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  • Does a static object within a function introduce a potential race condition?

    - by Jeremy Friesner
    I'm curious about the following code: class MyClass { public: MyClass() : _myArray(new int[1024]) {} ~MyClass() {delete [] _myArray;} private: int * _myArray; }; // This function may be called by different threads in an unsynchronized manner void MyFunction() { static const MyClass _myClassObject; [...] } Is there a possible race condition in the above code? Specifically, is the compiler likely to generate code equivalent to the following, "behind the scenes"? void MyFunction() { static bool _myClassObjectInitialized = false; if (_myClassObjectInitialized == false) { _myClassObjectInitialized = true; _myClassObject.MyClass(); // call constructor to set up object } [...] } ... in which case, if two threads were to call MyFunction() nearly-simultaneously, then _myArray might get allocated twice, causing a memory leak? Or is this handled correctly somehow?

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  • How do I prevent race condition WITHOUT using locks in C++?

    - by Hristo
    How do I prevent a race condition WITHOUT locking or using mutexes/semaphors in C++? I'm dealing with a nested for loop in which I will be setting a value in an array: for (int i = 0; i < m; ++i) for (int j = 0; j < n; ++j) for (int k = 0; k < o; ++k) array[k] += foo(...); More or less, I want to deal with this so that I can ensure different threads running at the same time don't write to array[k] at the same time. Any suggestions on how to approach this? Edit: I am running on a Linux machine and I also have to use the Intel compiler. I will be using "icc" instead of "gcc" to compile the code.

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  • How to set user environment variables in Windows Server 2008 R2 as a normal user?

    - by likm
    In older versions of Windows, it was just open the Control Panel, select the System applet, select the Advanced tab, and then hit the Environment variables button. As a normal user, you could edit the "User variables" but not the "System variables". In Windows Server 2008 R2, if I try to hit the Advanced System settings option in the System applet, it prompts for the Administrator password.

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  • Will my shared variables loose value? (asp.net vb)

    - by Phil
    I have a class includes.vb that holds some variables (sharing them with other pages) like: Public Shared pageid As Integer = 0 I then have a function that does some work with these variables returning them with values; Return pageid When I step through the code, the variables have values (while stepping through the function), but when they are returned to the page, they come back null. Do they loose value everytime a page is loaded? Can you suggest an alternative method? Thanks a lot.

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  • SSIS Basics: Introducing Variables

    In the third of her SSIS Basics articles, Annette Allen shows you how to use Variables in your SSIS Packages, and explains the functions of the system-defined variables. Are you sure you can restore your backups? Run full restore + DBCC CHECKDB quickly and easily with SQL Backup Pro's new automated verification. Check for corruption and prepare for when disaster strikes. Try it now.

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  • Using Variables Within Crystal Report Formulas

    This article demonstrates how to create formulas in a Crystal Report and use the Crystal scripting language to create variables, use built in functions, perform conditional logic, and manipulate dates. After a brief introduction, the article provides the steps required to create the database, the website, and the report, including how to add fields and formulas to the report. Near the end, the article examines the steps required to create formulas with variables.

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  • More Server Variables in ASP.NET 3.5

    The first part of this series served as a basic introduction to server variables and their application in ASP.NET 3.5. You learned how to output server variables using classic ASP tags and using ASP.NET visual basic code file. This article will pick up where the previous part left off.... GoGrid Cloud Center Connect Cloud and Dedicated Servers on Your Private Data Center

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  • More than 5 custom variables across multiple websites using Google Analytics

    - by brakes
    We have multiple websites using the same Google Analytics account number so we can track visitors across multiple websites. One of these websites has set 5 custom variables. We want to introduce a new custom variable to track logged in users for our single sign-on (SSO) system to find out what parts of which website they are accessing. Is this possible or is it a case that all the custom variables have been used up by 1 of the sites?

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  • How do I make this Java code operate properly? [Multi-threaded, race condition]

    - by Fixee
    I got this code from a student, and it does not work properly because of a race condition involving x++ and x--. He added synchronized to the run() method trying to get rid of this bug, but obviously this only excludes threads from entering run() on the same object (which was never a problem in the first place) but doesn't prevent independent objects from updating the same static variable x at the same time. public class DataRace implements Runnable { static volatile int x; public synchronized void run() { for (int i = 0; i < 10000; i++) { x++; x--; } } public static void main(String[] args) throws Exception { Thread [] threads = new Thread[100]; for (int i = 0; i < threads.length; i++) threads[i] = new Thread(new DataRace()); for (int i = 0; i < threads.length; i++) threads[i].start(); for (int i = 0; i < threads.length; i++) threads[i].join(); System.out.println(x); // x not always 0! } } Since we cannot synchronize on x (because it is primitive), the best solution I can think of is to create a new static object like static String lock = ""; and enclose the x++ and x-- within a synchronized block, locking on lock. But this seems really awkward. Is there a better way?

