Welcome to the list Nathan!
I would be cautious in removing such lazy initialization patterns: even
when the array is not immediately allocated, we still often have reasons to
not want to allocate the wrapping object.
While of course each such choice relates to a specific context, so this
should not be taken as a golden rule nor enforced globally, there are
several examples of large classes in Hibernate ORM which *might* need a
significant amount of collections to be initialized, but only to deal with
very specific corner cases, sometimes only in combination with obscure
configurations.
Combining such considerations about instances which are very rarely used
with further considerations such as how wide-spread this library is used in
the world, and how "hot" some of these code paths are, then I feel we are
responsible to make these as efficient as possible. A NPE is certainly
something we need to avoid but it's a concern which we can address with
just a little bit of care.
I'll also remind that most of such patterns have been introduced only after
a problem was noted during profiling; in case of new code I'm occasionally
guilty of writing code in such style on first shot, but I generally do so
only when I think it's worth it - as I would agree that code readability
and ease of maintenance has a value as well.
Finally, remember one nice hint I got from the OpenJDK engineers: a
null-check is most often free in terms of code efficiency.
Thanks
On Tue, 18 Aug 2020 at 21:18, Nathan Xu <nathan.qingyang...@gmail.com>
wrote:
> This is my first message posted here after I finally succeeded in
> subscribing to Hibernate dev mail list.
>
> As well known, we utilized the following 'lazy initialization' pattern
> extensively in our codebase to save memory:
>
> if ( activeFactoryNames == null ) {
> activeFactoryNames = new ArrayList<>();
> }
>
> However, even since JDK7, ArrayList has gone through refactoring to keep from
> allocating
>
> memory for 10 elements in advance, if the instance was created by default
> constructor and the allocation of memory
>
> is only done when some element is really added in future. Namely, ArrayList
> has the lazy initialization feature built-in.
>
> E.g., see
> https://stackoverflow.com/questions/33688753/jdk-api-documentation-is-incorrect-for-arraylist-constructor-is-that-a-bug
>
> for details. You can also browse the source code of ArrayList to confirm.
>
> [image: Screen Shot 2020-08-18 at 4.06.58 PM.png]
>
> Needless to say, the lazy initialization pattern has serious NPE issue if it
> is not coded carefully (which is tedious and error-prone per se).
>
> As an active Hibernate v6 contributor, I am troubled by such NPE issue again
> and again.
>
> Is it a good timing to get rid of the above lazy initialization pattern for
> now?
>
> Hopefully my message is good food for thought. No finger pointing. Just
> curious.
>
>
>
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