JUC(八) - 线程按序交替

8. 线程按序交替

编写一个程序，开启 3 个线程，这三个线程的 ID 分别为A、B、C，每个线程将自己的 ID 在屏幕上打印 10 遍，要求输出的结果必须按顺序显示。

class AlternateDemo {
    /**
     * 标记启动顺序
     */
    private int number = 1;

    private Lock lock = new ReentrantLock();

    private Condition condition1 = lock.newCondition();
    private Condition condition2 = lock.newCondition();
    private Condition condition3 = lock.newCondition();

    /**
     * A线程
     * @param totalLoop
     */
    public void loopA(int totalLoop) {
        lock.lock();

        try {
            //1.判断
            if (number != 1) {
                condition1.await();
            }
            //2.打印
            for (int i = 1; i <= 1; i++) {
                System.out.println(Thread.currentThread().getName() + "\t" + i + "\t" + totalLoop);
            }

            //3.唤醒
            number = 2;
            condition2.signal();
        } catch (InterruptedException e) {
            e.printStackTrace();
        } finally {
            lock.unlock();
        }
    }

    /**
     * B线程
     * @param totalLoop
     */
    public void loopB(int totalLoop) {
        lock.lock();

        try {
            //1.判断
            if (number != 2) {
                condition2.await();
            }
            //2.打印
            for (int i = 1; i <= 1; i++) {
                System.out.println(Thread.currentThread().getName() + "\t" + i + "\t" + totalLoop);
            }

            //3.唤醒
            number = 3;
            condition3.signal();
        } catch (InterruptedException e) {
            e.printStackTrace();
        } finally {
            lock.unlock();
        }
    }

    /**
     * C线程
     * @param totalLoop
     */
    public void loopC(int totalLoop) {
        lock.lock();

        try {
            //1.判断
            if (number != 3) {
                condition3.await();
            }
            //2.打印
            for (int i = 1; i <= 1; i++) {
                System.out.println(Thread.currentThread().getName() + "\t" + i + "\t" + totalLoop);
            }

            //3.唤醒
            number = 1;
            condition1.signal();
        } catch (InterruptedException e) {
            e.printStackTrace();
        } finally {
            lock.unlock();
        }
    }
}

测试

    public static void main(String[] args) {
        final AlternateDemo ad  = new AlternateDemo();
        new Thread(new Runnable() {
            @Override
            public void run() {
                for (int i = 1; i <= 5; i++) {
                    ad.loopA(i);
                }
            }
        }, "A").start();
        new Thread(new Runnable() {
            @Override
            public void run() {
                for (int i = 1; i <= 5; i++) {
                    ad.loopB(i);
                }
            }
        }, "B").start();
        new Thread(new Runnable() {
            @Override
            public void run() {
                for (int i = 1; i <= 5; i++) {
                    ad.loopC(i);
                }
            }
        }, "C").start();
    }