Search Results

Search found 3766 results on 151 pages for 'singleton scope'.

Page 2/151 | < Previous Page | 1 2 3 4 5 6 7 8 9 10 11 12 | Next Page >

Using singleton instead of a global static instance

- by Farstucker

I ran into a problem today and a friend recommended I use a global static instance or more elegantly a singleton pattern. I spent a few hours reading about singletons but a few things still escape me. Background: What Im trying to accomplish is creating an instance of an API and use this one instance in all my classes (as opposed to making a new connection, etc). There seems to be about 100 ways of creating a singleton but with some help from yoda I found some thread safe examples. ..so given the following code: public sealed class Singleton { public static Singleton Instance { get; private set; } private Singleton() { APIClass api = new APIClass(); //Can this be done? } static Singleton() { Instance = new Singleton(); } } How/Where would you instantiate the this new class and how should it be called from a separate class? EDIT: I realize the Singleton class can be called with something like Singleton obj1 = Singleton.Instance(); but would I be able to access the methods within the APIs Class (ie. obj1.Start)? (not that I need to, just asking) EDIT #2: I might have been a bit premature in checking the answer but I do have one small thing that is still causing me problems. The API is launching just fine, unfortunately Im able to launch two instances? New Code public sealed class SingletonAPI { public static SingletonAPI Instance { get; private set; } private SingletonAPI() {} static SingletonAPI() { Instance = new SingletonAPI(); } // API method: public void Start() { API myAPI = new API();} } but if I try to do something like this... SingletonAPI api = SingletonAPI.Instance; api.Start(); SingletonAPI api2 = SingletonAPI.Instance; // This was just for testing. api2.Start(); I get an error saying that I cannot start more than one instance.

Read the article
Singleton class in DLL used on multiple virtual directories

- by Drejc

I have the following situation: multiple virtual directories under same application pool in IIS copy of same DLL in all those directories (same version number) a singleton class in one in this DLL The question is, is this singleton class created only once for all those Virtual Directory instances or is there for each of there one singleton class. The code looks something like this: [ Transaction(TransactionOption.Supported), ClassInterface(ClassInterfaceType.AutoDispatch), Guid("7DE45C4D-19BE-4AA4-A2DA-F4D86E6502A8") ] public class SomeClass { private static readonly Singleton singleton = new Singleton();

Read the article
Can't add object to Array in jQuery's getJSON data function (scope issue)

- by seo20

I have a person object and wants to store it into a global ArrayCollection I have made. Works great in normal scope: var s = new ArrayCollection(); s.add(new person("Knud", "Mikkelsen", 35)); The problem is when I want to add people inside my jQuery function "mainFunction". I can't seem to get it right. I know it's something to do with scope and I have to wrap something in functions like in my ArrayCollection. Please help me - thanks a lot. function ArrayCollection() { var myArray = new Array; return { empty: function () { myArray.splice(0, myArray.length); }, add: function (myElement) { myArray.push(myElement); }, getAll: function () { return myArray; } } } function person(firstName, lastName, age) { this.firstName = firstName; this.lastName = lastName; this.age = parseInt(parseFloat(age)); } function mainFunction() { //.... var s = new ArrayCollection(); s.add(new person("Knud", "Mikkelsen", 35)); $.getJSON(url, function (data) { for (var x = 0; x < data.length; x++) { var myPerson = new person(data[x].FirstName.toString(), data[x].LastName.toString(), data[x].Age.toString()); s.add(myPerson); } }); alert(drawArray(s.getAll())); } function drawArray(myArray) { var v = ""; for (var i = 0; i < myArray.length; i++) { v += myArray[i].firstName + " " + myArray[i].lastName + " (" + myArray[i].age + ")\n"; } return v; }

Read the article
Changing a Variable Out of Scope?

- by Matrym

Is there any way to change a variable while out of scope? I know in general, you cannot, but I'm wondering if there are any tricks or overrides. For example, is there any way to make the following work: function blah(){ var a = 1 } a = 2; alert(blah());

Read the article
C# Anonymous method variable scope problem with IEnumerable<T>

- by PaN1C_Showt1Me

Hi. I'm trying to iterate through all components and for those who implements ISupportsOpen allow to open a project. The problem is when the anonymous method is called, then the component variable is always the same element (as coming from the outer scope from IEnumerable) foreach (ISupportsOpen component in something.Site.Container.Components.OfType<ISupportsOpen>()) { MyClass m = new MyClass(); m.Called += new EventHandler(delegate(object sender, EventArgs e) { if (component.CanOpenProject(..)) component.OpenProject(..); }); itemsList.Add(m); } How should it be solved, please?

