ConcurrentHashMap JDK1.7中的“Scan andLockForPut”

Question

private HashEntry<K,V> scanAndLockForPut(K key, int hash, V value) {
HashEntry<K,V> first = entryForHash(this, hash);
HashEntry<K,V> e = first;
HashEntry<K,V> node = null;
int retries = -1; // negative while locating node
while (!tryLock()) {
    HashEntry<K,V> f; // to recheck first below
    if (retries < 0) {
        if (e == null) {
            if (node == null) // speculatively create node
                node = new HashEntry<K,V>(hash, key, value, null);
            retries = 0;
        }
        else if (key.equals(e.key))
            retries = 0;
        else
            e = e.next;
    }
    else if (++retries > MAX_SCAN_RETRIES) {
        lock();
        break;
    }
    else if ((retries & 1) == 0 &&
             (f = entryForHash(this, hash)) != first) {
        e = first = f; // re-traverse if entry changed
        retries = -1;
    }
}
return node;

Answer 1

具体来说，“未筛选”是指什么？

在这种情况下，“筛选”意味着在调用Equals之前检查身份。以下语句的左侧也取自CHM：

if ((k = e.key) == key || (e.hash == hash && key.equals(k)))

因此，“未筛查”意味着跳过身份检查。