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• CoreData and many NSArrayController

  - by unixo

  In my CoreData Application, I've an outline view on left of main window, acting as source list (like iTunes); on the right I display a proper view, based on outline selection. Each view has its components, such as table view, connected to array controller, owned by the specific view. Very often different views display same data, for example, a table view of the same entity. From a performance point of view, is better to have a single array controller per entity and share it between all views or does CoreData cache avoid memory waste?

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• Use of private constructor to prevent instantiation of class?

  - by cringe

  Hi guys! Right now I'm thinking about adding a private constructor to a class that only holds some String constants. public class MyStrings { // I want to add this: private MyString() {} public static final String ONE = "something"; public static final String TWO = "another"; ... } Is there any performance or memory overhead if I add a private constructor to this class to prevent someone to instantiate it? Do you think it's necessary at all or that private constructors for this purpose are a waste of time and code clutter?

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• Best and safest Java Profiler for production use?

  - by Pete

  I'm looking for a Java Profiler for use in a very high demand production environment, either commercial or free, that meets all of the following requirements: Lightweight integration with code (no recompile with special options, no code hooks, etc). Dropping some profiler specific .jars alongside the application code is ok. Should be able to connect/disconnect to the JVM without restarting the application. When profiling is not active, no impact to performance When profiling is active, negligible impact to performance. Very slight degradation is acceptable. Must do all the 'expected' stuff a profiler does - time spent in each method to find hotspots, object allocation/memory profiling, etc. Essentially I need something that can sit dormant in production when everything is fine without anyone knowing or caring that it is there, but then be able to connect to it hassle (and performance degradation) free to pinpoint the hard to find problems like hotspots and synchronization issues.

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• Result of Long Positive Integers & Search and element in array..

  - by AGeek

  Hi, I have two Questions for which I cannot find answers by googling, but I find these questions very important for preparation.. Kindly explain only the logic, I will be able to code. In Search of Efficient Logic..... in terms of Memory and Time. WAP to add two long positive integers. What Data structure / data type we can use to store the numbers and result. What is the best way to search an element from an array in shortest time. Size of the array could be large enough, and any elements could be stored in the array(i.e. no range). Thanks.

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• Can you iterate over chunks() with request.POST in Django?

  - by Sebastian

  I'm trying to optimize a site I'm building with Django/Flash and am having a problem using Django's iterate over chunks() feature. I'm sending an image from Flash to Django using request.POST data rather than through a form (using request.FILES). The problem I foresee is that if there is large user volume, I could potentially kill memory. But it seems that Django only allows iterating over chunks with request.FILES. Is there a way to: 1) wrap my request.POST data into a request.FILES (thus spoofing Django) or 2) use chunks() with request.POST data

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• Reading file data during form's clean method

  - by Dominic Rodger

  So, I'm working on implementing the answer to my previous question. Here's my model: class Talk(models.Model): title = models.CharField(max_length=200) mp3 = models.FileField(upload_to = u'talks/', max_length=200) Here's my form: class TalkForm(forms.ModelForm): def clean(self): super(TalkForm, self).clean() cleaned_data = self.cleaned_data if u'mp3' in self.files: from mutagen.mp3 import MP3 if hasattr(self.files['mp3'], 'temporary_file_path'): audio = MP3(self.files['mp3'].temporary_file_path()) else: # What goes here? audio = None # setting to None for now ... return cleaned_data class Meta: model = Talk Mutagen needs file-like objects - the first case (where the uploaded file is larger than the size of file handled in memory) works fine, but I don't know how to handle InMemoryUploadedFile that I get otherwise. I've tried: # TypeError (coercing to Unicode: need string or buffer, InMemoryUploadedFile found) audio = MP3(self.files['mp3']) # TypeError (coercing to Unicode: need string or buffer, cStringIO.StringO found) audio = MP3(self.files['mp3'].file) # Hangs seemingly indefinitely audio = MP3(self.files['mp3'].file.read()) Is there something wrong with mutagen, or am I doing it wrong?

