src/base/singleton.h

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#ifndef MOZC_BASE_SINGLETON_H_
#define MOZC_BASE_SINGLETON_H_

#include "base/mutex.h"

namespace mozc {

class SingletonFinalizer {
 public:
  typedef void (*FinalizerFunc)();

  // Do not call this method directly.
  // use Singleton<Typename> instead.
  static void AddFinalizer(FinalizerFunc func);

  // Call Finalize() if you want to finalize
  // all instances created by Sigleton.
  //
  // Mozc UI for Windows (DLL) can call
  // SigletonFinalizer::Finalize()
  // at an appropriate timing.
  static void Finalize();
};

// Thread-safe Singleton class.
// Usage:
//
// class Foo {}
//
// Foo *instance = mozc::Singleton<Foo>::get();
template <typename T>
class Singleton {
 public:
  static T *get() {
    CallOnce(&once_, &Singleton<T>::Init);
    return instance_;
  }

 private:
  static void Init() {
    SingletonFinalizer::AddFinalizer(&Singleton<T>::Delete);
    instance_ = new T;
  }

  static void Delete() {
    delete instance_;
    instance_ = NULL;
    ResetOnce(&once_);
  }

  static once_t once_;
  static T *instance_;
};

template <typename T>
once_t Singleton<T>::once_ = MOZC_ONCE_INIT;

template <typename T>
T* Singleton<T>::instance_ = NULL;
}  // namespace mozc

#endif  // MOZC_BASE_SINGLETON_H_