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From Mike Kienenberger <mkien...@gmail.com>
Subject Re: [core] performance: use indices instead of iterator (MYFACES-3130)
Date Tue, 10 May 2011 20:48:40 GMT
It's not dangerous or risky.   It's just slower.  It won't break anything.
The common case is that this change will have better performance in
all known situations.

I haven't looked at the code, but what about creating a static
Iterator instead of creating a new one each time?
Or picking whether to use iterator() or "for" based on the list type?



On Tue, May 10, 2011 at 4:29 PM, Martin Koci
<martin.kocicak.koci@gmail.com> wrote:
>
> Hi,
>
> yes, every List support indexes, but it dependes on implementation if
> that index-based access is fast or not. For example, ArrayList is fast,
> because it uses array internally; and also flags that with interface
> java.util.RandomAccess
>
> But LinkedList for example just iterates the list until it reaches the
> index you specified - there is the dangerous problem.
>
>
>
> Mike Kienenberger píše v Út 10. 05. 2011 v 16:17 -0400:
>> If getChildren() is always of type List, then it really doesn't matter
>> if it's ArrayList or ChildArrayList or some other kind of list.   You
>> can use indexes for any type of List.
>>
>> On Tue, May 10, 2011 at 4:11 PM, Martin Koci
>> <martin.kocicak.koci@gmail.com> wrote:
>> > Hi,
>> >
>> > in current codebase, myfaces use mostly enhanced loop for iterating over
>> > chidren:
>> >
>> > for (UIComponent child: getChildren())
>> >
>> > that creates new instance of iterator.
>> >
>> > After change to plain old indices:
>> >
>> > for (i = 0; i < childCount; i++)
>> >  child = getChildren().get(i);
>> >
>> > I achieved following results in my test case:
>> >
>> > 1) number of AbstractList$Itr from ~ 100 000 down to ~1500 instances per
>> > one render/response
>> >
>> > 2) time for one render/response from ~1500ms down to ~900ms
>> >
>> > please see https://issues.apache.org/jira/browse/MYFACES-3130 for more
>> > details.
>> >
>> > We know that getChildren() is type of ArrayList
>> > (javax.faces.component._ComponentChildrenList) - in this situation is
>> > index-based loop safe change.
>> >
>> > But custom component can override implementation of getChildren() and
>> > provide own implementation which can be slower: I know about Trinidad:
>> > uses ArrayList  too, so no risk here
>> > (org.apache.myfaces.trinidad.component.ChildArrayList)
>> >
>> > I use RichFaces and PrimeFaces too and don't see custom implementation
>> > of children in their codebase.
>> >
>> > What do you think about this problem? The performance gain is pretty big
>> > but also risky.
>> >
>> >
>> > Regards,
>> >
>> > Kočičák
>> >
>> >
>>
>
>
>

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