本文主要是介绍多线程处理哲学家就餐问题(GUI动态演示)，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！
问题描述：
餐桌前坐着5位哲学家，两个人中间有一只筷子，桌子中央有面条。哲学家思考问题，当饿了的时候拿起左右两只筷子吃饭，必须同时拿到两只筷子才能吃饭。当5个哲学家都拿起自己右手边的筷子，准备拿左手边的筷子时可能产生死锁现象。
为了解决互斥问题，必须将筷子资源作为同步资源。在同一时刻，对于一个筷子对象，只能由一个哲学家（线程）对其进行访问。由于Java程序语言提供了同步机制，可以轻松解决线程互斥问题。
算法设计思路：将哲学家、筷子、房间分别定义为三个独立的类。其中，哲学家继承自线程，
拥有think()和eat()两个同步方法。筷子属于共享资源，定义takeup()和putdown()为PV操作。
算法的伪代码如下：
var chopstick:array[0..4] of semaphore(:=1);i:integer;room:semaphore(:=4);
procedure philosopher(i:integer, chopstick left, chopstick right)
begin repeatthink();room.enter();left.takeup();right.takeup();eat();right.putdown();left.putdown();room.exit();forever;
end;
begin(*main)parbeginphilosopher(1).start();philosopher(2).start();philosopher(3).start();philosopher(4).start();philosopher(5).start();parend
end.1. 定义筷子类。筷子属于同步资源，被持有者持有，同时被索取者竞争。因此，取筷子和放筷子的操作必须作好同步。
public class Chopstick
{private boolean avilable; //筷子是否可用标记private Philosopher taker; //索取者private Philosopher owner;//占有者private Dinner.DinnerTable table;public Chopstick(int id, Dinner.DinnerTable table) {this.table = table;avilable = true;}//取筷子,相当于P操作public synchronized void takeup(Philosopher taker) {this.setTaker(taker);while (!avilable) {try {//System.out.println("哲学家等待另一根筷子");taker.setFace(2);wait();}catch (InterruptedException e) {}}avilable = false;this.setOwner(taker);table.repaint();}//放下筷子，相当于V操作public synchronized void putdown() {avilable = true;this.setOwner(null);notify(); //唤醒其他等待的线程table.repaint();}public int getOwnerId(){return this.getOwner().getPersonId();}public Philosopher getTaker() {return taker;}public void setTaker(Philosopher taker) {this.taker = taker;}public Philosopher getOwner() {return owner;}public void setOwner(Philosopher owner) {this.owner = owner;}
}2.定义哲学家类。哲学家参与资源的竞争，申明为一个线程，其run()方法为一个死循环操作，
不断切换思考和吃饭两个动作（思考和吃饭设置一个随机时间）。
import java.util.Random;import javax.swing.ImageIcon;public class Philosopher extends Thread
{public static final byte STATUS_OF_NORMAL = 0; //初始表情public static final byte STATUS_OF_THINK =1; //思考表情public static final byte STATUS_OF_HUNGRY = 2; //饥饿表情public static final byte STATUS_OF_EAT = 3; //就餐表情private Room room;private Chopstick left, right;private int personId;private ImageIcon init, eat, think, hungry;private ImageIcon currentFace;private Random rand = new Random(); //随机休眠时间public Philosopher(Room room, int id, Chopstick left, Chopstick right) {this.room = room;this.personId = id;this.left = left;this.right = right;eat = new ImageIcon("eat.png");think = new ImageIcon("think.png");hungry = new ImageIcon("hungry.png");init = new ImageIcon("init.png");currentFace = init;setFace(Philosopher.STATUS_OF_NORMAL);}public void eat() {left.takeup(Philosopher.this);right.takeup(Philosopher.this);setFace(Philosopher.STATUS_OF_EAT);// System.out.println("哲学家" + this.philoId + "正在用餐");}public void think() {left.putdown();right.putdown();setFace(Philosopher.STATUS_OF_THINK);// System.out.println("哲学家" + this.philoId + "正在思考");}/*** 设置表情图片*/public void setFace(int faceId) {switch (faceId) {case Philosopher.STATUS_OF_NORMAL:currentFace = init;break;case Philosopher.STATUS_OF_THINK:currentFace = think;break;case Philosopher.STATUS_OF_HUNGRY:currentFace = hungry;break;case Philosopher.STATUS_OF_EAT:currentFace = eat;break;}}public ImageIcon getFace() {return currentFace;}public void run() {while (true) {think();//哲学家思考try {sleep((int) ((rand.nextFloat() + 0.5) * 3000));}catch (InterruptedException e) {}
// room.enter();//进入房间eat();//哲学家就餐try {sleep((int) ((rand.nextFloat() + 0.5) * 4000));}catch (InterruptedException e) {}
