#include <iostream>
 using namespace std;
   
 /* Place holder for thread synchronization mutex */
 class Mutex
 {   /* placeholder for code to create, use, and free a mutex */
 };
   
 /* Place holder for thread synchronization lock */
 class Lock
 {   public:
         Lock(Mutex& m) : mutex(m) { /* placeholder code to acquire the mutex */ }
         ~Lock() { /* placeholder code to release the mutex */ }
     private:
         Mutex & mutex;
 };
   
 class Singleton
 {   public:
         static Singleton* GetInstance();
         int a;
         ~Singleton() { cout << "In Destructor" << endl; }
   
     private:
         Singleton(int _a) : a(_a) { cout << "In Constructor" << endl; }
   
   
         static Mutex mutex;
   
         // Not defined, to prevent copying
         Singleton(const Singleton& );
         Singleton& operator =(const Singleton& other);
 };
   
 Mutex Singleton::mutex;
   
 Singleton* Singleton::GetInstance()
 {
     Lock lock(mutex);
   
     cout << "Get Instance" << endl;
   
     // Initialized during first access
     static Singleton inst(1);
   
     return &inst;
 }
   
 int main()
 {
     Singleton* singleton = Singleton::GetInstance();
     cout << "The value of the singleton: " << singleton->a << endl;
     return 0;
}