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• Objective-C NSString Assignment Problem

  - by golfromeo

  In my Cocoa application, in the header file, I declare a NSString ivar: NSString *gSdkPath; Then, in awakeFromNib, I assign it to a value: gSdkPath = @"hello"; Later, it's value is changed in the code: gSdkPath = [NSString stringWithString:[folderNames objectAtIndex:0]]; (the object returned from objectAtIndex is an NSString) However, after this point, in another method when I try to NSLog() (or do anything with) the gSdkPath variable, the app crashes. I'm sure this has something to do with memory management, but I'm beginning with Cocoa and not sure exactly how this all works. Thanks for any help in advance.

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• Recognize active objects with a capacitive touch screen display

  - by lucgian84

  I'm trying to develop an app that can recognize an active object (for example: a memory) that touch the smartphone display. Before I start to develop I've to know if there's any objects that my touch screen display can recognize? Which device can be recognizable by a smartphone display? I'm interested to know that for iPhone or for Android phone. I found this app and you can see that with a card I can interact with a mobile device, now I'm asking you if anyone know how to do this kind of app with an iPhone or with an Android phone. Does anyone knows how to do that? There's a library (iOS or Android) to recognize object that I put over the display?

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• What is the '^' in Objective-C

  - by Chris Paterson

  What does the '^' mean in the code below? @implementation AppController - (IBAction) loadComposition:(id)sender { void (^handler)(NSInteger); NSOpenPanel *panel = [NSOpenPanel openPanel]; [panel setAllowedFileTypes:[NSArray arrayWithObjects: @"qtz", nil]]; handler = ^(NSInteger result) { if (result == NSFileHandlingPanelOKButton) { NSString *filePath = [[[panel URLs] objectAtIndex:0] path]; if (![qcView loadCompositionFromFile:filePath]) { NSLog(@"Could not load composition"); } } }; [panel beginSheetModalForWindow:qcWindow completionHandler:handler]; } @end === I've searched and searched - is it some sort of particular reference to memory?

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• Would using a MemoryMappedFile for IPC across AppDomains be faster than WCF/named pipes?

  - by Morten Mertner

  Context: I am loading and executing untrusted code in a separate AppDomain and am currently communicating between the two using WCF (using named pipes as the underlying transport). I am exchanging relatively simple object graphs using a reasonably coarse-grained API, but would like to use a more fine-grained API if it does not cost me performance-wise. I've noticed that 4.0 adds a MemoryMappedFile class (which doesn't need a physical file, so could be entirely memory based). What kind of performance gains could I expect to see (if any) by using this new class? I know that it would take some "infrastructure code" to get the request/response behavior of WCF, but for now I'm only interested in the performance difference.

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• Backbone JS central model where all views can use

  - by chchrist

  I am new to backbone js and require js. I use requirejS to organize my backbone code into modules. I don't know if this has any importance to what I want though. I want to have a central model where all my views will have access to. They should be able to get and set values. I don't want to use it as each view model though. I need to keep in memory search options, user status (logged in/out) etc. Any ideas? EDIT Maybe the answer is here? Share resources across different amd modules

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• Reducing unnecessary same values in Class member variables ....

  - by Freshblood

  class A { public int a; public int c; } i will create 10 instances from A.Then i will create 15 instances from A again... go on. first 10 instance will have same value for a variable and next 15 instances will have again same value for a.But I don't mean that both group has same values for a .Problem is create same a value 10 times in first group and 15 times in second group on memory unnecessary. What would be Best solution or solutions for reduce unnecessary datas in this situation?

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• [CA_COLOR_OPAQUE] things that make a layer non-opaque. scaled CAGradientLayer?

  - by mahal tertin

  i spent some time with the environment variable CA_COLOR_OPAQUE = 1 and have my findings to share. things that make a CALayer non-opaque (slow, more memory, ...): * contents with alpha (like an NSImage with an icon) * NSImage/CGImage from a pdf as contents (even when the pdf does not contain any alpha and opaque=YES) * backgroundColor = nil * CATextLayer with text in a (because it is contents with alpha) * rounded corners? maybe/sometimes * masksToBounds? not necessarily as we scale most of tree with CATransform3DScale on sublayerTransform i found also these rather irritating non-opaque: * CAGradientLayer that is somewhere down in this scaled tree (even when set all the gradient colors without alpha) * edgeAntialiasingMask != 0 of a layer that is somewhere down in this scaled tree the last two do not make sense to me. why should it be non opaque? what do i see? if anyone has any thoughts on these findings, i'm happy to learn as i couldn't find such a list yet.

