#include <iostream>
#include <boost/thread.hpp>
#include <boost/thread/shared_mutex.hpp>
#include <boost/thread/locks.hpp>

using namespace std;

class Test { 
 public:
   static Test *Instance();
   virtual ~Test();
   
 private:
   Test();
   static Test *instance;
   static boost::shared_mutex instanceMutex;   
};

Test *Test::instance = NULL;
boost::shared_mutex Test::instanceMutex;

Test::Test() { };

Test *Test::Instance() {
   boost::upgrade_lock<boost::shared_mutex> lock(instanceMutex);
   if (!instance) {
      boost::upgrade_to_unique_lock<boost::shared_mutex> uniqueLock(lock);
      instance = new Test();
   }
   return instance;
};

Test::~Test() {
   boost::upgrade_lock<boost::shared_mutex> lock(instanceMutex);
   if (instance) {
      boost::upgrade_to_unique_lock<boost::shared_mutex> uniqueLock(lock);
      instance = NULL;
   }  
};

int main() {
   Test *i = Test::Instance();
   delete i;
   
   return(0);
}