Singleton.h

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// -*- C++ -*-
#ifndef COIL_SINGLETON_H
#define COIL_SINGLETON_H

#include <coil/Mutex.h>
#include <coil/Guard.h>

namespace coil
{
  template <class SingletonClass>
  class Singleton
  {
  public:
    typedef SingletonClass* SingletonClassPtr;
    typedef ::coil::Mutex Mutex;

    static SingletonClass& instance()
    {

      // DLC pattern
      if (!m_instance)
      {
        coil::Guard<coil::Mutex> guard(m_mutex);
        if (!m_instance)
          {
            m_instance = new SingletonClass();
          }
      }
      return *m_instance;
    }

  protected:
    Singleton(){};

    ~Singleton(){};

  private:
    Singleton(const Singleton& x);
    Singleton& operator=(const Singleton& x);

  protected:
    static coil::Mutex m_mutex;

    static SingletonClass* m_instance;
  };

  template <class SingletonClass>
  typename Singleton<SingletonClass>::SingletonClassPtr
  Singleton<SingletonClass>::m_instance;
  
  template <class SingletonClass>
  typename Singleton<SingletonClass>::Mutex
  Singleton<SingletonClass>::m_mutex;
}; // namepsace coil

#endif // COIL_SINGLETON_H