RFR: 8283063: Optimize Observable{List/Set/Map}Wrapper.retainAll/removeAll

[Nir Lisker]

On Sat, 12 Mar 2022 04:57:37 GMT, Michael Strauß <mstrauss at 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.

Not sure if you want to do this as part of this fix, but `ModifiableObservableListBase#addAll` can also be optimized in a similar way by checking if `c` is empty. The other methods there can also be optimized, but the `ObservableListWrappe` class overrides them anyway, so it depends on how inclusive you want this change to be.

modules/javafx.base/src/main/java/com/sun/javafx/collections/ObservableSetWrapper.java line 359:

> 357: 
> 358:             return false;
> 359:         }

This is good, but if `!c.isEmpty()` then we can optimize too, I think: if `backingSet.isEmpty()`, then removing/retaining all will also return `false`. Then again, the iterator will return quickly, so it might not do much.

If you take this path, I think that doing these optimizations in the `removeAll` and `retainAll` before calling this method will be clearer, similarly to how it's done in the `List` case.

Same comment for the `Map` wrapper.

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PR: https://git.openjdk.org/jfx/pull/751