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• Maintaining a pool of DAO Class instances vs doing new operator

  - by Fazal

  we have been trying to benchmark our application performance in multiple way for sometime now. I always believed that object creation in java using Class.newInstance() was not slow (at least after 1.4 version of java). But we anyways did a test to use newInstance method vs mainitain an object pool of 1000 objects. We did about 200K iterations of loading data from DB using JDBC and populating these objects. I was amazed (even shocked) to see that newInstance code compared to object pool code was almost 10 times slower. These objects represent tables with about 50 fields and all string type. Can someone share there thoughts on this issue as now I am more confused if object pooling of atleast some DAO instances is a better option. The pool size as I see right now should be large enough to meet size of average requests. There is a flip side as my memory footprint will go up but I am beginning to wonder if this kind of idea makes sense atleast for some of the DAO entities representing tables of about 50 or more columns Please share your ideas and let me know if this has been tried by someone or am I missing some point here

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• Im Stumped, Why is UIImage\Texture2d memory not being freed

  - by howsyourface

  I've been looking everywhere trying to find a solution to this problem. Nothing seems to help. I've set up this basic test to try to find the cause of why my memory wasn't being freed up: if (texture != nil) { [texture release]; texture = nil; } else { UIImage* ui = [UIImage imageWithContentsOfFile:[[NSBundle mainBundle] pathForResource:@"image" ofType:@"png"]]; texture = [[Texture2D alloc] initWithImage:ui]; } Now i would place this in the touches began and test by monitoring the memory usage using intstruments at the start (normally 11.5 - 12mb) after the first touch, with no object existing the texture is created and memory jumps to 13.5 - 14 However, after the second touch the memory does decrease, but only to around 12.5 - 13. There is a noticeable chunk of memory still occupied. I tested this on a much larger scale, loading 10 of these large textures at a time The memory jumps to over 30 mb and remains there, but on the second touch after releasing the textures it only falls to around 22mb. I tried the test another time loading the images in with [uiimage imagenamed:] but because of the caching this method performs it just means that the full 30mb remains in memory.

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• t-sql most efficient row to column? crosstab for xml path, pivot

  - by ajberry

  I am looking for the most performant way to turn rows into columns. I have a requirement to output the contents of the db (not actual schema below, but concept is similar) in both fixed width and delimited formats. The below FOR XML PATH query gives me the result I want, but when dealing with anything other than small amounts of data, can take awhile. select orderid ,REPLACE(( SELECT ' ' + CAST(ProductId as varchar) FROM _details d WHERE d.OrderId = o.OrderId ORDER BY d.OrderId,d.DetailId FOR XML PATH('') ),'&#x20;','') as Products from _orders o I've looked at pivot but most of the examples I have found are aggregating information. I just want to combine the child rows and tack them onto the parent. I should also point out I don't need to deal with the column names either since the output of the child rows will either be a fixed width string or a delimited string. For example, given the following tables: OrderId CustomerId ----------- ----------- 1 1 2 2 3 3 DetailId OrderId ProductId ----------- ----------- ----------- 1 1 100 2 1 158 3 1 234 4 2 125 5 3 101 6 3 105 7 3 212 8 3 250 for an order I need to output: orderid Products ----------- ----------------------- 1 100 158 234 2 125 3 101 105 212 250 or orderid Products ----------- ----------------------- 1 100|158|234 2 125 3 101|105|212|250 Thoughts or suggestions? I am using SQL Server 2k5. Example Setup: create table _orders ( OrderId int identity(1,1) primary key nonclustered ,CustomerId int ) create table _details ( DetailId int identity(1,1) primary key nonclustered ,OrderId int ,ProductId int ) insert into _orders (CustomerId) select 1 union select 2 union select 3 insert into _details (OrderId,ProductId) select 1,100 union select 1,158 union select 1,234 union select 2,125 union select 3,105 union select 3,101 union select 3,212 union select 3,250 using FOR XML PATH: select orderid ,REPLACE(( SELECT ' ' + CAST(ProductId as varchar) FROM _details d WHERE d.OrderId = o.OrderId ORDER BY d.OrderId,d.DetailId FOR XML PATH('') ),'&#x20;','') as Products from _orders o which outputs what I want, however is very slow for large amounts of data. One of the child tables is over 2 million rows, pushing the processing time out to ~ 4 hours. orderid Products ----------- ----------------------- 1 100 158 234 2 125 3 101 105 212 250

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• Fast, very lightweight algorithm for camera motion detection?

