常惠琢 201771010102《面向对象程序设计（java）》第十七周学习总结

Posted 2021-01-29 hongyanohongyan

实验十七  线程同步控制

实验时间 2018-12-10

1、实验目的与要求

(1) 掌握线程同步的概念及实现技术； 

(2) 线程综合编程练习

2、实验内容和步骤

实验1：测试程序并进行代码注释。

测试程序1：

l 在Elipse环境下调试教材651页程序14-7，结合程序运行结果理解程序；

l 掌握利用锁对象和条件对象实现的多线程同步技术。

 1 package synch;
 2 
 3 import java.util.*;
 4 import java.util.concurrent.locks.*;//导入locks包
 5 
 6 /**
 7  * 具有多个银行帐户的银行，使用锁序列化访问
 8  * @version 1.30 2004-08-01
 9  * @author Cay Horstmann
10  */
11 public class Bank
12 {
13    private final double[] accounts;//使银行运转的基础数据
14    private Lock bankLock;
15    private Condition sufficientFunds;//扩张的两个私有属性lock and Condition的一个锁对象一个条件对象
16 
17    /**
18     * 建设银行。
19     * @param 账号
20     * @param 每个账户的初始余额 
21     */
22    public Bank(int n, double initialBalance)
23    {
24       accounts = new double[n];//n个账户
25       Arrays.fill(accounts, initialBalance);//每个账户初始资金为1000元
26       bankLock = new ReentrantLock();//建立锁对象（避免线程共享的bank对象内容发生混乱）
27       sufficientFunds = bankLock.newCondition();//建立条件对象（便于得到锁对象的线程在不能做有用的工作时对该线程进行处理）
28    }
29 
30    /**
31     * 把钱从一个账户转到另一个账户
32     * @param 从账户转账 
33     * @param 转到要转账的账户
34     * @param 转账金额 
35     */
36    public void transfer(int from, int to, double amount) throws InterruptedException
37    {
38       bankLock.lock();//在邻接区加锁（线程进入的条件）
39       try
40       {//临界区
41          while (accounts[from] < amount)//账户余额不满足支出时
42             sufficientFunds.await();
43          System.out.print(Thread.currentThread());//打印当前线程信息
44          accounts[from] -= amount;//该账户支出一笔钱
45          System.out.printf(" %10.2f from %d to %d", amount, from, to);
46          accounts[to] += amount;//一个随机账户得到这笔钱
47          System.out.printf(" Total Balance: %10.2f%n", getTotalBalance());
48          sufficientFunds.signalAll();//唤醒所有等待的线程
49       }
50       finally
51       {
52          bankLock.unlock();//unlock()解锁   lock上锁
53       }
54    }
55 
56    /**
57     * 获取所有帐户余额的总和。
58     * @return 总余额 
59     */
60    public double getTotalBalance()//加锁行为
61    {
62       bankLock.lock();
63       try
64       {
65          double sum = 0;
66 
67          for (double a : accounts)
68             sum += a;
69 
70          return sum;
71       }
72       finally
73       {
74          bankLock.unlock();//释放锁
75       }
76    }
77 
78    /**
79     * 获取银行中的帐户数量。 
80     * @return 账号 
81     */
82    public int size()
83    {
84       return accounts.length;
85    }
86 }

View Code

 1 package synch;
 2 
 3 /**
 4  * 这个程序显示了多个线程如何安全地访问数据结构 
 5  * @version 1.31 2015-06-21
 6  * @author Cay Horstmann
 7  */
 8 public class SynchBankTest
 9 {
10    public static final int NACCOUNTS = 100;//帐目
11    public static final double INITIAL_BALANCE = 1000;//期初余额
12    public static final double MAX_AMOUNT = 1000;//最大金额
13    public static final int DELAY = 10;//延迟时间
14    
15    public static void main(String[] args)
16    {
17       Bank bank = new Bank(NACCOUNTS, INITIAL_BALANCE);//创建一个银行对象，这个银行有一百个用户，一百个用户使用这个银行
18       for (int i = 0; i < NACCOUNTS; i++)
19       {
20          int fromAccount = i;
21          Runnable r = () -> {
22             try
23             {
24                while (true)
25                {
26                   int toAccount = (int) (bank.size() * Math.random());//拿出一个随机账户
27                   double amount = MAX_AMOUNT * Math.random();//设定随机一笔钱（支出/得到）
28                   bank.transfer(fromAccount, toAccount, amount);//转账操作
29                   Thread.sleep((int) (DELAY * Math.random()));//随机的休眠时间
30                }
31             }
32             catch (InterruptedException e)
33             {
34             }            
35          };
36          Thread t = new Thread(r);//调用了Thread(Runnable target)方法。且父类对象变量指向子类对象。
37          t.start();//使线程处于可运行状态
38       }
39    }
40 }

View Code

测试程序2：

l 在Elipse环境下调试教材655页程序14-8，结合程序运行结果理解程序；

l 掌握synchronized在多线程同步中的应用。

 

