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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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• Is there a c++ library that provides functionality to execute an external program and read its outpu

  - by BD at Rivenhill

  Basically, I'm looking for something that will allow me to replicate the following Perl code: my $fh = new FileHandle; $fh->open("foo |"); while (<$fh>) { # Do something with this line of data. } This is in the context of Linux, so a library that is specific to Windows will not help. I know how to write a program that does fork/exec/dup2 and all that basic shell-type jazz, but there are some fiddly details involving terminals that I don't feel like messing around with (and I don't have a copy of "Advanced Programming in the UNIX Environment" or a similar reference handy), so I'm hoping that someone has already solved this problem.

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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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• What is your favorite Project Euler question?

  - by A. Rex

  I was searching around for questions related to Project Euler on Stack Overflow, and it seems that there were plenty of people asking about it, and even more people recommending it, whether for fun, to learn a new language, or to practice for interview questions. All this seems to imply to me that there are lots of people on SO that solve Project Euler problems now and then. I just started, so I was wondering: What was your favorite Project Euler question? Why? Did you think of a clever trick, or did you learn some new math, or did you discover a feature of a new programming language? (If possible, please include the actual question in your answer.)

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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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• 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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• 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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• 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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• Keeping track of threads when creating them recursively

  - by 66replica

  I'm currently working on some code for my Programming Languages course. I can't post the code but I'm permitted to talk about some high level concepts that I'm struggling with and receive input on them. Basically the code is a recursive DFS on a undirected graph that I'm supposed to convert to a concurrent program. My professor already specified that I should create my threads in the recursive DFS method and then join them in another method. Basically, I'm having trouble thinking of how I should keep track of the threads I'm creating so I can join all of them in the other method. I'm thinking an array of Threads but I'm unsure how to add each new thread to the array or even if that's the right direction.

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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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• 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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• 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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• the use of private keyword

  - by LAT

  Hi everyone I am new to programming. I am learning Java now, there is something I am not really sure, that the use of private. Why programmer set the variable as private then write , getter and setter to access it. Why not put everything in public since we use it anyway. public class BadOO { public int size; public int weight; ... } public class ExploitBadOO { public static void main (String [] args) { BadOO b = new BadOO(); b.size = -5; // Legal but bad!! } } I found some code like this, and i saw the comment legal but bad. I don't understand why, please explain me.

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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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• Do (statically linked) DLLs use a different heap than the main program?

  - by happy_emi

  I'm new to Windows programming and I've just "lost" two hours hunting a bug which everyone seems aware of: you cannot create an object on the heap in a DLL and destroy it in another DLL (or in the main program). I'm almost sure that on Linux/Unix this is NOT the case (if it is, please say it, but I'm pretty sure I did that thousands of times without problems...). At this point I have a couple of questions: 1) Do statically linked DLLs use a different heap than the main program? 2) Is the statically linked DLL mapped in the same process space of the main program? (I'm quite sure the answer here is a big YES otherwise it wouldn't make sense passing pointers from a function in the main program to a function in a DLL). I'm talking about plain/regular DLL, not COM/ATL services EDIT: By "statically linked" I mean that I don't use LoadLibrary to load the DLL but I link with the stub library

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• What is an instance of a field called?

  - by waxwing

  This might be an odd question, but it has actually caused me some headache. In Object oriented programming, there are accepted names for key concepts. In our model, we have classes with methods and fields. Now, going to the data world: An instance of a class is called an object. An instance of a field is called... what? A value? Isn't the term value a little broad for this? I have been offered "property" as well, but isn't property also part of the model and not the data? (This is not purely academic, I am actually coding these concepts.)

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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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• C++ code generation for repeted task

  - by sateesh

  Hi, I have something like below which will get repeated many times based on the function that get called for e.g acceptfunction() { inserter["quantity"] = sdd.getfloat(quantity); inserter["prodtype"] = sdd.getstring(prodtype); : : so on } Like accept above there are 20 more functions(reject,cancel etc) which will do the similar thing.But the parameteres they insert can differ based on function called. How can I automate this kind of code.So that I dont need to write new function from scratch.Basically what I need is if i provide parametres like ("quantity",prodtype) through some text file or xml, it should generate the required function with the input parametres. Is this task can be handled through C++ tempalte Meta programming or someother code generation tool will help me to do this?

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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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• How can I declare a pointer structure using {}?

  - by Y_Y

  This probably is one of the easiest question ever in C programming language... I have the following code: typedef struct node { int data; struct node * after; struct node * before; }node; struct node head = {10,&head,&head}; Is there a way I can make head to be *head [make it a pointer] and still have the availability to use '{ }' [{10,&head,&head}] to declare an instance of head and still leave it out in the global scope? For example: //not legal!!! struct node *head = {10,&head,&head};

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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 compiling circular dependencies works?

  - by Fabio F.

  I've made the example in Java but I think (not tested) that it works in other (all?) languages. You have 2 files M.java that says public class MType{ XType x; MType(){ x = null;} } and another file XType.java (in the same directory) public class XType{ MType m; public XType(MType m){ this.m=m;} } Ok it's BAD programming , but.. if you run javac XType it compiles: compiles even MTypes because XType needs it. But.. MType needs XType.. how it works? How does the compiler know what is happening? Probably is a stupid question, but I would like to know how the compiler (javac or other compilers if you know.) manages that situation, not how to avoid it. I'm asking because i'm writing a precompiler and I would like to manage that situation.. Thank you

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• How can I get the domain name for a user logged into a Mac via Active Directory

  - by Lawrence Johnston

  In my Cocoa app how can I get the current user's domain when they're logged in via Active Directory? I need to determine two things: 1. If the current user is logged on to an Active Directory domain (only need to handle Active Directory). 2. If 1, the domain of the user. I've found references to Directory Services and the Open Directory Programming Guide but the latter is 10.6 only (I must support 10.5+) and I could not find any examples for the former that gave me an idea of what I needed to do.

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• Is there a server side API for Team Foundaion Server

  - by Ralph Shillington

  It would seem there is precious little documentation on programming against a TFS 2010 instance. What bits I have found, have next to nothing in the case of documentation beyond barebones listing of client access classes and their members, most likely autogenerated from the code comments. As I'm interested in building a silverlight client against TFS, I will need access to server side API (ideally the silverlight app will talk to my server (mainly for work items) and my server will in turn talk to the TFS server for the goods. Where is the doumentation (if any) for this kind of TFS integration?

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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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