刘志梅201771010115.《面向对象程序设计（java）》第十七周学习总结

实验十七线程同步控制

实验时间 2018-12-10

1、实验理论知识

多线程
    多线程是进程执行过程中产生的多条执行线索。
进程
    线程是比进程执行更小的单位。线程不能独立存在，必须存在于进程中，同一进程的各线程间共享进程空间的数据。每个线程有它自身的产生、存在和消亡的过程，是一个动态的概念。线程创建、销毁和切换的负荷远小于进程，又称为轻量级进程（lightweight process）。
Java实现多线程
    -创建Thread类的子类
    -在程序中定义实现Runnable接口的类
用Thread类的子类创建线程
    首先需从Thread类派生出一个子类，在该子类中重写run()方法。
    class hand extends Thread { public void run() {……} }
    然后用创建该子类的对象
    Lefthand left=new Lefthand();
    Righthand right=new Righthand();
    最后用start()方法启动线程
        left.start();
        right.start();
用Runnable()接口实现线程
    首先设计一个实现Runnable接口的类；
    然后在类中根据需要重写run方法；
    再创建该类对象，以此对象为参数建立Thread 类的对象；
    调用Thread类对象的start方法启动线程，将 CPU执行权转交到run方法。
线程的终止：调用interrupt()方法。
多线程并发运行不确定性问题解决方案：引入线程同步机制，使得另一线程要使用该方法，就只能等待。
在Java中解决多线程同步问题的方法有两种： - Java SE 5.0中引入ReentrantLock类。 - 在共享内存的类方法前加synchronized修饰符。

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。

import java.util.*;
import java.util.concurrent.locks.*;

/**
 * A bank with a number of bank accounts that uses locks for serializing access.
 * @version 1.30 2004-08-01
 * @author Cay Horstmann
 */
public class Bank//Bank类
{
   private final double[] accounts;//银行运转的基础数据
   private Lock bankLock;
   private Condition sufficientFunds;

   /**
    * Constructs the bank.
    * @param n the number of accounts
    * @param initialBalance the initial balance for each account
    */
   public Bank(int n, double initialBalance)
   {
      accounts = new double[n];
      Arrays.fill(accounts, initialBalance);//调用initialBalance生成锁对象属性
      bankLock = new ReentrantLock();
      sufficientFunds = bankLock.newCondition();
   }

   /**
    * Transfers money from one account to another.
    * @param from the account to transfer from
    * @param to the account to transfer to
    * @param amount the amount to transfer
    */
   public void transfer(int from, int to, double amount) throws InterruptedException
   {
      bankLock.lock();   //临界区加锁
      try
      {
         while (accounts[from] < amount)
            sufficientFunds.await();//用锁对象生成条件对象sufficientFunds
         System.out.print(Thread.currentThread());
         accounts[from] -= amount;
         System.out.printf(" %10.2f from %d to %d", amount, from, to);
         accounts[to] += amount;
         System.out.printf(" Total Balance: %10.2f%n", getTotalBalance());
         sufficientFunds.signalAll();
      }
      finally
      {
         bankLock.unlock();
      }
   }

   /**
    * Gets the sum of all account balances.
    * @return the total balance
    */
   public double getTotalBalance()
   {
      bankLock.lock();
      try
      {
         double sum = 0;

         for (double a : accounts)
            sum += a;

         return sum;
      }
      finally
      {
         bankLock.unlock();
      }
   }

   /**
    * Gets the number of accounts in the bank.
    * @return the number of accounts
    */
   public int size()
   {
      return accounts.length;
   }
}

/**
 * This program shows how multiple threads can safely access a data structure.
 * @version 1.31 2015-06-21
 * @author Cay Horstmann
 */
public class SynchBankTest
{
   public static final int NACCOUNTS = 100;
   public static final double INITIAL_BALANCE = 1000;
   public static final double MAX_AMOUNT = 1000;
   public static final int DELAY = 10;
   
   public static void main(String[] args)
   {
      Bank bank = new Bank(NACCOUNTS, INITIAL_BALANCE);
      for (int i = 0; i < NACCOUNTS; i++)
      {
         int fromAccount = i;
         Runnable r = () -> {
            try
            {
               while (true)
               {
                  int toAccount = (int) (bank.size() * Math.random());
                  double amount = MAX_AMOUNT * Math.random();
                  bank.transfer(fromAccount, toAccount, amount);
                  Thread.sleep((int) (DELAY * Math.random()));
               }
            }
            catch (InterruptedException e)
            {
            }            
         };
         Thread t = new Thread(r);
         t.start();
      }
   }
}

