singleton

问题 The source code of singleton of boost is there ,I don't understand two notations in the source file below: // ***include this to provoke instantiation at pre-execution time*** static void use(T const &) {}; BOOST_DLLEXPORT static T & get_instance() { static detail::singleton_wrapper< T > t; ***// refer to instance, causing it to be instantiated (and // initialized at startup on working compilers)*** BOOST_ASSERT(! detail::singleton_wrapper< T >::m_is_destroyed); use(instance); return static

问题 I am trying to write a Singleton Lazy Loading Pattern. Here is the class: public class IMDBLookup { private static class LazyLoad { private static final IMDBLookup IMDB_LOOKUP; static { IMDB_LOOKUP = new IMDBLookup(); } } public static IMDBLookup getInstance() { return IMDBLookup.LazyLoad.IMDB_LOOKUP; } } I am wondering whether or not I am doing it in a right way? Thanks in advance. 回答1: I prefer to use enum for simplicity. public enum IMDBLookup { INSTANCE; // add fields and methods here. }

问题 I'm creating a game that uses cards. I have an AppController class with one instance in the nib. The AppController instance has an NSArray instance variable called wordList. On init, the nib's instance of AppController generates a new GameCard. Every gamecard has an array of words containing 5 words selected at random from the the list in AppController. Because the list is large, I'd like to read it into memory only once. Therefore, I want only one instance of AppController, as a singleton

问题 If a singleton implements IDisposable, what is the right way of disposing and re-creating an instance? One way would be to keep _disposed flag and check for it in the Instance property, but I'm not sure it is the right way to do this. A simple example: public sealed class Singleton: IDisposable { private static Singleton _instance; private object _lock; private UnmanagedResource _unmanaged; private bool _disposed; private Singleton() { _unmanaged = new UnmanagedResource(); _disposed = false;

问题 Normally, I would expect a function variable to be lost after execution of that function. In the below case where I wrote a Singleton following some tutorials, it works, though. One could argue that instances should be empty again everytime the singleton function is called. def singleton(cls): instances = {} def get_instance(*args, **kwargs): if cls not in instances: instances[cls] = cls(*args, **kwargs) return instances[cls] return get_instance @singleton class cls(object): pass My

问题 Here's the one I'm using: <?php final class Database { private static $oDb; public static function init() { if(self::$oDb == NULL) { self::$oDb = mysql_connect('localhost', 'mysql_user', 'mysql_password') or die(mysql_error()); mysql_select_db('mysql_db_name', self::$oDb) or die (mysql_error());; } return self::$oDb; } public function query($sql) { return mysql_query($sql) or die(mysql_error()); } } ?> Usage: $oDb = Database::init(); $sql = foo; $oDb->query($sql); Assuming that I only want it

问题 Currently, I have the following code in one of my methods: let formatter = NSNumberFormatter() formatter.numberStyle = .DecimalStyle formatter.currencyGroupingSeparator? formatter.minimumFractionDigits = 2 Because I have to repeat these in various functions in different view controllers, how do I create a singleton in Swift to call for the NSNumberFormatter and avoid duplicates? I assume that I have to create a new Swift file, but unsure of how to construct the class? 回答1: update: Xcode 8.2.1

问题 When running a large set of testsuites, I noticed that one of my Android Services isn't singleton anymore. An Android Service is supposed to be singleton but when using a ServiceTestCase my reference count went above 1. (incremented in onCreate, decremented in onDestroy). Calling startService or bindService from a testcase should result in a second onBind or onStartCommand but should never result in a second onCreate before the first onDestroy. Is this because the unit test is bypassing

问题 I need to create a WCF service that only allows a single client at a time. All other requests should be rejected, and the client must retry again later. The service will take around a minute to complete the request. I've tried: [ServiceBehavior(IncludeExceptionDetailInFaults=true, InstanceContextMode=InstanceContextMode.Single, ConcurrencyMode=ConcurrencyMode.Single)] but if I request the service multiple times (using multiple threads) in a client, I get a timeout exception on the 3rd request

问题 How to use delegate methods of singleton/shared class? There is one singleton class having some protocol defined but I'm not getting how to access the delegate functions in other classes. Code snippet for a reference (swift): protocol AClassDelegate { func method1() } class A { static let shared = A() override init() { //initialisation of member variables } var delegate: AClassDelegate func foo() { } } class B: AClassDelegate { func bar() { // Note: not getting call to 'foo' method of class