Java:多线程模拟多站点售票过程

简介:
这是一个在并发状态下对共享资源的多线程访问。这些访问必须是互斥的进行,因为涉及到对资源的修改。假设现在销售火车票。目的地有 3 个,分别是北京,天津和上海。使用一个枚举类型表示。
Destation.java
package  com.zj.tickets;
 
public   enum  Destation {
     BEIJING SHANGHAI TIANJING
}
下面设计车票类, final   int   original 表示车票基数; int   current 表示当前还有多少张票; Destation  destation 表示目的地,它必须从上面的枚举型中取出其一。
Ticket.java
package  com.zj.tickets;
 
public   class  Ticket {
     private   final   int   original ;
     private   int   current ;
     private   final  Destation  destation ;
 
     public  Ticket( int  nums, Destation where) {
        current  =  original  = nums;
        destation  = where;
    }
 
     public   int  degress() {
        return  -- current ;
    }
 
     public   int  original() {
        return   original ;
    }
 
     public   boolean  soldout() {
        return   current  <= 0;
    }
 
     public  Destation getDestation() {
        return   destation ;
    }
 
     public   int  getCurrent() {
        return   current ;
    }
}
下面设计售票厅类, Map<Destation, Ticket>  tickets 表示目前可销售的车票种类,它通过一个 static 块初始化。 Map<Destation, Integer>  records 是当前售票厅的火车票销售情况。 List<BookingOffice>  offices 表示当前可工作的所有售票厅,每个售票厅是一个线程。 int   ticketsSold 表示当前售票厅售出的火车票总数。 int   id 表示当前售票厅编号。
每个线程都会模拟客户买票、工作人员查询数据库和售票交易过程。
模拟的数据为,当前发往北京、上海和天津的火车票各 5 张;每个售票厅交易 5 次(无论交易成功或失败)后关闭。
BookingOffice.java
package  com.zj.tickets;
import  java.util.ArrayList;
import  java.util.HashMap;
import  java.util.List;
import  java.util.Map;
import  java.util.Random;
import  java.util.concurrent.TimeUnit;
 
public   class  BookingOffice  implements  Runnable {
     private   static  Map<Destation, Ticket>  tickets  =  new  HashMap<Destation, Ticket>();
     private  Map<Destation, Integer>  records ;
     private   static  List<BookingOffice>  offices  =  new  ArrayList<BookingOffice>();
     private   int   ticketsSold  = 0;
     private   final   int   id ;
 
     // now today's tickets for sell:
     static  {
        tickets .put(Destation. BEIJING new  Ticket(5, Destation. BEIJING ));
        tickets .put(Destation. SHANGHAI new  Ticket(5, Destation. SHANGHAI ));
        tickets .put(Destation. TIANJING new  Ticket(5, Destation. TIANJING ));
    }
 
     public  BookingOffice( int  id) {
        this . id  = id;
        offices .add( this );
       resetRecords();
    }
 
     private   void  resetRecords() {
        records  =  new  HashMap<Destation, Integer>();
    }
 
     private   void  addRecords(Destation d) {
       Integer freq =  records .get(d);
        records .put(d, freq ==  null  ? 1 : freq + 1);
    }
 
     public   void  run() {
        int  transaction = 5;
        while  (transaction-- > 0) {
            // simulate a customer's coming:
           Destation d = Destation.values()[ new  Random().nextInt(Destation
                  .values(). length )];
           print( this  +  "i want a ticket for "  + d);
            // simulate the officer's checking:
            try  {
              TimeUnit. SECONDS .sleep(1);
            catch  (InterruptedException e) {
              e.printStackTrace();
           }
            // simulate the transaction:
           Ticket wanted =  tickets .get(d);
            synchronized  ( wanted ) {
               if  (!wanted.soldout()) {
                  print( this  +  "sold a ticket for "  + d);
                  wanted.degress();
                  addRecords(d);
                  ++ ticketsSold ;
                  print( this  +  ""  + d +  " tickets still have "
                         + wanted.getCurrent());
               else
                  print( this  +  "tickets for "  + d +  " have been sold out." );
           }
       }
       print( this  +  "closed" );
       print( this  +  "totally sold tickets:"  +  ticketsSold  +  ",sell records:"
               records );
    }
 
     public   synchronized   int  getValue() {
        return   ticketsSold ;
    }
 
     public  String toString() {
        return   "<Officce-"  +  id  +  ">" ;
    }
 
     static   void  print(String s) {
       System. out .println(s);
    }
}
模拟售票过程如下,启动 5 个售票厅。
Sell.java
package  com.zj.tickets;
import  java.util.concurrent.ExecutorService;
import  java.util.concurrent.Executors;
 
