! Instead of posting to the API im posting to a document called target, but the xml its outputting its recording seems to be really wrong. Here is my target script, note that the posting script posts 3 items, so the file being written should have details of each post request one after the other. <?php error_reporting(E_ALL); ini_set('display_errors', 1); // get the request data... $payload = ''; $fp = fopen('php://input','r'); $output_file = fopen('output.txt', 'w'); while (!feof($fp)) { $payload .= fgets($fp); fwrite($output_file, $payload); } fclose($fp); fclose($output_file); ?> I also tried the following, but this just recorded the last post request so only 1 collection item was recorded in the txt file, instead of all 3 output_file = fopen('output.txt', 'w'); while (!feof($fp)) { $payload .= fgets($fp); } fwrite($output_file, $payload); fclose($fp); fclose($output_file); I know im missing something really obvious, but ive been looking at this all morning!

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• Sqlite3 "chained" query

  - by Arrieta

  I need to create a configuration file from a data file that looks as follows: MAN1_TIME '01-JAN-2010 00:00:00.0000 UTC' MAN1_RX 123.45 MAN1_RY 123.45 MAN1_RZ 123.45 MAN1_NEXT 'MAN2' MAN2_TIME '01-MAR-2010 00:00:00.0000 UTC' MAN2_RX 123.45 [...] MAN2_NEXT 'MANX' [...] MANX_TIME [...] This file describes different "legs" of a trajectory. In this case, MAN1 is chained to MAN2, and MAN2 to MANX. In the original file, the chains are not as obvious (i.e., they are non-sequential). I've managed to read the file and store in an Sqlite3 database (I'm using the Python interface). The table is stored with three columns: Id, Par, and Val; for instance, Id='MAN1', Par='RX', and Val='123.45'. I'm interested in querying such database for obtaining the information related to 'n' legs. In English, that would be: "Select RX,RY,RZ for the next five legs starting on MAN1" So the query would go to MAN1, retrieve RX, RY, RZ, then read the parameter NEXT and go to that Id, retrieve RX, RY, RZ; read the parameter NEXT; go to that one ... like this five times. How can I pass such query with "dynamic parameters"? Thank you.

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• Error in {% markdown %} filter in Django Nonrel

  - by Robert Smith

  I'm having trouble using Markdown in Django Nonrel. I followed this instructions (added 'django.contrib.markup' to INSTALLED_APPS, include {% load markup %} in the template and use |markdown filter after installing python-markdown) but I get the following error: Error in {% markdown %} filter: The Python markdown library isn't installed. In this line: /path/to/project/django/contrib/markup/templatetags/markup.py in markdown they will be silently ignored. """ try: import markdown except ImportError: if settings.DEBUG: raise template.TemplateSyntaxError("Error in {% markdown %} filter: The Python markdown library isn't installed.") ... return force_unicode(value) else: # markdown.version was first added in 1.6b. The only version of markdown # to fully support extensions before 1.6b was the shortlived 1.6a. if hasattr(markdown, 'version'): extensions = [e for e in arg.split(",") if e] It seems obvious that import markdown is causing the problem but when I run: $ python manage.py shell >>> import elementtree >>> import markdown everthing works alright. Running Markdown 2.0.3, Django 1.3.1, Python 2.7. UPDATE: I thought maybe this was an issue related to permissions, so I changed my project via chmod 777 -R, but it didn't work. Ideas? Thanks!

