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;

/**
 * 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()));// 在指定的毫秒數內讓當前正在執行的執行緒休眠
                    }
                } catch (InterruptedException e) {
                }
            };
            Thread t = new Thread(r);// 分配新的 Thread 物件
            t.start();// 開始執行緒
        }
    }
}

SynchBankTest

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();// 加鎖
        try {
            while (accounts[from] < amount)
                sufficientFunds.await();// 鎖物件的條件物件
            System.out.print(Thread.currentThread());// 返回對當前正在執行的執行緒物件的引用
            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();// 喚醒所有等待執行緒
        } finally {
            bankLock.unlock();// 解鎖
        }
    }

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

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

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

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

Bank

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;

/**
 * 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()));// 在指定的毫秒數內讓當前正在執行的執行緒休眠
                    }
                } catch (InterruptedException e) {
                }
            };
            Thread t = new Thread(r);// 分配新的 Thread 物件
            t.start();// 使執行緒開始執行
        }
    }
}

SynchBankTest2

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();// 新增一個執行緒到等待集中
        System.out.print(Thread.currentThread());// 返回對當前正在執行的執行緒物件的引用
        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();// 解除等待執行緒的阻塞狀態
    }

    /**
     * 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

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 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();

  }

}

執行結果：

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

public class Demo {
    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 = 1;
    boolean flag = true;

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

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

        }

    }
}

三、實驗總結：

這次實驗比起前幾次來說不算難，完成得也比較輕鬆，接下來的時間主要是複習之前的知識，為期末考試做準備。