Singleton(17)

最新推荐文章于 2022-05-08 23:16:35 发布

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本文介绍了一种基于Boost库的线程安全单例模式实现方法，并通过一个测试程序展示了其实现过程及效果。该单例模式利用了pthread_once确保初始化只执行一次，并在程序退出时释放资源。

Singleton class uml

Singleton源代码

// 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

测试程序：

#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());
}

程序输出：

[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]#