singleton

问题 What happens to my static variables when app-engine spins new instances? More specifically I am using a Task Queue that can have 40 instances/thread. Within the Servlet in question, I am using a singleton, as in public class WorkerThread extends HttpServlet { @Override protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { .. MySingleton single = MySingleton.getInstance(); .. } ... } Here is how the singleton is created public

问题 This question already has answers here : Closed 7 years ago . Possible Duplicate: Is there a simple, elegant way to define Singletons in Python? I have the following example code, in which I derive a class from a Singleton (hope it is one): class Singleton(object): _instance = None def __new__(cls, *args, **kwargs): if not cls._instance: cls._instance = object.__new__(cls, *args, **kwargs) return cls._instance class Tracer(Singleton): def __init__(self): print "Init" a = Tracer() b = Tracer()

问题 I've got the following Singleton class: class Singleton { static let sharedInstance = Singleton() } I can find very little online about how to use the numerous swift implementations of the Singleton pattern. I have used it before in Objective-C on a previous application but to me it seemed much more straight forward. For instance, if I wanted to create an array of custom objects that could be used anywhere in the application, how would I declare it, and how would I implement it. In my

问题 I've created two enum classes as singleton: public enum A { INSTANCE; public void init(param p1, param p2) { } public void connect() { } public void disconnect() { } public bool isConnected() { } } public enum B { INSTANCE; public void init(param p1) { } public void connect() { } public void disconnect() { } public bool isConnected() { } } As you can see both enum classes are very similar so I was wondering if I should create some kind of base abstract class/enum or interface and then have

问题 I have a Dao which is not Singleton, if other objetcs extend from him, is singleton or not ? code example <bean id="dao" class="parentDao" scope="prototype"> </bean> <bean id="childrenDao" class="some.dao.extends.parentDao" parent="parentDao"> </bean> the childrenDao is it singleton? 回答1: Update : Verified through a test, the scope is also inherited from the parent bean and can be overridden by the child. So in this case childrendDao will be a prototype. This is what is stated in the

问题 I have created an overlay to run while I run an async data grab to the server so that users won't continue pressing buttons in the UI until the data grab is done. I have put the function into a global singleton class and I call it while passing in a bool to say whether or not I want to show or hide. I can get it to show but I cannot get it to hide. Here is the code: class DataModel { static let sharedInstance = DataModel() func accessNetworkData(vc: UIViewController, params: [String:Any],

问题 I'm using PowerMock with EasyMock, and wondered how I might mock a singleton with a private constructor? Let's say I have the following class: public class Singleton { private static Singleton singleton = new Singleton(); private Singleton() { } public static Singleton getInstance() { return singleton; } public int crazyServerStuff() { ... } } And a class which uses this: public class Thing { public Thing() {} public int doStuff(Singleton s) { return s.crazyServerStuff() + 42; } } How might I

问题 I'm following this link and trying to make a singleton class. But, taking arguments (passed while initiating a class) into account so that the same object is returned if the arguments are same. So, instead of storing class name/class reference as a dict key, I want to store passed arguments as keys in dict . But, there could be unhashable arguments also (like dict , set itself). What is the best way to store class arguments and class objects mapping? So that I can return an object

问题 I have a WPF singleton application, wherein only one instance is running at any time, if user tries to launch another instance, we check if its already running then we kill this new process and bring to front the existing one. Now, we have a requirement to open/access and send message (set of arguments) to this WPF application from another process which can be xls, word, or another standalone application. We also want to make sure that if the process is already running, that process should

问题 In spring the classes annotated with @Controller , @Service , @Repository , @Component act as Spring beans and will be instantiated by Spring container in singleton (Default scope). Here the model beans are not annotated with any stereo type annotations. My question here is whether the model beans are singleton or not i.e., if they come under Spring container. If it is true then, how has the concurrency issue been handled? 回答1: Model attributes, ex. from @ModelAttribute annotated parameters,