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javaconcurrencyhashmapconcurrenthashmap

Simple, inexpensive concurrent list or set?

Let's say I could have thousands of objects of a certain type, and in each object there is one field for a List or set, but this list or set needs to be concurrent. A concurrent hashmap in each of hundreds or thousands of objects seems like overkill (or is it?). I also needs an atomic put-if-absent operation in each list/set. Is a ConcurrentHashMap overkill or too expensive? Is there a more lightweight alternative? I'd prefer not to do a synchronized set or list...

Solution

  • There is concurrent CopyOnWriteArraySet which is good only for sets which rarely change.

    Another option is to make a Set from ConcurrentHashMap

    Set<Object> set1 = Collections.newSetFromMap(new ConcurrentHashMap<Object, Boolean>());