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• How can I print the cookie_jar values in Perl's WWW::Mechanize?

  - by Phill Pafford

  How can I print the values of the cookie/cookie_jar being set? Trying: ##my $cookie_jar=HTTP::Cookies->new(file => "cookie.jar",autosave=>1,ignore_discard=>1); my $cookie_jar=HTTP::Cookies->new(); ## Would like it to be in memory my $agent = WWW::Mechanize->new(cookie_jar => $cookie_jar); ##my $agent = WWW::Mechanize->new(); ##my $agent = WWW::Mechanize->new(autocheck => 1); ##$agent->cookie_jar( {} ); # we need cookies ##$agent->cookie_jar(HTTP::Cookies->new); print "Set Cookie Jar?\n"; print $agent->cookie_jar->as_string(); print "\n"; $agent->get($url); // url is a https site Not too much luck with any of these, what am I doing wrong?

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• C++ is there a difference between assignment inside a pass by value and pass by reference function?

  - by Rémy DAVID

  Is there a difference between foo and bar: class A { Object __o; void foo(Object& o) { __o = o; } void bar(Object o) { __o = o; } } As I understand it, foo performs no copy operation on object o when it is called, and one copy operation for assignment. Bar performs one copy operation on object o when it is called and another one for assignment. So I can more or less say that foo uses 2 times less memory than bar (if o is big enough). Is that correct ? Is it possible that the compiler optimises the bar function to perform only one copy operation on o ? i.e. makes __o pointing on the local copy of argument o instead of creating a new copy?

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• size of an image

  - by Mike

  From times to times I have to know the width and height of images. I am using the following code: UIImage *imageU = [UIImage imageWithContentsOfFile:[[[NSBundle mainBundle] resourcePath] stringByAppendingPathComponent:@"myImage.png"]]; CGFloat imageW = CGImageGetWidth(imageU.CGImage); CGFloat imageH = CGImageGetHeight(imageU.CGImage); My question is that if it is there any other way to know the width and height of an image, in pixels, without having to load the image on a variable, that's probably consuming memory. Can the dimensions be read from the file directly without loading the whole image? thanks.

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• How to remove duplicate records in a table?

  - by Mason Wheeler

  I've got a table in a testing DB that someone apparently got a little too trigger-happy on when running INSERT scripts to set it up. The schema looks like this: ID UNIQUEIDENTIFIER TYPE_INT SMALLINT SYSTEM_VALUE SMALLINT NAME VARCHAR MAPPED_VALUE VARCHAR It's supposed to have a few dozen rows. It has about 200,000, most of which are duplicates in which TYPE_INT, SYSTEM_VALUE, NAME and MAPPED_VALUE are all identical and ID is not. Now, I could probably make a script to clean this up that creates a temporary table in memory, uses INSERT .. SELECT DISTINCT to grab all the unique values, TRUNCATE the original table and then copy everything back. But is there a simpler way to do it, like a DELETE query with something special in the WHERE clause?

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• Get a value from hashtable by a part of its key

  - by htf

  Hi. Say I have a Hashtable<String, Object> with such keys and values: apple => 1 orange => 2 mossberg => 3 I can use the standard get method to get 1 by "apple", but what I want is getting the same value (or a list of values) by a part of the key, for example "ppl". Of course it may yield several results, in this case I want to be able to process each key-value pair. So basically similar to the LIKE '%ppl%' SQL statement, but I don't want to use a (in-memory) database just because I don't want to add unnecessary complexity. What would you recommend?

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• Are @property's necessary for Interface Builder?

  - by Rits

  In my UIViewController subclass, I have 3 UIView's with each a @property as an IBOutlet. I do not use these properties at all in my code. The views get instantiated as soon as the view controller is created and they are deallocated when the view controller is deallocated. I was thinking; can't I just remove the @property's? I did, and I could still connect my instance variables (with IBOutlet) in Interface Builder. So my question now is; is there any use for properties in combination with Interface Builder, or is it OK to leave them out? Is it required for some memory management or something? Or are they really just for use in your own code? And if I do leave them out, do I still need to release them in dealloc?

