1115. 交替打印 FooBar(中等)twice

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1，问题描述

1115. 交替打印 FooBar

难度：中等

给你一个类：

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class FooBar {
  public void foo() {
    for (int i = 0; i < n; i++) {
      print("foo");
    }
  }

  public void bar() {
    for (int i = 0; i < n; i++) {
      print("bar");
    }
  }
}

两个不同的线程将会共用一个 FooBar 实例：

  • 线程 A 将会调用 foo() 方法，而
  • 线程 B 将会调用 bar() 方法

请设计修改程序，以确保 "foobar" 被输出 n 次。

示例 1：

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输入：n = 1
输出："foobar"
解释：这里有两个线程被异步启动。其中一个调用 foo() 方法, 另一个调用 bar() 方法，"foobar" 将被输出一次。

示例 2：

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输入：n = 2
输出："foobarfoobar"
解释："foobar" 将被输出两次。

提示：

  • 1 <= n <= 1000

2，初步思考

​ 首先声明，我不会。因为日常工作中使用到的地方少，并且也是用的时候临时查找

​ 看了别人的答案才逐渐会的

3，代码处理

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import java.util.Map;
import java.util.concurrent.*;
import java.util.concurrent.locks.LockSupport;
import java.util.concurrent.locks.ReentrantLock;

class FooBar_CyclicBarrier {
    private int n;
    private CyclicBarrier cb = new CyclicBarrier(2);
    volatile boolean fooExec = true;

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

    public void foo(Runnable printFoo) throws InterruptedException {
        for (int i = 0; i < n; i++) {
            while (!fooExec) {// 自旋
            }
            printFoo.run();
            fooExec = false;//设置变量
            try {
                System.out.println("foo-Up");
                cb.await();//线程foo到达同步点
                System.out.println("foo-Down");
            } catch (BrokenBarrierException e) {
                e.printStackTrace();
            }
        }
    }

    public void bar(Runnable printBar) throws InterruptedException {
        for (int i = 0; i < n; i++) {
            try {
                System.out.println("bar-Up");
                cb.await();
                System.out.println("bar-Dwon");
            } catch (BrokenBarrierException e) {
                e.printStackTrace();
            }
            printBar.run();
            fooExec = true;
        }
    }
}

class FooBar_Semaphore {
    private int n;
    private Semaphore fooSemahore = new Semaphore(1);
    private Semaphore barSemahore = new Semaphore(0);

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

    public void foo(Runnable printFoo) throws InterruptedException {

        for (int i = 0; i < n; i++) {
            fooSemahore.acquire();
            printFoo.run();
            barSemahore.release();
        }
    }

    public void bar(Runnable printBar) throws InterruptedException {
        for (int i = 0; i < n; i++) {
            barSemahore.acquire();
            printBar.run();
            fooSemahore.release();
        }
    }
}

class FooBar_yield {
    private int n;
    volatile boolean fooExec = true;//foo可以执行

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

    public void foo(Runnable printFoo) throws InterruptedException {
        for (int i = 0; i < n; ) {
            System.out.println("foo-i:" + i);
            if (fooExec) {
                printFoo.run();
                fooExec = false;
                i++;
            } else {
                Thread.yield();
            }
        }
    }

    public void bar(Runnable printBar) throws InterruptedException {
        for (int i = 0; i < n; ) {
            System.out.println("bar-i:" + i);
            if (!fooExec) {
                printBar.run();
                fooExec = true;
                i++;
            } else {
                Thread.yield();
            }
        }
    }
}


class FooBar_ReentrantLock {
    private int n;
    private ReentrantLock lock = new ReentrantLock(true);
    volatile boolean fooExec = true;

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

    public void foo(Runnable printFoo) throws InterruptedException {
        for (int i = 0; i < n; ) {
            System.out.println("foo-up-i:" + i);
            lock.lock();// 获取锁
            System.out.println("foo-dw-i:" + i);

            try {
                if (fooExec) {
                    printFoo.run();
                    fooExec = false;
                    i++;
                }
            } finally {
                lock.unlock();
            }
        }
    }

    public void bar(Runnable printBar) throws InterruptedException {
        for (int i = 0; i < n; ) {
            System.out.println("bar-up-i:" + i);
            lock.lock();
            System.out.println("bar-dw-i:" + i);
            try {
                if (!fooExec) {
                    printBar.run();
                    fooExec = true;
                    i++;
                }
            } finally {
                lock.unlock();
            }
        }
    }
}

class FooBar_BlockingQueue {
    private int n;
    private BlockingQueue<Integer> fooQueue = new LinkedBlockingQueue<Integer>() {{
        add(0);
    }};
    private BlockingQueue<Integer> barQueue = new LinkedBlockingQueue<>();

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

    public void foo(Runnable printFoo) throws InterruptedException {

        for (int i = 0; i < n; i++) {
            fooQueue.take();// 如果为空的话，会阻塞等待，消费者会一直等待
            printFoo.run();
            barQueue.add(0);
        }
    }

    public void bar(Runnable printBar) throws InterruptedException {

        for (int i = 0; i < n; i++) {
            barQueue.take();
            printBar.run();
            fooQueue.add(0);
        }
    }
}

class FooBar_synchronized {
    private int n;
    private Object obj = new Object();
    private volatile boolean fooExec = true;

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

    public void foo(Runnable printFoo) throws InterruptedException {
        for (int i = 0; i < n; i++) {
            synchronized (obj) {
                if (!fooExec) {
                    obj.wait();
                }
                printFoo.run();
                fooExec = false;
                obj.notifyAll();
            }
        }
    }

    public void bar(Runnable printBar) throws InterruptedException {
        for (int i = 0; i < n; i++) {
            synchronized (obj) {
                if (fooExec) {
                    obj.wait();
                }
                printBar.run();
                fooExec = true;
                obj.notifyAll();
            }
        }
    }
}

class FooBar_LockSupport {
    private int n;
    private Map<String, Thread> map = new ConcurrentHashMap<>();
    private volatile boolean fooExec = true;

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

    public void foo(Runnable printFoo) throws InterruptedException {
        map.put("foo", Thread.currentThread());
        for (int i = 0; i < n; i++) {
            while (!fooExec) {
                LockSupport.park();
            }
            printFoo.run();
            fooExec = false;
            LockSupport.unpark(map.get("bar"));
        }
    }

    public void bar(Runnable printBar) throws InterruptedException {
        map.put("bar", Thread.currentThread());
        for (int i = 0; i < n; i++) {
            while (fooExec) {
                LockSupport.park();
            }
            printBar.run();
            fooExec = true;
            LockSupport.unpark(map.get("foo"));
        }
    }
}


public class _1115交替打印FooBar {
    public static void main(String[] args) throws InterruptedException {
        FooBar_LockSupport fooBar = new FooBar_LockSupport(2);
        Thread bar = new Thread(() -> {
            try {
                fooBar.bar(() -> System.out.println("bar"));
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        });
        Thread foo = new Thread(() -> {
            try {
                fooBar.foo(() -> System.out.println("foo"));
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        });
        foo.start();
        bar.start();
    }
}