On Thu, 17 Mar 2022 21:10:14 GMT, Marius Hanl <mh...@openjdk.org> wrote:
> This simple PR optimizes the observable `ArrayList` creation by using the
> ArrayList constructor/array size so that the underlying array will be
> initialized at the correct size which will speed up the creation as the array
> does not need to grow as a result of the `addAll` call.
>
> I also added tests which will succeed before and after to verify that nothing
> got broken by this change.
> Also I made a benchmark test. Results:
>
> | Benchmark | Mode| Cnt | Score | Error | Units
> | ------------- | ------------- | ------------- | ------------- |
> ------------- | ------------- |
> | ListBenchmark OLD | thrpt | 25 | 722,842 | ± 26,93 | ops/s
> | ListBenchmark NEW | thrpt | 25 | 29262,274 | ± 2088,712 | ops/s
>
> <details><summary>Benchmark code</summary>
>
>
> import javafx.collections.FXCollections;
> import javafx.collections.ObservableList;
> import org.openjdk.jmh.annotations.Benchmark;
> import org.openjdk.jmh.annotations.Scope;
> import org.openjdk.jmh.annotations.Setup;
> import org.openjdk.jmh.annotations.State;
> import org.openjdk.jmh.annotations.TearDown;
>
> import java.util.ArrayList;
> import java.util.List;
>
> @State(Scope.Benchmark)
> public class ListBenchmark {
>
> List<String> strings;
>
> @Setup
> public void setup() {
> strings = new ArrayList<>();
> for(int i = 0; i< 100000;i++) {
> strings.add("abc: " + i);
> }
> }
>
> @TearDown
> public void tearDown() {
> strings = null;
> }
>
> @Benchmark
> public ObservableList<String> init() {
> return FXCollections.observableArrayList(strings);
> }
> }
>
>
> </details>
The following pieces of code should be identical:
var list = FXCollections.observableArrayList();
list.addAll(source);
var list = FXCollections.observableList(new ArrayList<>(source));
Any observable difference in behavior would be unspecified. When it comes to
`modCount`, that's an internal field of `AbstractList`.
`FXCollections.observableArrayList()` and `FXCollections.observableList(...)`
are not the right place to test this.
-------------
PR: https://git.openjdk.java.net/jfx/pull/758
