单例模式的优化-双重锁定

Posted 2022-07-31 真爱无限

三种单例模式写法：

    public class Singleton
    
        private static Singleton instance;
        private static readonly object syncRoot = new object();
        private Singleton()  
        public static Singleton GetInstance()
        
            if (instance == null)//Double-Check Locking 双重锁定，比直接lock性能更好，最完美的模式（懒汉式单例）
            
                lock (syncRoot)
                
                    if (instance == null)
                    
                        instance = new Singleton();
                    
                
            
            return instance;
        
    
    public class Singleton1
    
        private static Singleton1 instance;
        private static readonly object syncRoot = new object();
        private Singleton1()  
        public static Singleton1 GetInstance()
        
            lock (syncRoot)//每次调用GetInstance都需要lock，影响性能（懒汉式单例）
            
                if (instance == null)
                
                    instance = new Singleton1();
                
            
            return instance;
        
    
    public class Singleton2
    
        private static Singleton2 instance=new Singleton2();//静态初始化方式（饿汉式单例），类一加载就实例化对象，一般这样用也没问题，缺点：提前占用系统资源
        private Singleton2()  
        public static Singleton2 GetInstance()
        
            return instance;
        
    

双重锁定性能优化分析：