可重入不可重入锁，自旋锁，独占锁（写锁），共享锁（读锁），互斥锁，学习案例

可重入不可重入锁

/**
 * @ClassName ReenterLockDemo
 * @Description 可重入锁（也叫递归锁）
 *
 * 指的是同一线程 外层函数获得锁之后，内层递归函数仍然能获得该锁的代码
 * 在同一个线程的外层方法获取锁的时候，进入内层方法时会自动获得该锁
 *
 * 也就是说 线程可以进入任何一个他已经拥有的锁所同步着的代码块
 **/
public class ReenterLockDemo {
    public static void main(String[] args) {
        Phone phone = new Phone();
        ExecutorService executorService = Executors.newFixedThreadPool(2);
//        for(int i =0; i < 100; i++){
//            executorService.execute(()-> {
//                try {
//                    phone.sendMsg();
//                } catch (Exception e) {
//                    e.printStackTrace();
//                }
//            });
//        }
        for(int i =0; i < 2; i++){
            executorService.execute(phone);
        }
        executorService.shutdown();
    }
}
class Phone implements Runnable{
    public synchronized void sendMsg() throws Exception{
        System.out.println(Thread.currentThread().getName() + "sendMsg");
        sendEmail();
    }
    public synchronized void sendEmail() throws Exception{
        System.out.println(Thread.currentThread().getName() + "sendEmail");
    }
    Lock lock = new ReentrantLock();
    @Override
    public void run() {
        get();
    }
    public void get(){
        lock.lock();
        try {
            System.out.println(Thread.currentThread().getName() + "get");
            set();
        }finally {
            lock.unlock();
        }
    }
    public void set(){
        lock.lock();
        System.out.println(Thread.currentThread().getName() + "set");
        lock.unlock();
    }
}

自旋锁

/**
 * @ClassName SpinLockDemo
 * @Description 自旋锁
 *
 * 自旋锁是指尝试获取锁的线程不会立即堵塞，而是采用循环的方式尝试去获取锁
 * 这样的好处是可以减少线程上下文的切换， 缺点是循环会消耗cpu
 **/
public class SpinLockDemo {
    AtomicReference<Thread> atomicReference = new AtomicReference<>();

    public void myLock(){
        Thread thread = Thread.currentThread();
        System.out.println(thread.getName() + "\t come in !");
        while (!atomicReference.compareAndSet(null,thread)){
        //    System.out.println("我转！我转！");
        }
    }
    public void myUnLock(){
        Thread thread = Thread.currentThread();
        atomicReference.compareAndSet(thread,null);
        System.out.println(thread.getName() + "\t myUnLock !");
    }
    public static void main(String[] args) throws InterruptedException {
        SpinLockDemo demo = new SpinLockDemo();
        new Thread(() ->{
            demo.myLock();
            try {
                TimeUnit.SECONDS.sleep(5);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            demo.myUnLock();
        },"AA").start();

        TimeUnit.SECONDS.sleep(1);

        new Thread(() ->{
            demo.myLock();
            demo.myUnLock();
        },"BB").start();
    }
}

独占锁（写锁），共享锁（读锁），互斥锁

/**
 * @ClassName ReadWriteLockDemo
 * @Description 互斥锁
 *
 * 多个线程同时读一个资源类没有任何问题，所以为了满足并发量，读取共享资源时，应该可以同时进行
 * 但是如果有一个线程尝试去写共享资源时，就不应该有其他的线程去读或者写
 * 小总结： 读-读 能共存
 *          读-写 不能共存
 *          写-写 不能共存
 **/
class MyCache{
    private volatile Map<String, Object> map = new HashMap<>();
    private ReentrantReadWriteLock rwLock = new ReentrantReadWriteLock();

    public void put(String key, Object value) {
        rwLock.writeLock().lock();
        try {
            System.out.println(Thread.currentThread().getName() + "\t 正在写入: " + key);
            try {
                TimeUnit.MILLISECONDS.sleep(300);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            map.put(key, value);
            System.out.println(Thread.currentThread().getName() + "\t 写入完成 ");
        }catch (Exception e){
        }finally {
            rwLock.writeLock().unlock();
        }

    }
    public void get(String key) {
        rwLock.readLock().lock();
            try {
            System.out.println(Thread.currentThread().getName() + "\t 正在读取");
            try {
                TimeUnit.MILLISECONDS.sleep(300);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            System.out.println(Thread.currentThread().getName() + "\t 读取完成: " + map.get(key));
        }catch (Exception e){
        }finally {
            rwLock.readLock().unlock();
        }
    }
}
public class ReadWriteLockDemo {

    public static void main(String[] args) {
        MyCache myCache = new MyCache();

        for(int i = 1; i <= 5; i++){
            final int ii = i;
            new Thread(()-> myCache.put(ii + "", ii + "")
            ,String.valueOf(i)).start();
        }

        for(int i = 1; i <= 5; i++){
            final int ii = i;
            new Thread(()-> myCache.get(ii + "")
                    ,String.valueOf(i)).start();
        }
    }
}

本文地址：https://blog.csdn.net/qq_38854914/article/details/107379037