排他锁

• 排他锁：独享锁、独占锁。一个线程获取锁，其他线程等待。也就是：synchronized

共享锁

• 共享锁：在锁中，有个叫读锁。读锁也就是共享锁。也就是说多个线程可以同时获取读锁。有了读锁，必然有写锁。写锁的话只能一个线程写，多个线程同时写肯定会有问题，是不是。

我们来总结一下：

• 多个线程可以同时读，只能一个线程写操作。

我就来代码实现一把，哈哈哈

案例：线程1线程2 读数据（是不是同时读）线程3线程4是写数据（不能同时写，只能排队写）

code

/** * 功能描述： *案例：线程1线程2 读数据（是不是同时读）线程3线程4是写数据（不能同时写，只能排队写） * @author Songxianyang * @date 2022-06-11 21:56 */public class ReadWriteLock11Day {    /**     * 主锁     */    private static ReentrantReadWriteLock readWriteLock = new ReentrantReadWriteLock(); /**     * 读锁     */    private static ReentrantReadWriteLock.ReadLock readLock = readWriteLock.readLock(); /**     * 写锁     */    private static ReentrantReadWriteLock.WriteLock writeLock = readWriteLock.writeLock(); public static void main(String[] args) { ReadWriteLock11Day lock11Day = new ReadWriteLock11Day(); new Thread(() -> {     lock11Day. read(); }, "线程1").start(); new Thread(() -> {     lock11Day. read(); }, "线程2").start(); new Thread(() -> {     lock11Day. write(); }, "线程3").start(); new Thread(() -> {     lock11Day. write(); }, "线程4").start();    } private void read() { readLock.lock(); try {     System.out.println("当前："+Thread.currentThread().getName()+"正在执行（读锁）"); } finally {     readLock.unlock(); }    } private void write() { writeLock.lock(); try {     Thread.sleep(1000);     System.out.println("当前："+Thread.currentThread().getName()+"正在执行（写锁）"); } catch (InterruptedException e) {     e.printStackTrace(); } finally {     writeLock.unlock(); }    }}

执行效果

总结：读锁同时读。写锁排队写。

读写锁中的 公平与非公平

• 不公平的的想看不就是 插队现象。哈哈 没毛病

说一线非公平插队

看一下源码的构造方法：

检测头节点是否是写，如果是写 必须去排队

代码：

/** * 功能描述： *案例：线程1线程2 读数据（是不是同时读）线程3线程4是写数据（不能同时写，只能排队写） * @author Songxianyang * @date 2022-06-11 21:56 */public class ReadWriteLock11Day {    /**     * 主锁     */    private static ReentrantReadWriteLock readWriteLock = new ReentrantReadWriteLock(false); /**     * 读锁     */    private static ReentrantReadWriteLock.ReadLock readLock = readWriteLock.readLock(); /**     * 写锁     */    private static ReentrantReadWriteLock.WriteLock writeLock = readWriteLock.writeLock(); public static void main(String[] args) { ReadWriteLock11Day lock11Day = new ReadWriteLock11Day(); new Thread(() -> {     lock11Day. read(); }, "线程1").start(); new Thread(() -> {     lock11Day. read(); }, "线程2").start(); new Thread(() -> {     lock11Day. write(); }, "线程3").start(); new Thread(() -> {     lock11Day. write(); }, "线程4").start(); new Thread(() -> {     lock11Day.read(); }, "线程5").start();    } private void read() { readLock.lock(); try {     System.out.println("当前："+Thread.currentThread().getName()+"正在执行（读锁）"); } finally {     readLock.unlock(); }    } private void write() { writeLock.lock(); try {     Thread.sleep(1000);     System.out.println("当前："+Thread.currentThread().getName()+"正在执行（写锁）"); } catch (InterruptedException e) {     e.printStackTrace(); } finally {     writeLock.unlock(); }    }}

效果图