Singleton(17)

Singleton class uml

// Use of this source code is governed by a BSD-style license
// that can be found in the License file.
//
// Author: Shuo Chen (chenshuo at chenshuo dot com)

#ifndef MUDUO_BASE_SINGLETON_H
#define MUDUO_BASE_SINGLETON_H

#include <boost/noncopyable.hpp>
#include <pthread.h>
#include <stdlib.h> // atexit

namespace muduo
{

template<typename T>
class Singleton : boost::noncopyable //不可复制的
{
public:
static T& instance() //单例一个对象
{
pthread_once(&ponce_, &Singleton::init); //线程安全，并且一次调用
return *value_;
}

private:
Singleton();
~Singleton();

//初始化对象value
static void init()
{
value_ = new T();
//加入释放队列
::atexit(destroy);
}

static void destroy()
{
//T_must_be_complete_type 完全类型
typedef char T_must_be_complete_type[sizeof(T) == 0 ? -1 : 1];
//真正释放实例资源
delete value_;
}

private:
static pthread_once_t ponce_;
static T*             value_;
};

template<typename T>
pthread_once_t Singleton<T>::ponce_ = PTHREAD_ONCE_INIT;

template<typename T>
T* Singleton<T>::value_ = NULL;

}
#endif

#include <muduo/base/Singleton.h>
#include <muduo/base/CurrentThread.h>
#include <muduo/base/Thread.h>

#include <boost/noncopyable.hpp>
#include <stdio.h>

class Test : boost::noncopyable
{
public:
Test()
{
printf("tid=%d, constructing %p\n", muduo::CurrentThread::tid(), this);
}

~Test()
{
printf("tid=%d, destructing %p %s\n", muduo::CurrentThread::tid(), this, name_.c_str());
}

const muduo::string& name() const { return name_; }
void setName(const muduo::string& n) { name_ = n; }

private:
muduo::string name_;
};

void threadFunc()
{
printf("tid=%d, %p name=%s\n",
muduo::CurrentThread::tid(),
&muduo::Singleton<Test>::instance(),
muduo::Singleton<Test>::instance().name().c_str());
muduo::Singleton<Test>::instance().setName("only one, changed");
}

int main()
{
//muduo::Singleton<Test>::instance() 单例化 Test
muduo::Singleton<Test>::instance().setName("only one");
muduo::Thread t1(threadFunc);
t1.start();
t1.join();
printf("tid=%d, %p name=%s\n",
muduo::CurrentThread::tid(),
&muduo::Singleton<Test>::instance(),
muduo::Singleton<Test>::instance().name().c_str());
}

[root@localhost bin]# ./singleton_test
tid=2777, constructing 0x87cc008
tid=2778, 0x87cc008 name=only one
tid=2777, 0x87cc008 name=only one, changed
tid=2777, destructing 0x87cc008 only one, changed
[root@localhost bin]#