Re: need feedback on singleton template

From:

"Chris Thomasson" <cristom@comcast.net>

Newsgroups:

comp.lang.c++.moderated

Date:

Thu, 27 Mar 2008 11:02:48 CST

Message-ID:

<nPSdnfIfOY4KgnbanZ2dnUVZ_o6knZ2d@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.

[...]

Not going to work as-is because shared_ptr honors only basic thread-safety.
Here is an outline of an atomically thread-safe singleton:
_______________________________________________________________
template<typename T>
class once {
  static T* m_state;
  static pthread_mutex_t m_mtx;

public:
  static T* get() {
    T* local = ATOMIC_LOADPTR_MBDEPENDS(&m_state);
    if (local == NULL) {
      pthread_mutex_lock(&m_mtx);
      if ((local = m_state) == NULL) {
        try {
          local = new T;
        } catch (...) {
          pthread_mutex_unlock(&m_mtx);
          throw;
        }
        ATOMIC_STOREPTR_MBRELEASE(&m_state, local);
      }
      pthread_mutex_unlock(&m_mtx);
    }
    return local;
  }
};

template<typename T>
T* once<T>::m_state = NULL;

template<typename T>
pthread_mutex_t once<T>::m_mtx = PTHREAD_MUTEX_INITIALIZER;
_______________________________________________________________

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