Threadsafe Circular Queue

Hi,

I have the following working code for implementing a Circular Queue. How do I modify it to make it thread safe?

const int MAX = 5;
class CQueueImp
{
      int a[MAX],front,rear;
        
      public :
               void initialize();                // initialize
                  void enqueue(int );
               int dequeue();
               void display();
};




        void CQueueImp ::initialize()
        {
            front=rear=-1;
        }

        void CQueueImp :: enqueue(int val)
        {
             if((front==0 && rear==MAX-1) || (rear+1==front))
                    std::cout<<" Circular Queue is Full";
             else
             {
               if(rear==MAX-1)
                    rear=0;
               else
                   rear++;
               a[rear]=val;
             }
             if(front==-1)
               front=0;
        }
        int CQueueImp :: dequeue()
        {
             int k;
             if(front==-1)
                  std::cout<<"Circular Queue is Empty";
             else
             {
                  k=a[front];
                  if(front==rear)
                     front=rear=-1;
                  else
                  {
                     if(front==MAX-1)
                          front=0;
                     else
                          front++;
                  }
             }
             return k;
        }
        void CQueueImp :: display()
        {
              int i;
              if(front==-1)
                   std::cout<<"Circular Queue is Empty";
              else
              {
                   if(rear < front)
                   {
                        for(i=front;i<=MAX-1;i++)
                           std::cout<<a[i]<<"   ";
                        for(i=0;i<=rear;i++)
                           std::cout<<a[i]<<"   ";
                   }
                   else
                   {
                        for(i=front;i<=rear;i++)
                           std::cout<<a[i]<<"   ";
                        printf("\n");
                   }
              }
        }

        void main()
        {
             CQueueImp c1;
             c1.initialize();

             int ch,val;
             char op;
             do
             {
               std::cout<<"-----------Menu-------------";
               std::cout<<"1.Insertion 2.Deletion 3.Display 4.Exit ";
               std::cout<<"Enter Your Choice <1..4> ?";
               std::cin>>ch;
               switch(ch)
               {
                     case 1 : std::cout<<"Enter Element to Insert ?";
                                std::cin>>val;
                                    c1.enqueue(val);
                                    break;
                     case 2 : val=c1.dequeue();
                                    std::cout<<"Deleted Element :"<<val;
                                    break;
                     case 3 : c1.display();
                                    break;
                  }
                  std::cout<<"Do you want to continue<Y/N> ?";
                  std::cin>>op;
              }while(op=='Y' || op=='y');
            }