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• Backreferences in lookbehind

  - by polygenelubricants

  Can you use backreferences in a lookbehind? Let's say I want to split wherever behind me a character is repeated twice. String REGEX1 = "(?<=(.)\\1)"; // DOESN'T WORK! String REGEX2 = "(?<=(?=(.)\\1)..)"; // WORKS! System.out.println(java.util.Arrays.toString( "Bazooka killed the poor aardvark (yummy!)" .split(REGEX2) )); // prints "[Bazoo, ka kill, ed the poo, r aa, rdvark (yumm, y!)]" Using REGEX2 (where the backreference is in a lookahead nested inside a lookbehind) works, but REGEX1 gives this error at run-time: Look-behind group does not have an obvious maximum length near index 8 (?<=(.)\1) ^ This sort of make sense, I suppose, because in general the backreference can capture a string of any length (if the regex compiler is a bit smarter, though, it could determine that \1 is (.) in this case, and therefore has a finite length). So is there a way to use a backreference in a lookbehind? And if there isn't, can you always work around it using this nested lookahead? Are there other commonly-used techniques?

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• How to speed up marching cubes?

  - by Dan Vinton

  I'm using this marching cube algorithm to draw 3D isosurfaces (ported into C#, outputting MeshGeomtry3Ds, but otherwise the same). The resulting surfaces look great, but are taking a long time to calculate. Are there any ways to speed up marching cubes? The most obvious one is to simply reduce the spatial sampling rate, but this reduces the quality of the resulting mesh. I'd like to avoid this. I'm considering a two-pass system, where the first pass samples space much more coarsely, eliminating volumes where the field strength is well below my isolevel. Is this wise? What are the pitfalls? Edit: the code has been profiled, and the bulk of CPU time is split between the marching cubes routine itself and the field strength calculation for each grid cell corner. The field calculations are beyond my control, so speeding up the cubes routine is my only option... I'm still drawn to the idea of trying to eliminate dead space, since this would reduce the number of calls to both systems considerably.

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• Switching from Sourcesafe - What to look for in a product

  - by asp316

  We're looking to move off of sourcesafe and on to a more robust source control system for our .Net apps. We're also looking for scripted/automated deployments. I'm a .Net developer (web and winforms). However, most of our development staff is RPG for the IBM iSeries and the devs use Aldon's LMI for source control and deployment. Our manager would prefer to stick with Aldon so all of our products are in the same system. However, I don't have experience with Aldon's products on the .Net side. I've used TFS and Subversion with Tortoise a bit, but not enough to recommend one or the other, especially in comparison to Aldon's product. Does anybody have experience with Aldon's products? If so, thoughts please? Also, other than the obvious things source control systems do, are there things I should avoid or are there must haves? I'm open to any system. A bit of background, I'm the only .Net dev in our company but I let operations do the deployments. I do want the ability to support concurrent checkouts if we hire a new dev.

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• After Navigate2 Method returns S_OK Stuck at READYSTATE of READYSTATE_LOADING

  - by Stone Free

  I am working on a MFC Document View architecture application which has multiple documents and views and a tabbed window interface. I have been tasked with making an automatic switch to another tab on the press of the OK button in one of the other tabs. When the other tab is clicked on it uses a C++ wrapper over IWebBrowser2 to navigate to a specific web page. When this is done manually by clicking on the tab everything is fine and the webpage within the view loads successfully. In my first attempt at doing this the tab successfully switched in response to a call to AfxGetMainWnd()->SendMessageToDescendants(SOME_MESSAGE, ...); however by sending this windows message at the wrong point the application would crash once control returned because the chain of events caused the (modeless) dialog (*) that sent the message, to no longer exist. I then found the correct place to make the call, but now when the other tab is activated, it no longer displays the webpage as it should. To debug this problem I added code to check the READYSTATE in both the situation where it works and the situation where it does not. When the page fails to load (despite the call to Navigate2 returning S_OK), the READYSTATE just stays at READYSTATE_LOADING. Unfortunately now I am to many edits away from when I had it partially working. I have added TRACE statements to the most obvious events such as OnSetFocus, CView::OnActivateView but all traces come out in the same order despite the behaviour being different * hosted in the view

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• Core data relationship memory leak

