RFR : 8016446 : (m) Add override forEach/replaceAll to HashMap, Hashtable, IdentityHashMap, WeakHashMap, TreeMap (original) (raw)
Remi Forax forax at univ-mlv.fr
Thu Jun 13 21:56:08 UTC 2013
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On 06/13/2013 04:47 PM, Paul Sandoz wrote:
On Jun 13, 2013, at 4:06 PM, Remi Forax <forax at univ-mlv.fr> wrote:
There is a difference between an Iterator/forEach and a spliterator/stream, with a stream you know that the called lambdas will not interfere and mutate the source collection.
You do? I don't think there is any conceptual difference between the following w.r.t. interference: ArrayList l = ... l.stream().filter(...).forEach(e -> l.add(e)); l.spliterator().forEachRemaining(e -> l.add(e)); and: ArrayList l = ... l.forEach(e -> l.add(e)); l.iterator().forEachRemaining(e -> l.add(e)); Of course we have (or will have) strong wording saying don't implement interfering lambdas, but we still have to check for co-modification in the traversal methods of ArrayList spliterator. Isn't it because if you remove an element from an ArrayList while iterating you can see a stale value ? While with a HashMap, if you have only one thread, you can not see a stale entry ? Assuming just one thread do you agree that in all of the above examples the only way the list can be interfered with is by the Consumer instance e -> l.add(s) ?
yes, as I said to Mike, what is important IMO is that the semantics of forEach and the semantics of for(:) should be the same.
So a spliterator on HashMap can only check the modCount at the end unlike the one on ArrayList that need to check at each step. The ArrayList.spliterator.forEachRemaining implementation also checks at the end.
Given that a spliterator is something new which is weaker than an iterator, the semantics can be relaxed. For ArrayList, because you can see a stale entry if you mutate during a forEachRemaining, you have no choice but checking at each step. And because the semantics is not tight to the iterator one, I agree that you can also perform a check at the end. For HashMap.spliterator.forEachRemaining, because you can not see stale entry (without concurrency), you can only perform a check at the end. It's IMO also a valid semantics.
Paul.
Rémi
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