RFR: 8342040: Further improve entry lookup performance for multi-release JARs [v2]

[Eirik Bjørsnøs]

On Tue, 15 Oct 2024 05:13:14 GMT, Chen Liang <liach at openjdk.org> wrote:

>> I like simple. 
>> 
>> Mixing Set.of and HashSet means a lot of semantic fu-fu (throwing/not throwing on nulls) and risks being suboptimal due making some call sites megamorphic.
>
> Yep, looks good. And I agree with Claes' evaluation that we should not complicate this construction further, especially that the result is quickly garbage collected when we compile into the string to int array map.

We could also just use `Map<String, int[]>`. This would allow us to skip the whole `Set<Integer>` to `int[]`  transition step, and the temporary `HashMap` is no longer needed.

Deduplication could occur during registration:


metaVersions.merge(name, new int[] {version}, (current, val) -> {
    // Check duplicates
    for (int v : current) {
        if (v == version) {
            return current;
        }
    }
    // Add version
    int[] merged = Arrays.copyOf(current, current.length + 1);
    merged[merged.length - 1] = version;
    return merged;
});


while the postprocessing step would simply sort each array:


for (int[] versions : metaVersions.values()) {
    // JarFile::getVersionedEntry expects sorted versions
    Arrays.sort(versions);
}


This performs ~10% better on a version-heavy `ZipFileOpen`, and I think the code is reasonably simple compared to the current state of the PR. Thoughts?

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

PR Review Comment: https://git.openjdk.org/jdk/pull/21489#discussion_r1800657937