同步锁Lock & 生产者和消费者案例

显示锁 Lock

①在 Java 5.0 之前，协调共享对象的访问时可以使用的机 制只有 synchronized 和 volatile 。

Java 5.0 后增加了一些 新的机制，但并不是一种替代内置锁的方法，

而是当内置锁不适用时，作为一种可选择的高级功能。

②ReentrantLock 实现了 Lock 接口，并提供了与 synchronized 相同的互斥性和内存可见性。

但相较于 synchronized 提供了更高的处理锁的灵活性。

TestLock

package com.aff.juc;

import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
/*
synchronized:隐式锁
  1.同步代码快
  2.同步锁
  jdk 1.5后
  3.同步锁Lock
    注意：是一个显示锁，需要lock()方法上锁，必须通过unlock()方法进行释放锁
 */

public class TestLock {
    public static void main(String[] args) {
        Ticket t = new Ticket();
        Thread t1 = new Thread(t,"窗口1");
        Thread t2 = new Thread(t,"窗口2");
        Thread t3 = new Thread(t,"窗口3");
        Thread t4 = new Thread(t,"窗口4");

        t1.start();
        t2.start();
        t3.start();
        t4.start();
    }
}

class Ticket implements Runnable {
    private int tick = 10000;
    private Lock lock = new ReentrantLock();

    @Override
    public void run() {
        while (true) {
            lock.lock();// 先上锁
            try {
                if (tick > 0) {
                    Thread.sleep(10);
                    System.out.println(Thread.currentThread().getName() + "还剩票数" + --tick);
                }
            } catch (Exception e) {
                e.printStackTrace();
            } finally {
                lock.unlock();// 执行完得解锁，必须执行 放在finally中
            }
        }
    }
}

生产者和消费者案例，等待唤醒机制

TestProductorAndConsumer

package com.aff.juc;

//生产者消费者案例，等待唤醒机制
public class TestProductorAndConsumer {
    public static void main(String[] args) {
        Clerk clerk = new Clerk();
        Productor pro = new Productor(clerk);
        Consumer cus = new Consumer(clerk);

        new Thread(pro, "生产者A").start();
        new Thread(cus, "消费者B").start();
        new Thread(pro, "生产者C").start();
        new Thread(cus, "消费者D").start();
    }

}

// 店员
class Clerk {
    private int product = 0;

    // 进货
    public synchronized void get() {
        while (product >= 1) {//为了避免虚假唤醒问题，应该总是使用在循环中
            System.out.println("产品已满");
            try {
                this.wait();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
        System.out.println(Thread.currentThread().getName() + ":" + ++product);
        this.notifyAll();

    }

    // 卖货
    public synchronized void sale() {
        while (product <= 0) {
            System.out.println("缺货");
            try {
                this.wait();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
        System.out.println(Thread.currentThread().getName() + ":" + --product);
        this.notifyAll();

    }
}

// 生产者
class Productor implements Runnable {
    private Clerk clerk;

    public Productor(Clerk clerk) {
        this.clerk = clerk;
    }

    @Override
    public void run() {
        for (int i = 0; i < 20; i++) {
            try {
                Thread.sleep(200);
            } catch (Exception e) {
            }
            clerk.get();
        }
    }
}

// 消费者
class Consumer implements Runnable {
    private Clerk clerk;

    public Consumer(Clerk clerk) {
        this.clerk = clerk;
    }

    @Override
    public void run() {
        for (int i = 0; i < 20; i++) {
            clerk.sale();
        }
    }
}