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java – Guava CacheBuilder删除监听器

发布时间:2020-12-15 05:08:34 所属栏目:Java 来源:网络整理
导读:请告诉我我遗失的地方. 我在DataPool中有一个CacheBuilder构建的缓存. DataPool是一个单例对象,其实例可以获取各种线程并进行操作.现在我有一个生成数据的线程并将其添加到所述缓存中. 要显示代码的相关部分: private InputDataPool(){ cache=CacheBuilder.
请告诉我我遗失的地方.

我在DataPool中有一个CacheBuilder构建的缓存. DataPool是一个单例对象,其实例可以获取各种线程并进行操作.现在我有一个生成数据的线程并将其添加到所述缓存中.

要显示代码的相关部分:

private InputDataPool(){

    cache=CacheBuilder.newBuilder().expireAfterWrite(1000,TimeUnit.NANOSECONDS).removalListener(
            new RemovalListener(){
                {
                    logger.debug("Removal Listener created");
                }
                                public void onRemoval(RemovalNotification notification) {
                                    System.out.println("Going to remove data from InputDataPool");
                                    logger.info("Following data is being removed:"+notification.getKey());
                                    if(notification.getCause()==RemovalCause.EXPIRED)
                                    {
                                        logger.fatal("This data expired:"+notification.getKey());
                                    }else
                                    {
                                        logger.fatal("This data didn't expired but evacuated intentionally"+notification.getKey());
                                    }

                                }}
                    ).build(new CacheLoader(){

                        @Override
                        public Object load(Object key) throws Exception {
                                logger.info("Following data being loaded"+(Integer)key);
                                Integer uniqueId=(Integer)key;
                                return InputDataPool.getInstance().getAndRemoveDataFromPool(uniqueId);

                        }

                    });
}

public static InputDataPool getInstance(){
        if(clsInputDataPool==null){
            synchronized(InputDataPool.class){
                if(clsInputDataPool==null)
                {
                    clsInputDataPool=new InputDataPool();
                }
            }
        }
    return clsInputDataPool;
}

从所述线程中进行的调用就像这样简单

while(true){
 inputDataPool.insertDataIntoPool(inputDataPacket);
     //call some logic which comes with inputDataPacket and sleep for 2 seconds.
}

和inputDataPool.insertDataIntoPool一样

inputDataPool.insertDataIntoPool(InputDataPacket inputDataPacket){ 
 cache.get(inputDataPacket.getId());
}

现在问题是,缓存中的元素应该在1000 nanosec之后到期.所以当第二次调用inputDataPool.insertDataIntoPool时,第一次插入的数据将被撤离,因为它必须已经过期,因为调用是在插入2秒钟.然后应该调用相应的删除侦听器.
但这不会发生.我查看了缓存统计信息,并且evictionCount始终为零,无论调用cache.get(id)多少时间.

但重要的是,如果我扩展inputDataPool.insertDataIntoPool

inputDataPool.insertDataIntoPool(InputDataPacket inputDataPacket){ 
 cache.get(inputDataPacket.getId());
    try{
     Thread.sleep(2000);
   }catch(InterruptedException ex){ex.printStackTrace();
     }
cache.get(inputDataPacket.getId())
}

那么驱逐就像预期的那样发生,并且调用了移除侦听器.

现在我非常无能为力,因为我错过了一些期待这种行为的东西.如果你看到了什么,请帮我看看.

附:请忽略任何拼写错误.也没有进行任何检查,没有使用泛型,因为这只是在测试CacheBuilder功能的阶段.

谢谢

解决方法

正如javadoc和 user guide中所解释的那样,没有任何线程可以确保在延迟过后立即从缓存中删除条目.相反,在写入操作期间删除条目,如果写入很少,则偶尔在读取操作期间删除条目.这是为了实现高吞吐量和低延迟.当然,每次写操作都不会导致清理:

Caches built with CacheBuilder do not perform cleanup and evict values
“automatically,” or instantly after a value expires,or anything of
the sort. Instead,it performs small amounts of maintenance during
write operations,or during occasional read operations if writes are
rare.

The reason for this is as follows: if we wanted to perform Cache maintenance continuously,we would need to create a thread,and its operations would be competing with user operations for shared locks. Additionally,some environments restrict the creation of threads,which would make CacheBuilder unusable in that environment.

(编辑:李大同)

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