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• Grand Central Strategy for Opening Multiple Files

  - by user276632

  I have a working implementation using Grand Central dispatch queues that (1) opens a file and computes an OpenSSL DSA hash on "queue1", (2) writing out the hash to a new "side car" file for later verification on "queue2". I would like to open multiple files at the same time, but based on some logic that doesn't "choke" the OS by having 100s of files open and exceeding the hard drive's sustainable output. Photo browsing applications such as iPhoto or Aperture seem to open multiple files and display them, so I'm assuming this can be done. I'm assuming the biggest limitation will be disk I/O, as the application can (in theory) read and write multiple files simultaneously. Any suggestions? TIA

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• Dependency Injection with @Inject in Weld (JSR-299 RI). How is the corresponding @Produces found?

  - by Thorbjørn Ravn Andersen

  I have played with the JSR-299 Reference Implementation "Weld" with the purpose of using it in a stand-alone application, and I have had a look at the documentation, and marveled at the magic. My question is how the producer of a given object to be @Inject'ed is found? Either the java compiler produces hints for annotations which is easily found by the classloader, or the complete classpath must be traversed loading all classes to see what they do which sounds highly inefficient to me, or it is a completely different approach. What is the trick?

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• IoC from start to finish

  - by Dave

  I'm quite sure that IoC is the way to go for my application. There are a ton of articles and even questions here on SO that discuss the different containers. I've read several blogs today with partial examples. I am personally leaning towards starting with the CommonServiceLocator and Unity as two way to solve the same problem -- I just need a bunch of assemblies to get data from a database, which I assume is what needs to be injected everywhere. I've yet to find any sites that really take a problem from beginning to end, with concrete code examples. For example, I've yet to find one that discusses an IServiceLocator and how to actually register it (or do whatever is required to make it known). What are your favorite posts / articles / SO questions that can take a noob from start to finish with the implementation?

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• how start implement MVVM pattern

  - by netmajor

  Hello, So i decide to to develop my asp.net site into Silverlight. I today start to search articles about MVVM pattern which i want use in my Silverlight app, and i am confused :/ It's hart to me understand how works this pattern. I am find 3 frameworks which supports MVVM pattern in Silverlight - Caliburn, MVVM Light Toolkit and GoodLight. Should i start from own implementation of pattern or use framework? Is this frameworks only a project solutions in which i can insert my code? Which framework is the best for novice and which for professional? I ask for this, cause i must start to rewrite my app from asp.net to Silverlight and i don't know that i can do it first and later (when i understand MVVM pattern and framework) implement this pattern in finished app ? Or from begining rewrite project to MVVM framework?

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• How Do You Profile & Optimize CUDA Kernels?

  - by John Dibling

  I am somewhat familiar with the CUDA visual profiler and the occupancy spreadsheet, although I am probably not leveraging them as well as I could. Profiling & optimizing CUDA code is not like profiling & optimizing code that runs on a CPU. So I am hoping to learn from your experiences about how to get the most out of my code. There was a post recently looking for the fastest possible code to identify self numbers, and I provided a CUDA implementation. I'm not satisfied that this code is as fast as it can be, but I'm at a loss as to figure out both what the right questions are and what tool I can get the answers from. How do you identify ways to make your CUDA kernels perform faster?

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• iPhone switch statement using enum

  - by Boris

  I have defined an enum in a header file of a class : typedef enum{ RED = 0, BLUE, Green } Colors; - (void) switchTest:(Colors)testColor; and in the implementation file I have : - (void) switchTest:(Colors)testColor{ if(testColor == RED){ NSLog(@"Red selected"); } switch(testColor){ case RED: NSLog(@"Red selected again !"); break; default: NSLog(@"default selected"); break; } } My code compiles correctly without warrnings. When calling the switchTest method with RED, the output is : "Red selected" but once the first line of the switch runs, the application quits unexpectedly and without warrnings/errors. I don't mind using if/else syntax but I would like to understand my mistake.

