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  • How can I get read-ahead bytes?

    - by Bruno Martinez
    Operating systems read from disk more than what a program actually requests, because a program is likely to need nearby information in the future. In my application, when I fetch an item from disk, I would like to show an interval of information around the element. There's a trade off between how much information I request and show, and speed. However, since the OS already reads more than what I requested, accessing these bytes already in memory is free. What API can I use to find out what's in the OS caches? Alternatively, I could use memory mapped files. In that case, the problem reduces to finding out whether a page is swapped to disk or not. Can this be done in any common OS?

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  • iPhone app crashes at the mid of running or during launch

    - by Sankar Chandra Bose
    Goodafternoon All! I have an issue in my application.My iphone application crashes at mid of running or during the application launch at times both in iPhone and simulator. I know that memory management is not proper or is it because os some other reason. My application is using a web service that pulls the data and displays it in the view,the working of web service is proper,because i see the data coming from the service in my app. Can anybody suggest how to manage memory properly (i.e,) where i have to release the objects,what are the objects that has to be released and the objects that should not be released. Kindly suggest a solution to the problem. Thanks in advance

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  • How to use OCL constraints to prevent node creation in an GMF generated editor

    - by TheMorph
    Hello, I am working on editors created with GMF and struggling with OCL right now. Is there a possibilty to prevent a node to be created if an OCL statement in the mapping evaluates to false? If tried adding an OCL statement to a node and all it does is making the node not visible in the editor, but it is created. There is also an OCL statement in the ecore file, but this way it is only evaluated when there should be something done with the created model. I does not prevent a user to construct an invalid model but this is what I intend to prevent. Thanks in advance, Morph

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  • OCL constraints intended prevent node creation in an GMF generated editor only makes it invisible

    - by TheMorph
    Hello, I am working on editors created with GMF and struggling with OCL right now. Is there a possibilty to prevent a node to be created if an OCL statement in the mapping evaluates to false? If tried adding an OCL statement to a node and all it does is making the node not visible in the editor, but it is created. There is also an OCL statement in the ecore file, but this way it is only evaluated when there should be something done with the created model. I does not prevent a user to construct an invalid model but this is what I intend to prevent. Thanks in advance, Morph

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  • JAVA - Strange problem (probably thread problem) with JTable & Model

    - by Stefanos Kargas
    I am using 2 Tables (JTable) with their DefaultTableModels. The first table is already populated. The second table is populated for each row of the first table (using an SQL Query). My purpose is to export every line of the first table with it's respective lines of the second in an Excel File. I am doing it with a for (for each line of 1st table), in which I write a line of the 1st table in the Excel File, then I populate the 2nd table (for this line of 1st Table), I get every line from the Table (from it's Model actually) and put it in the Excel File under the current line of 1st table. This means that if I have n lines in first table I will clear and populate again the second table n times. All this code is called in a seperate thread. THE PROBLEM IS: Everything works perfectly fine ecxept that I am getting some exceptions. The strange thing is that I'm not getting anything false in my result. The Excel file is perfect. Some of the lines of the exceptions are: Exception in thread "AWT-EventQueue-0" java.lang.ArrayIndexOutOfBoundsException: 0 = 0 at java.util.Vector.elementAt(Vector.java:427) at javax.swing.table.DefaultTableModel.getValueAt(DefaultTableModel.java:632) at javax.swing.JComponent.paint(JComponent.java:1017) at javax.swing.RepaintManager.paint(RepaintManager.java:1220) at javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:803) I am assuming that the problem lies in the fact that the second table needs some more time to be populated before I try to get any data from it. That's why I see RepaintManager and paintDirtyRegions in my exceptions. Another thing I did is that I ran my program in debug mode and I put a breakpoint after each population of the 2nd table. Then I pressed F5 to continue for each population of 2nd table and no exception appeared. The program came to it's end without any exceptions. This is another important fact that tells me that maybe in this case I gave the table enough time to be populated. Of course you will ask me: If your program works fine, why do you care about the exceptions? I care for avoiding any future problems and I care to have a better understanding of Java and Java GUI and threads. Why do you depend on a GUI component (and it's model) to get your information and why don't you recreate the resultset that populates your tables using an SQL Query and get your info from the resultset? That would be the best and the right way. The fact is that I have the tables code ready and it was easier for me to just get the info from them. But the right way would be to get everything direct from database. Anyway what I did brought out my question, and answering it would help me understand more things about java. So I posted it.

