singleton

问题 How does Singleton behave when two threads call the "getInstance()" at the same time? What are the best practices to protect it? 回答1: Firstly, two threads can't call the method at the "same time" - one will be deemed to call it first... called a "race condition". Next, any properly implemented singleton will handle a race condition cleanly. IMHO, this is the cleanest way to implement a thread-safe singleton without synchronization : public class MySingleton { private static class Holder {

问题 What is the advantage of using this: + (CardPainter*) sharedPainter { static CardPainter* sp = nil; if (nil == sp) { sp = [[CardPainter alloc] init]; } return sp; } instead of this: + (CardPainter*) sharedPainter { static CardPainter* sp = [[CardPainter alloc] init]; return sp; } The static variable initialization is performed only once, so I see no advantage of the former. 回答1: Well, at a compiler level there's several overlapping reasons… the simplest to think about is that static variables

问题 Let's say that I'm currently designing an application where I will need to use a global timing system (it's a cross-cutting concern). I'll need to access data from that global timing system from basically anywhere in my app and it's not like I can see that "this part of the application will need it while the other won't". My question is.. should I design that as a kind Ambient Context (in this case, Singleton), or should I try to devise other way to accomodate for this? I certainly don't feel

问题 Let's say that I'm currently designing an application where I will need to use a global timing system (it's a cross-cutting concern). I'll need to access data from that global timing system from basically anywhere in my app and it's not like I can see that "this part of the application will need it while the other won't". My question is.. should I design that as a kind Ambient Context (in this case, Singleton), or should I try to devise other way to accomodate for this? I certainly don't feel

问题 I have a trivial singleton class. My singleton.h file looks something like this: class singleton { ... public: static singleton& instance(); }; And my singleton.cpp looks like this: ... singleton& singleton::instance() { static singleton * const _instance(new singleton); return *_instance; } In writing this class, I thought I was relying on thread-safe function-local static initialization, which I understand to be set out in section 6.7 of the C++ standard as described here. Hopefully I

问题 I am creating a Python application that includes socket communication with a server. I would like to have a module which can be used throughout my entire application (several other modules). Currently my module look like this: class SocketCommunication: def __init__(self): self.socketIO = SocketIO(settings.ADDRESS, settings.PORT, Namespace) def emit(self, message, data): json_data = json.dumps(data.__dict__) self.socketIO.emit(message, json_data) class Namespace(BaseNamespace): def on_connect

问题 A recent question here had the following code (well, similar to this) to implement a singleton without synchronisation. public class Singleton { private Singleton() {} private static class SingletonHolder { private static final Singleton INSTANCE = new Singleton(); } public static Singleton getInstance() { return SingletonHolder.INSTANCE; } } Now, I think understand what this is doing. Since the instance is static final , it's built long before any threads will call getInstance() so there's

问题 The singleton pattern is a design pattern that is used to restrict instantiation of a class to one object instance. Although I know how to code the singleton pattern in C++ and Java, I was wondering if anyone know how to implement it in Ruby? 回答1: Actually, the above answer was not completely correct. require 'singleton' class Example include Singleton end You also need to include the require 'singleton' statement. 回答2: Use the singleton module: class Clazz include Singleton end See http:/

问题 Ok, if I create a singleton class and expose the singleton object through a public static property...I understand that. But my singleton class has other properties in it. Should those be static? Should those also be private? I just want to be able to access all properties of my singleton class by doing this: MySingletonClass.SingletonProperty.SomeProperty2 Where SingletonProperty returns me the single singleton instance. I guess my question is, how do you expose the other properties in the

问题 Ok, if I create a singleton class and expose the singleton object through a public static property...I understand that. But my singleton class has other properties in it. Should those be static? Should those also be private? I just want to be able to access all properties of my singleton class by doing this: MySingletonClass.SingletonProperty.SomeProperty2 Where SingletonProperty returns me the single singleton instance. I guess my question is, how do you expose the other properties in the