17muduo_base库源码分析（八）

1.Singleton类图

线程安全Singleton类实现

(1)pthread_once

(2)atexit

(3)typedef char T_must_be_complete_type[sizeof(T) == 0 ? -1 : 1];

2.代码

Singleton.h

// 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 
#include 
#include  // atexit

namespace muduo
{

template
class Singleton : boost::noncopyable
{
 public:
  static T& instance()
  {
    pthread_once(&ponce_, &Singleton::init);
    return *value_;
  }

 private:
  Singleton();
  ~Singleton();

  static void init()
  {
    value_ = new T();
    ::atexit(destroy);
  }

  static void destroy()
  {
    typedef char T_must_be_complete_type[sizeof(T) == 0 ? -1 : 1];
    delete value_;
  }

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

template
pthread_once_t Singleton::ponce_ = PTHREAD_ONCE_INIT;

template
T* Singleton::value_ = NULL;

}
#endif

Singleton_test.cc

#include 
#include 
#include 

#include 
#include 

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::instance(),
         muduo::Singleton::instance().name().c_str());
  muduo::Singleton::instance().setName("only one, changed");
}

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

运行结果