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  • How to isolate data per customer, Django powered website

    - by Sawwy
    I have recently started learning python and django and working on a project that includes building a website for collecting information from customers. I am currently trying to figure out best way to isolate the customer data (collected information is sensitive and should only be accessible by customer and the service provider). I found this post Postgresql - one database for everyone, or one-database per customer and my question is that can I automate the model inheritance with customer creation via admin? To be specific, when save() is called for adding customer via django admin, this should create the customer specific tables (create a new set of tables with 'company_name' -prefix). For more information of the environment, I have extended the basic user registration with custom UserProfile adding 'company' and 'role' fields for each user. Upon login, the 'company' of the user will be checked to filter out tables without the 'company_name' prefix. 'Role' will further filter the which company-specific tables and set rights (view, edit). will appreciate any suggestions if more elegant methods could be used to solve the data isolation problem than model inheritance.

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  • [objective C] IPhone question about UIImageView memory menagement

    - by BQuadra
    Hi, i have a UIImageView of 1024x768 (the room of my game) and other various UIIMageView on it (the object of my game). The iPhone screen is smaller than the room (UIImageView 1024x768) .. i want to understand if the iPhone's system automatically intercepts the graphic elements outside the visible area of Room (the player's view) and unload temporarily (for memory optimization) or i must do this by hand?? thanks

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  • Using Apache Velocity with StringBuilders/CharSequences

    - by mindas
    We are using Apache Velocity for dynamic templates. At the moment Velocity has following methods for evaluation/replacing: public static boolean evaluate(Context context, Writer writer, String logTag, Reader reader) public static boolean evaluate(Context context, Writer out, String logTag, String instring) We use these methods by providing StringWriter to write evaluation results. Our incoming data is coming in StringBuilder format so we use StringBuilder.toString and feed it as instring. The problem is that our templates are fairly large (can be megabytes, tens of Ms on rare cases), replacements occur very frequently and each replacement operation triples the amount of required memory (incoming data + StringBuilder.toString() which creates a new copy + outgoing data). I was wondering if there is a way to improve this. E.g. if I could find a way to provide a Reader and Writer on top of same StringBuilder instance that only uses extra memory for in/out differences, would that be a good approach? Has anybody done anything similar and could share any source for such a class? Or maybe there any better solutions to given problem?

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  • Memory allocation in java

    - by Girish
    class Someobject { int i=10; } public class OtherObject { public static void main(String args[]) { Someobject obj=new Someobject(); System.out.println(obj.i); } } Please tell me in which section of the memory: This entire code will load. Where will someobject will be stored. Where will obj will be stored Where will i be stored. Thanks every one in advance.

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  • How to learn to program C the right way

    - by sfactor
    i have been programming in C/C++ for my academic courses a lot and was under the impression i had a pretty good grasp of it. but lately i had to work in a bluetooth application that had a server and client implementation in a Linux box and an embedded system. i learned bluez bluetooth API, socket/network programming and coded it. however i ran into a lot of problems with memory leaks and segmentation faults and other memory related errors along the way.as the code grew more complex i all but lost control of the pointers and threads and sockets. this got me wondering that i had a lot to learn that they didn't say in the basic C/C++ books. so i wanted to ask for the resources that are available that'll help be code better in a professional way in C/C++ .especially for the Linux/Mac environment (gcc compiler).

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  • Suggestions on documentation of a DB model when using Entity Framework 4

    - by Junior Ewing
    Any experiences on how to document Entity Framework 4 based Database projects? There is the Document and Summary properties on the Entities, but if we want to regenerate the model from the database at some point, it will be lost! Is there some way to map documentation data inside SQL to the Entities in the EDMX file so it is safe. Suggestions of other best practices? Ideally I want to be able to augo generate html/helpfile documentation from the DB when we deploy.

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  • Why my json_encode get corrupted