  - by Ertebolle

  I'm working on an augmented reality app for iPhone that involves a very processor-intensive object recognition algorithm (pushing the CPU at 100% it can get through maybe 5 frames per second), and in an effort to both save battery power and make the whole thing less "jittery" I'm trying to come up with a way to only run that object recognizer when the user is actually moving the camera around. My first thought was to simply use the iPhone's accelerometers / gyroscope, but in testing I found that very often people would move the iPhone at a consistent enough attitude and velocity that there wouldn't be any way to tell that it was still in motion. So that left the option of analyzing the actual video feed and detecting movement in that. I got OpenCV working and tried running their pyramidal Lucas-Kanade optical flow algorithm, which works well but seems to be almost as processor-intensive as my object recognizer - I can get it to an acceptable framerate if I lower the depth levels / downsample the image / track fewer points, but then accuracy suffers and it starts to miss some large movements and trigger on small hand-shaking-y ones. So my question is, is there another optical flow algorithm that's faster than Lucas-Kanade if I just want to detect the overall magnitude of camera movement? I don't need to track individual objects, I don't even need to know which direction the camera is moving, all I really need is a way to feed something two frames of video and have it tell me how far apart they are.

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• How much should the AppDelegate do?

  - by Rudiger

  I'm designing quite a large App and on startup it will create sessions with a few different servers. As they are creating a session which is used across all parts of the app its something I thought would be best in App Delegate. But the problem is I need the session progress to be represented on the screen. I plan to have a UIToolBar at the bottom of the main menu which I don't want to cover with the progress bar but cover the UIView above it.So the way I see it I could do it a few different ways. 1) Have the App Delegate establish the sessions and report the progress to the main menu class so it can represent it in the progress bar (will I have any issues doing this if the sessions are created in a separate thread?), 2) have the App delegate display the main menu (UIView with a bunch of buttons and UIToolBar) and have it track and display the progress (I have never displayed anything in the App Delegate but assume you can do this but its not recommended) or 3) have the App Delegate just push the main menu and have the mainMenu class create the sessions and display the progress bar. 4) I think the other way to do it is to create the sessions in a delegate class and have the delegate set to mainMenu rather than self (AppDelegate), although I've never used anything other then self so not sure if this will work or if I will be able to close the thread (through calling super maybe?) as its running in the AppDelegate rather than the delegate of the class. As I've kinda said before the sessions are being created in a class in a separate thread so it wont lock the UI and I think the best way is the first but am I going to have issues having it running in a separate thread, reporting back to the app delegate and then sending that message to the mainMenu view? I hope that all makes sense, let me know if you need any further clarification. Any information is appreciated Cheers,

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• Nested namespaces, correct static library design issues

  - by PeterK

  Hello all, I'm currently in the process of developing a fairly large static library which will be used by some tools when it's finished. Now since this project is somewhat larger than anything i've been involved in so far, I realized its time to think of a good structure for the project. Using namespaces is one of those logical steps. My current approach is to divide the library into parts (which are not standalone, but their purpose calls for such a separation). I have a 'core' part which now just holds some very common typedefs and constants (used by many different parts of the library). Other parts are for example some 'utils' (hash etc.), file i/o and so on. Each of these parts has its own namespace. I have nearly finished the 'utils' part and realized that my approach probably is not the best. The problem (if we want to call it so) is that in the 'utils' namespace i need something from the 'core' namespace which results in including the core header files and many using directives. So i began to think that this probably is not a good thing and should be changed somehow. My first idea is to use nested namespaces as to have something like core::utils. Since this will require some heavy refactoring i want to ask here first. What do you think? How would you handle this? Or more generally: How to correctly design a static library in terms of namespaces and code organization? If there are some guidelines or articles about it, please mentoin them too. Thanks. Note: i'm quite sure that there are more good approaches than just one. Feel free to post your ideas, suggestions etc. Since i'm designing this library i want it to be really good. The goal is to make it as clean and FAST as possible. The only problem is that i will have to integrate a LOT of existing code and refactor it, which will really be a painful process (sigh) - thats why good structure is so important)