  - by cfihelp

  I have a strange (to me) memory leak when accessing an entity in a relationship. Series and Tiles have an inverse relationship to each other. // set up the fetch request NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init]; NSEntityDescription *entity = [NSEntityDescription entityForName:@"Series" inManagedObjectContext:managedObjectContext]; [fetchRequest setEntity:entity]; // grab all of the series in the core data store NSError *error = nil; availableSeries = [[NSArray alloc] initWithArray:[managedObjectContext executeFetchRequest:fetchRequest error:&error]]; [fetchRequest release]; // grab one of the series Series *currentSeries = [availableSeries objectAtIndex:1]; // load all of the tiles attached to the series through the relationship NSArray *myTiles = [currentSeries.tile allObjects]; // 16 byte leak here! Instruments reports back that the final line has a 16 byte leak cause by NSPlaceHolderString. Stack trace: 2 UIKit UIApplicationMain 3 UIKit -[UIApplication _run] 4 CoreFoundation CFRunLoopRunInMode 5 CoreFoundation CFRunLoopRunSpecific 6 GraphicsServices PurpleEventCallback 7 UIKit _UIApplicationHandleEvent 8 UIKit -[UIApplication sendEvent:] 9 UIKit -[UIApplication handleEvent:withNewEvent:] 10 UIKit -[UIApplication _runWithURL:sourceBundleID:] 11 UIKit -[UIApplication _performInitializationWithURL:sourceBundleID:] 12 Memory -[AppDelegate_Phone application:didFinishLaunchingWithOptions:] /Users/cfish/svnrepo/Memory/src/Memory/iPhone/AppDelegate_Phone.m:49 13 UIKit -[UIViewController view] 14 Memory -[HomeScreenController_Phone viewDidLoad] /Users/cfish/svnrepo/Memory/src/Memory/iPhone/HomeScreenController_Phone.m:58 15 CoreData -[_NSFaultingMutableSet allObjects] 16 CoreData -[_NSFaultingMutableSet willRead] 17 CoreData -[NSFaultHandler retainedFulfillAggregateFaultForObject:andRelationship:withContext:] 18 CoreData -[NSSQLCore retainedRelationshipDataWithSourceID:forRelationship:withContext:] 19 CoreData -[NSSQLCore newFetchedPKsForSourceID:andRelationship:] 20 CoreData -[NSSQLCore rawSQLTextForToManyFaultStatement:stripBindVariables:swapEKPK:] 21 Foundation +[NSString stringWithFormat:] 22 Foundation -[NSPlaceholderString initWithFormat:locale:arguments:] 23 CoreFoundation _CFStringCreateWithFormatAndArgumentsAux 24 CoreFoundation _CFStringAppendFormatAndArgumentsAux 25 Foundation _NSDescriptionWithLocaleFunc 26 CoreFoundation -[NSObject respondsToSelector:] 27 libobjc.A.dylib class_respondsToSelector 28 libobjc.A.dylib lookUpMethod 29 libobjc.A.dylib _cache_addForwardEntry 30 libobjc.A.dylib _malloc_internal I think I'm missing something obvious but I can't quite figure out what. Thanks for your help! Update: I've copied the offending chunk of code to the first part of applicationDidFinishLaunching and it still leaks. Could there be something wrong with my model?

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• Best approach to storing image pixels in bottom-up order in Java

  - by finnw

  I have an array of bytes representing an image in Windows BMP format and I would like my library to present it to the Java application as a BufferedImage, without copying the pixel data. The main problem is that all implementations of Raster in the JDK store image pixels in top-down, left-to-right order whereas BMP pixel data is stored bottom-up, left-to-right. If this is not compensated for, the resulting image will be flipped vertically. The most obvious "solution" is to set the SampleModel's scanlineStride property to a negative value and change the band offsets (or the DataBuffer's array offset) to point to the top-left pixel, i.e. the first pixel of the last line in the array. Unfortunately this does not work because all of the SampleModel constructors throw an exception if given a negative scanlineStride argument. I am currently working around it by forcing the scanlineStride field to a negative value using reflection, but I would like to do it in a cleaner and more portable way if possible. e.g. is there another way to fool the Raster or SampleModel into arranging the pixels in bottom-up order but without breaking encapsulation? Or is there a library somewhere that will wrap the Raster and SampleModel, presenting the pixel rows in reverse order? I would prefer to avoid the following approaches: Copying the whole image (for performance reasons. The code must process hundreds of large (= 1Mpixels) images per second and although the whole image must be available to the application, it will normally access only a tiny (but hard-to-predict) portion of the image.) Modifying the DataBuffer to perform coordinate transformation (this actually works but is another "dirty" solution because the buffer should not need to know about the scanline/pixel layout.) Re-implementing the Raster and/or SampleModel interfaces from scratch (but I have a hunch that I will be unable to avoid this.)

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• Nhibernate/Hibernate, lookup tables and object design

  - by Simon G

  Hi, I've got two tables. Invoice with columns CustomerID, InvoiceDate, Value, InvoiceTypeID (CustomerID and InvoiceDate make up a composite key) and InvoiceType with InvoiceTypeID and InvoiceTypeName columns. I know I can create my objects like: public class Invoice { public virtual int CustomerID { get; set; } public virtual DateTime InvoiceDate { get; set; } public virtual decimal Value { get; set; } public virtual InvoiceType InvoiceType { get; set; } } public class InvoiceType { public virtual InvoiceTypeID { get; set; } public virtual InvoiceTypeName { get; set; } } So the generated sql would look something like: SELECT CustomerID, InvoiceDate, Value, InvoiceTypeID FROM Invoice WHERE CustomerID = x AND InvoiceDate = y SELECT InvoiceTypeID, InvoiceTypeName FROM InvoiceType WHERE InvoiceTypeID = z But rather that having two select queries executed to retrieve the data I would rather have one. I would also like to avoid using child object for simple lookup lists. So my object would look something like: public class Invoice { public virtual int CustomerID { get; set; } public virtual DateTime InvoiceDate { get; set; } public virtual decimal Value { get; set; } public virtual InvoiceTypeID { get; set; } public virtual InvoiceTypeName { get; set; } } And my sql would look something like: SELECT CustomerID, InvoiceDate, Value, InvoiceTypeID FROM Invoice INNER JOIN InvoiceType ON Invoice.InvoiceTypeID = InvoiceType.InvoiceTypeID WHERE CustomerID = x AND InvoiceDate = y My question is how do I create the mapping for this? I've tried using join but this tried to join using CustomerID and InvoiceDate, am I missing something obvious? Thanks

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• Receiving DB update events in .NET from SQLite

  - by Dan Tao

  I've recently discovered the awesomeness of SQLite, specifically the .NET wrapper for SQLite at http://sqlite.phxsoftware.com/. Now, suppose I'm developing software that will be running on multiple machines on the same network. Nothing crazy, probably only 5 or 6 machines. And each of these instances of the software will be accessing an SQLite database stored in a file in a shared directory (is this a bad idea? If so, tell me!). Is there a way for each instance of the app to be notifiied if one instance updates the database file? One obvious way would be to use the FileSystemWatcher class, read the entire database into a DataSet, and then ... you know ... enumerate through the entire thing to see what's new ... but yeah, that seems pretty idiotic, actually. Is there such a thing as a provider of SQLite updates? Does this even make sense as a question? I'm also pretty much a newbie when it comes to ADO.NET, so I might be approaching the problem from the entirely wrong angle.