Read the article
Singleton with inheritance, Derived class is not able to get instantiated in parent?

- by yesraaj

Below code instantiates a derived singleton object based on environment variable. The compiler errors saying error C2512: 'Dotted' : no appropriate default constructor. I don't understand what the compiler is complaining about. #include <stdlib.h> #include <iostream> #include <string> using namespace std; class Dotted; class Singleton{ public: static Singleton instant(){ if (!instance_) { char * style = getenv("STYLE"); if (!style){ if (strcmp(style,"dotted")==0) { instance_ = new Dotted(); return *instance_; } } else{ instance_ = new Singleton(); return *instance_; } } return *instance_; } void print(){cout<<"Singleton";} ~Singleton(){}; protected: Singleton(){}; private: static Singleton * instance_; Singleton(const Singleton & ); void operator=(const Singleton & ); }; class Dotted:public Singleton{ public: void print(){cout<<"Dotted";} protected: Dotted(); }; Dotted::Dotted():Singleton(){} int main(){ Singleton::instant().print(); cin.get(); }

Read the article
How to structure javascript callback so that function scope is maintained properly

- by Chetan

I'm using XMLHttpRequest, and I want to access a local variable in the success callback function. Here is the code: function getFileContents(filePath, callbackFn) { var xhr = new XMLHttpRequest(); xhr.onreadystatechange = function() { if (xhr.readyState == 4) { callbackFn(xhr.responseText); } } xhr.open("GET", chrome.extension.getURL(filePath), true); xhr.send(); } And I want to call it like this: var test = "lol"; getFileContents("hello.js", function(data) { alert(test); }); Here, test would be out of the scope of the callback function, since only the enclosing function's variables are accessible inside the callback function. What is the best way to pass test to the callback function so the alert(test); will display test correctly?

Read the article
Thread safety in Singleton

- by Robert

I understand that double locking in Java is broken, so what are the best ways to make Singletons Thread Safe in Java? The first thing that springs to my mind is: class Singleton{ private static Singleton instance; private Singleton(){} public static synchronized Singleton getInstance(){ if(instance == null) instance = new Singleton(); return instance; } } Does this work? if so, is it the best way (I guess that depends on circumstances, so stating when a particular technique is best, would be useful)

Read the article
c++ function scope

- by Myx

I have a main function in A.cpp which has the following relevant two lines of code: B definition(input_file); definition.Print(); In B.h I have the following relevant lines of code: class B { public: // Constructors B(void); B(const char *filename); ~B(void); // File input int ParseLSFile(const char *filename); // Debugging void Print(void); // Data int var1; double var2; vector<char* > var3; map<char*, vector<char* > > var4; } In B.cpp, I have the following function signatures (sorry for being redundant): B::B(void) : var1(-1), var2(numeric_limits<double>::infinity()) { } B::B(const char *filename) { B *def = new B(); def->ParseLSFile(filename); } B::~B(void) { // Free memory for var3 and var 4 } int B::ParseLSFile(const char *filename) { // assign var1, var2, var3, and var4 values } void B::Print(void) { // print contents of var1, var2, var3, and var4 to stdout } So when I call Print() from within B::ParseLSFile(...), then the contents of my structures print correctly to stdout. However, when I call definition.Print() from A.cpp, my structures are empty or contain garbage. Can anyone recommend the correct way to initialize/pass my structures so that I can access them outside of the scope of my function definition? Thanks.

Read the article
BizTalk host throttling – Singleton pattern and High database size

- by S.E.R.

