生产者消费者问题

生产者消费者问题

单例模式、排序算法、生产者和消费者、死锁

Synchronized版本 wait notify

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{
    //资源类
    private int number = 0;
    //+1
    public synchronized void increment() throws InterruptedException {
        if (number !=0) {   //0才往下执行
            //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) {  //1才会自动往下执行
            //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

JUC 版的生产者消费者问题

通过Lock找到Condition

• 代码实现

/**
 * 线程时间的通信问题：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) {
        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{
    //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才往下执行
                //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 void decrement() throws InterruptedException {
        lock.lock();
        try {
            while (number == 0) {  //1才会自动往下执行
                //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，绝对不仅仅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

• 代码测试

/**
 * A 执行完调用B，B执行完调用C，C执行完调用A
 */
public class C {
    public static void main(String[] args) {
        Data3 data3 = new Data3();
        new Thread(()->{
            for (int i = 0; i < 10; i++) {
                data3.printA();
            }
        },"A").start();
        new Thread(()->{
            for (int i = 0; i < 10; i++) {
                data3.printB();
            }
        },"B").start();
        new Thread(()->{
            for (int i = 0; i < 10; i++) {
                data3.printC();
            }
        },"C").start();
    }
}

class Data3 {
    //资源类
    private Lock lock = new ReentrantLock();
    Condition condition1 = lock.newCondition();
    Condition condition2 = lock.newCondition();
    Condition condition3 = lock.newCondition();
    private int number = 1; //1A 2B 3C

    public void printA() {
        lock.lock();
        try {
            //业务代码，判断->执行->通知
            while (number != 1) {
                //等待
                condition1.await();
            }
            System.out.println(Thread.currentThread().getName()+"=>AAAAAA");
            //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 {
            //业务代码，判断->执行->通知
            while (number !=2) {
                //等待
                condition2.await();
            }
            System.out.println(Thread.currentThread().getName()+"=>BBBBBB");
            //唤醒C
            number = 3;
            condition3.signal();

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

    public void printC() {
        lock.lock();
        try {
            //业务代码，判断->执行->通知
            while (number != 3) {
                condition3.await();
            }
            System.out.println(Thread.currentThread().getName()+"=>CCCCCC");
            number = 1;
            condition1.signal();
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            lock.unlock();
        }
    }
}

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