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• Force Oracle error on fetch

  - by Dan

  I am trying to debug a strange behavior in my application. In order to do so, I need to reproduce a scenario where an SQL SELECT query will throw an error, but only while actually fetching from the cursor, not while executing the query itself. Can this be done? Any error will do, but ORA-01722: invalid number seems like the obvious one to try. I created a table with the follwing: KEYCOL INTEGER PRIMARY KEY OTHERCOL VARCHAR2(100) I then created a few hundred rows with unique values for the primary key and the value l for the othercol. I then ran a SELECT * query, picked a row somewhere in the middle, and updated it to the string abcd. I ran the query SELECT KEYCOL, TO_NUMBER(OTHERCOL) FROM SOMETABLE hoping to get some rows of good data an then an error later. But I keep getting ORA-01722: invalid number on the execute step itself. I have gotten this behavior programmatically using ADO (with server-side cursor) and JDBC, as well as from PL/SQL Developer. How can I get the result I'm looking for? thanks Edit - meant to add, when using ADO, I am only calling Command.Execute. I am not creating or opening a Recordset.

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• What are the most interesting equivalences arising from the Curry-Howard Isomorphism?

  - by Tom

  I came upon the Curry-Howard Isomorphism relatively late in my programming life, and perhaps this contributes to my being utterly fascinated by it. It implies that for every programming concept there exists a precise analogue in formal logic, and vice versa. Here's an "obvious" list of such analogies, off the top of my head: program/definition | proof type/declaration | proposition inhabited type | theorem function | implication function argument | hypothesis/antecedent function result | conclusion/consequent function application | modus ponens recursion | induction identity function | tautology non-terminating function | absurdity tuple | conjunction (and) disjoint union | exclusive disjunction (xor) parametric polymorphism | universal quantification So, to my question: what are some of the more interesting/obscure implications of this isomorphism? I'm no logician so I'm sure I've only scratched the surface with this list. For example, here are some programming notions for which I'm unaware of pithy names in logic: currying | "((a & b) => c) iff (a => (b => c))" scope | "known theory + hypotheses" And here are some logical concepts which I haven't quite pinned down in programming terms: primitive type? | axiom set of valid programs? | theory ? | disjunction (or)

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• Best pratice: How do I implement a list that can be rendered both server-side and client-side?

  - by André Pena

  Technologies involved: ASP.NET Web-forms Javascript (jQuery for instance) Case To make it clearer let's give the Stackoverflow authors list as an example. This list can be manipulated at client-side. I can search, page and so forth. So obviously we would need to call jQuery.ajax to retrieve the HTML of each page given a search. Alright. Now this leaves me with the first question: What is the best way to render the response for the jQuery.ajax at server-side? I can't use templates I suppose, so the most obvious solution I think is to create the HTML tags as server-controls and render them as the result of an ASHX request? Is this is best approach? Nice. That solved we have yet another problem: When the user first enters the Authors List the first list page should already come from the server completely rendered alright? Of course we could render the first page as well as an ajax call but I don't think it's better. This time I CAN use templates to render the list but this template couldn't be reused in case 1. What do I do? Now the final question: Now we have 2 rendering strategies: 1) Client and 2) Server. How do I reuse code for the 2 renderings? What are the best pratices for solving these problems?

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• Better ways to implement a modulo operation (algorithm question)

  - by ryxxui

  I've been trying to implement a modular exponentiator recently. I'm writing the code in VHDL, but I'm looking for advice of a more algorithmic nature. The main component of the modular exponentiator is a modular multiplier which I also have to implement myself. I haven't had any problems with the multiplication algorithm- it's just adding and shifting and I've done a good job of figuring out what all of my variables mean so that I can multiply in a pretty reasonable amount of time. The problem that I'm having is with implementing the modulus operation in the multiplier. I know that performing repeated subtractions will work, but it will also be slow. I found out that I could shift the modulus to effectively subtract large multiples of the modulus but I think there might still be better ways to do this. The algorithm that I'm using works something like this (weird pseudocode follows): result,modulus : integer (n bits) (previously defined) shiftcount : integer (initialized to zero) while( (modulus<result) and (modulus(n-1) != 1) ){ modulus = modulus << 1 shiftcount++ } for(i=shiftcount;i>=0;i++){ if(modulus<result){result = result-modulus} if(i!=0){modulus = modulus << 1} } So...is this a good algorithm, or at least a good place to start? Wikipedia doesn't really discuss algorithms for implementing the modulo operation, and whenever I try to search elsewhere I find really interesting but incredibly complicated (and often unrelated) research papers and publications. If there's an obvious way to implement this that I'm not seeing, I'd really appreciate some feedback.

