What is the replacement for Sets.newConcurrentHashSet()?

Question

I am upgrading from Google Collections 0.9 to 1.0. It seems Sets.newConcurrentHashSet() is no longer available. I was using it in the following construct:

public static <K, V> Multimap<K, V> newConcurrentMultimap()
{
    return Multimaps.newMultimap( new ConcurrentHashMap<K, Collection<V>>(), new Supplier<Collection<V>>()
    {
        @Override
        public Collection<V> get()
        {
             return Sets.<V>newConcurrentHashSet();
         }
    } );
}

What would be the best replacement for Sets.newConcurrentHashSet() ?

Edit: The reason for this construct is to have a multimap that is safe to read and write from multiple threads. It is used in a mostly-read scenario (and will be read a lot).

As you noted yourself in a comment below, this doesn't do what you want it to do anyway. — Kevin Bourrillion, Jan 13 '10 at 19:54

score 9 · Accepted Answer · answered Jan 13 '10 at 12:51

9

Sets.newConcurrentHashSet was withdrawn in 1.0rc1 (commit log). I don't know the reason for the withdrawal, but you could use the implementation yourself:

Sets.newSetFromMap(new ConcurrentHashMap<V, Boolean>());

answered Jan 13 '10 at 12:51

Ben Lings

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This is exactly what I have done for now. I am just wondering if it will do what I hope since the javadoc states that: "The multimap is not threadsafe when any concurrent operations update the multimap, even if map and the instances generated by factory are." I do not like to use the synchronized wrapper, since that no longer makes it concurrent but synchronized. – Wim Deblauwe Jan 13 '10 at 13:14
1

You're wondering whether it works because the javadoc tells you specifically that it doesn't work? :-) – Kevin Bourrillion Jan 13 '10 at 19:53
1

It was withdrawn in a "one step back, two steps forward" manner; since we have plans to support concurrent Sets with a decent fraction of the options you get for maps with `MapMaker`, we didn't want to also be stuck with that `newConcurrentHashSet` method for all eternity. Sorry that said functionality hasn't appeared yet. – Kevin Bourrillion Jan 13 '10 at 19:58

nanda · Answer 2 · 2010-01-13T15:18:59.127

1

Try to use MapMaker and then use newSetFromMap()

edited Jan 13 '10 at 15:18

answered Jan 13 '10 at 15:13

nanda

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score -1 · Answer 3 · edited Dec 25 '21 at 01:50

-1

You can use

Collections.newSetFromMap(new ConcurrentHashMap<>());

edited Dec 25 '21 at 01:50

Henry Ecker

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answered Dec 08 '21 at 07:57

user17623443

1

What is the replacement for Sets.newConcurrentHashSet()?

3 Answers3