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• Programmatically allow write access for a Registry key

  - by Kerido

  Hi everybody, I need to programmatically modify the Access Descriptors on a known Registry key during product installation. The way I want it to work is: The installer is run in Administrative mode. A Registry key is created. A function (the one I need) queries the ACL from the key. If this function finds that the group 'Users' already has write access, nothing should be done. If not, it should add a new permission allowing write access to the 'Users' group. The permissions are saved for the Registry key. This question is similar to Setting Registry key write permissions using .NET, however, I need a C++/Win32 implementation. Thanks in advance

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• Mathematica Plot3D does not produce a plot when graphing a user-defined function?

  - by pythonscript

  I'm writing a simple Mathematica implementation of the black-scholes model and using Plot3D to plot the pricing surface. However, when I run this code, no plot is produced. My call and put functions to produce correct values when run separately, but no plot is produced. Code: Clear[d1, d2, call, put, stockPrice, strikePrice, riskFreeRate, timeToExp, volatility] d1[stockPrice_, strikePrice_, riskFreeRate_, timeToExp_, volatility_] := (Log[stockPrice / strikePrice] + (riskFreeRate + 0.5*volatility^2)*timeToExp) / (volatility * Sqrt[timeToExp]) d2[stockPrice_, strikePrice_, riskFreeRate_, timeToExp_, volatility_] := d1[stockPrice, strikePrice, riskFreeRate, timeToExp, volatility] - volatility*Sqrt[timeToExp] call[stockPrice_, strikePrice_, riskFreeRate_, timeToExp_, volatility_] := stockPrice * CDF[NormalDistribution[0, 1], d1[stockPrice, strikePrice, riskFreeRate, timeToExp, volatility]] - strikePrice * Exp[-riskFreeRate*timeToExp] *CDF[NormalDistribution[0, 1], d2[stockPrice, strikePrice, riskFreeRate, timeToExp, volatility]] Plot3D[call[stockPrice, 500, 0.0030, timeToExp, 0.39], {stockPrice, 10, 1000}, {timetoExp, 0.0833333, 5}] Other plots, like this sample from the reference, do work. Plot3D[{x^2 + y^2, -x^2 - y^2}, {x, -2, 2}, {y, -2, 2}, RegionFunction -> Function[{x, y, z}, x^2 + y^2 <= 4], BoxRatios -> Automatic]

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• Implementing IComparer<T> For IComparer<DictionaryEntry>

  - by Phil Sandler

  I am using the ObservableSortedDictionary from Dr. WPF. The constructor looks like this: public ObservableSortedDictionary(IComparer<DictionaryEntry> comparer) I am really struggling to create an implementation that satisfies the constructor and works. My current code (that won't compile) is: public class TimeCreatedComparer<T> : IComparer<T> { public int Compare(T x, T y) { var myclass1 = (IMyClass)((DictionaryEntry)x).Value; var myclass2 = (IMyClass)((DictionaryEntry)y).Value; return myclass1.TimeCreated.CompareTo(myclass2.TimeCreated); } } It says I can't cast from T to DictionaryEntry. If I cast directly to IMyClass, it compiles, but I get a runtime error saying I can't cast from DictionaryEntry to IMyClass. At runtime, x and y are instances of DictionaryEntry, which each have the correct IMyClass as their Value.

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• Inherit from UINavigationController

  - by d.andreykiv

  Hi. I'm developing iphone app with UITabBarController as main view. Every ViewController in each tab is UINavigationController which must have a same button in leftBarButtonItem. Can I inherit some class from UINavigationController and override it's -(id) initWithRootViewController:(UIViewController *)rootViewController method to realize this ? I made something like this. But this code doesn't work; @implementation MainNavagaionController -(id) initWithRootViewController:(UIViewController *)rootViewController { if (self = [super initWithRootViewController:rootViewController]) { // Set user name title UIBarButtonItem * userNameButton = [[UIBarButtonItem alloc]initWithTitle:@"Title" style:UIBarButtonItemStylePlain target:self action:nil]; self.navigationItem.leftBarButtonItem = userNameButton; [userNameButton release]; } return self; } @end

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• Node.js for lua?

  - by Shahbaz

  I've been playing around with node.js (nodejs) for the past few day and it is fantastic. As far as I can tell, lua doesn't have a similar integration of libev and libio which let's one avoid almost any blocking calls and interact with the network and the filesystem in an asynchronous manner. I'm slowly porting my java implementation to nodejs, but I'm shocked that luajit is much faster than v8 JavaScript AND uses far less memory! I imagine writing my server in such an environment (very fast and responsive, very low memory usage, very expressive) will improve my project immensly. Being new to lua, I'm just not sure if such a thing exists. I'll appreciate any pointers. Thanks

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• JavaFX Threading issue - GUI freezing while method call ran.

