Java 多线程学习总结6
哲学家进餐问题http://users.rcn.com/ziring/java.html牛人网址，原版
由于这个问题比较复杂，本人也没细细分析，在网上搜出一个正确的解答，还有一些论文，给大家学习。
package Power.Thread.jincan2;import java.applet.*;import java.awt.*;import java.awt.event.*;import java.util.*;/** * A simple graphical applet to demonstrate a multi-thread solution * to the N dining philosophers problem. */public class DiningApplet extends Applet implements Observer, ActionListener, ItemListener { // GUI member variables DiningCanvas picture; TextArealogarea; Label legend; Label caption; Label status; CheckboxfastBox; TextField counterField; Button startButton; Polygon chopstickPics[]; Point philPics[]; double rad, philrad, stickrad; int runningthreads; boolean eatfast; // Constants - change these to adjust the simulation public static final int BASIC_DELAY = 2000; public static final int BASIC_APPETITE = 4; public static final int DEFAULT_PHILOSOPHERS = 5; // functional members, don't mess with these int count; Philosopher diners[]; Utensil chopsticks[]; public void init() {count = DEFAULT_PHILOSOPHERS;diners = null;chopsticks = null;// GUI stuffsetLayout(new GridLayout(2,1));picture = new DiningCanvas();add(picture);Panel bottompanel = new Panel();bottompanel.setLayout(new BorderLayout());logarea = new TextArea();bottompanel.add("Center", logarea);Panel controlpanel = new Panel();legend = new Label("Legend: Blue=thinking, Yellow=hungry, Green=eating, Gray=done", Label.CENTER);legend.setBackground(Color.pink);caption = new Label("Philosophers:", Label.RIGHT);counterField = new TextField("" + count, 3);startButton = new Button("START");fastBox = new Checkbox("Slow", false);status = new Label(" Initializing", Label.RIGHT);startButton.addActionListener(this);fastBox.addItemListener(this);controlpanel.add(caption);controlpanel.add(counterField);controlpanel.add(startButton);controlpanel.add(fastBox);controlpanel.add(status);bottompanel.add("North",legend);bottompanel.add("South", controlpanel);add(bottompanel);runningthreads = 0; } public void start() {status.setText("Click on START to start"); } public void beginSimulation() {int i;if (runningthreads > 0) { logarea.append("Aborting simulation before completion.\n"); for(i = 0; i < diners.length; i++) {diners.stop(); } runningthreads = 0;}picture.clear();String cntString = counterField.getText();try { count = Integer.parseInt(cntString); }catch (NumberFormatException nfe) { count = DEFAULT_PHILOSOPHERS; counterField.setText("" + count);}logarea.append("\nBeginning simulation with " + count + " philosophers\n");synchronized (picture) { diners = new Philosopher; chopsticks = new Utensil;}Dimension psize = picture.getSize();Point center = new Point(psize.width / 2, psize.height / 2);rad = ((psize.width < psize.height)? ((psize.width * 4)/5):((psize.height * 4) / 5)) / 2.0;philrad = (rad/count) * 2.1;stickrad = rad - philrad;philPics = new Point;int csx[] = new int;int csy[] = new int;chopstickPics = new Polygon;double phi;double div = (2 * Math.PI)/(count * 2);double swdiv = Math.PI / 90;int c;for(c = 0, phi = 0.0; c < count; c++, phi += div) { philPics = new Point((int)(rad * Math.sin(phi)) + center.x, (int)(rad * Math.cos(phi)) + center.y); phi += div; csx = (int)(rad * Math.sin(phi)) + center.x; csy = (int)(rad * Math.cos(phi)) + center.y; csx = (int)(stickrad * Math.sin(phi)) + center.x; csy = (int)(stickrad * Math.cos(phi)) + center.y; csx = (int)(stickrad * Math.sin(phi + swdiv)) + center.x; csy = (int)(stickrad * Math.cos(phi + swdiv)) + center.y; csx = (int)(rad * Math.sin(phi + swdiv)) + center.x; csy = (int)(rad * Math.cos(phi + swdiv)) + center.y; chopstickPics[(c + 1) % count] = new Polygon(csx,csy,4);}for(i = 0; i < count; i++) { chopsticks = new Utensil("Chopstick " + i, chopstickPics); chopsticks.addObserver(picture);}for(i = 0; i < count; i++) { diners = new Philosopher("Diner " + i, chopsticks,chopsticks[(i + 1) % count],philPics); diners.setEatFast(eatfast); diners.addObserver(this); diners.addObserver(picture);}for(runningthreads = 0; runningthreads < count; runningthreads++) { diners.start();}picture.repaint();status.setText("Simulated philosophers: " + count); } public void actionPerformed(ActionEvent evt) {beginSimulation(); } public void itemStateChanged(ItemEvent evt) {eatfast = (!(fastBox.getState()));if (diners != null) synchronized (this) { for(int i = 0; i < count; i++) {diners.setEatFast(eatfast); }}return; } public void stop() {if (runningthreads > 0) { for(int i = 0; i < diners.length; i++) {diners.stop(); } runningthreads = 0;}return; } public void update(Observable obj, Object r) {if (r instanceof String) synchronized(this) { logarea.append("\n"); logarea.append(r.toString()); if (obj instanceof Philosopher) {Philosopher p = (Philosopher)obj;if (p.status == Philosopher.STATUS_DONE) { runningthreads--;}if (runningthreads <= 0) { status.setText("Simulation done.");} }}return; } class DiningCanvas extends Canvas implements Observer {Color bg;Color statColors[];Color stickColor;Color textColor;public DiningCanvas() { bg = Color.pink; setBackground(bg); stickColor = new Color(0x33, 0x66, 0x33); textColor = Color.black; statColors = new Color; statColors = Color.darkGray; statColors = Color.blue; statColors = Color.yellow; statColors = Color.green;}public void clear() { Graphics g = getGraphics(); g.setColor(bg); Dimension d = getSize(); g.fillRect(0, 0, d.width, d.height);}public void paintItem(Object o, Graphics g) { if (o instanceof Utensil) {Utensil u = (Utensil)o;g.setColor((u.isAvailable())?