 1 package synch2;
 2 
 3 import java.util.*;
 4 
 5 /**
 6  * A bank with a number of bank accounts that uses synchronization primitives.
 7  * @version 1.30 2004-08-01
 8  * @author Cay Horstmann
 9  */
10 public class Bank
11 {
12    private final double[] accounts;
13 
14    /**
15     * Constructs the bank.
16     * @param n the number of accounts
17     * @param initialBalance the initial balance for each account
18     */
19    public Bank(int n, double initialBalance)
20    {
21       accounts = new double[n];
22       Arrays.fill(accounts, initialBalance);
23    }
24 
25    /**
26     * Transfers money from one account to another.
27     * @param from the account to transfer from
28     * @param to the account to transfer to
29     * @param amount the amount to transfer
30     */
31    public synchronized void transfer(int from, int to, double amount) throws InterruptedException
32    {
33       while (accounts[from] < amount)
34          wait();
35       System.out.print(Thread.currentThread());
36       accounts[from] -= amount;
37       System.out.printf(" %10.2f from %d to %d", amount, from, to);
38       accounts[to] += amount;
39       System.out.printf(" Total Balance: %10.2f%n", getTotalBalance());
40       notifyAll();
41    }
42 
43    /**
44     * Gets the sum of all account balances.
45     * @return the total balance
46     */
47    public synchronized double getTotalBalance()
48    {
49       double sum = 0;
50 
51       for (double a : accounts)
52          sum += a;
53 
54       return sum;
55    }
56 
57    /**
58     * Gets the number of accounts in the bank.
59     * @return the number of accounts
60     */
61    public int size()
62    {
63       return accounts.length;
64    }
65 }

View Code

 

 1 package synch2;
 2 
 3 /**
 4  * This program shows how multiple threads can safely access a data structure,
 5  * using synchronized methods.
 6  * @version 1.31 2015-06-21
 7  * @author Cay Horstmann
 8  */
 9 public class SynchBankTest2
10 {
11    public static final int NACCOUNTS = 100;
12    public static final double INITIAL_BALANCE = 1000;
13    public static final double MAX_AMOUNT = 1000;
14    public static final int DELAY = 10;
15 
16    public static void main(String[] args)
17    {
18       Bank bank = new Bank(NACCOUNTS, INITIAL_BALANCE);
19       for (int i = 0; i < NACCOUNTS; i++)
20       {
21          int fromAccount = i;
22          Runnable r = () -> {
23             try
24             {
25                while (true)
26                {
27                   int toAccount = (int) (bank.size() * Math.random());
28                   double amount = MAX_AMOUNT * Math.random();
29                   bank.transfer(fromAccount, toAccount, amount);
30                   Thread.sleep((int) (DELAY * Math.random()));
31                }
32             }
33             catch (InterruptedException e)
34             {
35             }
36          };
37          Thread t = new Thread(r);
38          t.start();
39       }
40    }
41 }

View Code

测试程序3:

l 在Elipse环境下运行以下程序，结合程序运行结果分析程序存在问题；

l 尝试解决程序中存在问题。

class Cbank {      private static int s=2000;      public   static void sub(int m)      {            int temp=s;            temp=temp-m;           try {       Thread.sleep((int)(1000*Math.random()));     }            catch (InterruptedException e)  {              }            s=temp;            System.out.println("s="+s);    } }     class Customer extends Thread {   public void run()   {    for( int i=1; i<=4; i++)      Cbank.sub(100);     }  } public class Thread3 {  public static void main(String args[])   {    Customer customer1 = new Customer();    Customer customer2 = new Customer();    customer1.start();    customer2.start();   } }

 1 public class Thread3
 2 {
 3  public static void main(String args[])
 4   {
 5    Customer customer1 = new Customer();
 6    Customer customer2 = new Customer();
 7    customer1.start();
 8    customer2.start();
 9   }
10 }

Thread3

1 class Customer extends Thread
2 {
3   public void run()
4   {
5    for( int i=1; i<=4; i++)
6      Cbank.sub(100);
7     }
8  }

Customer

 1 class Cbank
 2 {
 3      private static int s=2000;
 4      public   static void sub(int m)
 5      {
 6            int temp=s;
 7            temp=temp-m;
 8           try {
 9                  Thread.sleep((int)(1000*Math.random()));
10                }
11            catch (InterruptedException e)  {              }
12               s=temp;
13               System.out.println("s="+s);
14           }
15     }

Cbank

实验2 编程练习

利用多线程及同步方法，编写一个程序模拟火车票售票系统，共3个窗口，卖10张票，程序输出结果类似（程序输出不唯一，可以是其他类似结果）。

Thread-0窗口售：第1张票

Thread-0窗口售：第2张票

Thread-1窗口售：第3张票

Thread-2窗口售：第4张票

Thread-2窗口售：第5张票

Thread-1窗口售：第6张票

Thread-0窗口售：第7张票

Thread-2窗口售：第8张票

Thread-1窗口售：第9张票

Thread-0窗口售：第10张票

 1 import java.awt.geom.FlatteningPathIterator;
 2 
 3 public class Demo {
 4 
 5     public static void main(String[] args) {
 6         Myrhread myrhread=new Myrhread();
 7         Thread t1 = new Thread(myrhread);
 8         Thread t2 = new Thread(myrhread);
 9         Thread t3 = new Thread(myrhread);
10         t1.start();
11         t2.start();
12         t3.start();
13     }
14 
15 }
16 class Myrhread implements Runnable{
17 int t=1;
18 boolean flag =true; 
19     @Override
20     public void run() {
21         while (flag) {
22             try {
23                 Thread.sleep(500);
24             } catch (InterruptedException e) {
25                 // TODO Auto-generated catch block
26                 e.printStackTrace();
27             }
28             synchronized (this) {
29             if(t<=10) {
30                 System.out.println(Thread.currentThread().getName()+"窗口售：第"+t+"张票");
31                 t++;                
32             }
33             if(t>10) {
34                 flag=false;
35             }
36             
37         }
38             
39      }
40         
41   }
42     
43 }

Demo

实验总结：

       这次实验很少，最后一个程序的编程也学到了很多东西，比如unlock()解锁  ， lock上锁等。