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()); } }