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• Are spinlocks a good choice for a memory allocator?

  - by dsimcha

  I've suggested to the maintainers of the D programming language runtime a few times that the memory allocator/garbage collector should use spinlocks instead of regular OS critical sections. This hasn't really caught on. Here are the reasons I think spinlocks would be better: At least in synthetic benchmarks that I did, it's several times faster than OS critical sections when there's contention for the memory allocator/GC lock. Edit: Empirically, using spinlocks didn't even have measurable overhead in a single-core environment, probably because locks need to be held for such a short period of time in a memory allocator. Memory allocations and similar operations usually take a small fraction of a timeslice, and even a small fraction of the time a context switch takes, making it silly to context switch in the case of contention. A garbage collection in the implementation in question stops the world anyhow. There won't be any spinning during a collection. Are there any good reasons not to use spinlocks in a memory allocator/garbage collector implementation?

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• why am i getting an error SyntaxError : invalid syntax for this code

  - by eragon1189

  This is a code in python which calculates f (x) =? ((-1)*x)/(x*x+n*n) n from 1 to infinite.... correct to 0.0001, for the range 1 < x < 100 in steps of 0.1.But i am getting an syntax error,as i am new to programming in python... from scipy import * from matplotlib.pyplot import * x=arange(0.1,100,0.1) f=zeros(len(x)) s=-1 for n in range (1,10000): t=s*x/(x*x+n*n) f +=t s =-s if max(abs(t))< 1e-4 break for xx in c_[x,f]: print "%f %f" % (xx[0],xx[1])

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• iPhone xcode - Best way to control audio from several view controllers

  - by Are Refsdal

  Hi, I am pretty new to iPhone programming. I have a navBar with three views. I need to control audio from all of the views. I only want one audio stream to play at a time. I was thinking that it would be smart to let my AppDelegate have an instance of my audioplaying class and let the three other views use that instance to control the audio. My problem is that I don´t know how my views can use the audioplaying class in my AppDelegate. Is this the best approach and if so, how? Is there a better way?

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• Heap property of this array

  - by davit-datuashvili

  From programming pearls, it is known that array[1...n] has heap property if for all 2<=i<=n x[i/2]<=x[i]. Here is my code: import java.math.*; public class Heap { public static void main(String[]args){ int x[]=new int[]{12,20,15,29,23,17,22,35,40,26,51,19}; int i=1; while (i<x.length) { if (x[Math.round(i/2)]<=x[i]) System.out.println("heap"); i++; } System.out.println("not heap"); } } Here I used Math.round because 4/2 and 5/2 is same and =2. When I compile this code it shows me at last line that it is not heap. Maybe because the index starts from 1 and we don't pay attention to index 0, yes?

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• Querying associated images in one table after querying products from another

  - by Andy

  I used this code to connect to a database and fetch results. This worked perfectly until i tried to work in another query to the images table to get associated images. I'm not very experienced with OO programming. So hopefully someone can see where ive gone wrong and help me out. <?php global $__CMS_CONN__; $sql = "SELECT * FROM ecom_products"; $stmt = $__CMS_CONN__->prepare($sql); $stmt->execute(array($id)); while ($row = $stmt->fetchObject()) { $imagesql = "SELECT * FROM ecom_product_images where id = $row->id && where primaryImage = '1'"; $imagestmt = $__CMS_CONN__->prepare($sql); $imagestmt->execute(array($id)); $imageName = $imagestmt->fetchObject(); echo '<a href="'.URL_PUBLIC.$row->id.'">'.$row->productNm.'</a>'.$imageName; } ?>

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• Sync database from desktop system to remote server and vice versa?

  - by qulzam

  I make a application, which has to interfaces. one is desktop and other is web application. both have their own databases (which are same is structure). I want to sync the database from desktop to remote server and also from remote server to desktop but i have no idea that how it does. I use the MYSql database. and my desktop application is in .NET NOTE: There are more than one destop systems who update their databases and also sync databases.

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• C++ Types Impossible to Name

  - by Kirakun

  While reading Wikipedia's page on decltype, I was curious about the statement, Its [decltype's] primary intended use is in generic programming, where it is often difficult, or even impossible, to name types that depend on template parameters. While I can understand the difficulty part of that statement, what is an example where there is a need to name a type that cannot be named under C++03? EDIT: My point is that since everything in C++ has a declaration of types. Why would there ever be a case where it is impossible to name a type? Furthermore, aren't trait classes designed to yield type informations? Could trait classes be an alternative to decltype?

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• VBA long overflow

  - by HK_CH

  Hi I am trying to do some maths with my VBA excel (prime factorization) and I am hitting the limit of the long data type (runtime error 6 Overflow). Is there any way to get around this and still stay within VBA? (I am aware that the obvious one would be to use another more appropriate programming language) Thanks for help in advance! Thank you, it works in so far that I am able to get the big numbers into the variables now. However when I try to apply the MOD function (bignumber MOD 2 for example) it still fails with error message runtime error 6 Overflow.

