singleton

问题 It happens so that I have a need of the infamous singleton pattern. Better yet, it happens so that I have a need of infamous C++ templates in combination with that pattern. So, what troubles me is this: template <class T> class PDatabaseTable { ... static PDatabaseTable <T> & instance() { static PDatabaseTable <T> singleton; return singleton; } ... }; This is a typical way to implement a singleton that's supposed to be created on the first use. Now, here we have a static variable singleton .

问题 I am using mvc.net with StructureMap to scan and register all repositories and services for me. Now I want to register and cache by Singleton. How can I do? IContainer container = new Container(x => { // Register Repositories and Services x.Scan(y => { y.AssemblyContainingType<SomeRepository>(); y.AssemblyContainingType<SomeService>(); y.IncludeNamespaceContainingType<SomeRepository>(); y.IncludeNamespaceContainingType<SomeService>(); }); // Register Controllers x.Scan(y => { y

问题 Here is my code: public class RouteSingleton { private IDictionary<string, string> _dealCatLinks; private IDictionary<string, string> _sectionLinks; private IDictionary<string, string> _categoryLinks; private IDictionary<string, string> _materials; private IDictionary<string, string> _vendors; public RouteSingleton(IDealService dealService , ICategoryService categoryService , IVendorService vendorService) { this._dealCatLinks = dealService.GetDealCatLinks("PLV").Distinct().ToDictionary(x => x

问题 So, I've always implemented a singleton like so: class Singleton { private static $_instance = null; public static function getInstance() { if (self::$_instance === null) self::$_instance = new Singleton(); return self::$_instance; } private function __construct() { } } However, it recently struck me that I could also implement it with member-wise static variables: class Singleton { public static function getInstance() { //oops - can't assign expression here! static $instance = null; // = new

问题 someone can tell me why this is incorrect as a singleton pattern: class preSingleton(object): def __call__(self): return self singleton = preSingleton() # singleton is actually the singleton a = singleton() b = singleton() print a==b a.var_in_a = 100 b.var_in_b = 'hello' print a.var_in_b print b.var_in_a Edit: The above code prints: True hello 100 thank you very much Part Two Maybe this is better? class Singleton(object): def __new__(cls): return cls a = Singleton() b = Singleton() print a ==

问题 someone can tell me why this is incorrect as a singleton pattern: class preSingleton(object): def __call__(self): return self singleton = preSingleton() # singleton is actually the singleton a = singleton() b = singleton() print a==b a.var_in_a = 100 b.var_in_b = 'hello' print a.var_in_b print b.var_in_a Edit: The above code prints: True hello 100 thank you very much Part Two Maybe this is better? class Singleton(object): def __new__(cls): return cls a = Singleton() b = Singleton() print a ==

问题 I'm trying to track down an issue in our system and the following code worries me. The following occurs in our doPost() method in the primary servlet (names have been changed to protect the guilty): ... if(Single.getInstance().firstTime()){ doPreperations(); } normalResponse(); ... The singleton 'Single' looks like this: private static Single theInstance = new Single(); private Single() { ...load properties... } public static Single getInstance() { return theInstance; } With the way this is

问题 Due to the flooding examples of implementing logger using Singleton pattern, I have just written a simple C++ logger in the same approach for my program. However, since the famous double-checked locking approach is known to be no more thread-safe, I wonder if I should: 1) Forget about the use of Singleton pattern in this case? 2) Continue to use double-checked locking even though it is unsafe? 3) Use the expensive pure sync lock method for every access to its public interfaces? Any

问题 This question already has answers here : What is an efficient way to implement a singleton pattern in Java? [closed] (29 answers) Closed 5 years ago . This is the first time I am writing a Factory class. Below is my Factory class, I am not sure whether this is the correct way of making thread safe Singleton Factory class or not. I will be returning instance of my Client using this factory? public class ClientFactory { private static ClientFactory instance = null; private ClientFactory() { }

问题 This question, like my previous question, references Effective Java . This time I have quite a few sub-questions. A privileged client can invoke the private constructor reflectively with the aid of the AccessibleObject.setAccessible() method. If you need to defend against this, modify the constructor. How, exactly, can a private constructor be invoked? And what is AccessibleObject.setAccessible() ? What approach do you experts follow with singletons? // Approach A public class Test{ public