Java多线程编程 - 原子操作(Java multi-thread programming - atomic operation)

 我正在学习使用Java进行多线程编程。 这是我得到的困惑。 
 
class Cache<K, V> {
private ConcurrentMap<K, V> cache;
private ConcurrentLinkedQueue<K> lru;

public Cache () {
    // initiate cache and lru
}

public put (K key, V value) {
    // some pre-processing
    synchronized (this) {
        cache.put(key, value);
        lru.add(key);
    }
    // some post-processing
}

}
 
 这是一个非常简单的缓存，其中包含最近最少使用的记录（lru）。 显然我需要使这两个操作成为原子。 否则，缓存和lru的状态很可能会有所不同。 
 
 现在假设我想要一个计时器任务来清理缓存，说它会清理一半的缓存。 我的问题是我的代码是否确保这两个操作（put cache和add lru）对于clean任务看起来是原子的？ 我可以做以下的事情： 
 
class CleanTask {
    Cache cache;   // the reference of Cache
    public void run () {
        // some pre-processing
        for (int i = 0; i < n; i++) {   // Just suppose I need remove n element
            synchronized (XXX) {
                cache.getCache().remove(cache.getLru().poll());
            }
        }
    }
}
 
 我应该把什么放在XXX？ 
 
 非常感谢！！！ 

I am on my way learning multi-thread programming with Java. Here is a confusion I got.
 
class Cache<K, V> {
private ConcurrentMap<K, V> cache;
private ConcurrentLinkedQueue<K> lru;

public Cache () {
    // initiate cache and lru
}

public put (K key, V value) {
    // some pre-processing
    synchronized (this) {
        cache.put(key, value);
        lru.add(key);
    }
    // some post-processing
}

}
 
Here is some very simple cache with a least recently used record (lru). Obviously I need to make these two operations atomic. Otherwise it's very likely the state of cache and lru would be different.
 
Now assume I want to have a timer task to clean the cache, say it will clean half the cache. My question is does my code above ensure these two operations (put cache and add lru) appear atomic to the clean task? Can I do something like below:
 
class CleanTask {
    Cache cache;   // the reference of Cache
    public void run () {
        // some pre-processing
        for (int i = 0; i < n; i++) {   // Just suppose I need remove n element
            synchronized (XXX) {
                cache.getCache().remove(cache.getLru().poll());
            }
        }
    }
}
 
And what should I put in XXX?
 
Thanks a lot!!!

原文：https://stackoverflow.com/questions/14116572