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List:       openjdk-openjfx-dev
Subject:    Re: RFR: 8283063: Optimize Observable{List/Set/Map}Wrapper.retainAll/removeAll
From:       John Hendrikx <jhendrikx () openjdk ! org>
Date:       2023-03-30 13:14:00
Message-ID: _ixCsWPttlgmKoW--42gWJo0lEKTnMAcXqUt2KL19ik=.8a2a17cc-db25-4e38-a549-283a8d8dc4f8 () github ! com
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On Sat, 12 Mar 2022 04:57:37 GMT, Michael Strauß <mstrauss@openjdk.org> wrote:

> `Observable{List/Set/Map}Wrapper.retainAll/removeAll` can be optimized for some \
> edge cases. 
> 1. `removeAll(c)`:
> This is a no-op if 'c' is empty.
> For `ObservableListWrapper`, returning early skips an object allocation. For \
> `ObservableSetWrapper` and `ObservableMapWrapper`, returning early prevents an \
> enumeration of the entire collection. 
> 2. `retainAll(c)`:
> This is a no-op if the backing collection is empty, or equivalent to `clear()` if \
> `c` is empty. 
> I've added some tests to verify the optimized behavior for each of the three \
> classes.

Changes requested by jhendrikx (Committer).

modules/javafx.base/src/main/java/com/sun/javafx/collections/ObservableListWrapper.java \
line 172:

> 170:     @Override
> 171:     public boolean removeAll(Collection<?> c) {
> 172:         if (backingList.isEmpty() || c.isEmpty()) {

I think you should do an explicit `null` check here on `c` or swap the order of these \
arguments so it always throws an NPE here if `c` is `null` as per collection \
contract.  If you don't, it will do this implicit `null` check just after \
`beginChange`, and as I don't see a `try/finally` there to call `endChange`, it would \
mean the wrapper / changeListBuilder gets in a bad state.

modules/javafx.base/src/main/java/com/sun/javafx/collections/ObservableListWrapper.java \
line 195:

> 193:     @Override
> 194:     public boolean retainAll(Collection<?> c) {
> 195:         if (backingList.isEmpty()) {

I think we need to check `c` for `null` here first to conform to the collection \
contract.

modules/javafx.base/src/main/java/com/sun/javafx/collections/ObservableMapWrapper.java \
line 328:

> 326: 
> 327:         private boolean removeRetain(Collection<?> c, boolean remove) {
> 328:             if (c.isEmpty()) {

There is an implicit `null` check here, but it makes `removeAll` and `retainAll` \
conform to the collection contract at least.

If you want to make this explicit (or document it), then this comment should be \
applied to all the `removeRetain` methods.

-------------

PR Review: https://git.openjdk.org/jfx/pull/751#pullrequestreview-1365073384
PR Review Comment: https://git.openjdk.org/jfx/pull/751#discussion_r1153233153
PR Review Comment: https://git.openjdk.org/jfx/pull/751#discussion_r1153235221
PR Review Comment: https://git.openjdk.org/jfx/pull/751#discussion_r1153239642


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