RFR : 8016446 : (m) Add override forEach/replaceAll to HashMap, Hashtable, IdentityHashMap, WeakHashMap, TreeMap

Remi Forax forax at univ-mlv.fr
Thu Jun 13 14:06:21 UTC 2013

On 06/13/2013 10:44 AM, Paul Sandoz wrote:
> On Jun 13, 2013, at 10:15 AM, Remi Forax <forax at univ-mlv.fr> wrote:
>> On 06/13/2013 09:51 AM, Paul Sandoz wrote:
>>> On Jun 13, 2013, at 7:28 AM, Mike Duigou <mike.duigou at oracle.com> wrote:
>>>> I have updated my webrev with Remi's improvements and some other improvements to the fast-fail concurrent modification checking.
>>>> Revised webrev:
>>>> http://cr.openjdk.java.net/~mduigou/JDK-8016446/1/webrev/
>>> The approach we have taken for bulk traversal of fail-fast spliterators and ArrayList/Vector is to check the mod count at the end of the loop. I think we should be consistent with those.
>>> Paul.
>> Hi Paul,
>> ArrayList.forEach() does the modCount check at each step.
> Doh, yes, i mis read the logic in the for statement in ArrayList/Vector.
>> 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 ?
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.

> So we are still inconsistent between Spliterator.forEachRemaining and Iterator.forEachReamining/Collection.forEach.
> Paul.


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