Java 并发编程ReadWriteLock-蒲公英云

Java 并发编程ReadWriteLock

`一、ReadWriteLock`

ReadWriteLock 有一个实现类 ReentrantReadWriteLock 可以用来创建读写锁。在学习之前可以先学习一下
ReentrantLock。

ReadWriteLock特性：

支持公平锁与非公平锁；
可重入；
支持锁降级（写锁 -> 读锁），写锁降级成读锁，并不会自动释放当前线程获取的写锁，仍然需要显示的释放，否则别的线程永远也获取不到写锁；
读写锁之间是互斥关系；
写锁与写锁之间是互斥关系；
读锁与读锁之间可以同时进行。

`二、是例`

public class Test {
    public static void main(String[] args) throws Exception {
        ReadWriteLock readWriteLock = new ReentrantReadWriteLock();
        Lock writeLock = readWriteLock.writeLock();
        Lock readLock = readWriteLock.readLock();
        Runnable runnable1 = new Runnable() {
            @Override
            public void run() {
                writeLock.lock();
                System.out.println(Thread.currentThread().getName() + "开始写入数据....");
                try {
                    Thread.sleep(1000);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                System.out.println(Thread.currentThread().getName() + "写入完成!");
                writeLock.unlock();
            }
        };
        Runnable runnable2 = new Runnable() {
            @Override
            public void run() {
                readLock.lock();
                System.out.println(Thread.currentThread().getName() + "开始读取数据。。。");
                try {
                    Thread.sleep(1000);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                System.out.println(Thread.currentThread().getName() + "读取数据完成");
                readLock.unlock();
            }
        };
        Thread thread1 = new Thread(runnable1);
        Thread thread2 = new Thread(runnable2);
        thread2.start();
        thread1.start();
    }
}