實(shí)驗(yàn)十七 ?線程同步控制

實(shí)驗(yàn)時(shí)間 2018-12-10

一、理論部分

1.線程同步：多線程并發(fā)運(yùn)行不確定性問題解決方案：引入線程同步機(jī)制，使得另一線程要使用該方法，就只能等待。

解決方案：

1）鎖對(duì)象與條件對(duì)象

有關(guān)鎖對(duì)象和條件對(duì)象的關(guān)鍵要點(diǎn):

? 鎖用來保護(hù)代碼片段，保證任何時(shí)刻只能有一個(gè)線程執(zhí)行被保護(hù)的代碼。

? 鎖管理試圖進(jìn)入被保護(hù)代碼段的線程。

? 鎖可擁有一個(gè)或多個(gè)相關(guān)條件對(duì)象。

? 每個(gè)條件對(duì)象管理那些已經(jīng)進(jìn)入被保護(hù)的代碼段但還不能運(yùn)行的線程。

2）synchronized關(guān)鍵字

某個(gè)類內(nèi)方法用synchronized 修飾后，該方法被稱為同步方法；

只要某個(gè)線程正在訪問同步方法，其他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，其他線程方可能進(jìn)入同步方法。

一個(gè)線程在使用的同步方法中時(shí)，可能根據(jù)問題的需要，必須使用wait()方法使本線程等待，暫時(shí)讓出CPU的使用權(quán)，并允許其它線程使用這個(gè)同步方法。

線程如果用完同步方法，應(yīng)當(dāng)執(zhí)行notifyAll()方法通知所有由于使用這個(gè)同步方法而處于等待的線程結(jié)束等待。

二、實(shí)驗(yàn)部分

1、實(shí)驗(yàn)?zāi)康呐c要求

(1) 掌握線程同步的概念及實(shí)現(xiàn)技術(shù)；

(2) 線程綜合編程練習(xí)

2、實(shí)驗(yàn)內(nèi)容和步驟

實(shí)驗(yàn)1：測(cè)試程序并進(jìn)行代碼注釋。

測(cè)試程序1：

l?在Elipse環(huán)境下調(diào)試教材651頁(yè)程序14-7，結(jié)合程序運(yùn)行結(jié)果理解程序；

掌握利用鎖對(duì)象和條件對(duì)象實(shí)現(xiàn)的多線程同步技術(shù)。

程序如下：

package test2;/*** 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();}} } package test2;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.signalAll();}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;} }

程序運(yùn)行結(jié)果如下：

測(cè)試程序2：

l?在Elipse環(huán)境下調(diào)試教材655頁(yè)程序14-8，結(jié)合程序運(yùn)行結(jié)果理解程序；

l?掌握synchronized在多線程同步中的應(yīng)用。

程序如下：

?

package test2;/*** 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();}} }

?

package test2;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.signalAll();}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;} }

程序運(yùn)行結(jié)果：

測(cè)試程序3：

l?在Elipse環(huán)境下運(yùn)行以下程序，結(jié)合程序運(yùn)行結(jié)果分析程序存在問題；

l?嘗試解決程序中存在問題。

package test2; 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();} }

程序運(yùn)行后如圖：

分析程序，輸出結(jié)果應(yīng)為1900—1200，而控制臺(tái)上顯示結(jié)果有重復(fù)。因?yàn)闆]有對(duì)程序加上鎖功能。修改后程序如下：

package test2; 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();} }

程序運(yùn)行結(jié)果如下：

實(shí)驗(yàn)2?編程練習(xí)

利用多線程及同步方法，編寫一個(gè)程序模擬火車票售票系統(tǒng)，共3個(gè)窗口，賣10張票，程序輸出結(jié)果類似（程序輸出不唯一，可以是其他類似結(jié)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

程序如下：

?

package test2;public class Demo {public static void main(String[] args) {Mythread mythread = new Mythread();Thread ticket1 = new Thread(mythread);Thread ticket2 = new Thread(mythread);Thread ticket3 = new Thread(mythread);ticket1.start();ticket2.start();ticket3.start();} }class Mythread implements Runnable {int ticket = 1;boolean flag = true;@Overridepublic void run() {while (flag) {try {Thread.sleep(500);} catch (InterruptedException e) {// TODO Auto-generated catch block e.printStackTrace();}synchronized (this) {if (ticket <= 10) {System.out.println(Thread.currentThread().getName() + "窗口售：第" + ticket + "張票");ticket++;}if (ticket > 10) {flag = false;}}}}}

?

程序運(yùn)行結(jié)果如下：

三:實(shí)驗(yàn)總結(jié)

? ? ? 這周繼續(xù)學(xué)習(xí)了有關(guān)線程的知識(shí)，主要學(xué)習(xí)了有關(guān)線程同步的問題。線程同步主要是為了解決多線程并發(fā)運(yùn)行不確定性問題，使得多個(gè)線程中在一個(gè)線程使用某種方法時(shí)候，另一線程要使用該方法，就只能等待。實(shí)驗(yàn)課上，老師和學(xué)長(zhǎng)通過演示具體的例子給我們展現(xiàn)了多線程中在不加鎖時(shí)會(huì)出現(xiàn)的情況，讓我們對(duì)線程同步有了更加清晰地認(rèn)識(shí)。雖然很多地方還是不太懂還是存在很大的問題，但是實(shí)驗(yàn)課上講的內(nèi)容聽得比較清晰，課后自己再運(yùn)行試驗(yàn)時(shí)也有了更深的體會(huì)。

?

轉(zhuǎn)載于:https://www.cnblogs.com/JAVA-729/p/10159644.html

總結(jié)

以上是生活随笔為你收集整理的王艳 201771010127《面向对象程序设计（java）》第十七周学习总结的全部?jī)?nèi)容，希望文章能夠幫你解決所遇到的問題。

如果覺得生活随笔網(wǎng)站內(nèi)容還不錯(cuò)，歡迎將生活随笔推薦給好友。