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• Critical section initialization when creating thread-safe singleton (C++)

  - by user356145

  I'm trying to do the same thing as suggested in this solution: http://stackoverflow.com/questions/164496/how-can-i-create-a-thread-safe-singleton-pattern-in-windows/164640#164640 But, where should the critical section be initialized and uninitialized?

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• boost.threads Singleton initialization

  - by aaa

  hello. Is there preferred way to initialize (lazily) singleton data when using multiple threads from boost.threads? Thanks.

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• Singleton Pattern Implementation Issues?

  - by locky28

  Hi I am revising for an exam and need to know some implementation issues with the singleton pattern. they do not need to be too complex just basic things that would affect a developers decision to include them, Thanks P.S. Could any code examples be given in Java thanks.

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• Singleton rule questions (do not allow to create copy and deserialization)

  - by Petr

  Hi, Reading some article about singleton, I stopped at the point saying: "Do not allow to crate copy of existing instance". I realized that I do not know how would I do that! Could you tell me, please, how could I copy existing instance of class? And the second one: deserializaition. How it could be dangerous? And for both - how to deny creating copies or deserialization? Thanks

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• [iphone] method created in a seperate class returns "out of scope"

  - by Dror Sabbag

  Hey, I have created a Class (subclass of NSObject) which will hold all my SQLs/dbConnections etc.. in a seperate viewcontroller, i have instantiated the SQL's class and performed some actions, all went trough OK. but. one of my methods in the SQL's class is a method defined as follows: -(NSString *)queryTable:(NSUInteger *)fieldnum //query from db, and assign the field value into "fieldName" dbEntity = fieldName; [fieldName release]; } sqlite3_finalize(statement); } return dbEntity; } dbEntity is defined as NSString, and i have set it as a nonatoimc-retain property @property (nonatomic,retain) NSString *dbEntity; when ever i call this method out from my viewController and debug step by step, i see that the method is running, it is quering from the db as expected, but when it passes the value into dbEntity the values in dbEntity are suddenly "out of scope" that is... if i browse this specific action: dbEntity = fieldName; i can see values inside fieldName, but see "out of scope" in dbEntity. Why is that?!? what is wrong with dbEntity definitions? Any help will be appriciated.

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• Scope of variables inside anonymous functions in C#

  - by Vinod

  I have a doubt in scope of varibles inside anonymous functions in C#. Consider the program below: delegate void OtherDel(int x); public static void Main() { OtherDel del2; { int y = 4; del2 = delegate { Console.WriteLine("{0}", y);//Is y out of scope }; } del2(); } My VS2008 IDE gives the following errors: [Practice is a class inside namespace Practice] 1.error CS1643: Not all code paths return a value in anonymous method of type 'Practice.Practice.OtherDel' 2.error CS1593: Delegate 'OtherDel' does not take '0' arguments. It is told in a book: Illustrated C# 2008(Page 373) that the int variable y is inside the scope of del2 definition. Then why these errors.

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• How do I find out if the variable is declared in Python?

  - by golergka

  I want to use a module as a singleton referenced in other modules. It looks something like this (that's not actually a code I'm working on, but I simplified it to throw away all unrelated stuff): main.py import singleton import printer def main(): singleton.Init(1,2) printer.Print() if __name__ == '__main__': pass singleton.py variable1 = '' variable2 = '' def Init(var1, var2) variable1 = var1 variable2 = var2 printer.py import singleton def Print() print singleton.variable1 print singleton.variable2 I expect to get output 1/2, but instead get empty space. I understand that after I imported singleton to the print.py module the variables got initialized again. So I think that I must check if they were intialized before in singleton.py: if not (variable1): variable1 = '' if not (variable2) variable2 = '' But I don't know how to do that. Or there is a better way to use singleton modules in python that I'm not aware of :)

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• Accessing a parent scope from a child directive

  - by zok

  The following code does not work. Apparently I cannot access someFunction() from child-dir. Is it a matter of accessing a parent scope from a child directive? How to do it, when the child directive comes from an external library? Angular/HTML: <parent-dir ng-controller="parentCtrl"> <child-dir ng-click="someFunction()"> </child-dir> </parent-dir> JS: .controller('parentCtrl', function($scope) { $scope.someFunction() { console.log('hello'); } }

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• variable scope in statement blocks

  - by fearofawhackplanet

  for (int i = 0; i < 10; i++) { Foo(); } int i = 10; // error, 'i' already exists ---------------------------------------- for (int i = 0; i < 10; i++) { Foo(); } i = 10; // error, 'i' doesn't exist By my understanding of scope, the first example should be fine. The fact neither of them are allowed seems even more odd. Surely 'i' is either in scope or not. Is there something non-obvious about scope I don't understand which means the compiler genuinely can't resolve this? Or is just a case of nanny-state compilerism?

