JAVA小学生——java锁之读写锁，

JAVA小学生——java锁之读写锁，

1. 什么是独占锁？共享锁？

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2. 读写锁的作用

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3. 手写读写分离缓存

3.1 代码实现

public class WriteAndReadCacheDemo {
    /**
     * 加入volatile 线程间保证【可见性】
     */
    private volatile Map<String, Object> map = new HashMap<>();
    /**
     * 使用ReentrantReadWriteLock 读写锁，防止并发写入的情况
     */
    private ReentrantReadWriteLock lock = new ReentrantReadWriteLock();

    public void put(String key, Object obj) {
        lock.writeLock().lock();
        try {
            System.out.println(Thread.currentThread().getName() + "\t 正在写入");
            try {
                TimeUnit.SECONDS.sleep(2);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            map.put(key, obj);
            System.out.println(Thread.currentThread().getName() + "\t 正在完成");
        } finally {
            lock.writeLock().unlock();
        }
    }

    public void get(String key) {
        lock.readLock().lock();
        try {
            System.out.println(Thread.currentThread().getName() + "\t 正在获取");
            try {
                TimeUnit.SECONDS.sleep(1);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            Object result = map.get(key);
            System.out.println(Thread.currentThread().getName() + "\t 获取完成，value=" + result);
        } finally {
            lock.readLock().unlock();
        }
    }

    public static void main(String[] args) {

        WriteAndReadCacheDemo myCache = new WriteAndReadCacheDemo();

        for (int i = 0; i < 5; i++) {
            final int temp = i;
            new Thread(() -> {
                String key = "key" + temp;
                myCache.put(key, temp);
            }, "T" + i).start();
        }

        for (int i = 0; i < 5; i++) {
            final int temp = i;
            new Thread(() -> {
                String key = "key" + temp;
                myCache.get(key);
            }, "T" + i).start();
        }
    }
}

3.2 效果比对

读写分离效果

转载于:https://www.jianshu.com/p/927e7d817e84