哲学家问题(java)的三个解法
2024-09-24 08:26:34
//加synchronize进行同步
//释放资源又很快获得自身的资源，这样不妥，吃完的话休息100ms //每个人先申请编号小的筷子 public class Philosopher implements Runnable {
int[] fork=new int[5];
Thread thread1=new Thread(this,"1");
Thread thread2=new Thread(this,"2");
Thread thread3=new Thread(this,"3");
Thread thread4=new Thread(this,"4");
Thread thread5=new Thread(this,"5");
public void run() {
try {
while (true) {
if (Thread.currentThread().getName().equals("1")) {
while (fork[0]==1) {
synchronized (this) {
wait();
}
}
fork[0]=1;
while (fork[1]==1) {
synchronized (this) {
wait();
}
}
fork[1]=1;
System.out.println("1 eats for 3 seconds");
Thread.sleep(3000);
fork[0]=0;
fork[1]=0;
synchronized(this) {
notifyAll();
}
Thread.sleep(100);
}
else if (Thread.currentThread().getName().equals("2")) {
while (fork[1]==1) {
synchronized(this) {
wait();
}
}
fork[1]=1;
while (fork[2]==1) {
synchronized(this) {
wait();
}
}
fork[2]=1;
System.out.println("2 eats for 3 seconds");
Thread.sleep(3000);
fork[1]=0;
fork[2]=0;
synchronized(this) {
notifyAll();
}
Thread.sleep(100);
}
else if (Thread.currentThread().getName().equals("3")) {
while (fork[2]==1) {
synchronized(this) {
wait();
}
}
fork[2]=1;
while (fork[3]==1) {
synchronized(this) {
wait();
}
}
fork[3]=1;
System.out.println("3 eats for 3 seconds");
Thread.sleep(3000);
fork[2]=0;
fork[3]=0;
synchronized(this) {
notifyAll();
}
Thread.sleep(100);
}
else if (Thread.currentThread().getName().equals("4")) {
while (fork[3]==1) {
synchronized(this) {
wait();
}
}
fork[3]=1;
while (fork[4]==1) {
synchronized(this) {
wait();
}
}
fork[4]=1;
System.out.println("4 eats for 3 seconds");
Thread.sleep(3000);
fork[3]=0;
fork[4]=0;
synchronized(this) {
notifyAll();
}
Thread.sleep(100);
}
else if (Thread.currentThread().getName().equals("5")) {
while (fork[0]==1) {
synchronized(this) {
wait();
}
}
fork[0]=1;
while (fork[4]==1) {
synchronized(this) {
wait();
}
}
fork[4]=1;
System.out.println("5 eats for 3 seconds");
Thread.sleep(3000);
fork[0]=0;
fork[4]=0;
synchronized(this) {
notifyAll();
}
Thread.sleep(100);
}
}
} catch(Exception e) {
e.printStackTrace();
}
} public static void main(String[] args) {
Philosopher phi=new Philosopher();
for (int i=0;i<5;i++)
phi.fork[i]=0;
phi.thread1.start();
phi.thread2.start();
phi.thread3.start();
phi.thread4.start();
phi.thread5.start();
}
} //当某个线程试图等待一个自己并不拥有的对象（O）的监控器或者通知其他线程等待该对象（O）的监控器时，抛出该异常。
//让刚吃完的一个人阻塞，5根筷子供4个人选，则必有一个人获得在其左右的两双筷子
public class Philosopher1 implements Runnable {
int[] ifeat=new int[5];
int[] fork=new int[5];
int noteat;
Thread thread1=new Thread(this,"1");
Thread thread2=new Thread(this,"2");
Thread thread3=new Thread(this,"3");
Thread thread4=new Thread(this,"4");
Thread thread5=new Thread(this,"5");
public void run() {
try {
while (true) {
if (Thread.currentThread().getName().equals("1")) {
while (ifeat[0]==1) {
synchronized (this) {
wait();
}
}
while (fork[0]==1) {
synchronized (this) {
wait();
}
}
fork[0]=1;
while (fork[1]==1) {
synchronized (this) {
wait();
}
}
fork[1]=1;
System.out.println("1 eats for 3 seconds");
Thread.sleep(3000);
fork[0]=0;
fork[1]=0;
ifeat[noteat]=0;
noteat=0;
ifeat[0]=1;
synchronized(this) {
notifyAll();
}
Thread.sleep(100);
}
else if (Thread.currentThread().getName().equals("2")) {
while (ifeat[1]==1) {
synchronized (this) {
wait();
}
}
while (fork[1]==1) {
synchronized (this) {
wait();
}
}
fork[1]=1;
while (fork[2]==1) {
synchronized (this) {
wait();
}
}
fork[2]=1;
System.out.println("2 eats for 3 seconds");
Thread.sleep(3000);
fork[1]=0;
fork[2]=0;
ifeat[noteat]=0;
noteat=1;
ifeat[1]=1;
synchronized(this) {
notifyAll();
}
Thread.sleep(100);
}
else if (Thread.currentThread().getName().equals("3")) {
