生产者和消费者关于锁的案例

1. 老版案例

public class tets2 {
    public static void main(String[] args) {
        Data data = new Data();
        new Thread(()->{for(int i = 0 ;i<10;i++) {
            try {
                data.increment();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
        }).start();

        new Thread(()->{for(int i = 0 ;i<10;i++) {
            try {
                data.decrement();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
        }).start();

        new Thread(()->{for(int i = 0 ;i<10;i++) {
            try {
                data.increment();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
        }).start();
        new Thread(()->{for(int i = 0 ;i<10;i++) {
            try {
                data.decrement();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
        }).start();
    }
}
/*生产者与消费者: 先有，再消费*/
class Data{

    private int number = 0;

    //生产者
    public synchronized void increment() throws InterruptedException {
        //只生产一个，只要还有，就先不创造
        if(number != 0){
            this.wait();
        }
        number++;
        System.out.println(Thread.currentThread().getName()+">="+number);
        this.notifyAll();//唤醒其他线程
    }
    //消费者
    public synchronized void decrement() throws InterruptedException {
        //只要等于0，就等到去创造
        if(number == 0) {
            this.wait();
        }
        number--;
        System.out.println(Thread.currentThread().getName()+">="+number);
        this.notifyAll();//唤醒其他线程
    }
}

• increment 和 decrement 方法中的判断条件，得改成while循环，不然多个线程去操作同一个方法会出问题。
• 虚假唤醒
  

2.JUC版锁和监视器

public class tets3 {
    public static void main(String[] args) {
        Data2 data = new Data2();
        new Thread(()->{for(int i = 0 ;i<10;i++) {
            try {
                data.increment();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
        },"A").start();

        new Thread(()->{for(int i = 0 ;i<10;i++) {
            try {
                data.decrement();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
        },"B").start();

        new Thread(()->{for(int i = 0 ;i<10;i++) {
            try {
                data.increment();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
        },"C").start();
        new Thread(()->{for(int i = 0 ;i<10;i++) {
            try {
                data.decrement();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
        },"D").start();
    }
}

/*生产者与消费者: 先有，再消费*/
class Data2{

    private int number = 0;

    Lock lock = new ReentrantLock();
    Condition condition = lock.newCondition();
    //生产者
    public  void increment() throws InterruptedException {


        try {
            lock.lock();
            //只生产一个，只要还有，就先不创造
            while(number != 0){
                condition.await();
            }
            number++;
            System.out.println(Thread.currentThread().getName()+">="+number);
            condition.signalAll();//唤醒其他线程
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            lock.unlock();
        }
    }
    //消费者
    public  void decrement() throws InterruptedException {

        try {
            lock.lock();
            //只要等于0，就等到去创造
            while(number == 0) {
                condition.await();
            }
            number--;
            System.out.println(Thread.currentThread().getName()+">="+number);
            condition.signalAll();//唤醒其他线程
        } catch (InterruptedException e) {
            e.printStackTrace();
        } finally {
            lock.unlock();
        }
    }
}

• condition 的优势是，可以排序

打印案例

public class test4 {
    public static void main(String[] args) {
        Data4 data = new Data4();
        new Thread(()->{for(int i = 0 ;i<10;i++) {
            try {
                data.printA();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
        },"A").start();

        new Thread(()->{for(int i = 0 ;i<10;i++) {
            try {
                data.printB();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
        },"B").start();

        new Thread(()->{for(int i = 0 ;i<10;i++) {
            try {
                data.printC();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
        },"C").start();

    }
}

/*打印案例: 通过number判断和多个监视器，实现顺序打印*/
class Data4{
    int number = 1;
    Lock lock = new ReentrantLock();
    //一把锁可以创建多个监视器
    Condition condition1 = lock.newCondition();
    Condition condition2 = lock.newCondition();
    Condition condition3 = lock.newCondition();

    public void printA() throws InterruptedException {
        try {
            lock.lock();
            //业务：判断》执行》通知
            while(number != 1){
                condition1.await();
            }
            System.out.println(Thread.currentThread().getName()+">="+"AAAA");
            number = 2;
            condition2.signal();
        } catch (InterruptedException e) {
            e.printStackTrace();
        } finally {
            lock.unlock();
        }
    }
    public void printB() throws InterruptedException {
        try {
            lock.lock();
            //业务：判断》执行》通知
            while(number != 2){
                condition2.await();
            }
            System.out.println(Thread.currentThread().getName()+">="+"BBBBB");
            number = 3;
            condition3.signal();
        } catch (InterruptedException e) {
            e.printStackTrace();
        } finally {
            lock.unlock();
        }
    }
    public void printC() throws InterruptedException {
        try {
            lock.lock();
            //业务：判断》执行》通知
            while(number != 3){
                condition3.await();
            }
            System.out.println(Thread.currentThread().getName()+">="+"CCCCCC");
            number = 1;
            condition1.signal();
        } catch (InterruptedException e) {
            e.printStackTrace();
        } finally {
            lock.unlock();
        }
    }
}