java锁:第四章:读写锁
理论:
未使用读写锁的代码:
package com.javaliao.backstage;
import java.util.HashMap;
import java.util.Map;
class Data{
private volatile Map map = new HashMap<String,Object>();
//写
public void put(String key,Object value){
System.out.println(Thread.currentThread().getName()+"\t 正在写入:"+key);
try {
Thread.sleep(300);
map.put(key,value);
System.out.println(Thread.currentThread().getName()+"\t 写入完成");
} catch (InterruptedException e) {
e.printStackTrace();
}
}
//读
public void get(String key){
System.out.println(Thread.currentThread().getName()+"\t 正在读取");
try {
Thread.sleep(300);
Object value = map.get(key);
System.out.println(Thread.currentThread().getName()+"\t 读取完成:"+value);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
public class Demo {
public static void main(String[] args) {
Data data = new Data();
//五个写的线程
for (int i = 0; i < 5; i++) {
final int tempInt = i;
new Thread(()->{
data.put(tempInt+"",tempInt+"");
},String.valueOf(i)).start();
}
//五个读的线程
for (int i = 0; i < 5; i++) {
final int tempInt = i;
new Thread(()->{
data.get(tempInt+"");
},String.valueOf(i)).start();
}
}
}
控制台:
可以看到写的操作原子性和独占性没有得到保证,0线程正在写入共享资源的时候,其他线程有写入和读取的共享资源操作,导致数据不一致。
是否可以添加Lock锁解决原子性和独占性的问题?
不可以,因为添加
private Lock lock = new ReentrantLock();
只能保证一个线程读,不能让多个线程同时读取,不符合实际需求。
使用ReentrantReadWriteLock解决原子性和独占性,可以很好的解决并发性和数据的一致性
读写锁的代码:
package com.javaliao.backstage;
import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.locks.ReentrantReadWriteLock;
class Data{
private volatile Map map = new HashMap<String,Object>();
private ReentrantReadWriteLock lock = new ReentrantReadWriteLock();
public void put(String key,Object value){
//写锁
lock.writeLock().lock();
try {
System.out.println(Thread.currentThread().getName()+"\t 正在写入:"+key);
Thread.sleep(300);
map.put(key,value);
System.out.println(Thread.currentThread().getName()+"\t 写入完成");
} catch (InterruptedException e) {
e.printStackTrace();
}finally {
lock.writeLock().unlock();
}
}
public void get(String key){
//读锁
lock.readLock().lock();
try {
System.out.println(Thread.currentThread().getName()+"\t 正在读取");
Thread.sleep(300);
Object value = map.get(key);
System.out.println(Thread.currentThread().getName()+"\t 读取完成:"+value);
} catch (InterruptedException e) {
e.printStackTrace();
}finally {
lock.readLock().unlock();
}
}
}
public class Demo {
public static void main(String[] args) {
Data data = new Data();
//五个写的线程
for (int i = 0; i < 5; i++) {
final int tempInt = i;
new Thread(()->{
data.put(tempInt+"",tempInt+"");
},String.valueOf(i)).start();
}
for (int i = 0; i < 5; i++) {
final int tempInt = i;
new Thread(()->{
data.get(tempInt+"");
},String.valueOf(i)).start();
}
}
}
控制台:
比较: