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  • java并发编程-读写锁

    最近项目中需要用到读写锁

    读写锁适用于读操作多,写操作少的场景,假设你的程序中涉及到对一些共享资源的读和写操作,且写操作没有读操作那么频繁。在没有写操作的时候,两个线程同时读一个资源没有任何问题,所以应该允许多个线程能在同时读取共享资源。但是如果有一个线程想去写这些共享资源,就不应该再有其它线程对该资源进行读或写,也就是说 读-读能共存,读-写不能共存,写-写不能共存

    我们直接使用java的读写锁  ReadWriteLock

    如下代码是使用缓存的典型场景:

    public class ReadWriteLockTest {
    
        private static ReadWriteLock readWriteLock = new ReentrantReadWriteLock();
    
        private static LoadingCache<Long, LinkModel> windowCache = CacheBuilder
                .newBuilder()
                .expireAfterWrite(Config.ALL_RELOAD_CYCLE+1,TimeUnit.HOURS) //写入ALL_RELOAD_CYCLE小时后remove掉
                .build(new CacheLoader<Long, LinkModel>() {
                    @Override
                    public LinkModel load(Long key) throws Exception {
                        return LinkModelDAO.getLinkModelWindow(key);
                    }
                });
    
    
        public static LinkModel getLinkModelWindow(long linkId) {
            try {
                readWriteLock.readLock().lock();
                LinkModel model = windowCache.get(linkId);
                return model;
            } catch (ExecutionException e) {
                LOGGER.error(e.getMessage(), e);
            }finally {
                readWriteLock.readLock().unlock();
            }
            return null;
        }
    
    
        public static  void refershModelWindowCache(String partitionId){
    
            try {
                readWriteLock.writeLock().lock();
                HashMap<Long, LinkModel> linkModelHashMap = LinkModelDAO.getLinkModelWindowsByPartition(partitionId,Config.ALL_ROADCLASS_LIST);
                if(MapUtils.isNotEmpty(linkModelHashMap)){
                    windowCache.cleanUp();
                    windowCache.putAll(linkModelHashMap);
                }
            } catch (EventMiningException e) {
                LOGGER.error(e.getMessage(), e);
            }finally {
                readWriteLock.writeLock().unlock();
            }
    
        }
    }

     下面这篇文章写得比较详细:

     http://ifeve.com/read-write-locks/

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  • 原文地址:https://www.cnblogs.com/duanxingxing/p/5577466.html
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