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• The Singleton Pattern

  How to create an object using the Singleton pattern in VB.NET

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• Cannot get UISearchBar Scope Bar to appear in Toolbar (or anywhere) on iPad

  - by Jann

  This is really causing me fits. I see a lot of info on putting a UISearchBar in the top row of a UITableView -- but I am putting the UISearchBar into the Toolbar at the top of my screen (on the iPad). I cannot find ANYTHING regarding how to handle UISearchBar and UISearchDisplayController using a UIPopoverController on the iPad. Any more info about the UISearchDisplayController using a UIPopoverController would be greatly appreciated. Please help with this as I am at my wit's end. Using IB, I put a toolbar on the IUView on the iPad. I added the following: Search Bar (not Search Bar and Search Display) to the toolbar. I set the options to be as follows: Show Cancel Button, Show Scope Bar, Scope Button Titles are: "Title1" and "Title2" (with Title2's radio button selected). Opaque, Clear Context and Auto Resize are checked. I hooked up the delegate of Search Bar to the "File's Owner" and linked it to IBOutlet theSearchBar. In my viewWillAppear I have the following: //Just in case: [theSearchBar setScopeButtonTitles:[NSArray arrayWithObjects:@"Near Me",@"Everywhere",nil]]; //Just in case (again): [theSearchBar setShowsScopeBar:YES]; //doesn't seem to do anything: //[theSearchBar sizeToFit]; searchDisplayController = [[UISearchDisplayController alloc] initWithSearchBar:theSearchBar contentsController:self]; [self setSearchDisplayController:searchDisplayController]; [searchDisplayController setDelegate:self]; [searchDisplayController setSearchResultsDataSource:self]; //again--does not seem to do anything..but people have suggested it: [theSearchBar sizeToFit]; Okay, so far, I thought, so good. So, I made the File's Owner .m file to be a delegate for: UISearchBarDelegate, UISearchDisplayDelegate. My issue: I have yet to implement the delegates necessary to do the search but still... shouldn't I be seeing the scopeBar next to the search field when I click into the search field? Just so you know I DO see the log of the characters I type, so the delegate is working. I have the following dummy functions in the .m file (just in case) // called when keyboard search button pressed - (void)searchBarSearchButtonClicked:(UISearchBar *)searchBar { NSLog(@"Search Button Clicked\n"); [theSearchBar resignFirstResponder]; } // called when cancel button pressed - (void)searchBarCancelButtonClicked:(UISearchBar *)searchBar { NSLog(@"Cancel Button Clicked\n"); [theSearchBar resignFirstResponder]; } - (void)searchBar:(UISearchBar *)searchBar textDidChange:(NSString *)searchText { NSLog(@"Search Text So Far: '%@'\n",searchText); } - (BOOL)searchBarShouldBeginEditing:(UISearchBar *)searchBar { return YES; } - (BOOL)searchBarShouldEndEditing:(UISearchBar *)searchBar { return YES; } Why doesn't the Scope Bar appear? A results UIPopoverController appears with the title "Results" and "No results found" (of course) when i type the first character in my search...but no scope bar. (not that i expect anything other than "No Results Found". I am wondering where the scope bar is supposed to appear...in the titleView of the UIPopover? In the toolbar to the right of the search area? Where?

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• Boost C++ Singleton error LNK2001: unresolved external symbol "private: static long Nsp::HL::flag" (

  - by Soós Roland

  I try to create a multi-threaded singleton pattern class. Header: class HL{ public: static HL* getInstance(); ......... private: static HL* instance; static boost::once_flag flag; HL(); static void initOnce(); } CPP: HL* HL::instance = NULL; HL* HL::getInstance(){ if(instance == NULL){ boost::call_once(flag, initOnce); } return instance; } void HL::initOnce(){ instance = new HL(); } I get this error: error LNK2001: unresolved external symbol "private: static long Nsp::HL::flag" (?flag@HL@Nsp@@0JA) What's wrong?

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• Singleton pattern and broken double checked locking in real world java application

  - by saugata

  I was reading the article Double-checked locking and the Singleton pattern, on how double checked locking is broken, and some related questions here on stackoverflow. I have used this pattern/idiom several times without any issues. Since I have been using Java 5, my first thought was that this has been rectified in Java 5 memory model. However the article says This article refers to the Java Memory Model before it was revised for Java 5.0; statements about memory ordering may no longer be correct. However, the double-checked locking idiom is still broken under the new memory model. I'm wondering if anyone has actually run into this problem in any application and under what conditions.

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• some confusions to singleton pattern in PHP

  - by SpawnCxy

  Hi all, In my team I've been told to write resource class like this style: class MemcacheService { private static $instance = null; private function __construct() { } public static function getInstance($fortest = false) { if (self::$instance == null) { self::$instance = new Memcached(); if ($fortest) { self::$instance->addServer(MEMTEST_HOST, MEMTEST_PORT); } else { self::$instance->addServer(MEM_HOST, MEM_PORT); } } return self::$instance; } } But I think in PHP resource handles will be released and initialized again every time after a request over. That means MemcacheService::getInstance() is totally equal new Memcached() which cannot be called singleton pattern at all. Please correct me if I'm wrong. Regards

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• Circular reference problem Singleton

