普通单例模式
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| public class Singleton
{
private static Singleton instance = null;
private Singleton()
{
}
public static Singleton Instance
{
get
{
if (instance == null)
{
instance = new Singleton();
}
return instance;
}
}
}
|
缺点：
非线程安全
简单线程安全
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| public class Singleton
{
private static Singleton instance = null;
private static readonly object padlock = new object();
Singleton()
{
}
public static Singleton Instance
{
get
{
lock (padlock)
{
if (instance == null)
{
instance = new Singleton();
}
return instance;
}
}
}
}
|
优点：
使用锁去控制类的实例化，保证了线程安全。
缺点：
性能受影响，每次获取实例都需要先加锁。
双重检查
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| public class Singleton
{
private static Singleton instance = null;
private static readonly object padlock = new object();
Singleton()
{
}
public static Singleton Instance
{
get
{
if (instance == null)
{
lock (padlock)
{
if (instance == null)
{
instance = new Singleton();
}
}
}
return instance;
}
}
}
|
通过双重检查，减少加锁带来的性能问题。
不加锁版本
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| public class Singleton
{
private static readonly Singleton instance = new Singleton();
// Explicit static constructor to tell C# compiler
// not to mark type as beforefieldinit
static Singleton()
{
}
private Singleton()
{
}
public static Singleton Instance
{
get
{
return instance;
}
}
}
|
使用 Lazy<T> type
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| public sealed class Singleton
{
private static readonly Lazy<Singleton> lazy = new Lazy<Singleton>(() => new Singleton());
public static Singleton Instance
{
get
{
return lazy.Value;
}
}
private Singleton()
{
}
}
|
https://csharpindepth.com/articles/singleton
