LinkedIn: H2O

LinkedIn: H2O
实现两个函数: H() and O(), 这两个函数会被多线程调用。当一个线程调用H或O时
，如果当前已经有至少两个线程call H和一个线程call O。那么让两个call H和一个
call O的线程返回（产生一个水分子），其他的都block。
http://chengao789.blogspot.com/2014/07/java-h2o.html

class H2O {

    int Hcount;

    int Ocount;

    Lock lock = new ReentrantLock();

    Condition cH = lock.newCondition();

    Condition cO = lock.newCondition();

  

    public void H() {

        lock.lock();

        Hcount++;

        if (Hcount >= 2 && Ocount >= 1) {

            Hcount -= 2;

            Ocount -= 1;

            cH.signal();

            cO.signal();

            System.out.println("H2O");

        } else {

            try {

                cH.await();

            } catch (InterruptedException e) {

                // TODO Auto-generated catch block

                e.printStackTrace();

            }

        }

        lock.unlock();

    }

  

    public void O() {

        lock.lock();

        Ocount++;

        if (Hcount >= 2 && Ocount >= 1) {

            Hcount -= 2;

            Ocount -= 1;

            cH.signal();

            cH.signal();

            System.out.println("H2O");

        } else {

            try {

                cO.await();

            } catch (InterruptedException e) {

                // TODO Auto-generated catch block

                e.printStackTrace();

            }

        }

        lock.unlock();

    }

}

 

class Hclass implements Runnable {

    private H2O obj;

  

    public Hclass(H2O obj) {

        this.obj = obj;

    }

    @Override

    public void run() {

        // TODO Auto-generated method stub

        obj.H();

    }

  

}

 

class Oclass implements Runnable {

    private H2O obj;

  

    public Oclass(H2O obj) {

        this.obj = obj;

    }

    @Override

    public void run() {

        // TODO Auto-generated method stub

        obj.O();

    }

  

}

 

public class H2Oexample {

    final private static H2O obj = new H2O();

  

    public static void main(String[] args) {

        for (int i = 0; i< 10; i++) {

            new Thread(new Hclass(obj)).start();

        }

        for (int i = 0; i< 5; i++) {

            new Thread(new Oclass(obj)).start();

        }

    }

}

public class H2O {

    static final Lock LOCK = new ReentrantLock();

    static final Condition ENOUGH_H = LOCK.newCondition();

    static final Condition ENOUGH_O = LOCK.newCondition();

    static int H = 0;

    static int O = 0;

    static void check() {

        if (H >= 2 && O >= 1) {

            ENOUGH_H.signal();

            ENOUGH_H.signal();

            ENOUGH_O.signal();

            H -= 2;

            O -= 1;

        }

    }

    public static void h() {

        LOCK.lock();

        try {

            check();

            ++H;

            ENOUGH_H.awaitUninterruptibly();

        } finally {

            LOCK.unlock();

        }

    }

    public static void o() {

        LOCK.lock();

        try {

            check();

            ++O;

            ENOUGH_O.awaitUninterruptibly();

        } finally {

            LOCK.unlock();

        }

    }

}`

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