Re: need feedback on singleton template

From:

"Chris Thomasson" <cristom@comcast.net>

Newsgroups:

comp.lang.c++.moderated

Date:

Thu, 27 Mar 2008 11:03:11 CST

Message-ID:

<Z-OdnQsHWPnJvXbanZ2dnUVZ_oesnZ2d@comcast.com>

"Dmitry Teslenko" <dteslenko@gmail.com> wrote in message
news:b22cafae-d213-4d3e-b112-ec1ca39a4be5@m34g2000hsc.googlegroups.com...

Hello! I've come up with this singleton template. It works and seems
to correctly free resources.
One bad thing is WorkerSingleton's constructor/destructor must be
public in order to use Singleton template.

#include "boost/shared_ptr.hpp"
#include <iostream>

template <class T>
class Singleton
{
    protected:
        Singleton();
        ~Singleton();
    public:
        static T * instance();
};

template <class T>
Singleton<T>::Singleton()
{
    std::cout << "singleton was created" << std::endl;
}

template <class T>
Singleton<T>::~Singleton()
{
    std::cout << "singleton was destroyed" << std::endl;
}

template <class T>
T * Singleton<T>::instance()
{
    static boost::shared_ptr<T> p;
    if(!p.get())
    {
        p.reset(new T);
    }
    return p.get();
}

You can force this to work if you alter the 'Singleton<T>::instance()'
function. Something like:

<error check omitted for simplicity>
_______________________________________________________________
template <class T>
T * Singleton<T>::instance()
{
     static pthread_mutex_t mtx = PTHREAD_MUTEX_INITIALIZER;
     static boost::shared_ptr<T> p;
     pthread_mutex_lock(&mtx);
     if(!p.get())
     {
         p.reset(new T);
     }
     pthread_mutex_unlock(&mtx);
     return p.get();
}
_______________________________________________________________

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