目录 一、说明 二、读读不互斥 三、读写互斥 四、写写互斥 五、注意事项
一、说明
1.当读操作远远高于写操作时,使用读写锁让读读可以并发,来提高性能 2.类似于数据库中的select … from … lock in share mode 3.提供一个数据容器类,内部分别使用读锁保护数据的read()方法,写锁保护数据的write()方法
二、读读不互斥
2.1 代码示例
package com.learning;import lombok.extern.slf4j.Slf4j;import java.util.concurrent.locks.ReentrantReadWriteLock;@Slf4j
public class ReadWriteLockLearning {private Object data;private ReentrantReadWriteLock reentrantReadWriteLock = new ReentrantReadWriteLock();private ReentrantReadWriteLock.ReadLock readLock = reentrantReadWriteLock.readLock();private ReentrantReadWriteLock.WriteLock writeLock = reentrantReadWriteLock.writeLock();public Object read(){log.debug("获取读锁");readLock.lock();try {log.debug("读取");try {Thread.sleep(1000);}catch(Exception e){e.printStackTrace();}return data;}finally {log.debug("释放读锁");readLock.unlock();}}public void write(){log.debug("获取写锁");writeLock.lock();try{log.debug("写入");}finally {log.debug("释放写锁");writeLock.unlock();}}public static void main(String[] args) {ReadWriteLockLearning readWriteLockLearning = new ReadWriteLockLearning();new Thread(()->{readWriteLockLearning.read();}, "t1").start();new Thread(()->{readWriteLockLearning.read();}, "t2").start();}
}
2.2 截图示例
三、读写互斥
3.1 代码示例
package com.learning;import lombok.extern.slf4j.Slf4j;import java.util.concurrent.locks.ReentrantReadWriteLock;@Slf4j
public class ReadWriteLockLearning {private Object data;private ReentrantReadWriteLock reentrantReadWriteLock = new ReentrantReadWriteLock();private ReentrantReadWriteLock.ReadLock readLock = reentrantReadWriteLock.readLock();private ReentrantReadWriteLock.WriteLock writeLock = reentrantReadWriteLock.writeLock();public Object read(){log.debug("获取读锁");readLock.lock();try {log.debug("读取");return data;}finally {log.debug("释放读锁");readLock.unlock();}}public void write(){log.debug("获取写锁");writeLock.lock();try{log.debug("写入");try {Thread.sleep(1000);}catch(Exception e){e.printStackTrace();}}finally {log.debug("释放写锁");writeLock.unlock();}}public static void main(String[] args) {ReadWriteLockLearning readWriteLockLearning = new ReadWriteLockLearning();new Thread(()->{readWriteLockLearning.read();}, "t1").start();try {Thread.sleep(100);} catch (InterruptedException e) {e.printStackTrace();}new Thread(()->{readWriteLockLearning.write();}, "t2").start();}
}
3.2 截图示例
四、写写互斥
4.1 代码示例
package com.learning;import lombok.extern.slf4j.Slf4j;import java.util.concurrent.locks.ReentrantReadWriteLock;@Slf4j
public class ReadWriteLockLearning {private Object data;private ReentrantReadWriteLock reentrantReadWriteLock = new ReentrantReadWriteLock();private ReentrantReadWriteLock.ReadLock readLock = reentrantReadWriteLock.readLock();private ReentrantReadWriteLock.WriteLock writeLock = reentrantReadWriteLock.writeLock();public Object read(){log.debug("获取读锁");readLock.lock();try {log.debug("读取");return data;}finally {log.debug("释放读锁");readLock.unlock();}}public void write(){log.debug("获取写锁");writeLock.lock();try{log.debug("写入");try {Thread.sleep(1000);}catch(Exception e){e.printStackTrace();}}finally {log.debug("释放写锁");writeLock.unlock();}}public static void main(String[] args) {ReadWriteLockLearning readWriteLockLearning = new ReadWriteLockLearning();new Thread(()->{readWriteLockLearning.write();}, "t1").start();try {Thread.sleep(100);} catch (InterruptedException e) {e.printStackTrace();}new Thread(()->{readWriteLockLearning.write();}, "t2").start();}
}
4.2 截图示例
五、注意事项
1.读写不支持条件变量 2.不支持重入时升级:持有读锁的情况下去获取写锁,会导致获取写锁永久等待
5.2.1 代码示例
package com.learning;import lombok.extern.slf4j.Slf4j;import java.util.concurrent.locks.ReentrantReadWriteLock;@Slf4j
public class ReadWriteLockLearning2 {private Object data;private ReentrantReadWriteLock reentrantReadWriteLock = new ReentrantReadWriteLock();private ReentrantReadWriteLock.ReadLock readLock = reentrantReadWriteLock.readLock();private ReentrantReadWriteLock.WriteLock writeLock = reentrantReadWriteLock.writeLock();public void readWrite(){log.debug("获取读锁");readLock.lock();try {try{log.debug("获取写锁");writeLock.lock();}finally {log.debug("释放写锁");writeLock.unlock();}}finally {log.debug("释放读锁");readLock.unlock();}}public static void main(String[] args) {ReadWriteLockLearning2 readWriteLockLearning = new ReadWriteLockLearning2();readWriteLockLearning.readWrite();}
}
5.2.2 截图示例