  - by David Meadows

  Hi everyone, I hoped someone might be able to help as I'm a little stumped. I have a javafx class which runs a user interface, which includes a button to read some text out loud. When you press it, it invokes a Java object which uses the FreeTTS java speech synth to read out loud a String, which all works fine. The problem is, when the speech is being read out, the program stops completely until its completed. I'm not an expert on threaded applications, but I understand that usually if I extend the Thread class, and provided my implementation of the speech synth code inside an overridden run method, when I call start on the class it "should" create a new Thread, and run this code there, allowing the main thread which has the JavaFX GUI on to continue as normal. Any idea why this isn't the case? Thanks a lot in advance!

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• How does one go about understanding GNU source code?

  - by Max Dwayne

  I'm really sorry if this sounds kinda dumb. I just finished reading K&R and I worked on some of the exercises. This summer, for my project, I'm thinking of re-implementing a linux utility to expand my understanding of C further so I downloaded the source for GNU tar and sed as they both seem interesting. However, I'm having trouble understanding where it starts, where's the main implementation, where all the weird macros came from, etc. I have a lot of time so that's not really an issue. Am I supposed to familiarize myself with the GNU toolchain (ie. make, binutils, ..) first in order to understand the programs? Or maybe I should start with something a bit smaller (if there's such a thing) ? I have little bit of experience with Java, C++ and python if that matters. Thanks!

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• Objective-C: Protocols

  - by Stu

  I'd like an instance variable object to adopt a protocol. @interface GameScene : Scene <AVAudioPlayerDelegate> { @private Layer *content <CocosNodeOpacity>; } For example I'd like my Layer object to adopt the <CocosNodeOpacity> so that I can get the methods -(GLubyte) opacity; //and -(void) setOpacity: (GLubyte) opacity; for free. The syntax shown above is invalid. Is it possible to achieve this without creating a new implementation file and creating a custom object? Thanks.

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• Please suggest some alternative to Drupal

  - by abovesun

  Drupal propose completely different approach in web development (comparing with RoR like frameworks) and it is extremely good from development speed perspective. For example, it is quite easy to clone 90% of stackoverflow functionality using Drupal. But it has several big drawbacks: it is f''cking slow (100-400 requests per page) db structure very complicated, need at least 2 tables for easy content (entity) type, CCK fields very easy generate tons of new db tables anti-object oriented, rather aspect-oriented bad "view" layer implementation, no strange forward layouts and so on. After all this items I can say I like Drupal, but I would like something same, but more elegant and more object oriented. Probably something like http://drupy.net/ - drupal emulation on the top of django. P.S. I wrote this question not for new holy word flame, just write if you know alternative that uses something similar approach.

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• Examining mmaped addresses using GDB

  - by Mikeage

  I'm using the driver I posted at http://stackoverflow.com/questions/647783/direct-memory-access-in-linux/ to mmap some physical ram into a userspace address. However, I can't use GDB to look at any of the address; i.e., x 0x12345678 (where 0x12345678 is the return value of mmap) fails with an error "Cannot access memory at address 0x12345678". Is there any way to tell GDB that this memory can be viewed? Alternatively, is there something different I can do in the mmap (either the call or the implementation of foo_mmap there) that will allow it to access this memory? Note that I'm not asking about /dev/mem (as in the first snippet there) but amount a mmap to memory acquired via ioremap(), virt_to_phys() and remap_pfn_range()

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• Refactor/rewrite code or continue?

  - by Dan

  I just completed a complex piece of code. It works to spec, it meets performance requirements etc etc but I feel a bit anxious about it and am considering rewriting and/or refactoring it. Should I do this (spending time that could otherwise be spent on features that users will actually notice)? The reasons I feel anxious about the code are: The class hierarchy is complex and not obvious Some classes don't have a well defined purpose (they do a number of unrelated things) Some classes use others internals (they're declared as friend classes) to bypass the layers of abstraction for performance, but I feel they break encapsulation by doing this Some classes leak implementation details (eg, I changed a map to a hash map earlier and found myself having to modify code in other source files to make the change work) My memory management/pooling system is kinda clunky and less-than transparent They look like excellent reasons to refactor and clean code, aiding future maintenance and extension, but could be quite time consuming. Also, I'll never be perfectly happy with any code I write anyway... So, what does stackoverflow think? Clean code or work on features?

