JAVA 读写锁ReentrantReadWriteLock()

「爱情、让人受尽委屈。」 2024-03-24 13:32 53阅读 0赞

package com.test.rw;
    
    import java.util.HashMap;
    import java.util.Hashtable;
    import java.util.Map;
    import java.util.concurrent.locks.ReadWriteLock;
    import java.util.concurrent.locks.ReentrantReadWriteLock;
    /*
      独占锁(写锁) 一次只能被一个线程占有
      共享锁(读锁) 多规格线程可以同时占有
      ReadWriteLock
      读-读  可以共存
      读-写  不能共存
      写-写  不能共存
    
     */
    public class ReadWriteLockDemo {
        
        public static void main(String[] args) {
        
            MyCache2 myCache = new MyCache2();
            for (int i = 1; i <=5 ; i++) {
        
                final int temp = i;
                new Thread(()->{
        
                    myCache.put(temp+ "",temp+ "");
                },String.valueOf(i)).start();
            }
    
            for (int i = 1; i <=5 ; i++) {
        
                final int temp = i;
                new Thread(()->{
        
                    myCache.get(temp + "");
                },String.valueOf(i)).start();
            }
        }
    }
    // 加锁的
    class MyCache2 {
        
        private volatile Map<String,Object> map = new HashMap<>();
        // 读写锁  更加细粒度的控制
        private ReadWriteLock readWriteLock = new ReentrantReadWriteLock();
        // 存，写入的时候，只希望同时只有一个线程写
        public void put(String key,Object value){
        
            readWriteLock.writeLock().lock();
            try {
        
                System.out.println(Thread.currentThread().getName() + "write key :" + key);
                map.put(key,value);
                System.out.println(Thread.currentThread().getName() + "write Ok");
            }catch (Exception e){
        
                e.getStackTrace();
            }finally {
        
                readWriteLock.writeLock().unlock();
            }
        }
        // 取，读，所有人都可以读
        public void get(String key){
        
            readWriteLock.readLock().lock();
            try {
        
                System.out.println(Thread.currentThread().getName() + "Read key " + key);
                map.get(key);
                System.out.println(Thread.currentThread().getName() + "Read Ok");
            }catch (Exception e){
        
                e.getStackTrace();
            }finally {
        
                readWriteLock.readLock().unlock();
            }
    
        }
    
    }
    
    // 无锁的
    class MyCache {
        
        private volatile Map<String,Object> map = new HashMap<>();
    
        public void put(String key,Object value){
        
            System.out.println(Thread.currentThread().getName() + "write key :" + key);
            map.put(key,value);
            System.out.println(Thread.currentThread().getName() + "write Ok");
        }
    
        public void get(String key){
        
            System.out.println(Thread.currentThread().getName() + "Read key " + key);
            map.get(key);
            System.out.println(Thread.currentThread().getName() + "Read Ok");
        }
    
    }