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

public class ABC {

    //可重入锁
    private final static Lock lock = new ReentrantLock();
    //判断是否执行：1表示应该A执行，2表示应该B执行，3表示应该C执行
    private static int state = 1;
    //condition对象
    private static Condition a = lock.newCondition();
    private static Condition b = lock.newCondition();
    private static Condition c = lock.newCondition();

    public static void printA() {
        //通过循环，hang住线程
        for (int i = 0; i < 10; i++) {
            try {
                //获取锁
                lock.lock();
                //并发情况下，不能用if，要用循环判断等待条件，避免虚假唤醒
                while (state != 1) {
                    a.await();
                }
                System.out.print("A");
                state = 2;
                b.signal();
            } catch (InterruptedException e) {
                e.printStackTrace();
            } finally {
                //要保证不执行的时候，锁能释放掉
                lock.unlock();
            }
        }
    }

    public static void printB() throws InterruptedException {
        for (int i = 0; i < 10; i++) {
            try {
                lock.lock();
                //获取到锁，应该执行
                while (state != 2) {
                    b.await();
                }
                System.out.print("B");
                state = 3;
                c.signal();
            } finally {
                lock.unlock();
            }
        }
    }

    public static void printC() throws InterruptedException {
        for (int i = 0; i < 10; i++) {
            try {
                lock.lock();
                while (state != 3) {
                    c.await();
                }
                //获取到锁，应该执行
                System.out.print("C");
                state = 1;
                a.signal();
            } finally {
                lock.unlock();
            }
        }
    }


    public static void main(String[] args) {
        new Thread(new Runnable() {
            @Override
            public void run() {
                ABC.printA();
            }
        }, "A").start();

        new Thread(new Runnable() {
            @Override
            public void run() {
                try {
                    ABC.printB();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }, "B").start();

        new Thread(new Runnable() {
            @Override
            public void run() {
                try {
                    ABC.printC();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }, "C").start();
    }

}

ExecutorService executor = Executors.newSingleThreadExecutor();
SettableFuture<Integer> future = SettableFuture.create();
// 使用其他线程去 set 对应的结果。
executor.submit(() -> {
    future.set(1);
});

Futures.addCallback(future, new FutureCallback<>() {
    @Override
    public void onSuccess(Integer result) {
        // main线程执行的
        System.out.println("result=" + result + "线程名：" + Thread.currentThread().getName());//main
    }

    @Override
    public void onFailure(Throwable t) {
    }
}, MoreExecutors.directExecutor());