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• How difficult is it to migrate away from Google App Engine?

  - by Ignas Limanauskas

  I am thinking of making an (initially) small Web Application, which would eventually have a potential to grow. All things considered Google App Engine seems like a very attractive option. Say, user base and complexity grows and for one or other reason I needed to leave GAE behind. How difficult would it be to migrate away? 1) Does GAE provide a way to export the database? What format would it be? Would it be difficult to put it under MySQL (or similar)? 2) In which areas (ex. database access, others?) would I have to use GAE API? I.e. which parts of implementation would have to be abstracted away / interfaced? 3) Alternatively, is it even worth to keep GAE API outside, say, if there is nothing much I would need to use.

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• Pure Java open-source libraries for portfolio selection (= constrained, non-linear optimization)?

  - by __roland__

  Does anyone know or has experience with a pure Java library to select portfolios or do some similar kinds of quadratic programming with constraints? There seems to be a lot of tools, as already discussed elsewhere - but what I would like to use is a pure Java implementation. Since I want to call the library from within another open-source software with a BSD-ish license I would prefer LGPL over GPL. Any help is appreciated. If you don't know such libraries, which is the most simple algorithm you would suggest to implement? It has to cope with an inequality constraint (all x_i = 0) and an equality constraint (sum of all x_i = 1).

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• How to avoid having very large objects with Domain Driven Design

  - by Pablojim

  We are following Domain Driven Design for the implementation of a large website. However by putting the behaviour on the domain objects we are ending up with some very large classes. For example on our WebsiteUser object, we have many many methods - e.g. dealing with passwords, order history, refunds, customer segmentation. All of these methods are directly related to the user. Many of these methods delegate internally to other child object but this still results in some very large classes. I'm keen to avoid exposing lots of child objects e.g. user.getOrderHistory().getLatestOrder(). What other strategies can be used to avoid this problems?

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• Add XSLT 2 schema to Visual Studio 2010 for intellisense

  - by David Merrilees

  I'd like to add the XSLT 2 schema to Visual Studio 2010 to provide intellisense. I've added the schema to C:\Program Files\Microsoft Visual Studio 10.0\Xml\Schemas (removing the XSLT 1 schema), but to no avail. The schema seems to have been parsed by Visual Studio, as I can hover my cursor over the namespace declaration in the stylesheet (xmlns:xsl="http://www.w3.org/1999/XSL/Transform") and see the comments from the new schema, however, intellisense still refers to the XSLT 1 implementation. For example the element has a warning that 'xsl:function is not yet available'. Do I need to register the schema in some way? Any suggestions welcome.

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• posmax: like argmax but gives the position(s) of the element x for which f[x] is maximal

  - by dreeves

  Mathematica has a built-in function ArgMax for functions over infinite domains, based on the standard mathematical definition. The analog for finite domains is a handy utility function. Given a function and a list (call it the domain of the function), return the element(s) of the list that maximize the function. Here's an example of finite argmax in action: http://stackoverflow.com/questions/471029/canonicalize-nfl-team-names/472213#472213 And here's my implementation of it (along with argmin for good measure): (* argmax[f, domain] returns the element of domain for which f of that element is maximal -- breaks ties in favor of first occurrence. *) SetAttributes[{argmax, argmin}, HoldFirst]; argmax[f_, dom_List] := Fold[If[f[#1]>=f[#2], #1, #2]&, First[dom], Rest[dom]] argmin[f_, dom_List] := argmax[-f[#]&, dom] First, is that the most efficient way to implement argmax? What if you want the list of all maximal elements instead of just the first one? Second, how about the related function posmax that, instead of returning the maximal element(s), returns the position(s) of the maximal elements?

