Scoped Globals.cpp

#include <list>
#include <iostream>

// Replace with real mutex.
class Mutex
{
public:
   void lock () {}
   void unlock () {}
};

class Atomic
{
private:
   Mutex* mutex;

public:
   Atomic (Mutex* m) : mutex(m)
   {
       mutex->lock();
   }
   ~Atomic ()
   {
       mutex->unlock();
   }
};

template <class T>
class ScopedGlobal
{
private:
   static std::list<T> global;
   static Mutex mutex;

   std::_List_iterator<T> iter;

public:
   ScopedGlobal (T g)
   {
       Atomic atom(&mutex);
       iter = global.insert(global.end(), g);
   }
   ~ScopedGlobal ()
   {
       Atomic atom(&mutex);
       global.erase(iter);
   }

   static T& get ()
   {
       Atomic atom(&mutex);
       return *iter;
   }
};

template <class T>
std::list<T> ScopedGlobal<T>::global;

template <class T>
Mutex ScopedGlobal<T>::mutex;

int main ()
{
   ScopedGlobal<int> g(1);
   std::cout << ScopedGlobal<int>::get() << "\n";
   {
       ScopedGlobal<int> g(2);
       std::cout << ScopedGlobal<int>::get() << "\n";
   }
   std::cout << ScopedGlobal<int>::get() << "\n";
}