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• Error 1053: the service did not respond to the start or control request in a timely fashion

  - by deejjaayy

  i know this is very much a "how long is a piece of string" type of question, however i have recently inherited a couple of applications that run as windows services, and i am having problems providing a gui (accessible from a context menu in system tray) with both of them. before you ask, the reason why we need a gui for a windows service is in order to be able to re-configure the behaviour of the windows service(s) without resorting to stopping/re-starting. my code works fine in debug mode, and i get the context menu come up, and everything behaves correctly etc. when i install the service via "installutil" using a named account (i.e., not Local System Account), the service runs fine, but doesn't display the icon in the system tray (i know this is normal behaviour because i don't have the "interact with desktop" option). here is the problem though - when i choose the "LocalSystemAccount" option, and check the "interact with desktop" option, the service takes AGES to start up for no obvious reason, and i just keep getting "Could not start the ... service on Local Computer. Error 1053: the service did not respond to the start or control request in a timely fashion". incidentally, i increased the windows service timeout from the default 30 seconds to 2 minutes via a registry hack (see http://support.microsoft.com/kb/824344, search for TimeoutPeriod in section 3), however the service start up still times out. my first question is - why might the "Local System Account" login takes SOOOOO MUCH LONGER than when the service logs in with the non-LocalSystemAccount, causing the windows service time-out? what's could the difference be between these two to cause such different behaviour at start up? secondly - taking a step back, all i'm trying to achieve, is simply a windows service that provides a gui for configuration - I'd be quite happy to run using the non-Local System Account (with named user/pwd), if I could get the service to interact with the desktop (that is, have a context menu available from the system tray). is this possible, and if so how? any pointers to the above questions would be very much appreciated! thanks in advance for your help.

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• Does this use of Monitor.Wait/Pulse have a race condition?

  - by jw

  I have a simple producer/consumer scenario, where there is only ever a single item being produced/consumed. Also, the producer waits for the worker thread to finish before continuing. I realize that kind of obviates the whole point of multithreading, but please just assume it really needs to be this way (: This code doesn't compile, but I hope you get the idea: // m_data is initially null // This could be called by any number of producer threads simultaneously void SetData(object foo) { lock(x) // Line A { assert(m_data == null); m_data = foo; Monitor.Pulse(x) // Line B while(m_data != null) Monitor.Wait(x) // Line C } } // This is only ever called by a single worker thread void UseData() { lock(x) // Line D { while(m_data == null) Monitor.Wait(x) // Line E // here, do something with m_data m_data = null; Monitor.Pulse(x) // Line F } } Here is the situation that I am not sure about: Suppose many threads call SetData() with different inputs. Only one of them will get inside the lock, and the rest will be blocked on Line A. Suppose the one that got inside the lock sets m_data and makes its way to Line C. Question: Could the Wait() on Line C allow another thread at Line A to obtain the lock and overwrite m_data before the worker thread even gets to it? Supposing that doesn't happen, and the worker thread processes the original m_data, and eventually makes its way to Line F, what happens when that Pulse() goes off? Will only the thread waiting on Line C be able to get the lock? Or will it be competing with all the other threads waiting on Line A as well? Essentially, I want to know if Pulse()/Wait() communicate with each other specially "under the hood" or if they are on the same level with lock(). The solution to these problems, if they exist, is obvious of course - just surround SetData() with another lock - say, lock(y). I'm just curious if it's even an issue to begin with.

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• Is there a standard mapping between JSON and Protocol Buffers?

