C#中线程安全的单例模式_c#线程安全的单例模式有什么作用

一、单例模式

①单例模式的定义：是用来保证这个类在运行期间只会被创建一个实例，并提供一个访问它的全局访问点。

②单例模式的作用：保证一个类只有一个访问实例，节省系统资源。

③单例模式的特点：私有构造方法；私有成员变量；公有获取实例方法。

二、单例模式实现

①懒汉式单例

using System;
using System.Collections.Generic;
using System.Text;
 
namespace SingleModel
{
    //懒汉式单例模式
    public class Single
    {
        //私有构造
        private Single() { }
 
        //单例
        public static Single GetInstance()
        {
            return SingleHolder._Instance;
        }
 
        //内部类
        private static class SingleHolder
        {
            internal static readonly Single _Instance = new Single();
        }
 
    }//Class_end
}

②饿汉式单例

using System;
using System.Collections.Generic;
using System.Text;
 
namespace SingleModel
{
    //饿汉式单例模式
    public class Single2
    {
        private static readonly Single2 _Instance = new Single2();
        private Single2() { }
 
        public static Single2 GeInstance()
        {
            return _Instance;
        }
 
    }//Class_end
}

③懒汉式单例

using System;
using System.Collections.Generic;
using System.Text;
 
namespace SingleModel
{
    //懒汉式单例
    public class Single3
    {
        //定义一个保存实例的静态变量
        private static Single3 _Instance;
        //定义一个保证线程同步标识
        private static readonly object _Synchronized = new object();
        private Single3() { }
 
        public static Single3 GeInstance()
        {
            if (_Instance==null)
            {
                lock (_Synchronized)
                {
                    //双重锁定
                    if (_Instance==null)
                    {
                        _Instance = new Single3();
                    }
                }
            }
            return _Instance;
        }
 
    }//Class_end
}

 ④实现控制实例数目单例

using System;
using System.Collections.Generic;
using System.Text;
 
namespace SingleModel
{
    //实现控制实例数目
    public class SingleExtand
    {
        //私有构造
        private SingleExtand() { }
 
        //定义一个缺省的key值前缀 
        private static string _DefaultPreKey = "Cache";
        //记录当前实例
        public static int _SingleNum = 1;
 
        //定义实例的最大数目
        private static int _MaxSingleNum = 3;
 
        //定义一个保证线程同步的标识
        private static readonly object _Synchronized = new object();
        //缓存实例的容器
        private static Dictionary<String, SingleExtand> _SinleDic = new Dictionary<string, SingleExtand>();
 
        
        //本类实例
        public static SingleExtand GetInstance()
        {
            string key = _DefaultPreKey + _SingleNum;
            SingleExtand sinleExtand = null;
            if (_SinleDic.ContainsKey(key))
            {
                sinleExtand = _SinleDic[key];
            }
 
            if (sinleExtand==null)
            {
                lock (_Synchronized)
                {
                    if (sinleExtand == null)
                    {
                        sinleExtand = new SingleExtand();
                        _SinleDic.Add(key, sinleExtand);
                    }
                } 
            }
 
            _SingleNum++;
            if (_SingleNum>_MaxSingleNum)
            {
                _SingleNum = 1;
            }
 
            return sinleExtand;
        }
 
 
    }//Class_end
}

三、单例测试

using System;
 
namespace SingleModel
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine("（线程安全）单例模式");
 
            Console.WriteLine("饿汉式单例1");
            Single single1 = Single.GetInstance();
            Single single2 = Single.GetInstance();
            Single single3 = Single.GetInstance();
            Console.WriteLine("single1:" + single1.GetHashCode());
            Console.WriteLine("single2:" + single2.GetHashCode());
            Console.WriteLine("single3:" + single3.GetHashCode());
            Console.WriteLine("\n");
 
            Console.WriteLine("懒汉式单例2");
            Single2 single21 = Single2.GeInstance();
            Single2 single22 = Single2.GeInstance();
            Single2 single23 = Single2.GeInstance();
            Console.WriteLine("single21:" + single21.GetHashCode());
            Console.WriteLine("single22:" + single22.GetHashCode());
            Console.WriteLine("single23:" + single23.GetHashCode());
            Console.WriteLine("\n");
 
            Console.WriteLine("懒汉式单例3");
            Single3 single31 = Single3.GeInstance();
            Single3 single32 = Single3.GeInstance();
            Single3 single33 = Single3.GeInstance();
            Console.WriteLine("single31:" + single31.GetHashCode());
            Console.WriteLine("single32:" + single32.GetHashCode());
            Console.WriteLine("single33:" + single33.GetHashCode());
            Console.WriteLine("\n");
 
 
            Console.WriteLine("控制实例数目的单例");
            SingleExtand singleExtand1 = SingleExtand.GetInstance();
            SingleExtand singleExtand2 = SingleExtand.GetInstance();
            SingleExtand singleExtand3 = SingleExtand.GetInstance();
            SingleExtand singleExtand4 = SingleExtand.GetInstance();
            SingleExtand singleExtand5 = SingleExtand.GetInstance();
            SingleExtand singleExtand6 = SingleExtand.GetInstance();
            Console.WriteLine("singleExtand1:" + singleExtand1.GetHashCode());
            Console.WriteLine("singleExtand2:" + singleExtand2.GetHashCode());
            Console.WriteLine("singleExtand3:" + singleExtand3.GetHashCode());
            Console.WriteLine("singleExtand4:" + singleExtand4.GetHashCode());
            Console.WriteLine("singleExtand5:" + singleExtand5.GetHashCode());
            Console.WriteLine("singleExtand6:" + singleExtand6.GetHashCode());
            Console.WriteLine("\n");
 
 
 
            Console.ReadLine();
        }
    }
}

运行结果如下：