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• Saving HttpResponse/Request to file system

  - by chrisjlong

  Here is my scenario. User fills out this large page which is dynamically created based off DB values. Those values can change. When the user fills out the page and hits submit we want to save a copy of the page as html on the server, this way if the text or wording changes, when they go back to view their posted information, it is historically accurate. So I basically need to do this protected void buttonSave_Click(object sender, EventArgs e) { //collect information into an object to save it in the db bool result = BusinessLogic.Save(myBusinessObject); if (result) //!!! Here is where I need to save this page as an html file on my servers IFS!!!! else //whatever Response.Redirect("~/SomeOtherPage.aspx"); } Any help is greatly apprciated. Also I CANNOT just request the data from the url because query string parameters are a big no no in this case. The key to pull the database info up (at its highest level) is all in session so I cant just request a url and save it. Thanks!

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• How can I make an even more random number in ActionScript 2.0

  - by Theo

  I write a piece of software that runs inside banner ads which generates millions of session IDs every day. For a long time I've known that the random number generator in Flash is't random enough to generate sufficiently unique IDs, so I've employed a number of tricks to get even more random numbers. However, in ActionScript 2.0 it's not easy, and I'm seeing more and more collisions, so I wonder if there is something I've overlooked. As far as I can tell the problem with Math.random() is that it's seeded by the system time, and when you have sufficient numbers of simultaneous attempts you're bound to see collisions. In ActionScript 3.0 I use the System.totalMemory, but there's no equivalent in ActionScript 2.0. AS3 also has Font.enumerateFonts, and a few other things that are different from system to system. On the server side I also add the IP address to the session ID, but even that isn't enough (for example, many large companies use a single proxy server and that means that thousands of people all have the same IP -- and since they tend to look at the same sites, with the same ads, roughly at the same time, there are many session ID collisions). What I need isn't something perfectly random, just something that is random enough to dilute the randomness I get from Math.random(). Think of it this way: there is a certain chance that two people will generate the same random number sequence using only Math.random(), but the chance of two people generating the same sequence and having, say, the exact same list of fonts is significantly lower. I cannot rely on having sufficient script access to use ExternalInterface to get hold of things like the user agent, or the URL of the page. I don't need suggestions of how to do it in AS3, or any other system, only AS2 -- using only what's available in the standard APIs. The best I've come up with so far is to use the list of microphones (Microphone.names), but I've also tried to make some fingerprinting using some of the properties in System.capabilities, I'm not sure how much randomness I can get out of that though so I'm not using that at the moment. I hope I've overlooked something.

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• Calculate an Internet (aka IP, aka RFC791) checksum in C#

  - by Pat

  Interestingly, I can find implementations for the Internet Checksum in almost every language except C#. Does anyone have an implementation to share? Remember, the internet protocol specifies that: "The checksum field is the 16 bit one's complement of the one's complement sum of all 16 bit words in the header. For purposes of computing the checksum, the value of the checksum field is zero." More explanation can be found from Dr. Math. There are some efficiency pointers available, but that's not really a large concern for me at this point. Please include your tests! (Edit: Valid comment regarding testing someone else's code - but I am going off of the protocol and don't have test vectors of my own and would rather unit test it than put into production to see if it matches what is currently being used! ;-) Edit: Here are some unit tests that I came up with. They test an extension method which iterates through the entire byte collection. Please comment if you find fault in the tests. [TestMethod()] public void InternetChecksum_SimplestValidValue_ShouldMatch() { IEnumerable<byte> value = new byte[1]; // should work for any-length array of zeros ushort expected = 0xFFFF; ushort actual = value.InternetChecksum(); Assert.AreEqual(expected, actual); } [TestMethod()] public void InternetChecksum_ValidSingleByteExtreme_ShouldMatch() { IEnumerable<byte> value = new byte[]{0xFF}; ushort expected = 0xFF; ushort actual = value.InternetChecksum(); Assert.AreEqual(expected, actual); } [TestMethod()] public void InternetChecksum_ValidMultiByteExtrema_ShouldMatch() { IEnumerable<byte> value = new byte[] { 0x00, 0xFF }; ushort expected = 0xFF00; ushort actual = value.InternetChecksum(); Assert.AreEqual(expected, actual); }

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• Could Python's logging SMTP Handler be freezing my thread for 2 minutes?

