thread_AtomicBoolean

    public static void main(String[] args) {
        Thread t2 = new Thread(new BarWorker("bb"));
        Thread t1 = new Thread(new BarWorker("aa"));
        t2.run();
        t1.run();
    }

    private static class BarWorker implements Runnable {
        private static AtomicBoolean exists = new AtomicBoolean(false);
        private String name;

        public BarWorker(String name) {
            this.name = name;
        }

        public void run() {
            if (exists.compareAndSet(false, true)) {
                // 当第一个线程设置为true后，另外的线程是进不来的
                System.out.println(name + " enter" + "currentvalue=" + exists.get());
                try {
                    System.out.println(name + " working");
                    Thread.sleep(2000);
                } catch (InterruptedException e) {
                    // do nothing
                }
                System.out.println(name + " leave");
                exists.set(false);
            } else {
                System.out.println(name + " give up");
            }
        }
    }