  - by Daniel Earwicker

  From a comment on the announcement blog post: Regarding JSON: JSON is structured similarly to Protocol Buffers, but protocol buffer binary format is still smaller and faster to encode. JSON makes a great text encoding for protocol buffers, though -- it's trivial to write an encoder/decoder that converts arbitrary protocol messages to and from JSON, using protobuf reflection. This is a good way to communicate with AJAX apps, since making the user download a full protobuf decoder when they visit your page might be too much. It may be trivial to cook up a mapping, but is there a single "obvious" mapping between the two that any two separate dev teams would naturally settle on? If two products supported PB data and could interoperate because they shared the same .proto spec, I wonder if they would still be able to interoperate if they independently introduced a JSON reflection of the same spec. There might be some arbitrary decisions to be made, e.g. should enum values be represented by a string (to be human-readable a la typical JSON) or by their integer value? So is there an established mapping, and any open source implementations for generating JSON encoder/decoders from .proto specs?

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• text-overflow:ellipsis in Firefox 4?

  - by Spudley

  The text-overflow:ellipsis; CSS property must be one of the few things that Microsoft has done right for the web. All the other browsers now support it... except Firefox. The Firefox developers have been arguing over it since 2005 but despite the obvious demand for it, they can't seem to actually bring themselves to implement it (even an experimental -moz- implementation would be sufficient). A few years ago, someone worked out a way to hack Firefox 3 to make it support an ellipsis. The hack uses the -moz-binding feature to implement it using XUL. Quite a number of sites are now using this hack. The bad news? Firefox 4 is removing the -moz-binding feature, which means this hack won't work any more. So as soon as Firefox 4 is released (later this month, I hear), we're going to be back to the problem of having it not being able to support this feature. So my question is: Is there any other way around this? (I'm trying to avoid falling back to a Javascript solution if at all possible) [EDIT] Lots of up-votes, so I'm obviously not the only one who wants to know, but I've got one answer so far which basically says 'use javascript'. I'm still hoping for a solution that will either not need JS at all, or at worst only use it as a fall-back where the CSS feature doesn't work. So I'm going to post a bounty on the question, on the off chance that someone, somewhere has found an answer.

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• Are there any radix/patricia/critbit trees for Python?

  - by Andrew Dalke

  I have about 10,000 words used as a set of inverted indices to about 500,000 documents. Both are normalized so the index is a mapping of integers (word id) to a set of integers (ids of documents which contain the word). My prototype uses Python's set as the obvious data type. When I do a search for a document I find the list of N search words and their corresponding N sets. I want to return the set of documents in the intersection of those N sets. Python's "intersect" method is implemented as a pairwise reduction. I think I can do better with a parallel search of sorted sets, so long as the library offers a fast way to get the next entry after i. I've been looking for something like that for some time. Years ago I wrote PyJudy but I no longer maintain it and I know how much work it would take to get it to a stage where I'm comfortable with it again. I would rather use someone else's well-tested code, and I would like one which supports fast serialization/deserialization. I can't find any, or at least not any with Python bindings. There is avltree which does what I want, but since even the pair-wise set merge take longer than I want, I suspect I want to have all my operations done in C/C++. Do you know of any radix/patricia/critbit tree libraries written as C/C++ extensions for Python? Failing that, what is the most appropriate library which I should wrap? The Judy Array site hasn't been updated in 6 years, with 1.0.5 released in May 2007. (Although it does build cleanly so perhaps It Just Works.)

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• Best pratice: How do I implement a list similar to Stackoverflow's Users List?

  - by André Pena

  Technologies involved: ASP.NET Web-forms Javascript (jQuery for instance) Case To make it clearer let's give the Stackoverflow Users list as an example. This list can be manipulated at client-side. I can search, page and so forth. So obviously we would need to call jQuery.ajax to retrieve the HTML of each page given a search. Alright. Now this leaves me with the first question: What is the best way to render the response for the jQuery.ajax at server-side? I can't use templates I suppose, so the most obvious solution I think is to create the HTML tags as server-controls and render them as the result of an ASHX request? Is this is best approach? Nice. That solved we have yet another problem: When the user first enters the Authors List the first list page should already come from the server completely rendered alright? Of course we could render the first page as well as an ajax call but I don't think it's better. This time I CAN use templates to render the list but this template couldn't be reused in case 1. What do I do? Now the final question: Now we have 2 rendering strategies: 1) Client and 2) Server. How do I reuse code for the 2 renderings? What are the best pratices for solving these problems?