  - by Oddthinking

  A rather confusing sequence of events happened, according to my log-file, and I am about to put a lot of the blame on the Python logger, which is a bold claim. I thought I should get some second opinions about whether what I am saying could be true. I am trying to explain why there is are several large gaps in my log file (around two minutes at a time) during stressful periods for my application when it is missing deadlines. I am using Python's logging module on a remote server, and have set-up, with a configuration file, for all logs of severity of ERROR or higher to be emailed to me. Typically, only one error will be sent at a time, but during periods of sustained problems, I might get a dozen in a minute - annoying, but nothing that should stress SMTP. I believe that, after a short spurt of such messages, the Python logging system (or perhaps the SMTP system it is sitting on) is encountering errors or congestion. The call to Python's log is then BLOCKING for two minutes, causing my thread to miss its deadlines. (I was smart enough to move the logging until after the critical path of the application - so I don't care if logging takes me a few seconds, but two minutes is far too long.) This seems like a rather awkward architecture (for both a logging system that can freeze up, and for an SMTP system (Ubuntu, sendmail) that cannot handle dozens of emails in a minute**), so this surprises me, but it exactly fits the symptoms. Has anyone had any experience with this? Can anyone describe how to stop it from blocking? ** EDIT: I actually counted. A little under 4000 short emails in two hours. So far more than I suggested, sorry. But enough to over-fill a Sendmail's buffers?

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• Alternate widgets and logic for ManyToManyField with Django forms

  - by Jaearess

  In my Django project, I have a simple ticket system. When creating a ticket, certain users have the ability to assign the ticket to other users, and to email the ticket to other users as well (this is used as an FYI for those users, so they're aware of the ticket, even though it's not assigned to them.) At the moment, the form for adding a ticket is simply the default Django form, with the "assigned_to" and "email_to" fields being ManyToManyFields, and therefore displayed as MultipleSelect widgets, each with a list of all users. Due to the relatively large number of users, and general awkwardness of the MultipleSelect widget, and alternate layout is now required. The desired layout is a pair of simple Select widgets side-by-side. The first has the option of "Assign to" or "Email to" and the second is a list of the users. Essentially, like this: [Assign to] [John Doe] [Email to] [Jane Roe] [Jack Smith], etc. Of course, since an arbitrary number of users can be assigned or emailed a ticket, there's a simple button that runs some Javascript to add another set of widgets, to allow the user to assign and email as many people as they need to. So far all of that is fairly simple and straight forward. However, the problem I have is using this widget setup/logic setup with Django forms. Instead of lists of users to assign to and email, instead we're getting back pairs of information, one a user and the other which list that user should be placed in. What I'm looking for, but have yet to find, is a way to offload the translation between how the user uses the form, and how Django understands the model to the form itself, so I don't have to manually do the processing of the data before passing it to the form in each place this form is used. Additionally, there's a review screen with the option to go back and change the form before submitting it, so a way to have the form translate both to and from this format would be extremely helpful.

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• Android application listed as compatible with Sony Xperia S but still filtered from google play

  - by mlidal

  I have published an Android application and some users are complaining that it is listed as not compatible with Sony Xperia S. According to the developer console Xperia S (LT26i) is listed as compatible. Do anyone know of any reason why the app is still filtered from google play? I have seen people reporting problems with big apk files. This app is about 20Mb in size, with the largest file being 14Mb. Quite a bit but not enough to cause problems I think... Here is the output from aapt dump badging: package: name='no.bouvet.nrkut' versionCode='4' versionName='1.0' sdkVersion:'4' targetSdkVersion:'13' uses-permission:'android.permission.ACCESS_FINE_LOCATION' uses-permission:'android.permission.ACCESS_COARSE_LOCATION' uses-permission:'android.permission.ACCESS_WIFI_STATE' uses-permission:'android.permission.ACCESS_NETWORK_STATE' uses-permission:'android.permission.INTERNET' uses-permission:'android.permission.WRITE_EXTERNAL_STORAGE' application-label:'UT.no' application-icon-120:'res/drawable-ldpi/utno_launcher.png' application-icon-160:'res/drawable-mdpi/utno_launcher.png' application-icon-240:'res/drawable-hdpi/utno_launcher.png' application-icon-320:'res/drawable-xhdpi/utno_launcher.png' application: label='UT.no' icon='res/drawable-mdpi/utno_launcher.png' launchable-activity: name='no.bouvet.nrkut.MainActivity' label='UT.no' icon='' uses-feature:'android.hardware.location' uses-feature:'android.hardware.location.gps' uses-feature:'android.hardware.location.network' uses-feature:'android.hardware.wifi' uses-feature:'android.hardware.touchscreen' uses-feature:'android.hardware.screen.portrait' main other-activities search supports-screens: 'small' 'normal' 'large' 'xlarge' supports-any-density: 'true' locales: '--_--' densities: '120' '160' '240' '320'

