读写锁和缓存类实现

提高性能

读写锁&＃xff1a;分为读锁和写锁&＃xff0c;多个读锁不互斥&＃xff0c;读锁与写锁互斥&＃xff0c;写锁与写锁互斥&＃xff0c;这是由JVM控制的&＃xff0c;我们只需要上好相应的锁即可。如果代码只读数据&＃xff0c;可以很多人同时读&＃xff0c;但不能同时写&＃xff0c;那就上读锁&＃xff1b;如果代码修改数据&＃xff0c;只能有一个人在写&＃xff0c;且不能同时读取&＃xff0c;那就上写锁。总之&＃xff0c;读的时候上读锁&＃xff0c;写的时候上写锁。

import java.util.Random;
import java.util.concurrent.locks.ReadWriteLock;
import java.util.concurrent.locks.ReentrantReadWriteLock;public class ReadWriteLockTest {public static void main(String[] args) {final Queue3 q3 &＃61; new Queue3();for(int i&＃61;0;i<3;i&＃43;&＃43;){new Thread(){public void run(){while(true){q3.get();                        }}}.start();new Thread(){public void run(){while(true){q3.put(new Random().nextInt(10000));}}            }.start();}}
}class Queue3{private Object data &＃61; null;//共享数据&＃xff0c;只能有一个线程能写该数据&＃xff0c;但可以有多个线程同时读该数据。ReadWriteLock rwl &＃61; new ReentrantReadWriteLock();public void get(){rwl.readLock().lock();try {System.out.println(Thread.currentThread().getName() &＃43; " be ready to read data!");Thread.sleep((long)(Math.random()*1000));System.out.println(Thread.currentThread().getName() &＃43; "have read data :" &＃43; data);            } catch (InterruptedException e) {e.printStackTrace();}finally{rwl.readLock().unlock();}}public void put(Object data){rwl.writeLock().lock();try {System.out.println(Thread.currentThread().getName() &＃43; " be ready to write data!");                    Thread.sleep((long)(Math.random()*1000));this.data &＃61; data;        System.out.println(Thread.currentThread().getName() &＃43; " have write data: " &＃43; data);                    } catch (InterruptedException e) {e.printStackTrace();}finally{rwl.writeLock().unlock();}}
}

面试题缓存类实现

import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.locks.ReadWriteLock;
import java.util.concurrent.locks.ReentrantReadWriteLock;public class CacheDemo {private Map cache &＃61; new HashMap();public static void main(String[] args) {// TODO Auto-generated method stub}private ReadWriteLock rwl &＃61; new ReentrantReadWriteLock();public  Object getData(String key){rwl.readLock().lock();Object value &＃61; null;try{value &＃61; cache.get(key);if(value &＃61;&＃61; null){rwl.readLock().unlock();rwl.writeLock().lock();try{if(value&＃61;&＃61;null){value &＃61; "aaaa";//实际是去queryDB();}}finally{rwl.writeLock().unlock();}rwl.readLock().lock();}}finally{rwl.readLock().unlock();}return value;}
}

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