【设计模式】单例模式
定义
确保某个类只有一个实例
实现方式
饿汉式加载（线程安全）
public sealed class Singleton
{
private static Singleton _instance = new Singleton();
//将构造函数设置私有，外部不能new
private Singleton() { }
public static Singleton Instance => _instance;
}
等价于
public sealed class Singleton
{
private static Singleton _instance;
static Singleton()
{
_instance = new Singleton();
}
//将构造函数设置私有，外部不能new
private Singleton() { }
public static Singleton Instance => _instance;
}
懒汉式加载
- 非线程安全
public sealed class Singleton
{
private static Singleton _instance;
private Singleton() { }
public static Singleton Instance => _instance = _instance ?? new Singleton();
}
- 线程安全
- Double Check
public sealed class Singleton
{
private static readonly object _lock = new object();
private static Singleton _instance;
private Singleton()
{
Console.WriteLine("Singleton Constructor");
}
public static Singleton Instance
{
get
{
/// 避免走内核代码
if (_instance != null) return _instance;
lock (_lock)
{
if (_instance == null)
{
var temp = new Singleton();
//确保_instance写入之前，Singleton已经初始化完成
System.Threading.Volatile.Write<Singleton>(ref _instance, temp);
}
}
return _instance;
}
}
}
- 借助Lazy
public sealed class Singleton
{
private static Lazy<Singleton> _instance = new Lazy<Singleton>(() => new Singleton(), true);
private Singleton()
{
Console.WriteLine("Singleton Constructor");
}
public static Singleton Instance => _instance.Value;
}
