（转）进程同步之临界区域问题及Peterson算法

转自：http://blog.csdn.net/speedme/article/details/17595821

•  1. 背景                                                                                                                                                                                                            
•  首先，看个例子，进程P1，P2共用一个变量COUNT，初始值为0

• 2.临界区域问题

• 3.Peterson算法   

public class Peterson implements Runnable {

    private static boolean[] in = { false, false };
    private static volatile int turn = -1;

    public static void main(String[] args) {
        new Thread(new Peterson(0), "Thread - 0").start();
        new Thread(new Peterson(1), "Thread - 1").start();
    }

    private final int id;

    public Peterson(int i) {
        id = i;
    }

    private int other() {
        return id == 0 ? 1 : 0;
    }

    @Override
    public void run() {
        in[id] = true;
        turn = other();
        while (in[other()] && turn == other()) {
            System.out.println("[" + id + "] - Waiting...");
        }
        System.out.println("[" + id + "] - Working ("
                + ((!in[other()]) ? "other done" : "my turn") + ")");
        in[id] = false;
    }}