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  • Marionette js itemview not defined: then on browser refresh it is defined and all works well - race condition?

    - by Robert
    Yeah it's just the initial browser load or two after a cache clear. Subsequent refreshes clear the problem up. I'm thinking the item views just aren't fully constructed in time to be used in the collection views on the first load. But then they are on a refresh? Don't know. There must be something about the code sequence or loading or the load time itself. Not sure. I'm loading via require.js. Have two collections - users and messages. Each renders in its own list view. Each works, just not the first time or two the browser loads. The first time you load after clearing browser cache the console reports, for instance: "Uncaught ReferenceError: MessageItemView is not defined" A simple browser refresh clears it up. Same goes for the user collection. It's collection view says it doesn't know anything about its item view. But a simple browser refresh and all is well. My views (item and collection) are in separate files. Is that the problem? For instance, here is my message collection view in its own file: messagelistview.js var MessageListView = Marionette.CollectionView.extend({ itemView: MessageItemView, el: $("#messages") }); And the message item view is in a separate file: messageview.js var MessageItemView = Marionette.ItemView.extend({ tagName: "div", template: Handlebars.compile( '<div>{{fromUserName}}:</div>' + '<div>{{message}}</div>' + ) }); Then in my main module file, which references each of those files, the collection view is constructed and displayed: main.js //Define a model MessageModel = Backbone.Model.extend(); //Make an instance of MessageItemView - code in separate file, messagelistview.js MessageView = new MessageItemView(); //Define a message collection var MessageCollection = Backbone.Collection.extend({ model: MessageModel }); //Make an instance of MessageCollection var collMessages = new MessageCollection(); //Make an instance of a MessageListView - code in separate file, messagelistview.js var messageListView = new MessageListView({ collection: collMessages }); App.messageListRegion.show(messageListView); Do I just have things sequenced wrong? I'm thinking it's some kind of race condition only because over 3G to an iPad the item views are always undefined. They never seem to get constructed in time. PC on a hard wired connection does see success after a browser refresh or two.

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  • MySQL – Introduction to User Defined Variables

    - by Pinal Dave
    MySQL supports user defined variables to have some data that can be used later part of your query. You can save a value to a variable using a SELECT statement and later you can access its value. Unlike other RDBMSs, you do not need to declare the data type for a variable. The data type is automatically assumed when you assign a value. A value can be assigned to a variable using a SET command as shown below SET @server_type:='MySQL'; When you above command is executed, the value, MySQL is assigned to the variable called @server_type. Now you can use this variable in the later part of the code. Suppose if you want to display the value, you can use SELECT statement. SELECT @server_type; The result is MySQL. Once the value is assigned it remains for the entire session until changed by the later statements. So unlike SQL Server, you do not need to have this as part the execution code every time. (Because in SQL Server, the variables are execution scoped and dropped after the execution). You can give column name as below SELECT @server_type AS server_type; You can also SELECT statement to DECLARE and SELECT the values for a variable. SELECT @message:='Welcome to MySQL' AS MESSAGE; The result is Message -------- Welcome to MySQL You can make use of variables to effectively apply many logics. One of the useful method is to generate the row number as shown in this post MySQL – Generating Row Number for Each Row using Variable. Reference: Pinal Dave (http://blog.sqlauthority.com)Filed under: MySQL, PostADay, SQL, SQL Authority, SQL Query, SQL Tips and Tricks, T SQL

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  • Need help eliminating dead code paths and variables from C source code

    - by Anjum Kaiser
    I have a legacy C code on my hands, and I am given the task to filter dead/unused symbols and paths from it. Over the time there were many insertions and deletions, causing lots of unused symbols. I have identified many dead variables which were only being written to once or twice, but were never being read from. Both blackbox/whitebox/regression testing proved that dead code removal did not affected any procedures. (We have a comprehensive test-suite). But this removal was done only on a small part of code. Now I am looking for some way to automate this work. We rely on GCC to do the work. P.S. I'm interested in removing stuff like: variables which are being read just for the sake of reading from them. variables which are spread across multiple source files and only being written to. For example: file1.c: int i; file2.c: extern int i; .... i=x;

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  • How should I group these variables?

