未使用读写锁的代码:html
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:java
能够看到写的操做原子性和独占性没有获得保证,0线程正在写入共享资源的时候,其余线程有写入和读取的共享资源操做,致使数据不一致。并发
不能够,由于添加线程
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。code
读写锁的代码:htm
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:blog
比较:资源