On Mar 11 2014, at 17:42 , Martin Buchholz <[email protected]> wrote:
> I'm hoping y'all have evidence that empty ArrayLists are common in the wild.
Yes, certainly. From the original proposal:
> [This change] based upon analysis that shows that in large applications as
> much as 10% of maps and lists are initialized but never receive any entries.
> A smaller number spend a large proportion of their lifetime empty. We've
> found similar results across other workloads as well.
> It is curious that empty lists grow immediately to 10, while ArrayList with
> capacity 1 grows to 2, then 3... Some people might think that a bug.
Yes, that's unfortunate. I've made another version that uses a second sentinel
for the default sized but empty case.
Now I want to reduce the ensureCapacity reallocations! It seems like insane
churn to replace the arrays that frequently.
> There are more changes that need to be reverted.
> Else looks good.
> - * More formally, returns the lowest index <tt>i</tt> such that
> - *
> <tt>(o==null ? get(i)==null : o.equals(get(i)))</tt>,
> + * More formally, returns the lowest index {@code i} such that
> + * {@code
> (o==null ? get(i)==null : o.equals(get(i)))},
Corrected. Thank you.
http://cr.openjdk.java.net/~mduigou/JDK-8035584/2/webrev/
Mike
>
>
> On Tue, Mar 11, 2014 at 5:20 PM, Mike Duigou <[email protected]> wrote:
> I've actually always used scp. :-)
>
> Since I accepted all of your changes as suggested and had no other changes I
> was just going to go ahead and push once testing was done.
>
> I've now prepared a revised webrev and can still accept feedback.
>
> http://cr.openjdk.java.net/~mduigou/JDK-8035584/1/webrev/
>
> (Note: The webrev also contains
> https://bugs.openjdk.java.net/browse/JDK-8037097 since I am testing/pushing
> the two issues together.)
>
> Mike
>
> On Mar 11 2014, at 16:42 , Martin Buchholz <[email protected]> wrote:
>
>> I don't see the updated webrev. Maybe you also fell victim to "rsync to cr
>> no longer working"?
>>
>>
>> On Tue, Mar 11, 2014 at 4:34 PM, Mike Duigou <[email protected]> wrote:
>>
>> On Feb 21 2014, at 14:56 , Martin Buchholz <[email protected]> wrote:
>>
>>> You should do <tt> -> code conversion separately, and do it pervasively
>>> across the entire JDK.
>>
>> From your lips to God's ears.... I keep suggesting this along with a restyle
>> to official style every time we create new repos. Seems unlikely
>> unfortunately as it makes backports harder.
>>
>>> This is not right.
>>> + * {@code
>>> (o==null ? get(i)==null : o.equals(get(i)))}
>>
>> Corrected.
>>
>>> You accidentally deleted a stray space here?
>>>
>>> - this.elementData = EMPTY_ELEMENTDATA;
>>> + this.elementData = EMPTY_ELEMENTDATA;
>>
>> Corrected.
>>
>>> public ArrayList(int initialCapacity) {
>>> - super();
>>> if (initialCapacity < 0)
>>> throw new IllegalArgumentException("Illegal Capacity: "+
>>> initialCapacity);
>>> - this.elementData = new Object[initialCapacity];
>>> + this.elementData = (initialCapacity > 0)
>>> + ? new Object[initialCapacity]
>>> + : EMPTY_ELEMENTDATA;
>>> }
>>>
>>> When optimizing for special cases, we should try very hard minimize
>>> overhead in the common case. In the above, we now have two branches in the
>>> common case. Instead,
>>>
>>> if (initialCapacity > 0) this.elementData = new Object[initialCapacity];
>>> else if (initialCapacity == 0) this.elementData = EMPTY_ELEMENTDATA;
>>> else barf
>>
>> Corrected.
>>
>> Thanks as always for the feedback.
>>
>> Mike
>>
>>>
>>>
>>>
>>> On Fri, Feb 21, 2014 at 2:41 PM, Mike Duigou <[email protected]> wrote:
>>> Hello all;
>>>
>>> This changeset consists of two small performance improvements for
>>> ArrayList. Both are related to the lazy initialization introduced in
>>> JDK-8011200.
>>>
>>> The first change is in the ArrayList(int capacity) constructor and forces
>>> lazy initialization if the requested capacity is zero. It's been observed
>>> that in cases where zero capacity is requested that it is very likely that
>>> the list never receives any elements. For these cases we permanently avoid
>>> the allocation of an element array.
>>>
>>> The second change, noticed by Gustav Åkesson, involves the
>>> ArrayList(Collection c) constructor. If c is an empty collection then there
>>> is no reason to inflate the backing array for the ArrayList.
>>>
>>> http://cr.openjdk.java.net/~mduigou/JDK-8035584/0/webrev/
>>>
>>> I also took the opportunity to the <tt></tt> -> {@code } conversion for the
>>> javadoc.
>>>
>>> Enjoy!
>>>
>>> Mike
>>>
>>
>>
>
>
