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java鎖：第四章：讀寫鎖

理論：

未使用讀寫鎖的代碼：

    package com.javaliao.backstage;
     
    import java.util.HashMap;
    import java.util.Map;
     
    class Data{
        private volatile Map map = new HashMap<String,Object>();
     
        //寫
        public void put(String key,Object value){
            System.out.println(Thread.currentThread().getName()+"\t 正在寫入："+key);
            try {
                Thread.sleep(300);
                map.put(key,value);
                System.out.println(Thread.currentThread().getName()+"\t 寫入完成");
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
        //讀
        public void get(String key){
            System.out.println(Thread.currentThread().getName()+"\t 正在讀取");
            try {
                Thread.sleep(300);
                Object value = map.get(key);
                System.out.println(Thread.currentThread().getName()+"\t 讀取完成:"+value);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }
     
    public class Demo {
     
        public static void main(String[] args) {
            Data data = new Data();
            //五個(gè)寫的線程
            for (int i = 0; i < 5; i++) {
                final int tempInt = i;
                new Thread(()->{
                    data.put(tempInt+"",tempInt+"");
                },String.valueOf(i)).start();
            }
            //五個(gè)讀的線程
            for (int i = 0; i < 5; i++) {
                final int tempInt = i;
                new Thread(()->{
                    data.get(tempInt+"");
                },String.valueOf(i)).start();
            }
        }
    }

控制臺：

可以看到寫的操作原子性和獨(dú)占性沒有得到保證，0線程正在寫入共享資源的時(shí)候，其他線程有寫入和讀取的共享資源操作，導(dǎo)致數(shù)據(jù)不一致。
是否可以添加Lock鎖解決原子性和獨(dú)占性的問題？

不可以，因?yàn)樘砑?/p>

private Lock lock = new ReentrantLock();

只能保證一個(gè)線程讀，不能讓多個(gè)線程同時(shí)讀取，不符合實(shí)際需求。
使用ReentrantReadWriteLock解決原子性和獨(dú)占性，可以很好的解決并發(fā)性和數(shù)據(jù)的一致性

讀寫鎖的代碼：

    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){
            //寫鎖
            lock.writeLock().lock();
            try {
                System.out.println(Thread.currentThread().getName()+"\t 正在寫入："+key);
                Thread.sleep(300);
                map.put(key,value);
                System.out.println(Thread.currentThread().getName()+"\t 寫入完成");
            } catch (InterruptedException e) {
                e.printStackTrace();
            }finally {
                lock.writeLock().unlock();
            }
        }
     
        public void get(String key){
            //讀鎖
            lock.readLock().lock();
            try {
                System.out.println(Thread.currentThread().getName()+"\t 正在讀取");
                Thread.sleep(300);
                Object value = map.get(key);
                System.out.println(Thread.currentThread().getName()+"\t 讀取完成:"+value);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }finally {
                lock.readLock().unlock();
            }
        }
    }
     
     
    public class Demo {
     
        public static void main(String[] args) {
            Data data = new Data();
            //五個(gè)寫的線程
            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();
            }
        }
    }

控制臺：

比較：