1. 程式人生 > >第十七週作業

第十七週作業

姓名:鄒豐蔚

學號:201771010138

實驗十七  執行緒同步控制

實驗時間 2018-12-10

1、實驗目的與要求

(1) 掌握執行緒同步的概念及實現技術;

 

(2) 執行緒綜合程式設計練習

 

2、實驗內容和步驟

實驗1:測試程式並進行程式碼註釋。

測試程式1:

l  在Elipse環境下除錯教材651頁程式14-7,結合程式執行結果理解程式;

l  掌握利用鎖物件和條件物件實現的多執行緒同步技術。

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(); } /** * 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//通過鎖物件生成條件物件 { bankLock.lock();//加鎖 try { while (accounts[from] < amount) sufficientFunds.await();//條件物件如果被註釋會出現死鎖現象不能實現執行緒的有效呼叫 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; } }
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();
      }
   }
}

測試程式2:

l  在Elipse環境下除錯教材655頁程式14-8,結合程式執行結果理解程式;

l  掌握synchronized在多執行緒同步中的應用。

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();
     /* 該方法屬於Object的方法,wait方法的作用是使得當前呼叫wait方法所在部分(程式碼塊)的執行緒停止執行,
                    並釋放當前獲得的呼叫wait所在的程式碼塊的鎖,並在其他執行緒呼叫notify或者notifyAll方法時恢復到競爭鎖狀態(一旦獲得鎖就恢復執行)。*/
      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());
      notifyal();
   }

   private void notifyal() {
    // TODO Auto-generated method stub
    
}

private void notifyA() {
    // TODO Auto-generated method stub
    
}

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

 

測試程式3:

l  在Elipse環境下執行以下程式,結合程式執行結果分析程式存在問題;

l  嘗試解決程式中存在問題。

class test
{

     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();

  }

}

修改之後:

package test;

    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 程式設計練習

利用多執行緒及同步方法,編寫一個程式模擬火車票售票系統,共3個視窗,賣10張票,程式輸出結果類似(程式輸出不唯一,可以是其他類似結果)。

Thread-0視窗售:第1張票

Thread-0視窗售:第2張票

Thread-1視窗售:第3張票

Thread-2視窗售:第4張票

Thread-2視窗售:第5張票

Thread-1視窗售:第6張票

Thread-0視窗售:第7張票

Thread-2視窗售:第8張票

Thread-1視窗售:第9張票

Thread-0視窗售:第10張票

package ThreadTest;

public class Station extends Thread{
    public Station(String name) {
        super(name);
    }
    
    static int tickers=1;
    static Object ob="a";//指定一個共用物件
    
    //重寫run操作,實現賣票
    @Override
    public void run() {
        // TODO Auto-generated method stub
        super.run();
        while(tickers<=10){
            synchronized (ob) {
                if(tickers<=10){
                    System.out.println(getName()+"視窗售:第"+tickers+"張票");
                    tickers++;
                }
            }
            try {
                sleep(10);
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
    }
    
    public static void main(String[] args) {
        Station station1=new Station("Thread-0");
        Station station2=new Station("Thread-1");
        Station station3=new Station("Thread-2");
        station1.start();
        station2.start();
        station3.start();
    }
 
}

學習總結:

 1.執行緒同步

(1)多執行緒併發執行不確定性問題解決方案:引入線 程同步機制,使得另一執行緒要使用該方法,就只 能等待

(2)在Java中解決多執行緒同步問題的方法有兩種:

解決方案一:鎖物件與條件物件

用ReentrantLock保護程式碼塊的基本結構如下: myLock.lock();

try { critical section }

finally{ myLock.unlock(); }

(3)解決方案二: synchronized關鍵字

synchronized關鍵字作用: ➢ 某個類內方法用synchronized 修飾後,該方 法被稱為同步方法

2.Java通過多執行緒的併發執行提高系統資源利用 率,改善系統性能。

3.假設有兩個或兩個以上的執行緒共享 某個物件,每個執行緒都呼叫了改變該物件類狀態的方法,就會引起的不確定性。

4.多執行緒併發執行中的問題

多個執行緒相對執行的順序是不確定的。

執行緒執行順序的不確定性會產生執行結果的不確定性。

在多執行緒對共享資料操作時常常會產生這種不確定性。

5.多執行緒併發執行不確定性問題解決方案:引入執行緒同步機制。

這次實驗我掌握了利用鎖物件和條件物件實現的多執行緒同步技術。這次實驗是最後一次實驗了,回想一個學期的學習,我學到了很多。感謝老師和學長的幫助。