Originally posted on: http://geekswithblogs.net/SERivas/archive/2013/06/30/biztalk-host-throttling-ndash-singleton-pattern-and-high-database-size.aspxI have worked for some days around the singleton pattern (for those unfamiliar with it, read this post by Victor Fehlberg) and have come across a few very interesting posts, among which one dealt with performance issues (here, also by Victor Fehlberg). Simply put: if you have an orchestration which implements the singleton pattern, then performances will continuously decrease as the orchestration receives and consumes messages, and that behavior is more obvious when the orchestration never ends (ie : it keeps looping and never terminates or completes). As I experienced the same kind of problem (actually I was alerted by SCOM, which told me that the host was being throttled because of High database size), I thought it would be a good idea to dig a little bit a see what happens deep inside BizTalk and thus understand the reasons for this behavior. NOTE: in this article, I will focus on this High database size throttling condition. I will try and work on the other conditions in some not too distant future… Test conditions The singleton orchestration For the purpose of this study, I have created the following orchestration, which is a very basic implementation of a singleton that piles up incoming messages, then does something else when a certain timeout has been reached without receiving another message: Throttling settings I have two distinct hosts : one that hosts the receive port (basic FILE port) : Ports_ReceiveHostone that hosts the orchestration : ProcessingHost In order to emphasize the throttling mechanism, I have modified the throttling settings for each of these hosts are as follows (all other parameters are set to the default value): [Throttling thresholds] Message count in database: 500 (default value : 50000) Evolution of performance counters when submitting messages Since we are investigating the High database size throttling condition, here are the performance counter that we should take a look at (all of them are in the BizTalk:Message Agent performance object): Database sizeHigh database sizeMessage delivery throttling stateMessage publishing throttling stateMessage delivery delay (ms)Message publishing delay (ms)Message delivery throttling state durationMessage publishing throttling state duration (If you are not used to Perfmon, I strongly recommend that you start using it right now: it is a wonderful tool that allows you to open the hood and see what is going on inside BizTalk – and other systems) Database size It is quite obvious that we will start by watching the database size and high database size counters, just to see when the first reaches the configured threshold (500) and when the second rings the alarm. NOTE : During this test I submitted 600 messages, one message at a time every 10ms to see the evolution of the counters we have previously selected. It might not show very well on this screenshot, but here is what happened: From 15:46:50 to 15:47:50, the database size for the Ports_ReceiveHost host (blue line) kept growing until it reached a maximum of 504.At 15:47:50, the high database size alert fires At first I was surprised by this result: why is it the database size of the receiving host that keeps growing since it is the processing host that piles up messages? Actually, it makes total sense. This counter measures the size of the database queue that is being filled by the host, not consumed. Therefore, the high database size alert is raised on the host that fills the queue: Ports_ReceiveHost. More information is available on the Public MPWiki page. Now, looking at the Message publishing throttling state for the receiving host (green line), we can see that a throttling condition has been reached at 15:47:50: We can also see that the Message publishing delay(ms) (blue line) has begun growing slowly from this point. All of this explains why performances keep decreasing when a singleton keeps processing new messages: the database size grows and when it has exceeded the Message count in database threshold, the host is throttled and the publishing delay keeps increasing. Digging further So, what happens to the database queue then? Is it flushed some day or does it keep growing and growing indefinitely? The real question being: will the host be throttled forever because of this singleton? To answer this question, I set the Message count in database threshold to 20 (this value is very low in order not to wait for too long, otherwise I certainly would have fallen asleep in front of my screen) and I submitted 30 messages. The test was started at 18:26. At 18:56 (ie : exactly 30min later) the throttling was stopped and the database size was divided by 2. 30 min later again, the database size had dropped to almost zero: I guess I’ll have to find some documentation and do some more testing before I sort this out! My guess is that some maintenance job is at work here, though I cannot tell which one Digging even further If we take a look at the Message delivery throttling state counter for the processing host, we can see that this host was also throttled during the submission of the 600 documents: The value for the counter was 1, meaning that Message delivery incoming rate for the host instance exceeds the Message delivery outgoing rate * the specified Rate overdrive factor (percent) value. We will see this another day… :) A last word Let’s end this article with a warning: DO NOT CHANGE THE THROTTLING SETTINGS LIGHTLY! The temptation can be great to just bypass throttling by setting very high values for each parameter (or zero in some cases, which simply disables throttling). Nevertheless, always keep in mind that this mechanism is here for a very good reason: prevent your BizTalk infrastructure from exploding!! So whatever you do with those settings, do a lot of testing and benchmarking!