    - by stariz77
    I have a shape that will be defined by: char s_type; char color; double height; double width; These variables are scanned in from a request string sent to my server and passed into my printing function, which then prints out the shape. Currently they are just local variables sitting in my main(); however, I was wondering if there would be any advantage in creating a struct containing these variables, and then passing the struct to my printing function? or how else might I improve my program's structure/style, would passing a struct by reference have any kind of performance benefit if there were many requests and therefore many printing function calls? printer(char st, char cr, double ht, double wd); int main() { // Other main functionality. char s_type; char color; double height; double width; sscanf (serv_req, "GET /%c/%c/%lf/%lf", &s_type, &color, &height, &width); printer(s_type, color, height, width); // Other main functionality. return 0; } It seemed "neater" if I had a struct or something that didn't leave me with declarations in the middle of everything else going on in main. I'm interested in structure/style as well as performance. EDIT: didn't mean to put printer declaration inside main.

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  • PowerPivot FILTER condition optimizations

    - by Marco Russo (SQLBI)
    In the comments of a recent post from Alberto Ferrari there was an interesting note about different performance related to the order of conditions in a FILTER call. I investigated about that and Jeffrey Wang has been so nice to give me some info about actual implementation that I can share on a blog post. First of all, an important disclaimer: PowerPivot is intended to make life easier, not requiring the user to think how to write the order of elements in a formula just to get better performance....(read more)

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  • PowerPivot FILTER condition optimizations

    - by Marco Russo (SQLBI)
    In the comments of a recent post from Alberto Ferrari there was an interesting note about different performance related to the order of conditions in a FILTER call. I investigated about that and Jeffrey Wang has been so nice to give me some info about actual implementation that I can share on a blog post. First of all, an important disclaimer: PowerPivot is intended to make life easier, not requiring the user to think how to write the order of elements in a formula just to get better performance....(read more)

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  • improve if else statement for multiple condition

    - by kitokid
    My superior said the following is bad code. But he didn't mention anything how to improve it. What might be the alternative elegant way of coding below statements, without using if else? if(name.equalsIgnoreCase("AAA")){ //do something }else if(name.equalsIgnoreCase("BBB")){ //do something }else if(name.equalsIgnoreCase("CCC")){ //do something }else if(name.equalsIgnoreCase("DDD")){ //do something }else if(name.equalsIgnoreCase("EEE")){ //do something }else{ //do something } Edited: I am using Java 6.

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  • Avoid Code Repetition in Condition Statements

    - by Ethosik
    I have been programming for over 15 years now. I consider myself a very good programmer, but I understand (like all of us) there are things that I need to work on. One of these things is code repetition when dealing with conditions. I will give a generic sample: if(condition1) { //perform some logic if(condition2) { //perform some logic if(condition3) { //Perform logic } else { //MethodA(param) } } else { //MethodA(param) } } else { //MethodA() } Now, I cannot make it easy by doing the following: if(condition1 && condition2) { } else { } I cannot do this since I need to perform some logic if condition1 is true and before I test condition2. Is there a way to structure if...else blocks to where if you need to call a method in each else blocks, you are not repeating yourself?

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  • If and else condition not working properly in xna [closed]

    - by user1090751
    I am developing chess like game and i wanted to show error message if user try to place any player inside the box which is not empty. For example in certain place if there is empty then the object(2d object) is placed else it should show error message. However in my program it is showing message everytime i.e when i place object on empty place then also it is showing error message. Please see the below code: protected override void Update(GameTime gameTime) { // Allows the game to exit if (GamePad.GetState(PlayerIndex.One).Buttons.Back == ButtonState.Pressed) this.Exit(); // TODO: Add your update logic here for (int i = 0; i < 25; i++) { MouseState mouseState; mouseDiBack = false; mouseState = Mouse.GetState(); if (new Rectangle(mouseState.X, mouseState.Y, 1, 1).Intersects(rect_arr[i])) { background_color_arr[i] = Color.Red; } else { background_color_arr[i] = Color.White; } if (new Rectangle(mouseState.X, mouseState.Y, 1, 1).Intersects(rect_arr[i]) && (mouseState.LeftButton == ButtonState.Pressed)) { if (boxes[i] != "goat" && boxes[i] != "tiger") { place = i; if (turn == "goat") { boxes[i] = "goat"; turn = "tiger"; } else { boxes[i] = "tiger"; turn = "goat"; } } else { errMsg = "This " + i + " block is not empty to place " + turn + ". Please select empty block!!"; } } } base.Update(gameTime); }

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  • How can I pass environment variables to a WSGI script, using uWSGI?

