共享资源的简单示例

/** * 资源共享的示例 * 装饰性花园仿真程序 * 花园委员会希望知道每天通过多个大门进入公园的总人数  * 每个大门都有一个十字专转门或某种形式的计数器， * 并且任何一个十字转门的计数值递增时， * 就表示公园的总人数的共享计数值也会递增 *  * @author cxp * @data 2016-08-29 * @modify *  */class Count {    private int count = 0;    private Random rand = new Random(47);// 47为随机数生成器的种子，默认将当前时间作为随机数的种子    // 移除synchronized关键字，程序将会失败    public synchronized int increment() {        int temp = count;        if (rand.nextBoolean())// 把count读取到temp中到递增temp并将其存储回count的这段时间里，大约一半的时间产生让步            Thread.yield();        return (count = ++temp);    }    public synchronized int value() {        return count;    }}class Entrance implements Runnable {    private static Count count = new Count();    private static List<Entrance> entrances = new ArrayList<Entrance>();    private int number = 0;    // 不需要同步对其的访问    private final int id;    private static volatile boolean canceled = false;    // 在volatile域里是原子操作    public static void cancel() {        canceled = true;    }    public Entrance(int id) {        this.id = id;        entrances.add(this);    }    @Override    public void run() {        while (!canceled) {            synchronized (this) {                number++;            }            print(this + " Total:" + count.increment());            try {                TimeUnit.MILLISECONDS.sleep(100);            } catch (InterruptedException e) {                print("sleep interrupted");            }        }        print("Stopping" + this);    }    public synchronized int getValue() {        return number;    }    @Override    public String toString() {        return "Entrance " + id + ": " + getValue();    }    public static int getTotalCount() {        return count.value();    }    public static int sumEntrances() {        int sum = 0;        for (Entrance entrance : entrances)            sum += entrance.getValue();        return sum;    }}public class OrnamentalGarden {    public static void main(String[] args) throws Exception {        ExecutorService exec = Executors.newCachedThreadPool();        for (int i = 0; i < 5; i++)            exec.execute(new Entrance(i));        // 运行一段时间，然后停止和收集数据        TimeUnit.SECONDS.sleep(3);// 当前线程睡眠3秒        Entrance.cancel();// 发送cancel()消息        exec.shutdown();        if (!exec.awaitTermination(250, TimeUnit.MILLISECONDS))//等待每个任务结束，在超时时间达到之前全部结束返回true，否则返回false            print("Some task were not terminated");        print("Total:" + Entrance.getTotalCount());        print("Sum of Entrances:" + Entrance.sumEntrances());    }}