LeedCode多线程1195-交替打印字符串,CyclicBarrier屏障的应用

LeedCode多线程第六题-交替打印字符串
一.题目如下:


解题思路:
这里先说一下我自己的解题思路.

1. 使用三个信号量控制其他打印字母的线程是否为可执行.
2. 使用LockSupport.park(),unpark()控制主线程(打印普通数字的线程)是否可执行.

注意点:
      当线程执行acquire()方法获取不到信号量时,就会进入WAITING状态,一直在这等待,主线程执行完毕后,这几个线程还在等待,导致程序永远不会执行完,所以在开始的时候把几个线程都存到队列中,在主线程执行完后一一进行中断操作,保证线程正常退出.

class FizzBuzz {
    private int n;
    
    public FizzBuzz(int n) {
        this.n = n;
    }
    Semaphore fizzSemaphore=new Semaphore(0);
    Semaphore buzzSemaphore=new Semaphore(0);
    Semaphore fizzbuzzSemaphore=new Semaphore(0);
    BlockingQueue<Thread> threadQueue = new LinkedBlockingQueue<>(1);
    ArrayList<Thread> threadList=new ArrayList<>(3);
    
    // printFizz.run() outputs "fizz".
    public void fizz(Runnable printFizz) throws InterruptedException {
        
        threadList.add(Thread.currentThread());
        for(;;){
            try{
                fizzSemaphore.acquire();    
            }catch(InterruptedException e){
                break;
            }
            printFizz.run();
            LockSupport.unpark(threadQueue.poll());    
        }
    }

    // printBuzz.run() outputs "buzz".
    public void buzz(Runnable printBuzz) throws InterruptedException {
        threadList.add(Thread.currentThread());
        for(;;){
            
            try{
                buzzSemaphore.acquire();
            }catch(InterruptedException e){
                break;
            }
            printBuzz.run();
            LockSupport.unpark(threadQueue.poll());    
        }
    }

    // printFizzBuzz.run() outputs "fizzbuzz".
    public void fizzbuzz(Runnable printFizzBuzz) throws InterruptedException {
        threadList.add(Thread.currentThread());
        for(;;){
            try{
                fizzbuzzSemaphore.acquire();
            }catch(InterruptedException e){
                break;
            }
            printFizzBuzz.run();
            LockSupport.unpark(threadQueue.poll());    
        }
    }

    // printNumber.accept(x) outputs "x", where x is an integer.
    public void number(IntConsumer printNumber) throws InterruptedException {
         for(int i=1;i<=n;i++){
            if(i % 3!=0 && i % 5!=0){
                printNumber.accept(i);
            }else if(i % 5 !=0){
                threadQueue.put(Thread.currentThread());
                fizzSemaphore.release();
                LockSupport.park();
            }else if(i % 3!=0){
                threadQueue.put(Thread.currentThread());
                buzzSemaphore.release();
                LockSupport.park();
            }else{
                threadQueue.put(Thread.currentThread());
                fizzbuzzSemaphore.release();
                LockSupport.park();
            }
        }
        //将其他处于WAITING状态的线程中断退出
        for(int i=0;i<threadList.size();i++){
            Thread curThread=threadList.get(i);
            curThread.interrupt();
        }
    }
    
}

二.CyclicBarrier.
1.介绍.
这是Java并发包中的一个工具类java.util.concurrent.CyclicBarrier.
简单来说该工具类可以控制一组线程进行同步操作,也就是在一组线程都触发时才执行后续的代码,如果某个线程先触发,就会进入等待,直到一组中的最后一个线程完成触发操作.

有时候语言可能不太直观,看一下CyclicBarrier在该题目中的应用就理解了.

class FizzBuzz {
    private int n;
    
    //当四个线程都触发后才执行之后的代码
    private static CyclicBarrier barrier = new CyclicBarrier(4);

    public FizzBuzz(int n) {
        this.n = n;
    }

    // printFizz.run() outputs "fizz".
    public void fizz(Runnable printFizz) throws InterruptedException {
        for (int i = 1; i <= n; i++) {
            if (i % 3 == 0 && i % 5 != 0) {
                printFizz.run();
            }
            try {
                barrier.await();
            } catch (BrokenBarrierException e) {
                e.printStackTrace();
            }
        }
    }

    // printBuzz.run() outputs "buzz".
    public void buzz(Runnable printBuzz) throws InterruptedException {
        for (int i = 1; i <= n; i++) {
            if (i % 3 != 0 && i % 5 == 0) {
                printBuzz.run();
            }
            try {
                barrier.await();
            } catch (BrokenBarrierException e) {
                e.printStackTrace();
            }
        }
    }

    // printFizzBuzz.run() outputs "fizzbuzz".
    public void fizzbuzz(Runnable printFizzBuzz) throws InterruptedException {
        for (int i = 1; i <= n; i++) {
            if (i % 3 == 0 && i % 5 == 0) {
                printFizzBuzz.run();
            }
            try {
                barrier.await();
            } catch (BrokenBarrierException e) {
                e.printStackTrace();
            }
        }
    }

    // printNumber.accept(x) outputs "x", where x is an integer.
    public void number(IntConsumer printNumber) throws InterruptedException {
        for (int i = 1; i <= n; i++) {
            if (i % 3 != 0 && i % 5 != 0) {
                printNumber.accept(i);
            }
            try {
                barrier.await();
            } catch (BrokenBarrierException e) {
                e.printStackTrace();
            }
        }
    }

    
}