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• Is the Windows dev environment worth the cost?

  - by MCS

  I recently made the move from Linux development to Windows development. And as much of a Linux enthusiast that I am, I have to say - C# is a beautiful language, Visual Studio is terrific, and now that I've bought myself a trackball my wrist has stopped hurting from using the mouse so much. But there's one thing I can't get past: the cost. Windows 7, Visual Studio, SQL Server, Expression Blend, ViEmu, Telerik, MSDN - we're talking thousands for each developer on the project! You're definitely getting something for your money - my question is, is it worth it? [Not every developer needs all the aforementioned tools - but have you ever heard of anyone writing C# code without Visual Studio? I've worked on pretty large software projects in Linux without having to pay for any development tool whatsoever.] Now obviously, if you're already a Windows shop, it doesn't pay to retrain all your developers. And if you're looking to develop a Windows desktop app, you just can't do that in Linux. But if you were starting a new web application project and could hire developers who are experts in whatever languages you want, would you still choose Windows as your development platform despite the high cost? And if yes, why?

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• fastest SCM tool available for Embedded software development

  - by wrapperm

  Hi All, In my company, presently we are using Rational clearcase as the Software Configuration Management tool for our Embedded software development. The software is basically for Automobiles, to be specific for Engines (I dont think these information really matters). But I find Clearcase to be very slow is performing any the activities (accesing files, branching and labelling), in addition to which there are various other limitations. We have recently decided to research on some free & open source, distributed version control system which could be able to handle our large projects with speed and efficiency. This tool should be a full-fledged repository with complete history and full revision tracking capabilities, not dependent on network access or a central server. Branching and merging are fast and easy to do. It should have multisite development facility. With these above mentioned requirement, we have come up with some of the tools that are presently available in the market: GIT, Mercurial, Bazaar, Subversion, CVS, Perforce, and Visual SourceSafe. I need everybody's help in finding me an approrpiate SCM tool for me which meets the above mentioned requirements. Thanking you in Advance, Rahamath.

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• Help me avoid a resonance cascade.

  - by SLC

  Hi, my name is Dr. Kleiner, and I'm a senior scientist working at the Black Mesa Research Facility. I've just finished compiling my code to analyse a large unknown sample we've come across. Unfortunately, there were 19 build errors and 42 warnings, but I've been told the experiment must go ahead. Time is critical, we've already got one of our newest employees who is suiting up as I type this to complete the experiment. I really need some help. Can you think of anything last minute to stop a potential resonance cascade? Someone has hidden my glasses again... Anyway, I hope I never see a resonance cascade, and definitely don't want to create one. It's my lunch break in 5 minutes, and my casserole is already in the microwave ready. Please, give me some advice. If it helps I wrote all of the code to analyse the sample and activate the sampler machine in BASIC. Edit: Oh god! They're everywhere! Send assista

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• iPhone Multithreaded Search

