RFR: jsr166 jdk9 integration wave 12

[Martin Buchholz]

Un-OK. Sometimes when microbenchmarking, we stumble upon a code sequence
that hotspot likes.   I observed 20% improvement with the below, so
switching to that:

        public boolean tryAdvance(Consumer<? super E> action) {
            Objects.requireNonNull(action);
            final Object[] es = elements;
            if (fence < 0) { fence = tail; cursor = head; } // late-binding
            final int i;
            if ((i = cursor) == fence)
                return false;
            E e = nonNullElementAt(es, i);
            cursor = inc(i, es.length);
            action.accept(e);
            return true;
        }


On Thu, Nov 17, 2016 at 7:41 PM, Martin Buchholz <martinrb at google.com>
wrote:

>
>
> On Thu, Nov 17, 2016 at 12:03 PM, Paul Sandoz <Paul.Sandoz at oracle.com>
> wrote:
>
>>
>>  843         public boolean tryAdvance(Consumer<? super E> action) {
>>  844             if (action == null)
>>  845                 throw new NullPointerException();
>>  846             int t, i;
>>  847             if ((t = fence) < 0) t = getFence();
>>
>> Is that for optimisation purposes, since the same check is also performed
>> in getFence? If so that seems like overkill
>>
>>
> OK:
>
> --- src/main/java/util/ArrayDeque.java 18 Nov 2016 03:22:20 -0000 1.114
> +++ src/main/java/util/ArrayDeque.java 18 Nov 2016 03:38:23 -0000
> @@ -866,9 +866,8 @@
>          public boolean tryAdvance(Consumer<? super E> action) {
>              if (action == null)
>                  throw new NullPointerException();
> -            int t, i;
> -            if ((t = fence) < 0) t = getFence();
> -            if (t == (i = cursor))
> +            final int t, i;
> +            if ((t = getFence()) == (i = cursor))
>                  return false;
>              final Object[] es = elements;
>              cursor = inc(i, es.length);
>
>
>
>>
>>  848             if (t == (i = cursor))
>>  849                 return false;
>>  850             final Object[] es;
>>  851             action.accept(nonNullElementAt(es = elements, i));
>>  852             cursor = inc(i, es.length);
>>
>