Java:多线程模拟多站点售票过程

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}