  - by Ismail

  I'm trying to creating a Singleton class like below where MyRepository lies in separate DAL project. It's causing me a circular reference problem because GetMySingleTon() method returns MySingleTon class and needs its access. Same way I need MyRepository access in constructor of MySingleTon class. public class MySingleTon { static MySingleTon() { if (Instance == null) { MyRepository rep = new MyRepository(); Instance = rep.GetMySingleTon(); } } public static MySingleTon Instance { get; private set; } public string prop1 { get; set; } public string prop2 { get; set; } }

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• StructureMap 'conditional singleton' for Lucene.Net IndexReader

  - by Gareth D

  I have a threadsafe object that is expensive to create and needs to be available through my application (a Lucene.Net IndexReader). The object can become invalid, at which point I need to recreate it (IndexReader.IsCurrent is false, need a new instance using IndexReader.Reopen). I'd like to able to use an IoC container (StructureMap) to manage the creation of the object, but I can't work out if this scenario is possible. It feels like some kind of "conditional singleton" lifecycle. Does StructureMap provide such a feature? Any alternative suggestions?

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• Generic Abstract Singleton with Custom Constructor in C#

  - by Heka

  I want to write a generic singleton with an external constructor. In other words the constructor can be modified. I have 2 designs in my mind but I don't know whether they are practical or not. First one is to enforce derived class' constructor to be non-public but I do not know if there is a way of it? Second one is to use a delegate and call it inside the constructor? It isn't necessarily to be a constructor. The reason I chose custom constructor is doing some custom initializations. Any suggestions would be appreciated :)

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• Thread-safe use of a singleton's members

  - by Anthony Mastrean

  I have a C# singleton class that multiple classes use. Is access through Instance to the Toggle() method thread-safe? If yes, by what assumptions, rules, etc. If no, why and how can I fix it? public class MyClass { private static readonly MyClass instance = new MyClass(); public static MyClass Instance { get { return instance; } } private int value = 0; public int Toggle() { if(value == 0) { value = 1; } else if(value == 1) { value = 0; } return value; } }

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• C++ boost thread id and Singleton

  - by aaa

  hi. Sorry to flood so many questions this week. I assume thread index returned by thread.get_id is implementation specific. In case of the pthreads, is index reused? IE, if thread 0 runs and joins, is thread launched afterwords going to have a different ID? the reason I ask this is a need to implement Singleton pattern with a twist: each thread gets its own instance. I know it sounds very crazy, but threads control hardware (cuda) which does not permit device memory sharing. What is a good way to implement such pattern?

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• StructureMap singleton behavior not working

  - by user137348

  My code is public static class ContainerBootstrapper { public static void BootstrapStructureMap() { ObjectFactory.Initialize(x => x .ForRequestedType<ValueHolder>() .CacheBy(InstanceScope.Singleton) .TheDefaultIsConcreteType<ValueHolder>()); } } Initialization code (its a windows service) static class Program { static void Main() { ServiceBase[] ServicesToRun; ServicesToRun = new ServiceBase[] { new AppServer() }; ServiceBase.Run(ServicesToRun); ContainerBootstrapper.BootstrapStructureMap(); } } And then I call an instance like this: var valueHolder = ObjectFactory.GetInstance<ValueHolder>(); But I get everytime an new instance not the one used before.

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• singleton pattern in java- lazy Intialization

  - by flash

  public static MySingleton getInstance() { if (_instance==null) { synchronized (MySingleton.class) { _instance = new MySingleton(); } } return _instance; } 1.is there a flaw with the above implementation of the getInstance method? 2.What is the difference between the two implementations.? public static synchronized MySingleton getInstance() { if (_instance==null) { _instance = new MySingleton(); } return _instance; } I have seen a lot of answers on the singleton pattern in stackoverflow but the question I have posted is to know mainly difference of 'synchronize' at method and block level in this particular case.

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• UISearchBar- change scope without greying out table?

  - by Greg

  How can I allow a change in scope without having the table grey out, the search field become first responder and keyboard popup? I simply want to refresh the data shown based on the scope. Thanks Greg

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• Force scope bar below UISearchBar

  - by axiixc

  I have a UISearchBar and UISearchDisplayController, everything works great but my scope selector displays beside the text field instead of below it. I know that this is the expected action when the device is in landscape, but since I have the UISearchBar in the master view of a UISplitViewController it ends up looking like this http://cl.ly/BN9 Is there any way to force the scope bar to display below the text field in all interface orientations (I know that this works nicely in Mail.app on the iPad, so its possibly, but who knows if Apple decided to hide the option to do so)

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• uses for dynamic scope?

  - by Stephen

  Hi, I've been getting my hands wet with emacs lisp, and one thing that trips me up sometimes is the dynamic scope. Is there much of a future for it? Most languages I know use static scoping (or have moved to static scoping, like Python), and probably because I know it better I tend to prefer it. Are there specific applications/instances or examples where dynamic scope is more useful?

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• Custom scope for .NET application settings

  - by Valery Tydykov

  I can define my custom scope: [AttributeUsage(AttributeTargets.Property)] public sealed class SiteScopedSettingAttribute : SettingAttribute { } How do I use it in the Visual Studio Settings editor (make it available in the "Scope" combobox)?

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