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这篇文章主要介绍"singleton class是什么"，在日常操作中，相信很多人在singleton class是什么问题上存在疑惑，小编查阅了各式资料，整理出简单好用的操作方法，希望对大家解答"singleton class是什么"的疑惑有所帮助!接下来，请跟着小编一起来学习吧!

SystemVerilog中Singleton class是指只有一个对象（object）的类。这个对象只创建一次，为所需的全局变量提供一个namespaces。

Singleton class定义全局的行为，例如printing。

Singleton class 在compile-time创建一个对象，然后在run-time操作其中的成员,不需要用户在仿真时在建立一个新的实例。

program top;class singleton; int unsigned var1;

// Need to declare it as static, as it is accessed by static method 'create' static singleton single;

// Declared as 'protected', so user can't directly create instance of this class protected functionnew(); endfunction:new

static functionsingleton create(); if (single ==null) begin $display("Object single is null, so creating new object"); single =new(); end return single; endfunction:create endclass:singleton singleton s1, s2; initial begin s1 = singleton ::create(); $display (" 1 : s1.var1 = %0d", s1.var1); s1.var1 =10; $display (" 2 : s1.var1 = %0d", s1.var1);

s2 = singleton ::create(); $display (" 3 : s2.var1 = %0d", s2.var1);

s2.var1 =20; $display (" 4 : s2.var1 = %0d", s2.var1); $display (" 5 : s1.var1 = %0d", s1.var1); end endprogram

Output:

// 1 : s1.var1 = 0 // 2 : s1.var1 = 10 // 3 : s2.var1 = 10 // 4 : s2.var1 = 20 // 5 : s1.var1 = 20

A singleton object is a globally accessiblestatic object providing customizable service methods.

Synopsys UVM1.2 Workshop

在下面的例子中：

class service_class; protected static service_class me =get(); static function service_class get(); if(me = null) me = new() ; return me ; endfunctionextern virtual function void error (string msg) ;endclass

error method需要用户自行定义所需要的行为。

在UVM的workshop中使用了一个名称为proxy_class的singleton class很好地诠释了其在factory机制的应用。

class proxy_class#(type T =base) ; type proxy_class#(T) this_type ; //just for coding convenience protected function new();endfunction

static function this_type get(); if(me== null) me = new() ; return me;endfunctionstatic function T create(); create=new() ;functionendcase

class driver xtends base; typedef proxy_class(driver) proxy ;endclass

class monitor xtends base; typedef proxy_class(monitor) proxy ;endclass

class environment ; driver drv ; monitor mon; function new; drv = driver::proxy::create() ; mon = monitor::proxy::create() ; endfunctionendclass

这个proxy class提供了一个创建不同的singleton bject的机制。

为了使proxy class更有意义，我们需要一个virtual base class和factory机制。proxy class根据不同的factory注册和base class生成特定的proxy object。

到此，关于"singleton class是什么"的学习就结束了，希望能够解决大家的疑惑。理论与实践的搭配能更好的帮助大家学习，快去试试吧!若想继续学习更多相关知识，请继续关注网站，小编会继续努力为大家带来更多实用的文章!

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