java - concurrentMap.keySet().toArray() 线程安全吗？

Question

我有一个 ConcurrentHashMap<String, Object> concurrentMap;

我需要返回带有 map 键的 String[]。

是下面的代码:

  public String[] listKeys() {
    return (String[]) concurrentMap.keySet().toArray();
  }

线程安全吗？

Answer 1

虽然 ConcurrentHashMap 是线程安全的类，但在键上使用的 Iterator 是不确定与任何后续 HashMap 更改同步，一旦创建...

来自spec :

    public Set<K> keySet()

    Returns a Set view of the keys contained in this map......
    ...........................

    The view's iterator is a "weakly consistent" iterator that will 
    never throw ConcurrentModificationException, and guarantees to 
    traverse elements as they existed upon construction of the iterator, 
    and may (but is not guaranteed to) reflect any modifications 
    subsequent to construction.