RFR: 8283346: Optimize observable ArrayList creation in FXCollections [v6]

[Michael Strauß]

On Fri, 1 Jul 2022 12:16:36 GMT, Marius Hanl <mhanl at 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
>> 
>> Edit: I also made a synthetic benchmark by measuring the same code below 100 times with `System.nanoTime`.
>> ListBenchmark OLD (avg): 21-23ms
>> ListBenchmark NEW (avg): 2 ms
>> 
>> <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>
>
> Marius Hanl has updated the pull request incrementally with one additional commit since the last revision:
> 
>   8283346: Inline ArrayList creation

Marked as reviewed by mstrauss (Author).

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

PR: https://git.openjdk.org/jfx/pull/758