public   class  Sell {
     public   static   void  main(String[] args)  throws  Exception {
       ExecutorService exec = Executors.newCachedThreadPool();
        for  ( int  i = 0; i < 5; i++)
           exec.execute( new  BookingOffice(i));
       exec.shutdown();
    }
}
结果:
<Officce-0>i want a ticket for BEIJING
<Officce-1>i want a ticket for SHANGHAI
<Officce-2>i want a ticket for TIANJING
<Officce-3>i want a ticket for SHANGHAI
<Officce-4>i want a ticket for SHANGHAI
<Officce-0>sold a ticket for BEIJING
<Officce-0>BEIJING tickets still have 4
<Officce-0>i want a ticket for TIANJING
<Officce-1>sold a ticket for SHANGHAI
<Officce-1>SHANGHAI tickets still have 4
<Officce-1>i want a ticket for SHANGHAI
<Officce-2>sold a ticket for TIANJING
<Officce-2>TIANJING tickets still have 4
<Officce-2>i want a ticket for BEIJING
<Officce-3>sold a ticket for SHANGHAI
<Officce-3>SHANGHAI tickets still have 3
<Officce-3>i want a ticket for TIANJING
<Officce-4>sold a ticket for SHANGHAI
<Officce-4>SHANGHAI tickets still have 2
<Officce-4>i want a ticket for BEIJING
<Officce-4>sold a ticket for BEIJING
<Officce-4>BEIJING tickets still have 3
<Officce-4>i want a ticket for SHANGHAI
<Officce-3>sold a ticket for TIANJING
<Officce-3>TIANJING tickets still have 3
<Officce-3>i want a ticket for TIANJING
<Officce-2>sold a ticket for BEIJING
<Officce-2>BEIJING tickets still have 2
<Officce-2>i want a ticket for BEIJING
<Officce-1>sold a ticket for SHANGHAI
<Officce-1>SHANGHAI tickets still have 1
<Officce-1>i want a ticket for SHANGHAI
<Officce-0>sold a ticket for TIANJING
<Officce-0>TIANJING tickets still have 2
<Officce-0>i want a ticket for SHANGHAI
<Officce-4>sold a ticket for SHANGHAI
<Officce-4>SHANGHAI tickets still have 0
<Officce-4>i want a ticket for BEIJING
<Officce-3>sold a ticket for TIANJING
<Officce-3>TIANJING tickets still have 1
<Officce-3>i want a ticket for BEIJING
<Officce-2>sold a ticket for BEIJING
<Officce-2>BEIJING tickets still have 1
<Officce-2>i want a ticket for SHANGHAI
<Officce-1>tickets for SHANGHAI have been sold out.
<Officce-1>i want a ticket for SHANGHAI
<Officce-0>tickets for SHANGHAI have been sold out.
<Officce-0>i want a ticket for SHANGHAI
<Officce-4>sold a ticket for BEIJING
<Officce-4>BEIJING tickets still have 0
<Officce-4>i want a ticket for BEIJING
<Officce-3>tickets for BEIJING have been sold out.
<Officce-3>i want a ticket for BEIJING
<Officce-2>tickets for SHANGHAI have been sold out.
<Officce-2>i want a ticket for SHANGHAI
<Officce-1>tickets for SHANGHAI have been sold out.
<Officce-1>i want a ticket for BEIJING
<Officce-0>tickets for SHANGHAI have been sold out.
<Officce-0>i want a ticket for SHANGHAI
<Officce-4>tickets for BEIJING have been sold out.
<Officce-4>closed
<Officce-4>totally sold tickets:4,sell records:{BEIJING=2, SHANGHAI=2}
<Officce-3>tickets for BEIJING have been sold out.
<Officce-3>closed
<Officce-3>totally sold tickets:3,sell records:{TIANJING=2, SHANGHAI=1}
<Officce-2>tickets for SHANGHAI have been sold out.
<Officce-2>closed
<Officce-2>totally sold tickets:3,sell records:{BEIJING=2, TIANJING=1}
<Officce-1>tickets for BEIJING have been sold out.
<Officce-1>closed
<Officce-1>totally sold tickets:2,sell records:{SHANGHAI=2}
<Officce-0>tickets for SHANGHAI have been sold out.
<Officce-0>closed
<Officce-0>totally sold tickets:2,sell records:{BEIJING=1, TIANJING=1}


本文转自zhangjunhd51CTO博客,原文链接:http://blog.51cto.com/zhangjunhd/70767,如需转载请自行联系原作者
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