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• Win32_PageFileUsage WMI call returning 0 for CurrentUsage

  - by Ryan Duffield

  I am querying for the current page file usage on Windows-based systems. This is meant to run on the .NET Framework, version 2.0 SP1 and has been tested (and works!) on Windows Vista, Windows 7, Windows Server 2003 R2 and Windows Server 2008. On Windows Server 2003 SP2 (original release, not R2) it appears to return 0: using (var query = new ManagementObjectSearcher("SELECT CurrentUsage FROM Win32_PageFileUsage")) { foreach (ManagementBaseObject obj in query.Get()) { uint used = (uint)obj.GetPropertyValue("CurrentUsage"); return used; } } This is simply returning the results from the first row returned for the WMI call. Even when a page file is being used, it returns 0. What causes the result to be 0 when it should be returning a larger value? It may be something specific to the machine in question, and could have nothing to do with the operating system version. I've also tried this with and without elevated privileges with the same results.

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• What workflow should I use for JavaScript editing?

  - by Patrick

  Warning: I have very little JavsScript experience. In my past programming experience, I usually have a standalone interpreter/compiler, a text editor and a command line to compile/run my software or my tests (I love test driven development). I really like it this way, since I have the feeling of being in complete control over the tools. However, editing JavaScript I need to put statements in a text file , open my web browser and click on reload. I don't feel comfortable with it, as I cannot really see what is going on (besides some alert boxes). Can you suggest me (I'm on a Mac) another workflow? Perhaps with a debugger? Is there a standalone JavaScript interpreter?

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• Lib Files and Defines

  - by Paul

  I'm using a couple of external libraries and I'd rather not have to include all their source and header files in my main source directory or in my project file. One option would be to compile the libraries as lib files and link them like that. However I'm not sure the defines get evaluated before or after the lib file gets created (which one is it?). If it's before then obviously I can't just pack them because they might not work properly on different compilers or systems. So if I can't pack the libraries as lib files, is there any way for me to link in the c or cpp source files? Probably not, since they would have to be compiled first, but maybe I'm wrong. Edit: Here's a follow-up question, based on answers. Do you think it'd be too much of a hassle to have a makefile that creates the lib files? I'd still rather not add the sources to my project or in my source directory.

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• Reference variable to an object instantiated/initialized in another class in Java

  - by Alex

  The reason I'm asking is because I'm getting NullPointerException. I now this is very easy but I'm pretty new programming and find this a bit confusing. So say I have initialized an object in a class and want to access that same object from another class. Like now for instance I'm working on a small Chess game, in my model Game class I have an instance of Board, an object. Board, in turn, has an array of Squares. Square[][]. Game has board, board has Square[][]. Now if I want to access the Square[][] through the object board (in Game) of type Board. Do I just declare a variable with the same name and type or do I have to initialize it again? Board board OR Board board = new Board(); Note, I have already initialized board in the class Game so if I do it again, won't they be two totally different Board objects?

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• Are C++ Templates just Macros in disguise?

  - by Roddy

  I've been programming in C++ for a few years, and I've used STL quite a bit and have created my own template classes a few times to see how it's done. Now I'm trying to integrate templates deeper into my OO design, and a nagging thought keeps coming back to me: They're just a macros, really... You could implement (rather UGLY) auto_ptrs using #defines, if you really wanted to. This way of thinking about templates helps me understand how my code will actually work, but I feel that I must be missing the point somehow. Macros are meant evil incarnate, yet "template metaprogramming" is all the rage. So, what ARE the real distinctions? and how can templates avoid the dangers that #define leads you into, like Inscrutable compiler errors in places where you don't expect them? Code bloat? Difficulty in tracing code? Setting Debugger Breakpoints?

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• displaying the different uploaded files as thumbnails or any other way

  - by user1529342

  I have written code to upload the files of different types using php, and also i am saving their location information and date in database table. i made a query to display list of files i have uploaded...and resulting output on a html page as follows 1.uploads/clouds.png date and time 2.uploads/resume.pdf dare and time .......so on is there any different any way to display them by their file types as like an operating systems do..... or any better way.... I am curious to know it... Thanks for any help...

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• Array Related Doubt.......

  - by AGeek

  I have the following program........... int insert(int *array, int arraySize, int newElement) { array[arraySize + 1] = newElement; return (arraySize+1); // Return new Array size...... } int main() { int array[] = {1,2,3,4,5}; int arraySize = sizeof(array) / sizeof(int); insertInArray(array, arraySize,6); print(array); } I am trying to work out this program in C programming language... But when i print the array after insertion,,, it doesn't prints the desired output which is needed.. Please correct me if i am doing something wrong..... Thanks..

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• Python recursive program

  - by mathboy

  I'm relatively newcomer on programming as I'm educated a mathematician and have no experience on Python. I would like to know how to solve this problem in Python which appeared as I was studying one maths problem on my own: Program asks a positive integer m. If m is of the form 2^n-1 it returns T(m)=n*2^{n-1}. Otherwise it writes m to the form 2^n+x, where -1 < x < 2^n, and returns T(m)=T(2^n-1)+x+1+T(x). Finally it outputs the answer.

