生产者消费者问题

synchronized：wait notify

/*线程之间的通信问题，生产者和消费者问题  通知唤醒，等待唤醒
* 线程交替进行，A B操作统一变量 num=0
* A num+1
* B num-1
* */
public class Product {
    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();
                }
            }
        },"product").start();
        new Thread(()->{
            for (int i = 0; i < 10; i++) {
                try {
                    data.decrement();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        },"consumer").start();
    }
}
class Data{
    //资源类
    private int num=0;
    //+1
    public synchronized void increment() throws InterruptedException {
        /*等待*/
        if(num!=0)
        {
            //等待
            this.wait();
        }
        /*业务*/
        num++;
        System.out.println(Thread.currentThread().getName()+"=>"+num);
        /*通知*/
        //通知线程B，已经增加过了
        this.notifyAll();
    }

    //-1
    public synchronized void decrement() throws InterruptedException {
        /*等待*/
        if(num==0)
        {
            //等待
            this.wait();
        }
        /*业务*/
        num--;
        System.out.println(Thread.currentThread().getName()+"=>"+num);
        /*通知*/
        //通知线程A，已经减少过了
        this.notifyAll();
    }
}

问题：A,B,C,D 四个线程时还安全吗？

if判断只会判断一次。防止虚假唤醒

等待改为while判断

  while(num==0)
        {
            //等待
            this.wait();
        }

JUC版生产者消费者

public class Product2 {
    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();
                }
            }
        },"product").start();
        new Thread(()->{
            for (int i = 0; i < 10; i++) {
                try {
                    data.increment();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        },"product1").start();
        new Thread(()->{
            for (int i = 0; i < 10; i++) {
                try {
                    data.decrement();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        },"consumer").start();
        new Thread(()->{
            for (int i = 0; i < 10; i++) {
                try {
                    data.decrement();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        },"consumer1").start();
    }
}
class Data2{
    //资源类
    private int num=0;

    Lock lock=new ReentrantLock();
    Condition condition = lock.newCondition();
    //+1
    public void increment() throws InterruptedException {
       /* Condition condition = lock.newCondition();
        condition.await();//等待
        condition.signal();//唤醒全部*/
        /*等待*/
        /*业务*/
        lock.lock();
        try {
            while(num!=0)
            {
                condition.await();
            }
            num++;
            System.out.println(Thread.currentThread().getName()+"=>"+num);
            condition.signalAll();
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            lock.unlock();
        }
        /*通知*/
        //通知线程B，已经增加过了
    }

    //-1
    public void decrement() throws InterruptedException {
        /*等待*/
        /*业务*/
        lock.lock();
        try {
            while(num==0)
            {
                //等待
                condition.await();
            }
            num--;
            System.out.println(Thread.currentThread().getName()+"=>"+num);
            condition.signalAll();
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            lock.unlock();
        }
        /*通知*/
        //通知线程A，已经减少过了

    }
}

Condition 精准通知和唤醒线程

/*
* A执行完调用B，B执行完调用C*/
public class Product3 {
    public static void main(String[] args) {
        data3 data=new data3();
        new Thread(()->{
            for (int i = 0; i < 10; i++) {
                data.printA();
            }
        },"A").start();
        new Thread(()->{
            for (int i = 0; i < 10; i++) {
                data.printB();
            }
        },"B").start();
        new Thread(()->{
            for (int i = 0; i < 10; i++) {
                data.printC();
            }
        },"C").start();
    }
}
class data3{  //资源类
    Lock lock=new ReentrantLock();
    private int num=1;//1 A, 2 B, 3 C
    //监视器
    Condition condition = lock.newCondition();
    Condition condition1 = lock.newCondition();
    Condition condition2 = lock.newCondition();
    public void printA(){
        lock.lock();

        try {
            while(num!=1) {
                condition.await();
            }
            System.out.println("A");
            num=2;
            condition1.signal();
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            lock.unlock();
        }
    }
    public void printB(){
        lock.lock();

        try {
            while(num!=2) {
                condition1.await();
            }
            System.out.println("B");
            num=3;
            condition2.signal();
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            lock.unlock();
        }
    }
    public void printC(){
        lock.lock();

        try {
            while(num!=3) {
                condition2.await();
            }
            System.out.println("C");
            num=1;
            condition.signal();
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            lock.unlock();
        }
    }
}