201772020113 李清華《面向物件程式設計（java）》第17周學習總結
阿新 • • 發佈：2018-12-22
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。
1 package synch; 2 3 import java.util.*; 4 import java.util.concurrent.locks.*; 5 6 /** 7 * A bank with a number of bank accounts that uses locks for serializing access.View Code8 * @version 1.30 2004-08-01 9 * @author Cay Horstmann 10 */ 11 public class Bank 12 { 13 private final double[] accounts;//銀行的基本資料 14 private Lock bankLock;//鎖物件 15 private Condition sufficientFunds; 16 17 /** 18 * Constructs the bank. 19 * @param n the number of accounts 20 * @paraminitialBalance the initial balance for each account 21 */ 22 public Bank(int n, double initialBalance) 23 { 24 accounts = new double[n]; 25 Arrays.fill(accounts, initialBalance); 26 bankLock = new ReentrantLock(); 27 sufficientFunds = bankLock.newCondition(); 28 }29 30 /** 31 * Transfers money from one account to another. 32 * @param from the account to transfer from 33 * @param to the account to transfer to 34 * @param amount the amount to transfer 35 */ 36 public void transfer(int from, int to, double amount) throws InterruptedException 37 { 38 bankLock.lock(); 39 try 40 { //鎖物件的引用條件物件 41 while (accounts[from] < amount) 42 sufficientFunds.await(); 43 System.out.print(Thread.currentThread());//打印出執行緒號 44 accounts[from] -= amount; 45 System.out.printf(" %10.2f from %d to %d", amount, from, to); 46 accounts[to] += amount; 47 System.out.printf(" Total Balance: %10.2f%n", getTotalBalance()); 48 sufficientFunds.signalAll(); 49 } 50 finally 51 { 52 bankLock.unlock(); 53 } 54 } 55 56 /** 57 * Gets the sum of all account balances. 58 * @return the total balance 59 */ 60 public double getTotalBalance() 61 { 62 bankLock.lock();//加鎖 63 try 64 { 65 double sum = 0; 66 67 for (double a : accounts) 68 sum += a; 69 70 return sum; 71 } 72 finally 73 { 74 bankLock.unlock();//解鎖 75 } 76 } 77 78 /** 79 * Gets the number of accounts in the bank. 80 * @return the number of accounts 81 */ 82 public int size() 83 { 84 return accounts.length; 85 } 86 }
1 package synch; 2 3 /** 4 * This program shows how multiple threads can safely access a data structure. 5 * @version 1.31 2015-06-21 6 * @author Cay Horstmann 7 */ 8 public class SynchBankTest 9 { 10 public static final int NACCOUNTS = 100; 11 public static final double INITIAL_BALANCE = 1000; 12 public static final double MAX_AMOUNT = 1000; 13 public static final int DELAY = 10; 14 15 public static void main(String[] args) 16 { 17 Bank bank = new Bank(NACCOUNTS, INITIAL_BALANCE); 18 for (int i = 0; i < NACCOUNTS; i++) 19 { 20 int fromAccount = i; 21 Runnable r = () -> { 22 try 23 { 24 while (true) 25 { 26 int toAccount = (int) (bank.size() * Math.random()); 27 double amount = MAX_AMOUNT * Math.random(); 28 bank.transfer(fromAccount, toAccount, amount); 29 Thread.sleep((int) (DELAY * Math.random())); 30 } 31 } 32 catch (InterruptedException e) 33 { 34 } 35 }; 36 Thread t = new Thread(r); 37 t.start(); 38 } 39 } 40 }View Code
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。
