實驗十七 線程同步控制

時間  2019-11-10
標籤 實驗 十七 線程 同步 控制 简体版
原文   原文鏈接

 

實驗十七  線程同步控制java

實驗時間 2018-12-10編程

1、理論知識部分：多線程

⚫ 線程同步併發

（1）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，使得另外一線程要使用該方法，就只 能等待dom

（2）在Java中解決多線程同步問題的方法有兩種：ide

解決方案一：鎖對象與條件對象測試

用ReentrantLock保護代碼塊的基本結構以下： myLock.lock();this

try { critical section }spa

finally{ myLock.unlock(); }線程

（3）解決方案二： 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。

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

一個線程在使用的同步方法中時，可能根據問題 的須要，必須使用wait()方法使本線程等待，暫 時讓出CPU的使用權，並容許其它線程使用這個 同步方法。

線程若是用完同步方法，應當執行notifyAll()方 法通知全部因爲使用這個同步方法而處於等待的 線程結束等待。

二 實驗部分

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();
   }

   /**
    * 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 
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

 

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;

/**
 * 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

 

 

 

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

 

 

 

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();

  }

}

 

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

 

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 + "張票");
                        t++;
                    } else if(t>10)
                    {
                        flag = false;
                    }
                }
                
            }

        }

    }

 實驗總結    掌握了線程同步的概念及實現技術；

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