(stickColor):(bg));g.fillPolygon((Polygon)(u.observerRef)); } else if (o instanceof Philosopher) {Philosopher p = (Philosopher)o;g.setColor(statColors);Point pp = (Point)(p.observerRef);int pr = (int)philrad;g.fillOval(pp.x - ((int)(pr/2)), pp.y - ((int)(pr/2)), pr, pr);g.setColor(textColor);g.drawOval(pp.x - ((int)(pr/2)), pp.y - ((int)(pr/2)), pr, pr);// paintItem(p.sticks, g);// paintItem(p.sticks, g); } return;}public void paint(Graphics g) { int i; Utensil u; Philosopher p; if (diners != null && diners.length > 1) synchronized (this) {for(i = 0; i < count; i++) { u = chopsticks; paintItem(u,g);}for(i = 0; i < count; i++) { p = diners; paintItem(p,g);} } return;}public void update(Observable obj, Object r) { if (!(r instanceof String))paintItem(obj, getGraphics());} }}
package Power.Thread.jincan2;import java.util.*;public class Utensil extends Observable { String name; private boolean inuse; public Object observerRef; public Utensil(String n, Object r) {name = n;inuse = false;observerRef = r; } public synchronized boolean isAvailable() { return !inuse; } public synchronized void pick_up() { System.out.println("qu na@@@@@@@"+Thread.currentThread());inuse = true; setChanged();notifyObservers(observerRef); } public synchronized void put_down() { inuse = false; // when chopstick is dropped, do a notifySystem.out.println("qu fang#####"+Thread.currentThread());notify();setChanged();notifyObservers(observerRef); }}
package Power.Thread.jincan2;import java.util.*;public class Philosopher extends Observable implements Runnable { public static final int STATUS_DONE = 0; public static final int STATUS_THINKING = 1; public static final int STATUS_GRABBING = 2; public static final int STATUS_EATING = 3; String name; int status; Utensil sticks[]; Object observerRef; int appetite; int eaten; Thread myThread; boolean abort = false; boolean eatfast = false; public Philosopher(String n, Utensil r, Utensil l, Object ref) {name = n;sticks = new Utensil;sticks = l;sticks = r;eaten = 0;appetite = rand(DiningApplet.BASIC_APPETITE - 2, DiningApplet.BASIC_APPETITE + 2);observerRef = ref;myThread = new Thread(this, n);status = STATUS_THINKING; } int rand(int min, int max) {return (min + (int)(Math.random() * (max - min))); } void sleepFor(int ms) {try { Thread.sleep(ms * (eatfast?1:6)); } catch (InterruptedException e) { abort = true; } } public void setEatFast(boolean e) { eatfast = e; } public synchronized void start() {myThread.start(); } public synchronized void stop() {abort = true;myThread.interrupt(); } public void run() {message("arrived at table with appetite of " + appetite+" "+Thread.currentThread());int s1, s2;while(eaten < appetite && !abort) { // think for a while.. status = STATUS_THINKING; setChanged(); notifyObservers(observerRef); message("thinking...");//sleepFor(rand(0,4) * DiningApplet.BASIC_DELAY); message("trying to eat..."); // okay, philosopher has decided to have a bite status = STATUS_GRABBING; boolean gotboth = false; setChanged(); notifyObservers(observerRef); while(!gotboth && !abort) {// decide on a stick to acquire first, at randoms1 = rand(0,2);s2 = ((s1 == 0)?(1):(0)); // Attempt to acquire first stick.synchronized (sticks) { while(!(sticks.isAvailable())) {try { sticks.wait();} catch (Exception e) { if (abort) return;}// okay, if we get here then we own// stick 1 } // okay, first stick acquired sticks.pick_up();}// Attempt to acquire second stick, but give up// immediately if we can't get it.synchronized (sticks) { if (sticks.isAvailable()) {sticks.pick_up();gotboth = true; }}// If we didn't manage to get second stick,// then put first one down.if (!gotboth) { sticks.put_down();} } if (abort) return; // If we get here, we've got both sticks, so we // can eat for a while. status = STATUS_EATING; message("Got both chopsticks, EATING!"); setChanged(); notifyObservers(observerRef); // sleepFor(rand(2,5) * DiningApplet.BASIC_DELAY);//eaten += 1; if (abort) return; // Okay, we're done eating for now, put both // sticks down. message("done eating for the moment..."); sticks.put_down(); sticks.put_down(); if (abort) return;}status = STATUS_DONE;setChanged(); notifyObservers(observerRef);message("all full, leaving the table."); } public void message(String s) {setChanged();notifyObservers(myThread.getName() + ": " + s); }} 从这个代码分析，我猜测不能从理论上保证排除“饥饿”这种现象，但是这种现象是极其罕见的，也是不可能出现的。
排除饥饿的原理就是随机地选择左右哪个方向为第一手。
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