实验十七 线程同步控制

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实验十七  线程同步控制

实验时间 2018-12-10

一、理论知识部分:

? 线程同步

(1)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

(2)在Java中解决多线程同步问题的方法有两种:

解决方案一:锁对象与条件对象

用ReentrantLock保护代码块的基本结构如下: myLock.lock();

try { critical section }

finally{ myLock.unlock(); }

(3)解决方案二: synchronized关键字

synchronized关键字作用: ? 某个类内方法用synchronized 修饰后,该方 法被称为同步方法;

? 只要某个线程正在访问同步方法,其他线程欲要访问同步方法就被阻塞,直至线程从同步方法返回前唤醒被阻塞线程,其他线程方可能进入同步方法。

(4)在同步方法中使用wait()、notify 和notifyAll()方法

一个线程在使用的同步方法中时,可能根据问题 的需要,必须使用wait()方法使本线程等待,暂 时让出CPU的使用权,并允许其它线程使用这个 同步方法。

线程如果用完同步方法,应当执行notifyAll()方 法通知所有由于使用这个同步方法而处于等待的 线程结束等待。

二 实验部分

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。

技术分享图片

技术分享图片
package synch;

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
{
   private final double[] accounts;
   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);
      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();
      try
      {
         while (accounts[from] < amount)
         sufficientFunds.await();
         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.signal();
      }
      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;
   }
}
bank
技术分享图片
package synch;

/**
 * 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();
      }
   }
}
SynchBankTest

 

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。

技术分享图片技术分享图片

技术分享图片
package synch2;

/**
 * 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);
      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();
      }
   }
}
SynchBankTest2

 

 

 

技术分享图片
package synch;

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
{
   private final double[] accounts;
   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);
      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();
      try
      {
         while (accounts[from] < amount)
         sufficientFunds.await();
         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.signal();
      }
      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;
   }
}
bank

 

 

 

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();

  }

}

技术分享图片

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

技术分享图片

 

public class shi {
    public static void main(String[] args) {
        Mythread mythread = new Mythread();
        Thread t1 = new Thread(mythread);
        Thread t2 = new Thread(mythread);
        Thread t3 = new Thread(mythread);
        t1.start();
        t2.start();
        t3.start();
    }
}
    class Mythread implements Runnable {
        int t;
        boolean flag = true;

        @Override
        public void run() {
         
            // TODO Auto-generated method stub
            while (flag) {
                try {
                    Thread.sleep(500);
                } catch (Exception e) {
                    // TODO: handle exception
                }
                synchronized (this) {
                    if (t <= 10) {
                        System.out.println(Thread.currentThread().getName() + "窗口售:第" + t + "张票");
                        t++;
                    } else if(t>10)
                    {
                        flag = false;
                    }
                }
                
            }

        }

    }   

 实验总结    掌握了线程同步的概念及实现技术;

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