JUC-线程间通信-Lock实现案例

骑猪看日落 2024-04-06 09:50 145阅读 0赞

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package com.nanjing.juc;
    
    import java.util.concurrent.locks.Condition;
    import java.util.concurrent.locks.Lock;
    import java.util.concurrent.locks.ReentrantLock;
    
    //第一步 创建资源类，定义属性和操作方法
    class LockShare{
        //初始值
        private int number = 0;
        //创建Lock
        private Lock lock = new ReentrantLock();
        private Condition condition = lock.newCondition();
    
        //+1的方法
        public void add() throws InterruptedException {
            //上锁
            lock.lock();
            try {
                //第二步 判断 干活 通知
                while(number != 0){
                    //判断number的值是否是0，如果不是0，等待
                    condition.await();
                }
                //如果number是0，+1
                number++;
                System.out.println(Thread.currentThread().getName()+" ===== "+number);
                //通知其他的线程
                condition.signalAll();
            } finally {
                lock.unlock();
            }
        }
        //-1的方法
        public synchronized void delete() throws InterruptedException {
            //上锁
            lock.lock();
            try {
                //判断
                while(number != 1){
                    condition.await();
                }
                //干活
                number--;
                System.out.println(Thread.currentThread().getName()+" ===== "+number);
                //通知其他的线程
                condition.signalAll();
            } finally {
                lock.unlock();
            }
        }
    
    }
    
    public class ThreadDemo_05 {
        public static void main(String[] args) {
            //第三步 创建多个线程，调用资源类的操作方法
            LockShare lockShare = new LockShare();
            new Thread(()->{
                for (int i = 0; i < 30; i++) {
                    try {
                        lockShare.add();
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
            },"刘德华").start();
    
            new Thread(()->{
                for (int i = 0; i < 30; i++) {
                    try {
                        lockShare.delete();
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
            },"张学友").start();
    
            new Thread(()->{
                for (int i = 0; i < 30; i++) {
                    try {
                        lockShare.add();
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
            },"黎明").start();
    
            new Thread(()->{
                for (int i = 0; i < 30; i++) {
                    try {
                        lockShare.delete();
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
            },"郭富城").start();
        }
    
    }

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开发步骤：

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--------------------

拓展：[Java多线程：newCondition()方法 - 动力节点][Java_newCondition_ -]

关键字synchronized与wait()/notify()这两个方法一起使用可以实现等待/通知模式， Lock锁的newContition()方法返回Condition对象，Condition类也可以实现等待/通知模式。

用notify()通知时，JVM会随机唤醒某个等待的线程， 使用Condition类可以进行选择性通知， Condition比较常用的两个方法：

● await()会使当前线程等待,同时会释放锁,当其他线程调用signal()时,线程会重新获得锁并继续执行。

● signal()用于唤醒一个等待的线程。

注意：在调用Condition的await()/signal()方法前，也需要线程持有相关的Lock锁，调用await()后线程会释放这个锁，在singal()调用后会从当前Condition对象的等待队列中，唤醒 一个线程，唤醒的线程尝试获得锁， 一旦获得锁成功就继续执行。

import java.util.concurrent.locks.Condition;
    import java.util.concurrent.locks.Lock;
    import java.util.concurrent.locks.ReentrantLock;
    
    /**
     * Condition等待与通知
     */
    public class Test01 {
        //定义锁
        static Lock lock = new ReentrantLock();
        //获得Condtion对象
        static Condition condition = lock.newCondition();
    
        //定义线程子类
        static class SubThread extends Thread{
            @Override
            public void run() {
                try {
                    lock.lock();    //在调用await()前必须先获得锁
                    System.out.println("method lock");
                    condition.await();      //等待
                    System.out.println("method  await");
                } catch (InterruptedException e) {
                    e.printStackTrace();
                } finally {
                    lock.unlock();      //释放锁
                    System.out.println("method unlock");
                }
            }
        }
    
        public static void main(String[] args) throws InterruptedException {
            SubThread t = new SubThread();
            t.start();
            //子线程启动后,会转入等待状态
    
            Thread.sleep(3000);
            //主线程在睡眠3秒后,唤醒子线程的等待
            try {
                lock.lock();
                condition.signal();
            } finally {
                lock.unlock();
            }
        }
    }

import java.io.PipedOutputStream;
    import java.util.concurrent.locks.Condition;
    import java.util.concurrent.locks.ReentrantLock;
    
    /**
     * 多个Condition实现通知部分线程, 使用更灵活
     */
    public class Test02 {
        static class Service{
            private ReentrantLock lock = new ReentrantLock();       //定义锁对象
            //定义两个Condtion对象
            private Condition conditionA = lock.newCondition();
            private Condition conditionB = lock.newCondition();
    
            //定义方法,使用conditionA等待
            public void waitMethodA(){
                try {
                    lock.lock();
                    System.out.println(Thread.currentThread().getName() + " begin wait:" + System.currentTimeMillis());
                    conditionA.await();         //等待
                    System.out.println(Thread.currentThread().getName() + " end wait:" + System.currentTimeMillis());
                } catch (InterruptedException e) {
                    e.printStackTrace();
                } finally {
                    lock.unlock();
                }
            }
    