  - by Kulpreet

  I'm sort of new to any sort of multithreading and simply can't seem to get a simple search method working on a background thread properly. Everything seems to be in order with an NSAutoreleasePool and the UI being updated on the main thread. The app doesn't crash and does perform a search in the background but the search results yield the several of the same items several times depending on how fast I type it in. The search works properly without the multithreading (which is commented out), but is very slow because of the large amounts of data I am working with. Here's the code: - (void)filterContentForSearchText:(NSString*)searchText { isSearching = YES; NSAutoreleasePool *apool = [[NSAutoreleasePool alloc] init]; /* Update the filtered array based on the search text and scope. */ //[self.filteredListContent removeAllObjects]; // First clear the filtered array. for (Entry *entry in appDelegate.entries) { NSComparisonResult result = [entry.gurmukhiEntry compare:searchText options:(NSCaseInsensitiveSearch|NSDiacriticInsensitiveSearch) range:NSMakeRange(0, [searchText length])]; if (result == NSOrderedSame) { [self.filteredListContent addObject:entry]; } } [self.searchDisplayController.searchResultsTableView performSelectorOnMainThread:(@selector(reloadData)) withObject:nil waitUntilDone:NO]; //[self.searchDisplayController.searchResultsTableView reloadData]; [apool drain]; isSearching = NO; } - (BOOL)searchDisplayController:(UISearchDisplayController *)controller shouldReloadTableForSearchString:(NSString *)searchString { if (!isSearching) { [self.filteredListContent removeAllObjects]; // First clear the filtered array. [self performSelectorInBackground:(@selector(filterContentForSearchText:)) withObject:searchString]; } //[self filterContentForSearchText:searchString]; return NO; // Return YES to cause the search result table view to be reloaded. }

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• Can I automatically throw descriptive exceptions with parameter values and class feild information?

  - by Robert H.

  I honestly don't throw exceptions often. I catch them even less, ironically. I currently work in shop where we let them bubble up to avicode. For whatever reason, however, avicode isn't configured to capture some of the critical bits I need when these exceptions come bouncing back to my attention. Specifically, I'd like to see the parameter values and the class’s field data at the time of the exception. I’d guess with the large suite of .Net services that I could create a static method to crawl up the stack, gather these bits and store them in a string that I could stick in my exception message. I really don't are how long such a method would take to execute as performance is no longer a concern when I hit one of these scenarios. If it's possible, I'm sure someone has done it. If that's the case, I'm having a hard time finding it. I think any search containing "exception" brings back too many resutls. Anyway, can this be done? If so, some examples or links would be great. Thanks in advance for your time, Robert

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• NSUndoManager, Core Data and selective undo/redo

  - by Combat

  I'm working on a core data application that has a rather large hierarchy of managed objects similar to a tree. When a base object is created, it creates a few child objects which in turn create their own child objects and so on. Each of these child objects may gather information using NSURLConnections. Now, I'd like to support undo/redo with the undoManager in the managedObjectContext. The problem is, if a user creates a base object, then tries to undo that action, the base object is not removed. Instead, one or more of the child objects may be removed. Obviously this type of action is unpredictable and unwanted. So I tried disabling undo registration by default. I did this by calling disableUndoRegistration: before anything is modified in the managedObjectContext. Then, enabling undo registration before base operations such as creating a base object the again re-disabling registrations afterwords. Now when i try to undo, I get this error: undo: NSUndoManager 0x1026428b0 is in invalid state, undo was called with too many nested undo groups Thoughts?

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• Remove "Flash" between pages while using Internet Explorer modal boxes

  - by AaronS

  I have an internal web application, that is IE specific, and uses a lot of IE specific modal boxes: (window.showModalDialog). I recently received a request to remove the "flash" when navigating between pages of the site. To accomplish this, I just added a meta transition tag to my master page: <meta http-equiv="Page-Enter" content="blendTrans(duration=0.0)" /> This works perfectly except for the modal boxes. When you launch a modal box, and then move it around, the web page behind it keeps a trail of the modal box instead of re-drawing the web page content. This prevents the user from moving the modal box to read anything that was behind it. Is there a way to prevent the "flash" between pages in an IE specific site and have the site still work with modal boxes? Please note, this is a large and complex site, so re-architecting it to not use modal boxes isn't an option. This is an asp.net, c# web application, and all of my users are using IE 7 and IE 8 if it makes any difference. -Edit- To duplicate this, put the following into an html page, and open it in Internet Explorer: <html> <head> <title>Test</title> <meta content="blendTrans(duration=0.0)" http-equiv="Page-Exit"> </head> <body> <script language="javascript"> window.showModalDialog('modal.htm', window); </script> </body> </html>

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• Access cost of dynamically created objects with dynamically allocated members

