07 singleton mode

The singleton pattern / Singlet mode ： Create pattern , Create a class that produces only one object instance ---- Use private constructor to realize the definition of class .

One ： Basic concept and implementation of singleton class

GameConfig,Scott Meyers“ Make the interface or type easy to use correctly , Difficult to misuse ”
Only one class belonging to this class can be created, which is called singleton class .
（2） Problems that a singleton class can cause in multithreading
A good solution to multithreading creation GameConfig The method of class object problem is in main Main function （ Program execution entry ）, Before creating any other threads ,
Do it first GameConfig::getInstance(); Let's put this alone GameConfig Class object is created .
（3） Hungry and lazy
（4） Memory release problem of singleton class object
（5） Single piece class definition 、UML Figure and another implementation method
Single piece design pattern definition ： Ensure that only one instance of a class exists , At the same time, it provides a global method that can access the instance （getInstance Member functions ）.
Troubled problems ： There are two problems in the cross reference between multiple singleton classes . Log、GameConfig—— Do not reference other singleton objects in the destructor of singleton class .