李曉菁201771010114《面向對象程序設計（java）》第十七週學習總結

 1.Java經過多線程的併發運行提升系統資源利用率，改善系統性能。

2.假設有兩個或兩個以上的線程共享 某個對象，每一個線程都調用了改變該對象類狀態的方法，就會引發的不肯定性。

3.多線程併發執行中的問題

◆多個線程相對執行的順序是不肯定的。

◆線程執行順序的不肯定性會產生執行結果的不肯定性。

◆在多線程對共享數據操做時經常會產生這種不肯定性。

4.多線程併發運行不肯定性問題解決方案：引入線程同步機制。

5.（1）鎖對象與條件對象

           用ReentrantLock保護代碼塊的基本結構以下：

           myLock.lock();

           try { critical section }

           finally{

           myLock.unlock();

   }

   （2）synchronized關鍵字

          synchronized關鍵字做用：

         ➢ 某個類內方法用synchronized 修飾後，該方 法被稱爲同步方法；

         ➢ 只要某個線程正在訪問同步方法，其餘線程 欲要訪問同步方法就被阻塞，直至線程從同 步方法返回前喚醒被阻塞線程，其餘線程方 可能進入同步方法。

實驗十七  線程同步控制

實驗時間 2018-12-10

1、實驗目的與要求

(1) 掌握線程同步的概念及實現技術；

(2) 線程綜合編程練習

2、實驗內容和步驟

實驗1：測試程序並進行代碼註釋。

測試程序1：

l 在Elipse環境下調試教材651頁程序14-7，結合程序運行結果理解程序；

l 掌握利用鎖對象和條件對象實現的多線程同步技術。

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();//在等待條件前，鎖必須由當前線程保持。
   }

   /**
    * 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();//獲取鎖
      try
      {
         while (accounts[from] < amount)
            sufficientFunds.await();//形成當前線程在接到信號或被中斷以前一直處於等待狀態。
         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();//若是全部的線程都在等待此條件，則喚醒全部線程
      }
      finally
      {
         bankLock.unlock();//釋放鎖。 
      }
   }

   /**
    * 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

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();
      }
   }
}

synch

 

測試程序2：

l 在Elipse環境下調試教材655頁程序14-8，結合程序運行結果理解程序；

l 掌握synchronized在多線程同步中的應用。

 

package synch2;

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();//在其餘線程調用此對象的 notify() 方法或 notifyAll() 方法前，致使當前線程等待
      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();//喚醒在此對象監視器上等待的全部線程
   }

   /**
    * 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;
   }
}

bank

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();
      }
   }
}

synch

 

測試程序3：

l 在Elipse環境下運行如下程序，結合程序運行結果分析程序存在問題；

l 嘗試解決程序中存在問題。

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();   } }

運行結果顯示兩個線程各自運行各自的：

修改後的代碼：

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();

  }

}

實驗2 編程練習

利用多線程及同步方法，編寫一個程序模擬火車票售票系統，共3個窗口，賣10張票，程序輸出結果相似（程序輸出不惟一，能夠是其餘相似結果）。

Thread-0窗口售：第1張票

Thread-0窗口售：第2張票

Thread-1窗口售：第3張票

Thread-2窗口售：第4張票

Thread-2窗口售：第5張票

Thread-1窗口售：第6張票

Thread-0窗口售：第7張票

Thread-2窗口售：第8張票

Thread-1窗口售：第9張票

Thread-0窗口售：第10張票

import javax.swing.plaf.SliderUI;

public class Demo1 {
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();
}
}
 /*
    new Thread() {
        @Override
        public void run() {
            System.out.println();
    };
}.start();
}
}*/

class Mythread implements Runnable{
int t=1;
boolean flag=true;
    @Override
    public void run() {
        while(flag) {
            try {
        
            Thread.sleep(500);
            }
            catch (InterruptedException e) {
                // TODO: handle exception
                e.printStackTrace();
            }
            synchronized (this) {
            if(t<=10) {
                System.out.println(Thread.currentThread().getName()+"窗口售：第"+t+"張票");
                t++;
            }
            if(t<0) {
                flag=false;
            }
        }
    }
    }
}

    
    

 

實驗總結;經過本次實驗，我學習到了線程同步的概念，以及如何處理。經過本學期的學習，由剛開始的新手小白，對Java一無所知，

到經過大量的練習慢慢對Java編程有所熟悉，雖然如今還不是很熟練，但在課程結束後仍需繼續關注學習Java的知識及編程。