  - by user343547

  I'm building an application which will have dynamic allocated objects of type A each with a dynamically allocated member (v) similar to the below class class A { int a; int b; int* v; }; where: The memory for v will be allocated in the constructor. v will be allocated once when an object of type A is created and will never need to be resized. The size of v will vary across all instances of A. The application will potentially have a huge number of such objects and mostly need to stream a large number of these objects through the CPU but only need to perform very simple computations on the members variables. Could having v dynamically allocated could mean that an instance of A and its member v are not located together in memory? What tools and techniques can be used to test if this fragmentation is a performance bottleneck? If such fragmentation is a performance issue, are there any techniques that could allow A and v to allocated in a continuous region of memory? Or are there any techniques to aid memory access such as pre-fetching scheme? for example get an object of type A operate on the other member variables whilst pre-fetching v. If the size of v or an acceptable maximum size could be known at compile time would replacing v with a fixed sized array like int v[max_length] lead to better performance? The target platforms are standard desktop machines with x86/AMD64 processors, Windows or Linux OSes and compiled using either GCC or MSVC compilers.

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• How does CDI injection work in MDBs and @Scheduled beans?

  - by Nils-Petter Nilsen

  I'm working on a large Java EE 6 application that is deployed on JBoss 6 Final. My current tasks involve using @Inject consistently instead of @EJB, but I'm running into some problems on some types of beans, specifically @MessageDriven beans and beans with @Scheduled methods. What happens is that if I'm unlucky with the timing (for @Schedule) or if there are messages in the MDBs' queues at startup, instantiation of the beans will fail because the injected resources (which are EJBs themselves) are not bound yet. Because I use @Inject, I'm guessing that the EJB container considers my beans to be ready, since the container itself does not care about @Inject; it probably simply assumes that since there are no @EJB injections, the beans are ready for use. The injected CDI proxies will then fail because the resources to inject aren't actually bound yet. Tiny example: @Stateless @LocalBean public class MySupportingBean { public void doSomething() { ... } } @Singleton public class MyScheduledBean { @Inject private MySupportingBean supportingBean; @Schedule(second = "*/1", hour = "*", minute = "*", persistent = false) public void onTimeout() { supportingBean.doSomething(); } } The above example will probably not fail often because there are only two beans, but the project I'm working on binds lots of EJBs, which will amplify the problem. But it might fail because there is no guarantee that MySupportingBean is bound first, and if onTimeout is invoked before MySupportingBean is bound, then instantiation of MyScheduledBean will fail. If I used @EJB instead, MyScheduledBean wouldn't be bound until the dependency to MySupportingBean was satisfied. Note that the example will not fail in onTimeout itself, but when CDI attempts to inject MySupportingBean. I've read a lot of posts on different forums where many people argue that @Inject is always better. Generally, I agree, but how do they handle @Schedule or @MessageDriven combined with @Inject? In my experience, it comes down to dumb luck whether the beans will work or not in those cases, and the beans will fail arbitrarily, depending on which order the EJBs are deployed in, and when @Schedule or onMessage are invoked.

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• Is there a tool that can refactor this C code correctly?

  - by Alex

  Lets say I have the following code (the array* function are what we use for resizable arrays and they operate on pointers-to-arrays that are null initialized): typedef struct MyStruct { int i; } MyStruct; MyStruct* GetNewMyStruct(int i) { MyStruct* s = malloc(sizeof(MyStruct)); s->i = i; return s; } int SomeFunction(int number, MyStruct *elem) { MyStruct **structs = NULL; int i; for (i = 0; i < number; i++) arrayPush(&structs, GetNewMyStruct(i)); arrayPush(&structs, elem); return arraySize(&structs); } I decide that SomeFunction is too large and I want refactor it. Currently where I work we use VisualAssist X, which has some refactoring capabilities, but when I use it on this it does not work correctly. If I attempt to use it to refactor out the loop, this is what I get: void MyMethod( int number, MyStruct ** structs ) { int i; for (i = 0; i < number; i++) arrayPush(&structs, GetNewMyStruct(i)); } int SomeFunction(int number, MyStruct *elem) { MyStruct **structs = NULL; MyMethod(number, structs); arrrayPush(&structs, elem); return arraySize(&structs); } This is not correct. MyMethod should take a MyStruct ***, not a MyStruct **. This is because the code I'm refactoring takes the address of structs. The result is that the refactored version will always return 1 (since only one object has been pushed into my array) rather than number+1. Are there other tools out there that do this type of refactoring correctly?

