生产者和消费者问题

生产者和消费者问题

面试常问的问题：单例模式、排序算法、生产者和消费者、死锁

旧版 Synchronized wait notify

juc -->lock

生产者和消费者问题Synchronized 版

package com.chao.pc;

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

问题存在，A、B、C、D 4个线程！虚假唤醒

if 改为 while判断

package com.chao.pc;

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

JUC版的生产者和消费者问题

通过Lock找到Condition

代码实现：

package com.chao.pc;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

public class B {
    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();
    }
}
//判断等待，业务，通知
class Data2{//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 {
            //业务代码
            while(number!=0){
                //等待
                condition.await();
            }
            number++;
            System.out.println(Thread.currentThread().getName()+"=>"+number);
            //通知其他线程,我+1完毕了
            condition.signalAll();
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            lock.unlock();
        }
    }
    //-1
    public synchronized void decrement() throws InterruptedException {
        lock.lock();
        try {
            while(number==0){
                //等待
                condition.await();
            }
            number--;
            System.out.println(Thread.currentThread().getName()+"=>"+number);
            //通知其他线程,我-1完毕了
            condition.signalAll();
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            lock.unlock();
        }
    }
}

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 com.chao.pc;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
/**
 * @author  追梦王子Java 123456789@qq.com
 * A 执行完调用B,B执行完调用C,C执行完调用D
 *
 */
public class C {
    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
    private Lock lock = new ReentrantLock();
    private Condition condition1 = lock.newCondition();
    private Condition condition2 = lock.newCondition();
    private Condition condition3 = lock.newCondition();
    private int number = 1; //1A 2B 3C
    public void printA(){
        lock.lock();
        try {
            //业务，判断->执行->通知
            while(number != 1){
                //等待B
                condition1.await();
            }
            System.out.println(Thread.currentThread().getName()+"=>AAAAAAA");
            //唤醒，唤醒指定的人，B
            number = 2;
            condition2.signal();
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            lock.unlock();
        }
    }
    public void printB(){
        lock.lock();
        try {
            //业务，判断->执行->通知
            while(number != 2){
                condition2.await();
            }
            System.out.println(Thread.currentThread().getName()+"=>BBBBBBB");
            //唤醒，唤醒指定的人，C
            number = 3;
            condition3.signal();
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            lock.unlock();
        }
    }
    public void printC(){
        lock.lock();
        try {
            //业务，判断->执行->通知
            while(number != 3){
                condition3.await();
            }
            System.out.println(Thread.currentThread().getName()+"=>CCCCCCC");
            //唤醒，唤醒指定的人，A
            number = 1;
            condition1.signal();
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            lock.unlock();
        }
    }
    //生产线：购物：下单->支付->交易->物流
}