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。

/**
 * This program shows how multiple threads can safely access a data structure,
 * using synchronized methods.
 * @version 1.31 2015-06-21
 * @author Cay Horstmann
 */
public class SynchBankTest2
{
   public static final int NACCOUNTS = 100;
   public static final double INITIAL_BALANCE = 1000;
   public static final double MAX_AMOUNT = 1000;
   public static final int DELAY = 10;

   public static void main(String[] args)
   {
      Bank bank = new Bank(NACCOUNTS, INITIAL_BALANCE);//创建一个银行对象
      for (int i = 0; i < NACCOUNTS; i++)
      {
         int fromAccount = i;
         Runnable r = () -> {
            try
            {
               while (true)
               {
                  int toAccount = (int) (bank.size() * Math.random());//拿出一个随机账户
                  double amount = MAX_AMOUNT * Math.random();//设定随机一笔钱
                  bank.transfer(fromAccount, toAccount, amount);//转账操作
                  Thread.sleep((int) (DELAY * Math.random()));//随机休眠时间
               }
            }
            catch (InterruptedException e)
            {
            }
         };
         Thread t = new Thread(r);//创建一个线程
         t.start();//线程处于可运行状态
      }
   }
}

import java.util.*;

/**
 * A bank with a number of bank accounts that uses synchronization primitives.
 * @version 1.30 2004-08-01
 * @author Cay Horstmann
 */
public class Bank
{
   private final double[] accounts;

   /**
    * Constructs the bank.
    * @param n the number of accounts
    * @param initialBalance the initial balance for each account
    */
   public Bank(int n, double initialBalance)
   {
      accounts = new double[n];
      Arrays.fill(accounts, initialBalance);
   }

   /**
    * Transfers money from one account to another.
    * @param from the account to transfer from
    * @param to the account to transfer to
    * @param amount the amount to transfer
    */
   public synchronized void transfer(int from, int to, double amount) throws InterruptedException
   {
      while (accounts[from] < amount)
         wait();//使线程处于等待集中
      System.out.print(Thread.currentThread());
      accounts[from] -= amount;
      System.out.printf(" %10.2f from %d to %d", amount, from, to);
      accounts[to] += amount;
      System.out.printf(" Total Balance: %10.2f%n", getTotalBalance());
      notifyAll();//唤醒所有等待的线程
   }

   /**
    * Gets the sum of all account balances.
    * @return the total balance
    */
   public synchronized double getTotalBalance()
   {
      double sum = 0;

      for (double a : accounts)
         sum += a;

      return sum;
   }

   /**
    * Gets the number of accounts in the bank.
    * @return the number of accounts
    */
   public int size()
   {
      return accounts.length;
   }
}

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();

}

class Cbank
{
     private static int s=2000;//当类加载时s赋值为2000
     public   static void sub(int m)
     {
           int temp=s;
           temp=temp-m;
          try {
      Thread.sleep((int)(1000*Math.random()));
    }
           catch (InterruptedException e)  {              }//捕获中断异常
           s=temp;
           System.out.println("s="+s);
   }
}
 
 
class Customer extends Thread//继承
{
  public void run()//中值返回
  {
   for( int i=1; i<=4; i++)
     Cbank.sub(100);
    }
 }

public class Thread3
{
 public static void main(String args[])
  {
   Customer customer1 = new Customer();//把变量customer1的值设置为分配给新的Customer对象的内部地址
   Customer customer2 = new Customer();
   customer1.start();
   customer2.start();
  }
}

修改后的代码：

class Cbank

{

     private static int s=2000;

     public synchronized  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();

  }

}

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

package tracket;

public class tracket {
            public static void main(String[] args) {
                Mythread mythread = new Mythread();
                Thread t1 = new Thread(mythread);//实例化了一个Thread对象thread1
                Thread t2 = new Thread(mythread);
                Thread t3 = new Thread(mythread);
                t1.start();//线程启动
                t2.start();
                t3.start();
            }
        }

        class Mythread implements Runnable {
            int t = 1;
            boolean flag = true;

            @Override
            public void run() {
                // TODO Auto-generated method stub
                while (flag) {
                    try {
                        Thread.sleep(500);//休眠时间500毫秒
                    } catch (Exception e) {
                        // TODO: handle exception
                        e.printStackTrace();
                    }

                    synchronized (this) {
                        if (t <= 10) {
                            System.out.println(Thread.currentThread().getName() + "窗口售：第" + t + "张票");
                            t++;
                        }
                        if (t > 10) {
                            flag = false;
                        }
                    }

                }
            }
    }

实验总结：本周实验学习了线程的同步，对线程有了更能进一步的学习，最后的编程的练习题通过学长的讲解以及演示，代码语句的解释，深入了解线程同步问题；本周也是最后一周的实验，这学期通过老师和学长的教学学习到了不少java的知识，非常感谢。

刘志梅201771010115.《面向对象程序设计（java）》第十七周学习总结

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