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• NetBeans Tips and Tricks

  - by cdmckay

  I just saw an Eclipse tips & tricks post and was wondering if anyone had any tips & tricks for my IDE of choice: NetBeans. Here's a few I know and find to be useful: Removing a package: After you remove a package in NetBeans, it sticks around as a grayed-out package in your Project view. To get rid of that, switch to Files view and delete the directory. Alt-Insert (in Windows) opens up a Generate submenu at your cursor. A nice shortcut for quickly generating getters/setters (among other things). Selecting a chunk of code, right-clicking and then clicking "Refactor Introduce Method" will have NetBeans introduce a method, complete with arguments and return value. Of course you have to make sure the chunk of code only has one return value. Sometimes when you run a build and it crashes, the Java window sticks around at the bottom. I used to just click X until Windows let me End Task, but there's a nicer way to get rid of them. Click "Run Stop Build/Run" and NetBeans will close the window for you. It'll even let you close multiple applications at once. These may seem obvious to grizzled NetBeans developers, but I thought they might be useful for NetBeans newbs like me. Anyone else have any tips/tricks to share? Here are some from the comments: NetBeans allows for code templates. You can even add yours on the Code Templates tab under the Editor settings on the Options window. Some examples: Type sout and hit the tab key as a shorcut for System.out.println("") Type psvm and hit the tab key as a shorcut for public static void main(String args[]) {} Ctrl Shift C: Comments out the selected block of code. Alt Shift F: Formats the selected block of code. Ctrl E: Deletes current line. Ctrl Shift I: Fixes your imports, handy if you've just written a piece of code that needs a lot of packages imported.

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• Synchronizing ASP.NET MVC action methods with ReaderWriterLockSlim

  - by James D

  Any obvious issues/problems/gotchas with synchronizing access (in an ASP.NET MVC blogging engine) to a shared object model (NHibernate, but it could be anything) at the Controller/Action level via ReaderWriterLockSlim? (Assume the object model is very large and expensive to build per-request, so we need to share it among requests.) Here's how a typical "Read Post" action would look. Enter the read lock, do some work, exit the read lock. public ActionResult ReadPost(int id) { // ReaderWriterLockSlim allows multiple concurrent writes; this method // only blocks in the unlikely event that some other client is currently // writing to the model, which would only happen if a comment were being // submitted or a new post were being saved. _lock.EnterReadLock(); try { // Access the model, fetch the post with specificied id // Pseudocode, etc. Post p = TheObjectModel.GetPostByID(id); ActionResult ar = View(p); return ar; } finally { // Under all code paths, we must release the read lock _lock.ExitReadLock(); } } Meanwhile, if a user submits a comment or an author authors a new post, they're going to need write access to the model, which is done roughly like so: [AcceptVerbs(HttpVerbs.Post)] public ActionResult SaveComment(/* some posted data */) { // try/finally omitted for brevity _lock.EnterWriteLock(); // Save the comment to the DB, update the model to include the comment, etc. _lock.ExitWriteLock(); } Of course, this could also be done by tagging those action methods with some sort of "synchronized" attribute... but however you do it, my question is is this a bad idea? ps. ReaderWriterLockSlim is optimized for multiple concurrent reads, and only blocks if the write lock is held. Since writes are so infrequent (1000s or 10,000s or 100,000s of reads for every 1 write), and since they're of such a short duration, the effect is that the model is synchronized , and almost nobody ever locks, and if they do, it's not for very long.

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