哲学家进餐问题（含代码）

如图所示，桌上摆着五支（不是五双）筷子。哲学家的状态可能是“思考”和“饥饿”。如果饥饿，哲学家将拿起他两边的筷子并进餐一段时间。进餐结束，哲学家就会放回筷子。

package com.my.diningphilosopherscondition;

import java.util.concurrent.locks.ReentrantLock;

public class DiningPhilosophers {

	public static void main(String[] args) throws InterruptedException {
		final Philosopher[] philosophers = new Philosopher[5];
		final ReentrantLock table = new ReentrantLock();

		for (int i = 0; i < 5; ++i)
			philosophers[i] = new Philosopher(table);
		for (int i = 0; i < 5; ++i) {
			philosophers[i].setLeft(philosophers[(i + 4) % 5]);
			philosophers[i].setRight(philosophers[(i + 1) % 5]);
			philosophers[i].start();
		}
		class CountingThread extends Thread {
			@SuppressWarnings("static-access")
			public void run() {
				while (!interrupted()) {
					try {
						currentThread().sleep(100);
					} catch (InterruptedException e) {
					}
					for (int i = 0; i < 5; ++i){
						System.out.print("\r"+i+"号哲学家: " + (philosophers[i].isEating()?"正在进餐":"思考中..."));
					}
					System.out.println("\r==================");
					System.out.flush();
				}
			}
		}
		CountingThread t3 = new CountingThread();
		t3.start();
		for (int i = 0; i < 5; ++i)
			philosophers[i].join();
		t3.interrupt();
	}
}


​

package com.my.diningphilosopherscondition;

import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.ReentrantLock;

import java.util.Random;

class Philosopher extends Thread {

	private boolean eating;
	private Philosopher left;
	private Philosopher right;
	private ReentrantLock table;
	private Condition condition;
	private Random random;
	private int thinkCount;

	public Philosopher(ReentrantLock table) {
		eating = false;
		this.table = table;
		condition = table.newCondition();
		random = new Random();
	}

	public void setLeft(Philosopher left) {
		this.left = left;
	}

	public void setRight(Philosopher right) {
		this.right = right;
	}

	public void run() {
		try {
			while (true) {
				think();
				eat();
			}
		} catch (InterruptedException e) {
		}
	}

	private void think() throws InterruptedException {
		table.lock();
		try {
			eating = false;
			left.condition.signal();
			right.condition.signal();
		} finally {
			table.unlock();
		}
		++thinkCount;
		if (thinkCount % 10 == 0)
			System.out.println("Philosopher " + this + " has thought " + thinkCount + " times");
		Thread.sleep(random.nextInt(3000));
	}

	private void eat() throws InterruptedException {
		table.lock();
		try {
			while (left.eating || right.eating)
				condition.await();
			eating = true;
		} finally {
			table.unlock();
		}
		Thread.sleep(random.nextInt(3000));
	}

	public boolean isEating() {
		return eating;
	}

	public void setEating(boolean eating) {
		this.eating = eating;
	}
}


​