Read the article
Singleton: How should it be used

- by Loki Astari

Edit: From another question I provided an answer that has links to a lot of questions/answers about singeltons: More info about singletons here: So I have read the thread Singletons: good design or a crutch? And the argument still rages. I see Singletons as a Design Pattern (good and bad). The problem with Singleton is not the Pattern but rather the users (sorry everybody). Everybody and their father thinks they can implement one correctly (and from the many interviews I have done, most people can't). Also because everybody thinks they can implement a correct Singleton they abuse the Pattern and use it in situations that are not appropriate (replacing global variables with Singletons!). So the main questions that need to be answered are: When should you use a Singleton How do you implement a Singleton correctly My hope for this article is that we can collect together in a single place (rather than having to google and search multiple sites) an authoritative source of when (and then how) to use a Singleton correctly. Also appropriate would be a list of Anti-Usages and common bad implementations explaining why they fail to work and for good implementations their weaknesses. So get the ball rolling: I will hold my hand up and say this is what I use but probably has problems. I like "Scott Myers" handling of the subject in his books "Effective C++" Good Situations to use Singletons (not many): Logging frameworks Thread recycling pools /* * C++ Singleton * Limitation: Single Threaded Design * See: http://www.aristeia.com/Papers/DDJ_Jul_Aug_2004_revised.pdf * For problems associated with locking in multi threaded applications * * Limitation: * If you use this Singleton (A) within a destructor of another Singleton (B) * This Singleton (A) must be fully constructed before the constructor of (B) * is called. */ class MySingleton { private: // Private Constructor MySingleton(); // Stop the compiler generating methods of copy the object MySingleton(MySingleton const& copy); // Not Implemented MySingleton& operator=(MySingleton const& copy); // Not Implemented public: static MySingleton& getInstance() { // The only instance // Guaranteed to be lazy initialized // Guaranteed that it will be destroyed correctly static MySingleton instance; return instance; } }; OK. Lets get some criticism and other implementations together. :-)

Read the article
MooTools/JavaScript variable scope

- by 827

I am trying to make each number displayed clickable. "1" should alert() 80, "2" should produce 60, etc. However, when the alert(adjust) is called, it only shows 0, not the correct numbers. However, if the commented out alert(adjust) is uncommented, it produces the correct number on page load, but not on clicking. I was wondering why the code inside addEvents cannot access the previously defined variable adjust. <html> <head> <script type="text/javascript" charset="utf-8" src="mootools.js"></script> <script type="text/javascript" charset="utf-8"> window.addEvent('domready', function() { var id_numbers = [1,2,3,4,5]; for(var i = 0; i<id_numbers.length; i++) { var adjust = (20 * (5 - id_numbers[i])); // alert(adjust); $('i_' + id_numbers[i]).addEvents({ 'click': function() { alert(adjust); } }); } }); </script> </head> <body> <div id="i_1">1</div> <div id="i_2">2</div> <div id="i_3">3</div> <div id="i_4">4</div> <div id="i_5">5</div> </body> </html> Thanks.

Read the article
PHP Scope Resolution Operator Question

- by anthony

I'm having trouble with the MyClass::function(); style of calling methods and can't figure out why. Here's an example (I'm using Kohana framework btw): class Test_Core { public $var1 = "lots of testing"; public function output() { $print_out = $this->var1; echo $print_out; } } I try to use the following to call it, but it returns $var1 as undefined: Test::output() However, this works fine: $test = new Test(); $test->output(); I generally use this style of calling objects as opposed to the "new Class" style, but I can't figure out why it doesn't want to work.

Read the article
Scope of parameter names in Objective C methods

- by G.P. Burdell

// myClass.h @interface myClass : NSObject { int variable1; } - (int) addOne: (int)variable1; //myClass.m - (int) addOne: (int)variable1{ variable1++; } My question is: will [myClass addOne:aNumber] add 1 to aNumber or will it add 1 to the value of the ivar variable1?