    - by Cullen SUN
    $model = new XUploadForm; $model->file = CUploadedFile::getInstance( $model, 'file' ); //We check that the file was successfully uploaded if( $model->file !== null ) { //Grab some data $model->mime_type = $model->file->getType( ); $model->size = $model->file->getSize( ); $model->name = $model->file->getName( ); $file_extention = $model->file->getExtensionName( ); //(optional) Generate a random name for our file $file_tem_name = md5(Yii::app( )->user->id.microtime( ).$model->name); $file_thumb_name = $file_tem_name.'_thumb.'.$file_extention; $file_image_name = $file_tem_name.".".$file_extention; if( $model->validate( ) ) { //Move our file to our temporary dir $model->file->saveAs( $path.$file_image_name ); if(chmod($path.$file_image_name, 0777 )){ // Yii::import("ext.EPhpThumb.EPhpThumb"); // $thumb_=new EPhpThumb(); // $thumb_->init(); // $thumb_->create($path.$file_image_name) // ->resize(110,80) // ->save($path.$file_thumb_name); } //here you can also generate the image versions you need //using something like PHPThumb //Now we need to save this path to the user's session if( Yii::app( )->user->hasState( 'images' ) ) { $userImages = Yii::app( )->user->getState( 'images' ); } else { $userImages = array(); } $userImages[] = array( "filename" => $file_image_name, 'size' => $model->size, 'mime' => $model->mime_type, "path" => $path.$file_image_name, // "thumb" => $path.$file_thumb_name, ); Yii::app( )->user->setState('images', $userImages); //Now we need to tell our widget that the upload was succesfull //We do so, using the json structure defined in // https://github.com/blueimp/jQuery-File-Upload/wiki/Setup echo json_encode( array( array( "type" => $model->mime_type, "size" => $model->size, "url" => $publicPath.$file_image_name, //"thumbnail_url" => $publicPath.$file_thumb_name, //"thumbnail_url" => $publicPath."thumbs/$filename", "delete_url" => $this->createUrl( "upload", array( "_method" => "delete", "file" => $file_image_name ) ), "delete_type" => "POST" ) ) ); Above code give me correct response, [{"type":"image/jpeg","size":2266,"url":"/uploads/tmp/0b00cbaee07c6410241428c74aae1dca.jpeg","delete_url":"/api/imageUpload/upload?_method=delete&file=0b00cbaee07c6410241428c74aae1dca.jpeg","delete_type":"POST"}] but if I uncomment the following // Yii::import("ext.EPhpThumb.EPhpThumb"); // $thumb_=new EPhpThumb(); // $thumb_->init(); // $thumb_->create($path.$file_image_name) // ->resize(110,80) // ->save($path.$file_thumb_name); it gave me corrupted response: Mac OS X 2??ATTR?dA??Y?Ycom.apple.quarantine0001;50655994;Google\x20Chrome.app;2599ECF9-69C5-4386-B3D9-9F5CC7E0EE1D|com.google.ChromeThis resource fork intentionally left blank ??[{"type":"image/jpeg","size":1941,"url":"/uploads/tmp/409c5921c6d20944e1a81f32b12fc380.jpeg","delete_url":"/api/imageUpload/upload?_method=delete&file=409c5921c6d20944e1a81f32b12fc380.jpeg","delete_type":"POST"}]

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  • What is Erlang's concurrency model actually ?

    - by arun_suresh
    I was reading a paper recently Why Events are Bad. The paper is a comparative study of Event based and thread based highly concurrent servers and finally concludes stating that Threads are better than events in that scenario. I find that I am not able to classify what sort of concurrency model erlang exposes. Erlang provides Light Weight Processes, but those processes are suspended most of the time until it has received some event/message of some sort. /Arun

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  • Write large PDFs with Java sequentially

    - by Benjamin Muschko
    I am looking for a Java library that let's you write large PDFs sequentially with a minimum amount of memory. Most of the libraries I had a look at has to build up the document in memory first before you can actually write it. The problem I have to deal with are OutOfMemoryErrors. It would be great if I could flush the writer programmatically whenever needed e.g. for each page. Does anyone have any recommendations? I need something with a license along the lines of the LGPL (so not the GPL or the Affero GPL that iText uses).

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  • Tracking EXC_BAD_ACCESS on iPad

    - by Aleks
    I've been using this code to create my UIWindow UIMyWindow* win = [[UIMyWindow alloc] initWithFrame:[[UIScreen mainScreen] applicationFrame]]; UIMyWindow isn't anything special it just has a pointer to a C++ class that does some wrapping of ObjectiveC. Recently my application start crashing after adding some line of code that doesn't have to do anything with the error. The line of code that I added is just allocating a C++ object but the program execution never reaches this line. Interesting enough my code works in Release. My only guess is that I made some memory corruption on a completely different place. My questions are: What type of memory corruption that can be? And is there some good practices to track them down?

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  • Django finding which field matched in a multiple OR query

    - by Greg Hinch
    I've got a couple models which are set up something like this: class Bar(models.Model): baz = models.CharField() class Foo(models.Model): bar1 = models.ForeignKey(Bar) bar2 = models.ForeignKey(Bar) bar3 = models.ForeignKey(Bar) And elsewhere in the code, I end up with an instance of Bar, and need to find the Foo it is attached to in some capacity. Right now I came up with doing a multiple OR query using Q, something like this: foo_inst = Foo.objects.get(Q(bar1=bar_inst) | Q(bar2=bar_inst) | Q(bar3=bar_inst)) What I need to figure out is, which of the 3 cases actually hit, at least the name of the member (bar1, bar2, or bar3). Is there a good way to do this? Is there a better way to structure the query to glean that information?

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  • Garbage Collection leak? Scripting Bridge leak?

