// 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 <assert.h>
#include <stdlib.h> // atexit
#include <pthread.h>
namespace muduo
{
namespace detail
{
// This doesn't detect inherited member functions!
template<typename T>
struct has_no_destroy
{
#ifdef __GXX_EXPERIMENTAL_CXX0X__
template <typename C> static char test(decltype(&C::no_destroy));
#else
template <typename C> static char test(typeof(&C::no_destroy));
#endif
template <typename C> static int32_t test(...);
const static bool value = sizeof(test<T>(0)) == 1;
};
}
template<typename T>
class Singleton : boost::noncopyable
{
public:
static T& instance()
{
//保证init_routine()函数在本进程执行序列中仅执行一次。
pthread_once(&ponce_, &Singleton::init);
assert(value_ != NULL);
return *value_;
}
private:
//默认构造函数
Singleton();
//默认析构函数
~Singleton();
static void init()
{
//初始化value_,并把其清零
value_ = new T();
if (!detail::has_no_destroy<T>::value)
{
//在进程退出时回收资源
::atexit(destroy);
}
}
//回收资源
static void destroy()
{
typedef char T_must_be_complete_type[sizeof(T) == 0 ? -1 : 1];
T_must_be_complete_type dummy; (void) dummy;
delete value_;
value_ = NULL;
}
private:
//pthread_once参数
static pthread_once_t ponce_;
//指向一个实例
static T* value_;
};
//static需要在类外进行初始化
template<typename T>
pthread_once_t Singleton<T>::ponce_ = PTHREAD_ONCE_INIT;
template<typename T>
T* Singleton<T>::value_ = NULL;
}
#endif