Read the article
C# Using singleton instead of a global static instance

- by Farstucker

I ran into a problem today and a friend recommended I use a global static instance or more elegantly a singleton pattern. I spent a few hours reading about singletons but a few things still escape me. Background: What Im trying to accomplish is creating an instance of an API and use this one instance in all my classes (as opposed to making a new connection, etc). There seems to be about 100 ways of creating a singleton but with some help from yoda I found some thread safe examples. ..so given the following code: public sealed class Singleton { public static Singleton Instance { get; private set; } static Singleton() { Instance = new Singleton(); } } How/Where would you instantiate the this new class and how should it be called from a separate class? Thanks for your help.

Read the article
C++ Singleton design pattern

- by Artem Barger

Recently I've bumped into a realization/implementation of the Singleton design pattern for C++. It has looked like this (I have adopted it from the real life example): // a lot of methods are omitted here class Singleton { public: static Singleton* getInstance( ); ~Singleton( ); private: Singleton( ); static Singleton* instance; }; From this declaration I can deduce that the instance field is initiated on the heap. That means there is a memory allocation. What is completely unclear for me is when exactly the memory is going to be deallocated? Or is there a bug and memory leak? It seems like there is a problem in the implementation. My main question is, how do I implement it in the right way?

Read the article
Singleton Roles in Moose

- by mjn12

I am attempting to write a singleton role using Perl and Moose. I understand a MooseX::Singleton module is available but there is always resistance when requiring another CPAN module for our project. After trying this and having a little trouble I would like to understand WHY my method is not working. The singleton role I have written is as follows: package Singleton; use Moose::Role; my $_singleInstance; around 'new' => sub { my $orig = shift; my $class = shift; if (not defined $_singleInstance ){ $_singleInstance = $class->$orig(@_); } return $_singleInstance; }; sub getInstance { return __PACKAGE__->new(); } 1; This appears to work find when only one class uses the singleton role. However when two classes (ClassA and ClassB for example) both consume the Singleton role it appears as they are both referring to a shared $_singleInstance variable. If I call ClassA-getInstance it returns a reference to a ClassA object. If I call ClassB-getInstance sometime later in the same script it returns a reference to an object of type ClassA (even though I clearly called the getInstance method for ClassB). If I dont use a role and actually copy and paste the code from the Singleton role into ClassA and ClassB it appears to work fine. Whats going on here?

Read the article
Using Dispose on a Singleton to Cleanup Resources

- by ImperialLion

The question I have might be more to do with semantics than with the actual use of IDisposable. I am working on implementing a singleton class that is in charge of managing a database instance that is created during the execution of the application. When the application closes this database should be deleted. Right now I have this delete being handled by a Cleanup() method of the singleton that the application calls when it is closing. As I was writing the documentation for Cleanup() it struck me that I was describing what a Dispose() method should be used for i.e. cleaning up resources. I had originally not implemented IDisposable because it seemed out of place in my singleton, because I didn't want anything to dispose the singleton itself. There isn't currently, but in the future might be a reason that this Cleanup() might be called but the singleton should will need to still exist. I think I can include GC.SuppressFinalize(this); in the Dispose method to make this feasible. My question therefore is multi-parted: 1) Is implementing IDisposable on a singleton fundamentally a bad idea? 2) Am I just mixing semantics here by having a Cleanup() instead of a Dispose() and since I'm disposing resources I really should use a dispose? 3) Will implementing 'Dispose()' with GC.SuppressFinalize(this); make it so my singleton is not actually destroyed in the case I want it to live after a call to clean-up the database.

Read the article
What is the difference between all-static-methods and applying a singleton pattern?

- by shahensha

I am making a database to store information about the users of my website (I am using stuts2 and hence Java EE technology). For the database I'll be making a DBManager. Should I apply singleton pattern here or rather make all it's methods static? I will be using this DBManager for basic things like adding, deleting and updating User profiles. Along with it, I'll use for all other querying purposes, for instance to find out whether a username already exists and to get all users for administrative purposes and stuff like that. My questions What is the benefit of singleton pattern? Which thing is most apt here? All static methods or a singleton pattern? Please compare both of them. regards shahensha P.S. The database is bigger than this. Here I am talking only about the tables which I'll be using for storing User Information.

Read the article
Singleton object in IIS Web Garden

- by Anwar Chandra

I have a lot of Singleton implementation in asp.net application and want to move my application to IIS Web Garden environment for some performance reasons. CMIIW, moving to IIS Web Garden with n worker process, there will be one singleton object created in each worker process, which make it not a single object anymore because n 1. can I make all those singleton objects, singleton again in IIS Web Garden?