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• Closed Source Java Applications

  - by Paul

  I am taking programming courses and we have been discussing Open Source and having a bit of an argument over the confusion. Just because Java is Open Source, the licensing on developed applications starts at the developer, correct? Someone is arguing about the use of code from a complete program just because "Java is Open Source". If I write a Java application, what are the limitations on how I can distribute it or how someone else can use it? Assume here that I DO NOT want someone having access to my source. Thanks

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• python: find and replace numbers < 1 in text file

  - by hjp

  I'm pretty new to Python programming and would appreciate some help to a problem I have... Basically I have multiple text files which contain velocity values as such: 0.259515E+03 0.235095E+03 0.208262E+03 0.230223E+03 0.267333E+03 0.217889E+03 0.156233E+03 0.144876E+03 0.136187E+03 0.137865E+00 etc for many lines... What I need to do is convert all the values in the text file that are less than 1 (e.g. 0.137865E+00 above) to an arbitrary value of 0.100000E+01. While it seems pretty simple to replace specific values with the 'replace()' method and a while loop, how do you do this if you want to replace a range? thanks

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• How to run a command on a remote Windows system as a non-admin user with WMI?

  - by John

  I have a script written in Visual Basic that starts a process (given to the script as an argument) on a remote system (again, given as an argument) using WMI. This script works fine when using an Administrator account on the remote system, but when using a non-administrator account, I get the following error: ConnectServer Failed w/ (-2147024891) Access is denied. I'd like to be able to run processes on remote systems as a non-administrator user with this script, and I'm pretty sure the problem is due to security settings on the remote system, but I've not been able to reset the right ones.

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• How to handle huge table ?

  - by misha-moroshko

  I would like to display to user a table which contains ~500,000 rows. The table should be calculated based on a file (i.e. the table is known at the beginning, and does not change). I guess that building the HTML text of this table is not a good idea in terms of memory performance. So how can I build such table ? I would like user to be able to scroll the table using a vertical scroll bar. Is it possible to build on the fly only the visible part of the table ? I'm afraid to see delays because of this. Is it a better idea to use server side programming rather than Javascript ? Any advise would be appreciated.

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• Drawing unfilled rectangle shape in c++ openGL

  - by Bahaa

  I want to draw unfilled rectangle shape in openGL using c++ programming language but when I used the glBegin(GL_QUADS) or glBegin(GL_POLYGON), the resulted shape is filled but I want to be unfilled. How I can draw unfilled rectangle. void draweRect(void) { glClear(GL_COLOR_BUFFER_BIT); glColor3f(0.0,0.0,1.0); glLineWidth(30); glBegin(GL_POLYGON); glVertex2i(50,90); glVertex2i(100,90); glVertex2i(100,150); glVertex2i(50,150); glEnd(); glFlush(); }

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• Python design mistakes

  - by Andrea

  A while ago, when I was learning Javascript, I studied Javascript: the good parts, and I particularly enjoyed the chapters on the bad and the ugly parts. Of course, I did not agree with everything, as summing up the design defects of a programming language is to a certain extent subjective - although, for instance, I guess everyone would agree that the keyword with was a mistake in Javascript. Nevertheless, I find it useful to read such reviews: even if one does not agree, there is a lot to learn. Is there a blog entry or some book describing design mistakes for Python? For instance I guess some people would count the lack of tail call optimization a mistake; there may be other issues (or non-issues) which are worth learning about.

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• Expected symbol problems with this function declaration

  - by Derek

  I am just getting back into the C programming realm and I am having an issue that I think is linker related. I am using cmake for the first time as well, so that could be adding to my frustration. I have included a third party header file that contains a typedef that my code is trying to use, and it has this line: typedef struct a a_t so my code has a_t *var; //later..... var->member;// this line throws the error which throws the error: dereferencing pointer to incomplete type So am I just missing another include file, or is this a linker issue? I am building this code in QtCreator and using cmake. I can dive on a_t to see that typedef declaration in the included header, but I can't seem to dive on "struct a" itself to see where it's coming from. Thanks

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• Good real-world uses of metaclasses (e.g. in Python)

  - by Carles Barrobés

  I'm learning about metaclasses in Python. I think it is a very powerful technique, and I'm looking for good uses for them. I'd like some feedback of good useful real-world examples of using metaclasses. I'm not looking for example code on how to write a metaclass (there are plenty examples of useless metaclasses out there), but real examples where you have applied the technique and it was really the appropriate solution. The rule is: no theoretical possibilities, but metaclasses at work in a real application. I'll start with the one example I know: Django models, for declarative programming, where the base class Model uses a metaclass to fill the model objects of useful ORM functionality from the attribute definitions. Looking forward to your contributions.

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• How do you plan for starting a new web system?

  - by Kerry

  I've been creating more and more systems recently and I find more and more planning and preparation I do before starting the project. I determine what libraries or frameworks I will be using, what languages, the basic architecture of how the site will flow, etc. I've also heard of other design processes such as hanging styrofoam balls to show where classes are and how they relate, which is a process I've never heard of nor do I know how it works. Is there any software that helps with this process? Are there any guidelines or steps or do you have a recommended set of steps or guidelines that you follow when designing a new project?

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