// room.exit();//离开房间}}public int getPersonId() {return personId;}public void setPersonId(int personId) {this.personId = personId;}
}3. 用Swing实现图形界面，将界面和业务逻辑代码分开。
import java.awt.Color;
import java.awt.Dimension;
import java.awt.FlowLayout;
import java.awt.Graphics;
import java.awt.Toolkit;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;import javax.swing.BoxLayout;
import javax.swing.ImageIcon;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;public class Dinner extends JFrame
{private static final int personCount = 20; //哲学家数量private static Room room = new Room(personCount - 1);//房间锁变量,用于控制同时就餐的人数ddprivate JButton startBtn = new JButton("开始");private JButton stopBtn = new JButton("暂停");private JButton continueBtn = new JButton("继续");private JButton endBtn = new JButton("结束");private boolean started = false;private boolean stopped = false;final static Chopstick[] chopstick = new Chopstick[personCount];final static Philosopher[] philos = new Philosopher[personCount];ImageIcon normalFace, eatFace, thinkFace, hungryFace; //表情图片// 因Table(餐桌)类与Dinner类联系较为紧密，故将其作为内部类，方便消息的传递class DinnerTable extends JPanel{private int counts;private int r1 = 20;private int CHOPS_LENGTH = 35; //筷子的长度private int DISTANCE = 100; //筷子与人的距离private int VERTICAL_DIS = -20; //表情与名字的距离private int r2 = r1 + CHOPS_LENGTH;private int r3 = r2 + DISTANCE;private int delta;private int delta0 = -18;public DinnerTable(int counts) {setOpaque(false);this.setPreferredSize(new Dimension(550, 400));this.counts = counts;this.delta = 360 / counts;}public void paintComponent(Graphics page) {super.paintComponent(page);int x1, y1, x2, y2, x3, y3;page.fillOval(200, 150, 150, 150);//画餐桌上的筷子for (int i = 0; i < counts; i++) {page.setColor(Color.YELLOW);//根据坐标系 x = r*cos(delta) , y = r*sin(delta) 计算点x1 = 275 + (int) (r1 * Math.cos(((delta * i)+ delta0*(-5) ) * Math.PI / 180));y1 = 225 + (int) (r1 * Math.sin(((delta * i) + delta0*(-5) ) * Math.PI / 180));x2 = 275 + (int) (r2 * Math.cos(((delta * i) + delta0 *(-5) ) * Math.PI / 180));y2 = 225 + (int) (r2 * Math.sin(((delta * i) + delta0 *(-5) ) * Math.PI / 180));x3 = 275 + (int) (r3 * Math.cos(((delta * i) + delta0 ) * Math.PI / 180));y3 = 225 + (int) (r3 * Math.sin(((delta * i) + delta0 ) * Math.PI / 180));if (chopstick[i].getOwner() != null && philos[i].getPersonId() == chopstick[i].getOwnerId()) {//检查哲学家是否拿到左边筷子page.drawLine(x3 - 20, y3, x3 - 20, y3 + CHOPS_LENGTH);}if (chopstick[(i + 1) % personCount].getOwner() != null && philos[i].getPersonId() == chopstick[(i + 1) % personCount].getOwnerId() ) {//检查哲学家是否拿到右边筷子page.drawLine(x3 + 45, y3, x3 + 45, y3 + CHOPS_LENGTH);}if (chopstick[i].getOwner() == null) {//筷子在餐桌上page.drawLine(x1, y1, x2, y2);}philos[i].getFace().paintIcon(this, page, x3, y3); //画表情page.setColor(Color.BLUE);page.drawString("哲学家" + (i + 1), x3 - 5, y3 + VERTICAL_DIS);//画名字}}}/*** 设置窗口居中*/private void putUIInCenter(){int windowWidth = this.getWidth(); //获得窗口宽int windowHeight = this.getHeight(); //获得窗口高Toolkit kit = Toolkit.getDefaultToolkit(); //定义工具包Dimension screenSize = kit.getScreenSize(); //获取屏幕的尺寸int screenWidth = screenSize.width; //获取屏幕的宽int screenHeight = screenSize.height; //获取屏幕的高this.setLocation(screenWidth / 2 - windowWidth / 2, screenHeight / 2 - windowHeight / 2);}public Dinner() {setTitle("哲学家就餐");setPreferredSize(new Dimension(600, 650));setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);this.pack();setVisible(true);setResizable(false);putUIInCenter();normalFace = new ImageIcon("init.png");eatFace = new ImageIcon("eat.png");thinkFace= new ImageIcon("think.png");hungryFace = new ImageIcon("hungry.png");JPanel btnPanel = new JPanel();btnPanel.setBounds(160, 20, 300, 200);btnPanel.setOpaque(false);btnPanel.setLayout(new FlowLayout());btnPanel.add(startBtn);btnPanel.add(stopBtn);btnPanel.add(continueBtn);btnPanel.add(endBtn);//各种按钮增加点击事件startBtn.addActionListener(new startListener());continueBtn.addActionListener(new continueListener());stopBtn.addActionListener(new stopListener());endBtn.addActionListener(new endListener());JPanel mainPanel = new JPanel();mainPanel.setLayout(null);mainPanel.setBackground(Color.black);mainPanel.add(btnPanel);DinnerTable table = new DinnerTable(personCount);table.setBounds(20, 50, 500, 420);for (int i = 0; i < chopstick.length; i++) {chopstick[i] = new Chopstick(i, table);}for (int i = 0; i < philos.length; i++) {philos[i] = new Philosopher(room, i,chopstick[i], chopstick[(i + 1) % personCount]);}mainPanel.add(table);JPanel descipPanel = new JPanel();descipPanel.setBounds(20, 480, 200, 200);descipPanel.setOpaque(false);descipPanel.setForeground(Color.red);descipPanel.setLayout(new BoxLayout(descipPanel, BoxLayout.Y_AXIS));JLabel label0 = new JLabel("哲学家就餐问题（信号量解决）");label0.setForeground(Color.red);JLabel label1 = new JLabel("初始状态的哲学家", normalFace, JLabel.RIGHT);label1.setForeground(Color.red);JLabel label2 = new JLabel("思考状态的哲学家", thinkFace, JLabel.RIGHT);label2.setForeground(Color.red);JLabel label3 = new JLabel("饥饿状态的哲学家", hungryFace, JLabel.RIGHT);label3.setForeground(Color.red);JLabel label4 = new JLabel("正在吃饭的哲学家", eatFace, JLabel.RIGHT);label4.setForeground(Color.red);descipPanel.add(label0);descipPanel.add(label1);descipPanel.add(label2);descipPanel.add(label3);descipPanel.add(label4);mainPanel.add(descipPanel);getContentPane().add(mainPanel);}private class startListener implements ActionListener{public void actionPerformed(ActionEvent evt) {if (!started) {started=true;for (int i = 0; i < personCount; i++) {philos[i].start();}}}}private class stopListener implements ActionListener{public void actionPerformed(ActionEvent evt) {for (int i = 0; i < personCount; i++) {philos[i].suspend();}stopped = true;}}private class continueListener implements ActionListener{public void actionPerformed(ActionEvent evt) {if (stopped) {for (int i = 0; i < personCount; i++) {philos[i].resume();}stopped = false;}}}private class endListener implements ActionListener{public void actionPerformed(ActionEvent evt) {System.exit(1);}}public static void main(String[] args) {new Dinner();}
}4.程序运行结果如下：
5.若修改Dinner类设置的常量 personCount为10，重新运行程序，如下：
6.若继续添加限制，要求在一时刻只能有4个哲学家就餐，则可以再添加另外一个信号量（比如房间资源）。哲学家在竞争筷子之前，必须先进入一个房间才能参与下一步竞争。房间类的设计如下：
/** 限制多个哲学家同时就餐，增设一间房间， 哲学家在准备就餐之前，必须先进入该房间， 若人数超过房间容量，则阻塞该线程*/public class Room
{private static int capacity; //房间的容量上限public Room(int capacity) {this.capacity = capacity;}public synchronized void enter() {while (capacity == 0) {try {wait();}catch (InterruptedException e) {}}capacity--;}public synchronized void exit() {capacity++;notify();}
}同时，设置房间上限（Dinner类的Room字段的初始化）
private static Room room = new Room(4);//房间锁变量,用于控制同时就餐的人数修改哲学家线程的run()方法，竞争筷子资源前先进入一个房间，放下筷子的时候需要退出房间，代码如下：
public void run() {while (true) {think();//哲学家思考try {sleep((int) ((rand.nextFloat() + 0.5) * 3000));}catch (InterruptedException e) {}room.enter();//进入房间eat();//哲学家就餐try {sleep((int) ((rand.nextFloat() + 0.5) * 4000));}catch (InterruptedException e) {}room.exit();//离开房间}}可以观察到，在同一时刻最多只有4个哲学家在就餐
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