Test.java

package com.freemindcafe.concurrency.sample7;

import java.util.ArrayList;
import java.util.List;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.CopyOnWriteArrayList;

public class Test {
    
    @org.junit.Test
    public void calling_conditional_replace_will_work_only_if_the_state_has_not_been_changed_1() throws Exception{
        Map<Integer, List<Integer>> cache = new ConcurrentHashMap<Integer, List<Integer>>();
        List<Integer> l = new ArrayList<>();
        l.add(1);
        cache.put(1, l);
        
        Runnable r1 = () -> { 
            List<Integer> list  = cache.get(1);
            list.add(2);
            System.out.println(cache.replace(1, list, list));
        };
        
        Runnable r2 = () -> { 
            while(true){
                List<Integer> list  = cache.get(1);
                list.add(3);
                if(!cache.replace(1, list, list)){
                    continue;
                }
                break;
            }
        };
        
        new Thread(r1).start();
        new Thread(r2).start();
        
        synchronized (r2) {
            r2.wait();
        }
        
    }
    
    @org.junit.Test
    public void calling_conditional_replace_will_work_only_if_the_state_has_not_been_changed_2() throws Exception{
        Map<Integer, List<Integer>> cache = new ConcurrentHashMap<Integer, List<Integer>>();
        List<Integer> l = new CopyOnWriteArrayList<Integer>();
        l.add(1);
        cache.put(1, l);
        
        Runnable r1 = () -> { 
            List<Integer> list  = cache.get(1);
            list.add(2);
            System.out.println(cache.replace(1, list, list));
        };
        
        Runnable r2 = () -> { 
            while(true){
                List<Integer> list  = cache.get(1);
                list.add(3);
                if(!cache.replace(1, list, list)){
                    continue;
                }
                break;
            }
        };
        
        new Thread(r1).start();
        new Thread(r2).start();
        
        synchronized (r2) {
            r2.wait();
        }
        
    }   
    
    @org.junit.Test
    public void calling_conditional_replace_will_work_only_if_the_state_has_not_been_changed_3() throws Exception{
        Map<Integer, Object> cache = new ConcurrentHashMap<Integer, Object>();
        cache.put(1, new Object());
        
        Runnable r1 = () -> { 
            Object obj  = cache.get(1);
            System.out.println(cache.replace(1, obj, new Object()));
        };
        
        Runnable r2 = () -> { 
            while(true){
                Object obj  = cache.get(1);
                if(!cache.replace(1, obj, new Object())){
                    continue;
                }
                break;
            }
        };
        
        new Thread(r1).start();
        new Thread(r2).start();
        
        synchronized (r2) {
            r2.wait();
        }
        
    }

}