3.生产者和消费者问题

感谢秦疆老师的JUC并发编程视频，更多了解哔哩哔哩搜索【狂神说Java】。

本文内容源于秦疆老师的JUC并发编程视频教程。给狂神推荐，点赞吧！

Synchronized版生产者和消费者的问题

package demo2;

/**
 * 线程之间的通信问题： 生产者和消费者问题！ 等待唤醒，通知唤醒
 * 线程交替执行 A B 操作同一个变量 num = 0
 * A num+1
 * B num-1
 */
public class A {

    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();
                }
            }
        }, "A").start();

        new Thread(() -> {
            for (int i = 0; i < 10; i++) {

                try {
                    data.decrement();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }, "B").start();
    }

}

//等待 ，业务 ，通知
class Data {//数字 资源类

    private int number = 0;

    //+1
    public synchronized void increment() throws InterruptedException {
        if (number != 0) { //0
            //等待
            this.wait();
        }
        number++;
        System.out.println(Thread.currentThread().getName() + "=>" + number);
        //通知其他线程 ，我+1完毕
        this.notifyAll();
    }

    //-1
    public synchronized void decrement() throws InterruptedException {
        if (number == 0) { //1
            //等待
            this.wait();
        }
        number--;
        System.out.println(Thread.currentThread().getName() + "=>" + number);
        //通知其他线程 ，我-1完毕
        this.notifyAll();
    }


}

存在A B C D … 更多线程会出现问题 -->虚假唤醒

jdk1.8官方文档：

在这里插入图片描述

if 改为 while 判断

package demo2;

/**
 * 线程之间的通信问题： 生产者和消费者问题！ 等待唤醒，通知唤醒
 * 线程交替执行 A B 操作同一个变量 num = 0
 * A num+1
 * B num-1
 */
public class A {

    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();
                }
            }
        }, "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.decrement();
                } 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();
    }

}

//等待 ，业务 ，通知
class Data {//数字 资源类

    private int number = 0;

    //+1
    public synchronized void increment() throws InterruptedException {
        while (number != 0) { //0
            //等待
            this.wait();
        }
        number++;
        System.out.println(Thread.currentThread().getName() + "=>" + number);
        //通知其他线程 ，我+1完毕
        this.notifyAll();
    }

    //-1
    public synchronized void decrement() throws InterruptedException {
        while (number == 0) { //1
            //等待
            this.wait();
        }
        number--;
        System.out.println(Thread.currentThread().getName() + "=>" + number);
        //通知其他线程 ，我-1完毕
        this.notifyAll();
    }


}

JUC版的生产者和消费者问题

在这里插入图片描述

通过Lock找到Condition

在这里插入图片描述

代码：

package demo2;


import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

/**
 * 线程之间的通信问题： 生产者和消费者问题！ 等待唤醒，通知唤醒
 * 线程交替执行 A B 操作同一个变量 num = 0
 * A num+1
 * B num-1
 */
public class B {

    public static void main(String[] args) {
        DataB data = new DataB();

        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.decrement();
                } 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();
    }

}

//等待 ，业务 ，通知
class DataB {//数字 资源类

    private int number = 0;

    Lock lock = new ReentrantLock();
    Condition condition = lock.newCondition();
    // condition.await(); 等待
    // condition.signalAll(); 唤醒全部

    //+1
    public void increment() throws InterruptedException {

        lock.lock();
        try {

            while (number != 0) { //0
                //等待
                //this.wait();
                condition.await();
            }
            number++;
            System.out.println(Thread.currentThread().getName() + "=>" + number);
            //通知其他线程 ，我+1完毕
            // this.notifyAll();
            condition.signalAll();

        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            lock.unlock();
        }


    }

    //-1
    public void decrement() throws InterruptedException {

        lock.lock();

        try {
            while (number == 0) { //1
                //等待
                condition.await();
            }
            number--;
            System.out.println(Thread.currentThread().getName() + "=>" + number);
            //通知其他线程 ，我-1完毕
            condition.signalAll();
        } catch (InterruptedException e) {
            e.printStackTrace();
        } finally {

            lock.unlock();
        }

    }


}

输出结果：

A=>1
B=>0		//问题 随机的状态 
A=>1		//有序执行 A - B - C - D
C=>0
A=>1
C=>0
A=>1
C=>0
A=>1
C=>0
A=>1
D=>0
A=>1
D=>0
A=>1
D=>0
A=>1
D=>0
A=>1
D=>0

任何一个新的技术，绝对不是仅仅只是覆盖了原来的技术，优势和补充！

Condition 精准的通知和唤醒线程

package demo2;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

/**
 * A - B - C
 */
public class C {

    public static void main(String[] args) {
        DataC data = new DataC();

        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();


    }

}

//等待 ，业务 ，通知
class DataC {//数字 资源类

    private int number = 0;

    Lock lock = new ReentrantLock();
    Condition conditionA = lock.newCondition();
    Condition conditionB = lock.newCondition();
    Condition conditionC = lock.newCondition();

    // condition.await(); 等待
    // condition.signal(); 唤醒

    //执行A
    public void printA() throws InterruptedException {

        lock.lock();
        try {
            while (number != 0) { //0
                //等待
                conditionA.await();
            }
            number = 1;
            System.out.println(Thread.currentThread().getName() + "=>" + number + "唤醒B");
            //通知其他线程 ，我+1完毕
            conditionB.signal();

        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            lock.unlock();
        }


    }

    //执行B
    public void printB() throws InterruptedException {

        lock.lock();
        try {

            while (number != 1) { //0
                //等待
                //this.wait();
                conditionB.await();
            }
            number = 2;
            System.out.println(Thread.currentThread().getName() + "=>" + number + "唤醒C");
            conditionC.signal();

        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            lock.unlock();
        }


    }

    //执行C
    public void printC() throws InterruptedException {

        lock.lock();
        try {

            while (number != 2) { //0
                //等待
                conditionC.await();
            }
            number = 0;
            System.out.println(Thread.currentThread().getName() + "=>" + number + "唤醒A");

            conditionA.signal();

        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            lock.unlock();
        }


    }

}

输出：

A=>1唤醒B
B=>2唤醒C
C=>0唤醒A
A=>1唤醒B
B=>2唤醒C
C=>0唤醒A
A=>1唤醒B
B=>2唤醒C
C=>0唤醒A
A=>1唤醒B
B=>2唤醒C
C=>0唤醒A
A=>1唤醒B
B=>2唤醒C
C=>0唤醒A
A=>1唤醒B
B=>2唤醒C
C=>0唤醒A
A=>1唤醒B
B=>2唤醒C
C=>0唤醒A
A=>1唤醒B
B=>2唤醒C
C=>0唤醒A
A=>1唤醒B
B=>2唤醒C
C=>0唤醒A
A=>1唤醒B
B=>2唤醒C
C=>0唤醒A

posted @ 2020-05-23 18:13 我有满天星辰阅读(3) 评论(0) 编辑收藏举报

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3.生产者和消费者问题

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