ReentrantReadWriteLock(读写锁)

读 共享锁

写 排它锁

ReadLock可以被多个线程持有并且在作用时排斥任何的WriteLock，而WriteLock则是完全的互斥

对于高读取频率而相对较低写入的数据结构，使用此类锁同步机制则可以提高并发量。

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public class ReadWriteLockDemo {
    static Lock lock = new ReentrantLock();
    private static int value;

    static ReadWriteLock readWriteLock = new ReentrantReadWriteLock();
    static Lock readLock = readWriteLock.readLock();
    static Lock writeLock = readWriteLock.writeLock();

    public static void read(Lock lock) {
        try {
            lock.lock();
            Thread.sleep(1000);
            System.out.println("read over!");
            //模拟读取操作
        } catch (InterruptedException e) {
            e.printStackTrace();
        } finally {
            lock.unlock();
        }
    }

    public static void write(Lock lock, int v) {
        try {
            lock.lock();
            Thread.sleep(1000);
            value = v;
            System.out.println("write over! " + value);
            //模拟写操作
        } catch (InterruptedException e) {
            e.printStackTrace();
        } finally {
            lock.unlock();
        }
    }


    public static void main(String[] args) {
        //独占锁 ReentrantLock
        /*Runnable readR = ()-> read(lock);
        Runnable writeR = ()->write(lock, new Random().nextInt());*/

        //读写锁
        Runnable readR = () -> read(readLock);
        Runnable writeR = () -> write(writeLock, new Random().nextInt());

        for (int i = 0; i < 18; i++) new Thread(readR).start();
        for (int i = 0; i < 2; i++) new Thread(writeR).start();
    }
}

在main方法中有一段代码注释,可以解开,然后将另外两句代码注释掉,对比一下执行,就会很明显的看到执行效率