JUC基础（六）：Lock 同步锁

显示锁 Lock

 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。

 ReentrantLock 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。

package com.atguigu.juc;

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

/*
 * 一、用于解决多线程安全问题的方式：
 * 
 * synchronized:隐式锁
 * 1. 同步代码块
 * 
 * 2. 同步方法
 * 
 * jdk 1.5 后：
 * 3. 同步锁 Lock
 * 注意：是一个显示锁，需要通过 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 ticket = new Ticket();
        
        new Thread(ticket, "1号窗口").start();
        new Thread(ticket, "2号窗口").start();
        new Thread(ticket, "3号窗口").start();
    }

}

class Ticket implements Runnable{
    
    private int tick = 100;
    
    private Lock lock = new ReentrantLock();

    @Override
    public void run() {
        while(true){
            
            lock.lock(); //上锁
            
            try{
                if(tick > 0){
                    try {
                        Thread.sleep(200);
                    } catch (InterruptedException e) {
                    }
                    
                    System.out.println(Thread.currentThread().getName() + " 完成售票，余票为：" + --tick);
                }
            }finally{
                lock.unlock(); //释放锁
            }
        }
    }
    
}

 案例二：

package com.atguigu.juc;

/*
 * 生产者和消费者案例
 */
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(){//循环次数：0
        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) {
            }
            
        }
        
        System.out.println(Thread.currentThread().getName() + " : " + ++product);
        this.notifyAll();
    }
    
    //卖货
    public synchronized void sale(){//product = 0; 循环次数：0
        while(product <= 0){
            System.out.println("缺货！");
            
            try {
                this.wait();
            } catch (InterruptedException e) {
            }
        }
        
        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 (InterruptedException 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();
        }
    }
}*/

 

package com.atguigu.juc;

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

/*
 * 生产者消费者案例：
 */
public class TestProductorAndConsumerForLock {

    public static void main(String[] args) {
        Clerk clerk = new Clerk();

        Productor pro = new Productor(clerk);
        Consumer con = new Consumer(clerk);

        new Thread(pro, "生产者 A").start();
        new Thread(con, "消费者 B").start();

//         new Thread(pro, "生产者 C").start();
//         new Thread(con, "消费者 D").start();
    }

}

class Clerk {
    private int product = 0;

    private Lock lock = new ReentrantLock();
    private Condition condition = lock.newCondition();

    // 进货
    public void get() {
        lock.lock();

        try {
            if (product >= 1) { // 为了避免虚假唤醒，应该总是使用在循环中。
                System.out.println("产品已满！");

                try {
                    condition.await();
                } catch (InterruptedException e) {
                }

            }
            System.out.println(Thread.currentThread().getName() + " : "
                    + ++product);

            condition.signalAll();
        } finally {
            lock.unlock();
        }

    }

    // 卖货
    public void sale() {
        lock.lock();

        try {
            if (product <= 0) {
                System.out.println("缺货！");

                try {
                    condition.await();
                } catch (InterruptedException e) {
                }
            }

            System.out.println(Thread.currentThread().getName() + " : "
                    + --product);

            condition.signalAll();

        } finally {
            lock.unlock();
        }
    }
}

// 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 (InterruptedException e) {
                e.printStackTrace();
            }

            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();
        }
    }

}