concurrenthashmap - 直接在 ConcurrentHashMap 中更新 entry.value.field 的线程安全吗？

Question

有时，我们需要更新其中field一个entry.value. 线程安全的方法是构造一个新的entry.value并使用put方法来更新。也就是说，即使我只是做了一些小的修改，我也需要对原始值进行深度复制。

我可以像这样进行此更新吗

map[key].field = fieldValue;

Answer 1

Hash map returns an entry safely, but assignment of a field is out of scope of the map. So, you should do something here for thread safety. Your code is equivalent to:

Entry entry = map[key];
entry.field = fieldValue;

Obviously the field assignment operator doesn't know anything about the map.

Answer 2

也许需要对条目本身进行锁定。如果它只是一个作业，那么 volatile 。