            //定义方法,使用conditionB等待
            public void waitMethodB(){
                try {
                    lock.lock();
                    System.out.println(Thread.currentThread().getName() + " begin wait:" + System.currentTimeMillis());
                    conditionB.await();         //等待
                    System.out.println(Thread.currentThread().getName() + " end wait:" + System.currentTimeMillis());
                } catch (InterruptedException e) {
                    e.printStackTrace();
                } finally {
                    lock.unlock();
                }
            }
    
            //定义方法唤醒conditionA对象上的等待
            public void signalA(){
                try {
                    lock.lock();
                    System.out.println(Thread.currentThread().getName() + " sigal A time = " + System.currentTimeMillis());
                    conditionA.signal();
                    System.out.println(Thread.currentThread().getName() + " sigal A time = " + System.currentTimeMillis());
                } finally {
                    lock.unlock();
                }
            }
    
            //定义方法唤醒conditionB对象上的等待
            public void signalB(){
                try {
                    lock.lock();
                    System.out.println(Thread.currentThread().getName() + " sigal A time = " + System.currentTimeMillis());
                    conditionB.signal();
                    System.out.println(Thread.currentThread().getName() + " sigal A time = " + System.currentTimeMillis());
                } finally {
                    lock.unlock();
                }
            }
    
        }
    
        public static void main(String[] args) throws InterruptedException {
            Service service = new Service();
    
            //开启两个线程,分别调用waitMethodA(),waitMethodB()方法
            new Thread(new Runnable() {
                @Override
                public void run() {
                    service.waitMethodA();
                }
            }).start();
            new Thread(new Runnable() {
                @Override
                public void run() {
                    service.waitMethodB();
                }
            }).start();
    
            Thread.sleep(3000);         //main线程睡眠3秒
    //        service.signalA();          //唤醒 conditionA对象上的等待,conditionB上的等待依然继续等待
            service.signalB();
        }
    }

import java.util.concurrent.locks.Condition;
    import java.util.concurrent.locks.Lock;
    import java.util.concurrent.locks.ReentrantLock;
    
    /**
     *  使用Condition实现生产者/消费者设计模式, 两个 线程交替打印
     */
    public class Test03 {
        static class  MyService{
            private Lock lock = new ReentrantLock();        //创建锁对象
            private Condition condition = lock.newCondition();  //创建Condition对象
            private boolean flag = true;        //定义交替打印标志
    
            //定义方法只打印----横线
            public void printOne(){
                try {
                    lock.lock();        //锁定
                    while (flag){      //当flag为true等待
                        System.out.println(Thread.currentThread().getName() + " waiting...");
                        condition.await();
                    }
                    //flag为false时打印
                    System.out.println(Thread.currentThread().getName() + " ---------------- ");
                    flag = true;        //修改交替打印标志
                    condition.signal();     //通知另外的线程打印
                } catch (InterruptedException e) {
                    e.printStackTrace();
                } finally {
                    lock.unlock();      //释放锁对象
                }
            }
    
            //定义方法只打印***横线
            public void printTwo(){
                try {
                    lock.lock();        //锁定
                    while (!flag){      //当flag为false等待
                        System.out.println(Thread.currentThread().getName() + " waiting...");
                        condition.await();
                    }
                    //flag为true时打印
                    System.out.println(Thread.currentThread().getName() + " ****** ");
                    flag = false;        //修改交替打印标志
                    condition.signal();     //通知另外的线程打印
                } catch (InterruptedException e) {
                    e.printStackTrace();
                } finally {
                    lock.unlock();      //释放锁对象
                }
            }
    
        }
    
        public static void main(String[] args) {
            MyService myService = new MyService();
            //创建线程打印--
            new Thread(new Runnable() {
                @Override
                public void run() {
                    for (int i = 0; i < 100; i++) {
                        myService.printOne();
                    }
                }
            }).start();
            //创建线程打印**
            new Thread(new Runnable() {
                @Override
                public void run() {
                    for (int i = 0; i < 100; i++) {
                        myService.printTwo();
                    }
                }
            }).start();
        }
    }

[868c6ee133de48b08e5cccd97dfcb8e6.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/06/2ffc499b81be495596a918f1a4144943.png
[351a9bb656d24cf5ad04a28037d73f3a.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/06/6321e594bc7b45f3af51bdf1fb5cac6c.png
[0676ea1281d34e07b4babf1f0e431dd0.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/06/cf4f4bd9a03e491389e2f934d2ac04fb.png
[02c85bf52d574dc2b192236282abee03.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/06/fc69327703564aa9a55f201b5a3db9cb.png
[9e1f88bdff2b470688adbaadef96b376.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/06/6c9c5c514b654b95b463fed568ea9f76.png
[Java_newCondition_ -]: http://www.bjpowernode.com/javathread/1223.html