    - by Y.Vera
    Hello everyone! I'm always really picky about memory leaks and I cannot understand why my garbage collected application leaks. My code is entirely memory-managed and it runs great without garbage collection, not a single leak. However, as soon as I turn on garbage collection it leaks! Just to prove a point, why does this leak in a garbage collected app? (place this dummy code at applicationDidFinishLaunching:) NSOpenPanel *panel = [NSOpenPanel openPanel]; [panel beginSheetModalForWindow:window completionHandler:^(NSInteger result) {NSBeep();}]; Also, is there a way to prevent leaks in apps (garbage collected or otherwise) that use Scripting Bridge? it seems as if they all leak, even the sample ones in xcode. Thanks everybody!

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  • System.Timers.Timer leaking due to "direct delegate roots"

    - by alimbada
    Apologies for the rather verbose and long-winded post, but this problem's been perplexing me for a few weeks now so I'm posting as much information as I can in order to get this resolved quickly. We have a WPF UserControl which is being loaded by a 3rd party app. The 3rd party app is a presentation application which loads and unloads controls on a schedule defined by an XML file which is downloaded from a server. Our control, when it is loaded into the application makes a web request to a web service and uses the data from the response to display some information. We're using an MVVM architecture for the control. The entry point of the control is a method that is implementing an interface exposed by the main app and this is where the control's configuration is set up. This is also where I set the DataContext of our control to our MainViewModel. The MainViewModel has two other view models as properties and the main UserControl has two child controls. Depending on the data received from the web service, the main UserControl decides which child control to display, e.g. if there is a HTTP error or the data received is not valid, then display child control A, otherwise display child control B. As you'd expect, these two child controls bind two separate view models each of which is a property of MainViewModel. Now child control B (which is displayed when the data is valid) has a RefreshService property/field. RefreshService is an object that is responsible for updating the model in a number of ways and contains 4 System.Timers.Timers; a _modelRefreshTimer a _viewRefreshTimer a _pageSwitchTimer a _retryFeedRetrievalOnErrorTimer (this is only enabled when something goes wrong with retrieving data). I should mention at this point that there are two types of data; the first changes every minute, the second changes every few hours. The controls' configuration decides which type we are using/displaying. If data is of the first type then we update the model quite frequently (every 30 seconds) using the _modelRefreshTimer's events. If the data is of the second type then we update the model after a longer interval. However, the view still needs to be refreshed every 30 seconds as stale data needs to be removed from the view (hence the _viewRefreshTimer). The control also paginates the data so we can see more than we can fit on the display area. This works by breaking the data up into Lists and switching the CurrentPage (which is a List) property of the view model to the right List. This is done by handling the _pageSwitchTimer's Elapsed event. Now the problem My problem is that the control, when removed from the visual tree doesn't dispose of it's timers. This was first noticed when we started getting an unusually high number of requests on the web server end very soon after deploying this control and found that requests were being made at least once a second! We found that the timers were living on and not stopping hours after the control had been removed from view and that the more timers there were the more requests piled up at the web server. My first solution was to implement IDisposable for the RefreshService and do some clean up when the control's UnLoaded event was fired. Within the RefreshServices Dispose method I've set Enabled to false for all the timers, then used the Stop() method on all of them. I've then called Dispose() too and set them to null. None of this worked. After some reading around I found that event handlers may hold references to Timers and prevent them from being disposed and collected. After some more reading and researching I found that the best way around this was to use the Weak Event Pattern. Using this blog and this blog I've managed to work around the shortcomings in the Weak Event pattern. However, none of this solves the problem. Timers are still not being disabled or stopped (let alone disposed) and web requests are continuing to build up. Mem Profiler tells me that "This type has N instances that are directly rooted by a delegate. This can indicate the delegate has not been properly removed" (where N is the number of instances). As far as I can tell though, all listeners of the Elapsed event for the timers are being removed during the cleanup so I can't understand why the timers continue to run. Thanks for reading. Eagerly awaiting your suggestions/comments/solutions (if you got this far :-p)

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  • create a sparse BufferedImage in java

    - by elgcom
    I have to create an image with very large resolution, but the image is relatively "sparse", only some areas in the image need to draw. For example with following code /* this take 5GB memory */ final BufferedImage img = new BufferedImage( 36000, 36000, BufferedImage.TYPE_INT_ARGB); /* draw something */ Graphics g = img.getGraphics(); g.drawImage(....); /* output as PNG */ final File out = new File("out.png"); ImageIO.write(img, "png", out); The PNG image on the end I created is ONLY about 200~300 MB. The question is how can I avoid creating a 5GB BufferedImage at the beginning? I do need an image with large dimension, but with very sparse color information. Is there any Stream for BufferedImage so that it will not take so much memory?

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