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• SQLAlchemy custom sorting algorithms when using SQL indexes

  - by David M

  Is it possible to write custom collation functions with indexes in SQLAlchemy? SQLite for example allows specifying the sorting function at a C level as sqlite3_create_collation(). An implementation of some of the Unicode collation algorithm has been provided by James Tauber here, which for example sorts all the "a"'s close together whether they have accents on them or not. Other examples of why this might be useful is for different alphabet orders (languages other than English) and sorting numeric values (sorting 10 after 9 rather than codepoint order.) Is this possible in SQLAlchemy? If not, is it supported by the pysqlite3 or MySQLdb modules, or for any other SQL database modules supported by python for that matter? Any information would be greatly appreciated.

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• Pass a Delphi class to a C++ function/method that expects a class with __thiscall methods.

  - by Alan G.

  I have some MSVC++ compiled DLL's for which I have created COM-like (lite) interfaces (abstract Delphi classes). Some of those classes have methods that need pointers to objects. These C++ methods are declared with the __thiscall calling convention (which I cannot change), which is just like __stdcall, except a this pointer is passed on the ECX register. I create the class instance in Delphi, then pass it on to the C++ method. I can set breakpoints in Delphi and see it hitting the exposed __stdcall methods in my Delphi class, but soon I get a STATUS_STACK_BUFFER_OVERRUN and the app has to exit. Is it possible to emulate/deal with __thiscall on the Delphi side of things? If I pass an object instantiated by the C++ system then all is good, and that object's methods are called (as would be expected), but this is useless - I need to pass Delphi objects. Edit 2010-04-19 18:12 This is what happens in more detail: The first method called (setLabel) exits with no error (though its a stub method). The second method called (init), enters then dies when it attempts to read the vol parameter. C++ Side #define SHAPES_EXPORT __declspec(dllexport) // just to show the value class SHAPES_EXPORT CBox { public: virtual ~CBox() {} virtual void init(double volume) = 0; virtual void grow(double amount) = 0; virtual void shrink(double amount) = 0; virtual void setID(int ID = 0) = 0; virtual void setLabel(const char* text) = 0; }; Delphi Side IBox = class public procedure destroyBox; virtual; stdcall; abstract; procedure init(vol: Double); virtual; stdcall; abstract; procedure grow(amount: Double); virtual; stdcall; abstract; procedure shrink(amount: Double); virtual; stdcall; abstract; procedure setID(val: Integer); virtual; stdcall; abstract; procedure setLabel(text: PChar); virtual; stdcall; abstract; end; TMyBox = class(IBox) protected FVolume: Double; FID: Integer; FLabel: String; // public constructor Create; destructor Destroy; override; // BEGIN Virtual Method implementation procedure destroyBox; override; stdcall; // empty - Dont need/want C++ to manage my Delphi objects, just call their methods procedure init(vol: Double); override; stdcall; // FVolume := vol; procedure grow(amount: Double); override; stdcall; // Inc(FVolume, amount); procedure shrink(amount: Double); override; stdcall; // Dec(FVolume, amount); procedure setID(val: Integer); override; stdcall; // FID := val; procedure setLabel(text: PChar); override; stdcall; // Stub method; empty. // END Virtual Method implementation property Volume: Double read FVolume; property ID: Integer read FID; property Label: String read FLabel; end; I would have half expected using stdcall alone to work, but something is messing up, not sure what, perhaps something to do with the ECX register being used? Help would be greatly appreciated. Edit 2010-04-19 17:42 Could it be that the ECX register needs to be preserved on entry and restored once the function exits? Is the this pointer required by C++? I'm probably just reaching at the moment based on some intense Google searches. I found something related, but it seems to be dealing with the reverse of this issue.

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• Why isn't Hadoop implemented using MPI?

  - by artif

  Correct me if I'm wrong, but my understanding is that Hadoop does not use MPI for communication between different nodes. What are the technical reasons for this? I could hazard a few guesses, but I do not know enough of how MPI is implemented "under the hood" to know whether or not I'm right. Come to think of it, I'm not entirely familiar with Hadoop's internals either. I understand the framework at a conceptual level (map/combine/shuffle/reduce and how that works at a high level) but I don't know the nitty gritty implementation details. I've always assumed Hadoop was transmitting serialized data structures (perhaps GPBs) over a TCP connection, eg during the shuffle phase. Let me know if that's not true.

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