Hey Nathan,
I like the idea in general and but you have to be careful with changing
this as I assume this was done to save memory by creating the list, only
when at least one element would be added to the list. I guess if we
always initialize the list, we'd have to do something like the following
in the end `this.activeFactoryNames = activeFactoryNames.isEmpty() ?
Collections.emptyList() : activeFactoryNames` which is probably not that
bad, assuming we probably already do something similar.
I don't think anyone would object to such an improvement regarding NPE
safety as long as the final memory consumption stays the same. It would
be a pity though if we unnecessarily created lots of empty ArrayLists.
Am 18.08.2020 um 22:18 schrieb Nathan Xu:
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.
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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