base/memory/singleton.h

// Copyright (C) 2011 The Libphonenumber Authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

// Author: Philippe Liard

#ifndef I18N_PHONENUMBERS_BASE_MEMORY_SINGLETON_H_
#define I18N_PHONENUMBERS_BASE_MEMORY_SINGLETON_H_

#if defined(I18N_PHONENUMBERS_USE_BOOST)

#include <boost/scoped_ptr.hpp>
#include <boost/thread/once.hpp>
#include <boost/utility.hpp>

namespace i18n {
namespace phonenumbers {

template <class T>
class Singleton : private boost::noncopyable {
 public:
  virtual ~Singleton() {}

  static T* GetInstance() {
    boost::call_once(Init, flag);
    return instance.get();
  }

 private:
  static void Init() {
    instance.reset(new T());
  }

  static boost::scoped_ptr<T> instance;
  static boost::once_flag flag;
};

template <class T> boost::scoped_ptr<T> Singleton<T>::instance;
template <class T> boost::once_flag Singleton<T>::flag = BOOST_ONCE_INIT;

}  // namespace phonenumbers
}  // namespace i18n

#else  // !I18N_PHONENUMBERS_USE_BOOST

#include "phonenumbers/base/logging.h"
#include "phonenumbers/base/thread_checker.h"

#if !defined(__linux__) && !defined(__APPLE__)

namespace i18n {
namespace phonenumbers {

// Note that this implementation is not thread-safe. For a thread-safe
// implementation on non-POSIX platforms, please compile with
// -DI18N_PHONENUMBERS_USE_BOOST.
template <class T>
class Singleton {
 public:
  Singleton() : thread_checker_() {}

  virtual ~Singleton() {}

  static T* GetInstance() {
    static T* instance = NULL;
    if (!instance) {
      instance = new T();
    }
    DCHECK(instance->thread_checker_.CalledOnValidThread());
    return instance;
  }

 private:
  const ThreadChecker thread_checker_;
};

}  // namespace phonenumbers
}  // namespace i18n

#else
#include "phonenumbers/base/memory/singleton_posix.h"
#endif  // !defined(__linux__) && !defined(__APPLE__)

#endif  // !I18N_PHONENUMBERS_USE_BOOST
#endif  // I18N_PHONENUMBERS_BASE_MEMORY_SINGLETON_H_