Concurrency in Singleton Designing Pattern

      Please refer previous post for Singleton Designing Pattern. Concurrency is the one of the major issues with singleton designing pattern.

      There will be multiple client accessing same singleton resource instance. If this resource is mutable then concurrency need to be taken care . Example from previous post is being used here.

  1: package demo.singleton;
  2: import java.util.concurrent.locks.ReadWriteLock;
  3: import java.util.concurrent.locks.ReentrantReadWriteLock;
  4: /**
  5:  * Singleton Resource Class
  6:  * @author Yogesh
  7:  */
  8: public class SingletonResource {
  9:     private static SingletonResource resorce =null;
 10:     int count;
 11:     private ReadWriteLock writeLock = new ReentrantReadWriteLock();
 12: 
 13:     public static  SingletonResource getInstance(){
 14:         if(resorce ==null){
 15:             synchronized(SingletonResource.class){
 16:                 if(resorce==null){
 17:                     resorce = new SingletonResource();
 18:                 }
 19:             }
 20:         }
 21:         return resorce;
 22:     }
 23: 
 24:     private SingletonResource(){
 25:         // your initializing code here
 26:     }
 27:     
 28:     public void increament(){
 29:         writeLock.writeLock().lock();
 30:         count++;
 31:         writeLock.writeLock().unlock();            
 32:     }
 33:         
 34:      public void decreament(){
 35:         writeLock.writeLock().lock();
 36:         count--;
 37:         writeLock.writeLock().unlock();            
 38:     }
 39: }