Exchanger

A synchronization point at which threads can pair and swap elements within pairs. Each thread presents some object on entry to the exchange method, matches with a partner thread, and receives its partner's object on return. An Exchanger may be viewed as a bidirectional form of a SynchronousQueue. Exchangers may be useful in applications such as genetic algorithms and pipeline designs.

package exchange;

import java.util.concurrent.Exchanger;

/**   
 * @author YYZ  
 * @version 2011-10-26 上午11:37:44
 */
/** 
 * 案例：服务员向原有空杯中不断倒水，消费者不断从原有装满水的杯中喝水。  
 * 当服务员倒满水和消费者喝完水时，两个杯子进行交换。一直这样周而复始。 
 *  
 * @author Administrator 
 *  
 */  
public class TestExchanger {  
  
    static Exchanger<Cup> exchanger = new Exchanger<Cup>();  
    static Cup emptyCup = new Cup(0);  
    static Cup fullCup = new Cup(100);  
  
    public static void main(String[] args) {  
        new Thread(new Waiter(3)).start();  
        new Thread(new Customer(6)).start(); 
    }  
  
    /** 
     * 服务员 
     *  
     * @author Administrator 
     *  
     */  
    static class Waiter implements Runnable {  
  
        int addSpeed = 1;  
  
        public Waiter(int addSpeed) {  
            this.addSpeed = addSpeed;  
        }  
  
        @Override  
        public void run() {  
            while (emptyCup != null) {  
                // 如果发现杯子中的水没有满，则往杯中加水。  
                try {  
                    if (emptyCup.isFull()) {// 当emptyCup为装满水时并且fullCup为被喝完水时，进行交换。  
                        // 当Waiter把杯子水装满后，与Customer交换杯子。  
                        // exchange(emptyCup)中参数的emptyCup是waiter装满水后的，把装满水后的emptyCup参数传递给Cutomer线程。  
                        // 并且返回Cutomer线程中fullCup给Waiter的emptyCup，这样就达到了交换效果。  
                        emptyCup = exchanger.exchange(emptyCup);  
                        System.out.println("Waiter: " + emptyCup.capacity);  
                    } else {  
                        emptyCup.addWaterToCup(3);  
                        System.out.println("Waiter add " + addSpeed  
                                + " and current capacity is "  
                                + emptyCup.capacity);  
                        Thread.sleep((long) (Math  
                                .max(500, Math.random() * 2000)));  
                    }  
                } catch (InterruptedException e) {  
                    e.printStackTrace();  
                }  
            }  
        }  
    }  
  
    /** 
     * 消费者 
     *  
     * @author Administrator 
     *  
     */  
    static class Customer implements Runnable {  
  
        int drinkSpeed = 1;  
  
        public Customer(int drinkSpeed) {  
            this.drinkSpeed = drinkSpeed;  
        }  
  
        @Override  
        public void run() {  
            while (fullCup != null) {  
                // 如果发现杯子中的水没有满，则往杯中加水。  
                try {  
                    if (fullCup.isEmpty()) {  
                        // 水满后则交换子中的水  
                        fullCup = exchanger.exchange(fullCup);  
                        System.out.println("Customer: " + fullCup.capacity);  
                    } else {  
                        fullCup.drinkFormCup(drinkSpeed);  
                        System.out.println("Customer drinked " + drinkSpeed  
                                + " and current capacity is "  
                                + fullCup.capacity);  
                        Thread.sleep((long) (Math  
                                .max(500, Math.random() * 2000)));  
                    }  
  
                } catch (InterruptedException e) {  
                    e.printStackTrace();  
                }  
            }  
        }  
  
    }  
  
    static class Cup {  
  
        private int capacity = 0;  
  
        public Cup(int capacity) {  
            this.capacity = capacity;  
        }  
  
        public void addWaterToCup(int i) {  
            capacity += i;  
            capacity = capacity > 100 ? 100 : capacity;  
        }  
  
        public void drinkFormCup(int i) {  
            capacity -= i;  
            capacity = capacity < 0 ? 0 : capacity;  
        }  
  
        public boolean isFull() {  
            return capacity == 100 ? true : false;  
        }  
  
        public boolean isEmpty() {  
            return capacity == 0 ? true : false;  
        }  
    }  
  
}  

Customer drinked 6 and current capacity is 24
Waiter add 3 and current capacity is 3
Customer drinked 6 and current capacity is 18
Waiter add 3 and current capacity is 6
Customer drinked 6 and current capacity is 12
Waiter add 3 and current capacity is 9
Customer drinked 6 and current capacity is 6
Waiter add 3 and current capacity is 12
Waiter add 3 and current capacity is 15
Customer drinked 6 and current capacity is 0
Waiter add 3 and current capacity is 18
Waiter add 3 and current capacity is 21
Waiter add 3 and current capacity is 24
Waiter add 3 and current capacity is 27
Waiter add 3 and current capacity is 30
Waiter: 0
Waiter add 3 and current capacity is 3
Customer: 30
Customer drinked 6 and current capacity is 24
Waiter add 3 and current capacity is 6