while (ifeat[2]==1) {
synchronized (this) {
wait();
}
}
while (fork[2]==1) {
synchronized (this) {
wait();
}
}
fork[2]=1;
while (fork[3]==1) {
synchronized (this) {
wait();
}
}
fork[3]=1;
System.out.println("3 eats for 3 seconds");
Thread.sleep(3000);
fork[2]=0;
fork[3]=0;
ifeat[noteat]=0;
noteat=2;
ifeat[2]=1;
synchronized(this) {
notifyAll();
}
Thread.sleep(100);
}
else if (Thread.currentThread().getName().equals("4")) {
while (ifeat[3]==1) {
synchronized (this) {
wait();
}
}
while (fork[3]==1) {
synchronized (this) {
wait();
}
}
fork[3]=1;
while (fork[4]==1) {
synchronized (this) {
wait();
}
}
fork[4]=1;
System.out.println("4 eats for 3 seconds");
Thread.sleep(3000);
fork[3]=0;
fork[4]=0;
ifeat[noteat]=0;
noteat=3;
ifeat[3]=1;
synchronized(this) {
notifyAll();
}
Thread.sleep(100);
}
else if (Thread.currentThread().getName().equals("5")) {
while (ifeat[4]==1) {
synchronized (this) {
wait();
}
}
while (fork[4]==1) {
synchronized (this) {
wait();
}
}
fork[4]=1;
while (fork[0]==1) {
synchronized (this) {
wait();
}
}
fork[0]=1;
System.out.println("5 eats for 3 seconds");
Thread.sleep(3000);
fork[4]=0;
fork[0]=0;
ifeat[noteat]=0;
noteat=4;
ifeat[4]=1;
synchronized(this) {
notifyAll();
}
Thread.sleep(100);
}
}
} catch(Exception e) {
e.printStackTrace();
}
}
public static void main(String[] args) {
Philosopher1 phi=new Philosopher1();
for (int i=0;i<5;i++)
phi.fork[i]=0;
phi.ifeat[0]=1;
for (int i=0;i<5;i++)
phi.ifeat[i]=0;
phi.noteat=0;
phi.thread1.start();
phi.thread2.start();
phi.thread3.start();
phi.thread4.start();
phi.thread5.start();
}
}
//只有两双筷子都有，才获取，且同时获取两双筷子
public class Philosopher2 implements Runnable {
int[] fork=new int[5];
Thread thread1=new Thread(this,"1");
Thread thread2=new Thread(this,"2");
Thread thread3=new Thread(this,"3");
Thread thread4=new Thread(this,"4");
Thread thread5=new Thread(this,"5");
public void run() {
try {
while (true) {
if (Thread.currentThread().getName().equals("1")) {
while (fork[0]==1 || fork[1]==1) {
synchronized (this) {
wait();
}
}
fork[0]=1;
fork[1]=1;
System.out.println("1 eats for 3 seconds");
Thread.sleep(3000);
fork[0]=0;
fork[1]=0;
synchronized(this) {
notifyAll();
}
Thread.sleep(100);
}
else if (Thread.currentThread().getName().equals("2")) {
while (fork[1]==1 || fork[2]==1) {
synchronized (this) {
wait();
}
}
fork[1]=1;
fork[2]=1;
System.out.println("2 eats for 3 seconds");
Thread.sleep(3000);
fork[1]=0;
fork[2]=0;
synchronized(this) {
notifyAll();
}
Thread.sleep(100);
}
else if (Thread.currentThread().getName().equals("3")) {
while (fork[2]==1 || fork[3]==1) {
synchronized (this) {
wait();
}
}
fork[2]=1;
fork[3]=1;
System.out.println("3 eats for 3 seconds");
Thread.sleep(3000);
fork[2]=0;
fork[3]=0;
synchronized(this) {
notifyAll();
}
Thread.sleep(100);
}
else if (Thread.currentThread().getName().equals("4")) {
while (fork[3]==1 || fork[4]==1) {
synchronized (this) {
wait();
}
}
fork[3]=1;
fork[4]=1;
System.out.println("4 eats for 3 seconds");
Thread.sleep(3000);
fork[3]=0;
fork[4]=0;
synchronized(this) {
notifyAll();
}
Thread.sleep(100);
}
else if (Thread.currentThread().getName().equals("5")) {
while (fork[0]==1 || fork[4]==1) {
synchronized (this) {
wait();
}
}
fork[0]=1;
fork[4]=1;
System.out.println("5 eats for 3 seconds");
Thread.sleep(3000);
fork[0]=0;
fork[4]=0;
synchronized(this) {
notifyAll();
}
Thread.sleep(100);
}
}
} catch(Exception e) {
e.printStackTrace();
}
}
public static void main(String[] args) {
Philosopher2 phi=new Philosopher2();
for (int i=0;i<5;i++)
phi.fork[i]=0;
phi.thread1.start();
phi.thread2.start();
phi.thread3.start();
phi.thread4.start();
phi.thread5.start();
}
}
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