Singleton is use same object for all the request form the client side, means if first request comes to server it's generate the object and all are request will share same reference like score or stock sharing and if the Server will not get any request withing 5 minutes then it will destroy the object and again will create and repeat the same processSingle call: Each and every request will served one object at once. ATM machine has been designed on Single Call mechanism so that after one transaction will ask your card swipe again and do the same procedure for transaction.