Condition

• 简介

1、可以在一个锁里面，存在多种等待条件
2、主要的方法：
    await    挂起
    signal     随机唤醒1个线程
    signalAll    唤醒所有等待的线程

• 代码案例

/**
 * 生产者线程
 */
public class Producer implements Runnable{

    private Medium medium;

    public Producer(Medium medium) {
        this.medium = medium;
    }

    @Override
    public void run() {
        while (true) {
            medium.put();
        }
    }
    
}

/**
 * 消费者线程
 */
public class Consumer implements Runnable{

    private Medium medium;

    public Consumer( Medium medium) {
        this.medium = medium;
    }

    @Override
    public void run() {
        while (true) {
            medium.take();
        }
    }

}

/**
 * 中间商
 */
public class Medium {

    private int num = 0;
    // 库存量
    private static final int TOTAL = 20;

    private Lock lock = new ReentrantLock();
    // 创建生产者和消费者condition
    private Condition consumerCondition = lock.newCondition();
    private Condition producerCondition = lock.newCondition();

    /**
     * 接收生产数据
     */
    public void put() {
        lock.lock();
        try {
            //判断当前库存，是否已经是最大的库存容量，
            if (num < TOTAL) {
                System.out.println("新增库存---------> 当前库存：" + ++num);
                // 如果不是，生产完成之后，通知消费者进行消费
                try {
                    Thread.sleep(500L);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                consumerCondition.signalAll();  // 唤醒所有等待线程，进行生产
            } else {
                // 如果是，则通知生产者进行等待，
                try {
                    System.out.println("新增库存---------> 库存已满：" + num);
                    producerCondition.await();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        } finally {
            lock.unlock();
        }
    }

    /**
     * 获取消费数据
     */
    public void take() {
        lock.lock();
        try {
            //判断当前库存是否不足
            if (num > 0) {
                //如果充足，在消费完成之后，通知生产者进行生产
                System.out.println("消费库存------> 当前库存容量" + --num);
                try {
                    Thread.sleep(1000L);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                producerCondition.signalAll();
            } else {
                //如果不足，通知消费者暂停消费
                try {
                    System.out.println("消费库存---------> 库存不足：" + num);
                    consumerCondition.await();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        } finally {
            lock.unlock();
        }
    }

}

# 测试类
public class Main {

    public static void main(String[] args) {
        Medium medium = new Medium();
        new Thread(new Consumer(medium)).start();
        new Thread(new Consumer(medium)).start();
        new Thread(new Producer(medium)).start();
        new Thread(new Producer(medium)).start();
        new Thread(new Producer(medium)).start();
        new Thread(new Producer(medium)).start();
        new Thread(new Producer(medium)).start();
        new Thread(new Producer(medium)).start();
        new Thread(new Producer(medium)).start();
    }

}