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。
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()));// 在指定的毫秒数内让当前正在执行的线程休眠 } } catch (InterruptedException e) { } }; Thread t = new Thread(r);// 分配新的 Thread 对象 t.start();// 开始线程 } } } 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();// 加锁 try { while (accounts[from] < amount) sufficientFunds.await();// 锁对象的条件对象 System.out.print(Thread.currentThread());// 返回对当前正在执行的线程对象的引用 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();// 唤醒所有等待线程 } finally { bankLock.unlock();// 解锁 } } /** * Gets the sum of all account balances. * * @return the total balance */ public double getTotalBalance() { bankLock.lock();// 加锁 try { double sum = 0; for (double a : accounts) sum += a; return sum; } finally { bankLock.unlock();// 解锁 } } /** * Gets the number of accounts in the bank. * * @return the number of accounts */ public int size() { return accounts.length; } } Bank
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。
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()));// 在指定的毫秒数内让当前正在执行的线程休眠 } } catch (InterruptedException e) { } }; Thread t = new Thread(r);// 分配新的 Thread 对象 t.start();// 使线程开始执行 } } } 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();// 添加一个线程到等待集中 System.out.print(Thread.currentThread());// 返回对当前正在执行的线程对象的引用 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();// 解除等待线程的阻塞状态 } /** * 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
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();
}
}
运行结果：
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(); } }
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
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() + "窗口售：第" + t + "张票"); t++; } if (t > 10) { flag = false; } } } } }
三、实验总结：
这次实验比起前几次来说不算难，完成得也比较轻松，接下来的时间主要是复习之前的知识，为期末考试做准备。