Read the article
How to add a specific method to a particular scope in Visual Studion 2005

- by pragadheesh

Hi, In my visual studio project (C++), when i copy a method(meth1) of a particular scope say 'scope1' and paste it in the same code area, it is getting pasted in General Scope. i.e I want to add a method into a particular scope but when i try it is getting added in general scope. How can i solve this? For eg: There is an existing method: void add(int a, int b) { .... } This method is in File scope. i.e limited for that file. Now i want to add another method add2 in the same file scope. So I copied the existing add method and pasted it. void add2(int a, int b) { .... } But this method is getting added in the global scope and not in the file scope.

Read the article
Should I sacrifice code succintness to ensure the narrowest variable scope? [duplicate]

- by David Scholefield

This question already has an answer here: Is the usage of internal scope blocks within a function bad style? 3 answers In many languages (e.g. both Perl and Java - which are the two languages I work most with) it is possible to narrow the scope of local variables by declaring them within a block. Although it adds extra code length (the opening and closing block braces), and possibly reduces readability, should I create blocks purely to narrow the scope of variables to the statements that use the variables and to uphold the principle of narrowest scope or does this sacrifice succinctness and readability just to unnecessarily uphold an agreed 'best practice' principle? I usually declare local variables to functions/methods at the start of the function to aid readability, but I could not do this, and just create blocks throughout the function and declare the variables throughout the code - within those blocks - to narrow their scope.

Read the article
Singleton again, but with multi-thread and Objective-C

- by Tonny Xu

I know Singleton pattern has been discussed so much. But because I'm not fully understand the memory management mechanism in Objective-C, so when I combined Singleton implementation with multithreading, I got a big error and cost me a whole day to resolve it. I had a singleton object, let's call it ObjectX. I declared an object inside ObjectX that will detach a new thread, let's call that object objectWillSpawnNewThread, when I called [[ObjectX sharedInstance].objectWillSpawnNewThread startNewThread]; The new thread could not be executed correctly, and finally I found out that I should not declare the object objectWillSpawnNewThread inside the singleton class. Here are my questions: How does Objective-C allocate static object in the memory? Where does Objective-C allocate them(Main thread stack or somewhere else)? Why would it be failed if we spawn a new thread inside the singleton object? I had searched the Objective-C language [ObjC.pdf] and Objective-C memory management document, maybe I missed something, but I currently I could not find any helpful information.

Read the article
what is the exact difference between PHP static class and singleton class

- by Saif Bechan

I have always used a Singleton class for a registry object in PHP. As all Singleton classes I think the main method looks like this: class registry { public static function singleton() { if( !isset( self::$instance ) ) { self::$instance = new registry(); } return self::$instance; } public function doSomething() { echo 'something'; } } So whenever I need something of the registry class I use a function like this: registry::singleton()->doSomethine(); Now I do not understand what the difference is between creating just a normal static function. Will it create a new object if I just use a normal static class. class registry { public static function doSomething() { echo 'something'; } } Now I can just use: registry::doSomethine(); Can someone explain to me what the function is of the singleton class. I really do not understand this.

Read the article
Boost singleton and undefined reference

- by Ockonal

Hello, I globally use singleton pattern in my project. To make it easier - boost::singleton. Current project uses Ogre3d library for rendering. Here is some class: class GraphicSystem : public singleton<GraphicSystem> { private: Ogre::RenderWindow *mWindow; public: Ogre::RenderWindow *getWindow() const { return mWindow; } }; In GraphicSystem constructor I fill the mWindow value: mWindow = mRoot->createRenderWindow(...); I cheked it, everything makes normally. So, now I have to use handler for the window in input system (to get window handle). Somewhere else in another class: Ogre::RenderWindow *temp = GraphicSystem::get_mutable_instance().getWindow(); GraphicSystem::get_mutable_instance().getWindow()->getCustomAttribute("WINDOW", &mWindowHandle); temp is 0x00, and there is segfault at last line (getting custon attribute). I can't understand, why does singleton returns undefined pointer for the window. All another singleton-based classes work well.

Read the article

< Previous Page | 1 2 3 4 5 6 7 8 9 10 11 12 | Next Page >