    - by orokusaki
    I've added the following line to /etc/environment: FOO_DEPLOYMENT_ENV="vbox" Upon logging in via SSH, I can echo $FOO_DEPLOYMENT_ENV and, of course, see vbox output to the shell. If I open a Python shell and run os.getenv('FOO_DEPLOYMENT_ENV'), it will return 'vbox', but the same code in my Python application, when run by uWSGI (as the www-data user), it does not see the environment variable. Clearly, this isn't a problem of uWSGI, and is rather a problem with my understanding of environment variables, or how they're properly set, and the contexts in which they can be retrieved. What am I doing or understanding incorrectly?

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  • NullReferenceException when accessing variables in a 2D array in Unity

    - by Syed
    I have made a class including variables in Monodevelop which is: public class GridInfo : MonoBehaviour { public float initPosX; public float initPosY; public bool inUse; public int f; public int g; public int h; public GridInfo parent; public int y,x; } Now I am using its class variable in another class, Map.cs which is: public class Map : MonoBehaviour { public static GridInfo[,] Tile = new GridInfo[17, 23]; void Start() { Tile[0,0].initPosX = initPosX; //Line 49 } } I am not getting any error on runtime, but when I play in unity it is giving me error NullReferenceException: Object reference not set to an instance of an object Map.Start () (at Assets/Scripts/Map.cs:49) I am not inserting this script in any gameobject, as Map.cs will make a GridInfo type array, I have also tried using variables using GetComponent, where is the problem ?

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  • Clean Code says to avoid protected variables

    - by Matsemann
    I have a question to a statement in Clean Code. I don't fully understand the reasoning to why we should avoid protected variables. It's from the chapter about Formatting, section about Vertical Distance: Concepts that are closely related should be kept vertically close to each other. Clearly this rule doesn't work for concepts that belong in separate files. But then closely related concepts should not be separated into different files unless you have a very good reason. Indeed, this is one of the reasons that protected variables should be avoided.

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  • Missed environment variables in Eclipse Juno

    - by hara
    I recently moved from Eclipse Indigo to Juno. I installed the IDE in my Ubuntu 12.04 by downloading the archive from here. Then I created an entry in the unity launcher for Juno as I done before for Indigo. Here is what I wrote in ~/.local/share/applications/eclipse-juno.desktop: [Desktop Entry] Type=Application Name=Eclipse Juno Comment=Eclipse Integrated Developmentm Environment Icon=~/.eclipse-juno/icon.xpm Exec=~/.eclipse-juno/eclipse -vmargs -Duser.name="my name" Terminal=false Categories=Development;IDE;Java; When I run eclipse from the unity launcher, eclipse does not see environment variables that I set in ~/.bascrc. Instead, if I run eclipse from shell, it can see all the env variables. How can I fix the problem? Thanks a lot.

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  • Unable to access A class variables in B Class - Unity-Monodevelop

    - by Syed
    I have made a class including variables in Monodevelop which is: public class GridInfo : MonoBehaviour { public float initPosX; public float initPosY; public bool inUse; public int f; public int g; public int h; public GridInfo parent; public int y,x; } Now I am using its class variable in another class, Map.cs which is: public class Map : MonoBehaviour { public static GridInfo[,] Tile = new GridInfo[17, 23]; void Start() { Tile[0,0].initPosX = initPosX; //Line 49 } } Iam not getting any error on runtime, but when I play in unity it is giving me error NullReferenceException: Object reference not set to an instance of an object Map.Start () (at Assets/Scripts/Map.cs:49) I am not inserting this script in any gameobject, as Map.cs will make a GridInfo type array, I have also tried using variables using GetComponent, where is the problem ?

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  • Naming conventions used for variables and functions in C

    - by Zel
    While coding a large project in C I came upon a problem. If I keep on writing more code then there will be a time when it will be difficult for me to organize the code. I mean that the naming for functions and variables for different parts of the program may seem to be mixed up. So I was thinking whether there are useful naming conventions that I can use for C variables and functions? Most languages suggest a naming convention. But for C the only thing I have read so far is the names should be descriptive for code readability. EDIT: Examples of some examples of suggested naming conventions: Python's PEP 8 Java Tutorial I read some more naming conventions for java somewhere but couldn't remember where.

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