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• Database Functional Programming in Clojure

  - by Ralph

  "It is tempting, if the only tool you have is a hammer, to treat everything as if it were a nail." - Abraham Maslow I need to write a tool to dump a large hierarchical (SQL) database to XML. The hierarchy consists of a Person table with subsidiary Address, Phone, etc. tables. I have to dump thousands of rows, so I would like to do so incrementally and not keep the whole XML file in memory. I would like to isolate non-pure function code to a small portion of the application. I am thinking that this might be a good opportunity to explore FP and concurrency in Clojure. I can also show the benefits of immutable data and multi-core utilization to my skeptical co-workers. I'm not sure how the overall architecture of the application should be. I am thinking that I can use an impure function to retrieve the database rows and return a lazy sequence that can then be processed by a pure function that returns an XML fragment. For each Person row, I can create a Future and have several processed in parallel (the output order does not matter). As each Person is processed, the task will retrieve the appropriate rows from the Address, Phone, etc. tables and generate the nested XML. I can use a a generic function to process most of the tables, relying on database meta-data to get the column information, with special functions for the few tables that need custom processing. These functions could be listed in a map(table name -> function). Am I going about this in the right way? I can easily fall back to doing it in OO using Java, but that would be no fun. BTW, are there any good books on FP patterns or architecture? I have several good books on Clojure, Scala, and F#, but although each covers the language well, none look at the "big picture" of function programming design.

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• Comet, responseText and memory usage

  - by ithcy

  Is there a way to clear out the responseText of an XHR object without destroying the XHR object? I need to keep a persistent connection open to a web server to feed live data to a browser. The problem is, there is a relatively large amount of data coming through (several hundred K per second constantly), so memory usage is a big problem, because this connection must remain open for at least several minutes. responseText gets very big very quickly, even though the JSON I send back has been crunched as small as it can get. Due to the way the server-side app works, if I use AJAX-style short polling and just destroy the XHR object when I'm done with it, I miss significant amounts of important data even in the few milliseconds it takes to parse the response, create a new XHR and send it out. I do not have the option to use overlapping requests, as the web server only accepts one connection at a time. (Don't ask.) So Comet is exactly the model I need. What I would like to do is parse each JSON chunk as it comes back from the server, and then clear out responseText so that I can keep using the same connection. However, responseText is read-only. It cannot be directly emptied by any method I have found. Is there a part of the picture I am missing here? Does anyone know any tricks I can use to free up responseText when I'm done reading it? Or is there another place the server responses can go? I am not including code because this is really almost a code-agnostic question. The Javascript routines that spawn the XHRs and handle the returned data are very, very simple.

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• Testing Finite State Machines

  - by Pondidum

  I have inherited a large and firaly complex state machine at work. It has 31 possbile states to be in. It has the following inputs: Enum: Current State (so 0 - 30) Enum: source (currently only 2 entries) Boolean: Request Boolean: type Enum: Status (3 states) Enum: Handling (3 states) Boolean: Completed The 31 States are really needed (big business process). Breaking into seperate state machines doesnt seem feasable - each state is distinct. I have written tests for one set of inputs (the most common set), with one test per input (all inputs constant, except for the State input): [Subject("Application Process States")] public class When_state_is_meeting2Requested : AppProcessBase { Establish context = () => { //Setup.... }; Because of = () => process.Load(jas, vac); It Current_node_should_be_meeting2Requested = () => process.CurrentNode.ShouldBeOfType<meetingRequestedNode>(); It Can_move_to_clientDeclined = () => Check(process, process.clientDeclined); It Can_move_to_meeting1Arranged = () => Check(process, process.meeting1Arranged); It Can_move_to_meeting2Arranged = () => Check(process, process.meeting2Arranged); It Can_move_to_Reject = () => Check(process, process.Reject); It Cannot_move_to_any_other_state = () => AllOthersFalse(process); } As no one is entirely sure on what the output should be for each state and set of inputs i have been starting to write tests for it, however on calculation i will need to write 4320 ( 30*2*2*2*3*3*2 ) tests for it. Does anyone have any suggestions on how i should go about testing this?

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