JDK1.5以后,提供了读写锁ReentrantReadWriteLock,读写锁维护了一对锁,一个读锁,一个写锁,经过分离读锁和写锁,使得并发性相比通常的排他锁有了很大提高。在读多写少的状况下,读写锁可以提供比排他锁更好的并发性和吞吐量。java
从源码中能够看出,读写锁中一样依赖队列同步器Sync(AQS)实现同步功能,而读写状态就是其同步器的同步状态。下面从例子中来讲明:读读共享,读写互斥,写写互斥。并发
代码以下:线程
public class ReentrantWriteReadLockTest { ReentrantReadWriteLock lock = new ReentrantReadWriteLock(); ReadLock readLock = lock.readLock(); WriteLock writeLock = lock.writeLock(); public void read(){ try { readLock.lock(); System.out.println("线程"+Thread.currentThread().getName()+"进入。。。"); Thread.sleep(3000); System.out.println("线程"+Thread.currentThread().getName()+"退出。。。"); } catch (InterruptedException e) { e.printStackTrace(); }finally{ readLock.unlock(); } } public void write(){ try { writeLock.lock(); System.out.println("线程"+Thread.currentThread().getName()+"进入。。。"); Thread.sleep(3000); System.out.println("线程"+Thread.currentThread().getName()+"退出。。。"); } catch (InterruptedException e) { e.printStackTrace(); }finally{ writeLock.unlock(); } } public static void main(String[] args) { final ReentrantWriteReadLockTest wr = new ReentrantWriteReadLockTest(); Thread t1 = new Thread(new Runnable() { public void run() { wr.read(); } }, "t1"); Thread t2 = new Thread(new Runnable() { public void run() { wr.read(); } }, "t2"); Thread t3 = new Thread(new Runnable() { public void run() { wr.write(); } }, "t3"); Thread t4 = new Thread(new Runnable() { public void run() { wr.write(); } }, "t4"); t1.start(); t2.start(); //t3.start(); //t4.start(); } }
当咱们启动线程t1和t2时,结果以下:code
线程t1和t2能够同时进入,说明了读读共享!blog
当咱们启动线程t2和t3时,结果以下:队列
一个线程必须等待另外一个线程退出,才能进入,说明了读写互斥!get
当咱们启动线程t3和t4时,结果以下:同步
一个线程必须等待另外一个线程退出,才能进入,说明了写写互斥!源码
以上实例说明,读写锁ReentrantReadWriteLock:读读共享,读写互斥,写写互斥!it