Thread safe singleton methodes.

[Daniel R. Kĺsa]

The implementations for singleton patterns are not
thread safe. This means that it is possible to obtain
more than one instance of a category object across two threads. Especially since it is not a rare case that the static getInstance is called upon the Category object to obtain the category that is to be logged to.

example: (double locked pattern)

object& getInstance()
{
   // create when called.
   static pthread_mutex_t = PTHREAD_MUTEX_INITIALIZER;
   if (Object == 0)
   {
      // this should be fast, because this
      // point is only locked the first time.
      pthread_mutex_lock(&mutex);
      if (Object == 0)
      {
         m_Instance = new object;
      }
      pthread_mutex_unlock(&mutex);     
  }
}
}