[PATCH] Implement a noop clear() for Collections#EMPTY_LIST

[Mohamed Naufal]

Hi,

You're right of course, I should have been clearer, no allocation happens
for clear() on EmptyMap or EmptySet, but a lot of unnecessary calls are
made.

The call stack for clear() on EmptySet looks something like this:
AbstractCollection#clear() ->EmptySet#iterator() ->
Collections#emptyIterator() -> returns the singleton
EmptyIterator#EMPTY_ITERATOR on which hasNext() is called.

And for EmptyMap:
AbstractMap#clear() -> EmptyMap#entrySet() -> Collections#emptySet(), from
which point onwards, it's similar to that of EmptySet.

This could be avoided with the direct override.

Thanks,
Naufal

On 28 May 2016 at 22:32, Louis Wasserman <lowasser at google.com> wrote:

> Is it?  IIRC EmptyMap and EmptySet will use a singleton unmodifiable empty
> Iterator, so they won't incur any allocation, and the clear() will finish
> immediately with no work anyway.
>
> On Sat, May 28, 2016, 2:05 AM Mohamed Naufal <naufal11 at gmail.com> wrote:
>
>> Hi,
>>
>> I see that this is applicable to EmptyMap and EmptySet as well, here's an
>> updated patch with clear() overridden for all 3 classes.
>>
>> Thanks,
>> Naufal
>>
>> On 23 May 2016 at 16:13, Paul Sandoz <paul.sandoz at oracle.com> wrote:
>>
>> > Hi Naufal,
>> >
>> > Thanks for looking at this.
>> >
>> > For us to accept your patch (no matter how small) you need to become a
>> > contributor, which requires that you agree to the Oracle Contributor
>> > Agreement (OCA), see:
>> >
>> >   http://openjdk.java.net/contribute/
>> >
>> > Thanks,
>> > Paul.
>> >
>> > > On 22 May 2016, at 12:10, Mohamed Naufal <naufal11 at gmail.com> wrote:
>> > >
>> > > Hi,
>> > >
>> > > A call to clear() on Collections#EMPTY_LIST is currently redirected to
>> > > AbstractList#clear(), which performs a bunch of checks and creates a
>> > > ListItr object, all of which is unnecessary for an EmptyList.
>> > >
>> > > PFA a patch that implements a noop clear() for EmptyList.
>> > >
>> > > Thanks,
>> > > Naufal
>> > > <EmptyList_clear.diff>
>> >
>> >
>>
>