1 package synch2; 2 3 /** 4 * 這個程式顯示了多個執行緒如何安全地訪問資料結構,使用同步方法。 5 * @version 1.31 2015-06-21 6 * @author Cay Horstmann 7 */ 8 public class SynchBankTest2 9 { 10 public static final int NACCOUNTS = 100; 11 public static final double INITIAL_BALANCE = 1000; 12 public static final double MAX_AMOUNT = 1000; 13 public static final int DELAY = 10; 14 15 public static void main(String[] args) 16 { 17 Bank bank = new Bank(NACCOUNTS, INITIAL_BALANCE); 18 for (int i = 0; i < NACCOUNTS; i++) 19 { 20 int fromAccount = i; 21 Runnable r = () -> { 22 try 23 { 24 while (true) 25 { 26 int toAccount = (int) (bank.size() * Math.random()); 27 double amount = MAX_AMOUNT * Math.random(); 28 bank.transfer(fromAccount, toAccount, amount); 29 Thread.sleep((int) (DELAY * Math.random())); 30 } 31 } 32 catch (InterruptedException e) 33 { 34 } 35 }; 36 Thread t = new Thread(r); 37 t.start(); 38 } 39 } 40 }View Code
1 package synch2; 2 3 import java.util.*; 4 5 /** 6 * 具有多個使用同步原語的銀行賬戶的銀行。 7 * @version 1.30 2004-08-01 8 * @author Cay Horstmann 9 */ 10 public class Bank 11 { 12 private final double[] accounts; 13 14 /** 15 * 建設銀行。 16 * @param n the number of accounts 17 * @param initialBalance the initial balance for each account 18 */ 19 public Bank(int n, double initialBalance) 20 { 21 accounts = new double[n]; 22 Arrays.fill(accounts, initialBalance); 23 } 24 25 /** 26 * 把錢從一個賬戶轉到另一個賬戶。 27 * @param from the account to transfer from 28 * @param to the account to transfer to 29 * @param amount the amount to transfer 30 */ 31 public synchronized void transfer(int from, int to, double amount) throws InterruptedException 32 { 33 while (accounts[from] < amount) 34 wait();//導致執行緒進入等待狀態直到它被通知。該方法只能在一個同步方法中呼叫。 35 System.out.print(Thread.currentThread());//打印出執行緒號 36 accounts[from] -= amount; 37 System.out.printf(" %10.2f from %d to %d", amount, from, to);//第一個列印結果保留兩位小數（最大範圍是十位） 38 accounts[to] += amount; 39 System.out.printf(" Total Balance: %10.2f%n", getTotalBalance()); 40 notifyAll();//解除那些在該物件上呼叫wait方法的執行緒阻塞狀態。該方法只能在同步方法或同步塊內部呼叫。 41 } 42 43 /** 44 * 獲取所有帳戶餘額的總和。 45 * @return the total balance 46 */ 47 public synchronized double getTotalBalance() 48 { 49 double sum = 0; 50 51 for (double a : accounts) 52 sum += a; 53 54 return sum; 55 } 56 57 /** 58 * 獲取銀行中的帳戶數量。 59 * @return the number of accounts 60 */ 61 public int size() 62 { 63 return accounts.length; 64 } 65 }View Code
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(); } } |
改進後：
1 class Cbank { 2 private static int s = 2000; 3 4 public synchronized static void sub(int m) { 5 int temp = s; 6 temp = temp - m; 7 try { 8 Thread.sleep((int) (1000 * Math.random())); 9 } catch (InterruptedException e) { 10 } 11 s = temp; 12 System.out.println("s=" + s); 13 } 14 } 15 16 class Customer extends Thread { 17 public void run() { 18 for (int i = 1; i <= 4; i++) 19 Cbank.sub(100); 20 } 21 } 22 23 public class Thread3 { 24 public static void main(String args[]) { 25 Customer customer1 = new Customer(); 26 Customer customer2 = new Customer(); 27 customer1.start(); 28 customer2.start(); 29 } 30 }View Code
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
1 public class Main { 2 public static void main(String[] args) { 3 Mythread mythread=new Mythread(); 4 Thread t1=new Thread(mythread); 5 Thread t2=new Thread(mythread); 6 Thread t3=new Thread(mythread); 7 t1.start(); 8 t2.start(); 9 t3.start(); 10 } 11 } 12 class Mythread implements Runnable{ 13 int t=1; 14 boolean flag=true; 15 public void run() { 16 while(flag) { 17 try { 18 Thread.sleep(300); 19 }catch(InterruptedException e) { 20 e.printStackTrace(); 21 } 22 synchronized(this){ 23 if(t<=10) { 24 System.out.println(Thread.currentThread().getName() + "視窗售：第" + t + "張票"); 25 t++; 26 } 27 if(t>10) { 28 flag=false; 29 } 30 } 31 } 32 } 33 }View Code
實驗總結：本週實驗學會了如何使用執行緒同步機制來解決多執行緒併發導致的不確定性。