A thread safe base template class of c++ Singleton

Singleton.hpp

#include <stdlib.h>
#include <iostream>
#include <pthread.h>

#ifndef SINGLETON_H
#define SINGLETON_H

namespace util {
template <class T>
class Singleton {
public:
  static pthread_rwlock_t rwlock;

  Singleton(){
  };
  static T* GetInstance() {
    pthread_rwlock_rdlock(&rwlock);
    if (!_instance) {
      pthread_rwlock_unlock(&rwlock);
      pthread_rwlock_wrlock(&rwlock);
      if (!_instance) {
        _instance = new T;
        _instance->Init();
      }
    }
    pthread_rwlock_unlock(&rwlock);
    return _instance;
  };
  virtual ~Singleton() {};
  virtual void Init() = 0;
  static void Destroy() {
    pthread_rwlock_rdlock(&rwlock);
    if (_instance) {
      pthread_rwlock_unlock(&rwlock);
      pthread_rwlock_wrlock(&rwlock);
      if (_instance) {
        delete _instance;
        _instance = NULL;
      }
    }
    pthread_rwlock_unlock(&rwlock);
  }

private:
  static T* _instance;
  Singleton(Singleton const &s);
  Singleton & operator = (const Singleton &);
};

template<class T>
T* Singleton<T>::_instance = NULL;

template<class T>
pthread_rwlock_t Singleton<T>::rwlock = PTHREAD_RWLOCK_INITIALIZER;

} // namespace util
#endif

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