Singleton.hpp

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// Copyright 2025 Intelligent Robotics Lab
//
// 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.
 
 
#ifndef EASYNAV_COMMON__SINGLETON_HPP_
#define EASYNAV_COMMON__SINGLETON_HPP_
 
#include <mutex>
#include <utility>
 
namespace easynav
{
 
template<class C>
class Singleton
{
public:
  template<typename ... Args>
  static C * getInstance(Args &&... args)
  {
    std::lock_guard<std::mutex> lock(mutex_);
    if (!instance_) {
      instance_ = new C(std::forward<Args>(args)...);
    }
    return instance_;
  }

  static void removeInstance()
  {
    std::lock_guard<std::mutex> lock(mutex_);
    delete instance_;
    instance_ = nullptr;
  }
 
  template<typename ... Args>
  static C & get(Args &&... args)
  {
    return *getInstance(std::forward<Args>(args)...);
  }
 
protected:
  Singleton() = default;
  ~Singleton() = default;
 
  Singleton(const Singleton &) = delete;
  Singleton & operator=(const Singleton &) = delete;
 
private:
  // Never destroyed at exit: the plugin library that built it (its vtable) may be unloaded
  static C * instance_;
  static std::mutex mutex_;
};
 
template<class C>
C * Singleton<C>::instance_ = nullptr;
 
template<class C>
std::mutex Singleton<C>::mutex_;
 
#define SINGLETON_DEFINITIONS(ClassName) \
public: \
  static ClassName * getInstance() \
  { \
    return ::easynav::Singleton<ClassName>::getInstance(); \
  } \
  template<typename ... Args> \
  static ClassName * getInstance(Args && ... args) \
  { \
    return ::easynav::Singleton<ClassName>::getInstance( \
      std::forward<Args>(args)...); \
  }
 
}  // namespace easynav
 
#endif  // EASYNAV_COMMON__SINGLETON_HPP_