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• Reading a memorystream

  - by user1842828

  Using several examples here on StackOverflow I thought the following code would decompress a gzip file then read the memory-stream and write it's content to the console. No errors occur but I get no output. public static void Decompress(FileInfo fileToDecompress) { using (FileStream originalFileStream = fileToDecompress.OpenRead()) { string currentFileName = fileToDecompress.FullName; string newFileName = currentFileName.Remove(currentFileName.Length - fileToDecompress.Extension.Length); using (FileStream decompressedFileStream = File.Create(newFileName)) { using (GZipStream decompressionStream = new GZipStream(originalFileStream, CompressionMode.Decompress)) { MemoryStream memStream = new MemoryStream(); memStream.SetLength(decompressedFileStream.Length); decompressedFileStream.Read(memStream.GetBuffer(), 0, (int)decompressedFileStream.Length); memStream.Position = 0; var sr = new StreamReader(memStream); var myStr = sr.ReadToEnd(); Console.WriteLine("Stream Output: " + myStr); } } } }

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• append versus resize for numpy array

  - by Abruzzo Forte e Gentile

  Hi all I would like to append a value at the end of my numpy.array. I saw numpy.append function but this performs an exact copy of the original array adding at last my new value. I would like to avoid copies since my arrays are big. I am using resize method and then set the last index available to the new value. Can you confirm that resize is the best way to append a value at the end? Is it not moving memory around someway? Thanks AFG oldSize = myArray,shape(0) myArray.resize( oldSize + 1 ) myArray[oldSize] = newValue

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• Storing object into cache using Linq classes and velocity

  - by Arun

  I careated couple of linq classes & marked the datacontext as unidirectional. Out of four classes; one is main class while other three are having the one to many relationship with first one; When I load the object of main class & put into the memory OR serialize it into an XML file; I never get the child class data while it is maked as DataContractAttribute. How can I force object to put the child class data into XML file or into cache ?

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• Why does tokyo tyrant slow down exponentially even after adjusting bnum?

  - by HenryL

  Has anyone successfully used Tokyo Cabinet / Tokyo Tyrant with large datasets? I am trying to upload a subgraph of the Wikipedia datasource. After hitting about 30 million records, I get exponential slow down. This occurs with both the HDB and BDB databases. I adjusted bnum to 2-4x the expected number of records for the HDB case with only a slight speed up. I also set xmsiz to 1GB or so but ultimately I still hit a wall. It seems that Tokyo Tyrant is basically an in memory database and after you exceed the xmsiz or your RAM, you get a barely usable database. Has anyone else encountered this problem before? Were you able to solve it?

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• Where is the chink in Google Chrome's armor?

  - by kudlur

  While browsing with Chrome, I noticed that it responds extremely fast (in comparison with IE and Firefox on my laptop) in terms of rendering pages, including JavaScript heavy sites like gmail. This is what googlebook on Chrome has to say tabs are hosted in process rather than thread. compile javascript using V8 engine as opposed to interpreting. Introduce new virtual machine to support javascript heavy apps introduce "hidden class transitions" and apply dynamic optimization to speed up things. Replace inefficient "Conservative garbage colllection" scheme with more precise garbage collection scheme. Introduce their own task scheduler and memory manager to manage the browser environment. All this sounds so familiar, and Microsoft has been doing such things for long time.. Windows os, C++, C# etc compilers, CLR, and so on. So why isn't Microsoft or any other browser vendor taking Chrome's approach? Is there a flaw in Chrome's approach? If not, is the rest of browser vendor community caught unaware with Google's approach?

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• what changes when your input is giga/terabyte sized?

  - by Wang

  I just took my first baby step today into real scientific computing today when I was shown a data set where the smallest file is 48000 fields by 1600 rows (haplotypes for several people, for chromosome 22). And this is considered tiny. I write Python, so I've spent the last few hours reading about HDF5, and Numpy, and PyTable, but I still feel like I'm not really grokking what a terabyte-sized data set actually means for me as a programmer. For example, someone pointed out that with larger data sets, it becomes impossible to read the whole thing into memory, not because the machine has insufficient RAM, but because the architecture has insufficient address space! It blew my mind. What other assumptions have I been relying in the classroom that just don't work with input this big? What kinds of things do I need to start doing or thinking about differently? (This doesn't have to be Python specific.)

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