java 基础 HashMap 并发扩容问题

 

 存入的数据过多的时候,尤其是需要扩容的时候,在并发情况下是很容易出现问题.

resize函数：

void resize(int newCapacity) {
        Entry[] oldTable = table;
        int oldCapacity = oldTable.length;
        if (oldCapacity == MAXIMUM_CAPACITY) {
            threshold = Integer.MAX_VALUE;
            return;
        }
 
        Entry[] newTable = new Entry[newCapacity];
        boolean oldAltHashing = useAltHashing;
        useAltHashing |= sun.misc.VM.isBooted() &&
                (newCapacity >= Holder.ALTERNATIVE_HASHING_THRESHOLD);
        boolean rehash = oldAltHashing ^ useAltHashing;
        transfer(newTable, rehash);  //transfer函数的调用
        table = newTable;
        threshold = (int)Math.min(newCapacity * loadFactor, MAXIMUM_CAPACITY + 1);
    }

 

void transfer(Entry[] newTable, boolean rehash) {
        int newCapacity = newTable.length;
        for (Entry<K,V> e : table) { //这里才是问题出现的关键..
            while(null != e) {
                Entry<K,V> next = e.next;  //寻找到下一个节点..
                if (rehash) {
                    e.hash = null == e.key ? 0 : hash(e.key);
                }
                int i = indexFor(e.hash, newCapacity);  //重新获取hashcode
                e.next = newTable[i];  
                newTable[i] = e;
                e = next;
            }
        }
    }

并发导致死循环：

 

 

 

 

 

https://blog.csdn.net/z69183787/article/details/64920074?locationNum=15&fps=1