"Object Performance" mode of C + + design mode: Singleton, Flyweight

　　"Object Performance" mode
Object-oriented is a good solution to the "abstract" problem, but it must be paid a certain price. In general, object-oriented costs are largely negligible. In some cases, however, object-oriented costs must be handled with care.

　　Typical mode
# Singleton
# Flyweight

　　Part 1 Single-piece mode (single-case mode )

　　Motivation
#在软件系统中, there are often special classes that must be guaranteed to have only one instance of the system in order to ensure their logical correctness and good efficiency.
#如何绕过常规的构造器, provides a mechanism to guarantee that there is only one instance of a class?
#这应该是类设计者的责任, not the responsibility of the user.

　　Pattern definition
Ensure that a class has only one instance and provides a global access point for that instance. --"Design pattern" GoF

　　Code

classsingleton{Private StaticSingleton instance; Private Static ReadOnly ObjectSyncRoot =New Object();  Public StaticSingleton getinstance () {if(Instance = =NULL)        {            Lock(syncRoot) {if(Instance = =NULL) Instance=NewSingleton (); }        }                returninstance; }        Private StaticSingleton instance () {}}

　　Structure
　　

　　Summary of Points
# The instance constructor in Singleton mode can be set to protected to allow subclasses to derive.
# Singleton mode generally does not support copy constructors and Clone interfaces, because this can lead to multiple object instances, contrary to the original intention of the Singleton mode.
#如何实现多线程环境下安全的 Singleton? Note the correct implementation of the double check lock.

"Object Performance" mode of C + + design mode: Singleton, Flyweight