minor fixes to permit running with Java 25 in restricted mode.

[leerho]

Although it looks like a lot of changes, it actually consists of the following:

• Checkstyle identified a number of places that should have been qualified with "final".
• Checkstyle identified a few places in Javadocs where there were unnecessary <p> tags.
• The GitHub Actions workflows needed to be updated to v4 from v3. These changes were also proposed by @pan3793 in PR Allow to run ds-memory 3.0 on Java 25 #271.
• The GitHub Action workflow "javadoc.yml" had to be updated because GitHub no longer recognizes the specific JamesIves/github-pages-deploy-action version. The workflow has been converted to a script that does not depend on any 3rd party actions. This is the same script used in DS-Java 9.0.0.
• The changes in ResourceImpl.java requested by @pan3793 in PR Allow to run ds-memory 3.0 on Java 25 #271. is included here. But in addition, I added a warning message that is issued if the user attempts to run with Java versions greater than 11:
  "Warning: Java versions > Java 11 can only operate in restricted mode where no off-heap operations are allowed!"

None of these changes constitute a change in core logic.

[pan3793]

this makes sense, the only concern is, will it be too noisy? maybe add a static field JAVA_VERSION_WARNING_PRINTED as a flag, then we can print it just once.

[leerho]

Good point, but I’m not sure how to do that. I would think that even a static flag would be called every time a class is loaded. Which could be a lot.

[pan3793]

A field access is relatively cheap compared to the version check logic

[pan3793]

@leerho Awesome, thanks a lot!

For the testing plan you suggested at #271 (comment),

Please thoroughly test the new prepare_3.0.3 branch form 272 in your environment to make sure it works with 25 like you expect.

It already passes our internal test cases, which are a subset of Apache Spark's official test cases. The most confident approach would be:

• deploy 3.0.3-SNAPSHOT to Apache Maven SNAPSHOT repo (or a RC version in Staging repo)
• I create a PR on the Apache Spark repo to run full test cases with the ds-memory 3.0.3[-SNAPSHOT], the test report will be publicly available, and then it can be reviewed by both the Spark and DataSketches communities.

[leerho]

We can certainly test with a snapshot, but ultimately it will need to be released. And DS-Java will need a release to reference it. All this pain is why it is essential to get Spark on 25!

And since we will have to release I found some issues with the GHA workflows, which I want to fix.

[pan3793]

@leerho I can override the ds-memory version directly in pom.xml and sbt (Spark uses both Maven and SBT as building tools)

I have opened a draft PR on the Spark repo to collect anything that benefits Spark supports Java 25, the testing work will be based on that.

[pan3793]

checkJavaVersion can be called concurrently, it can be addressed by using AtomicBoolean, and the caller side can be

if (p0 > 11 && JAVA_VERSION_WARNING_PRINTED.compareAndSet(false, true)) {
   // print warning message
}

but this is not a big deal, there is no hurt to print a few more times.

[leerho]

Thanks! What I implemented so far is simpler, I think. I'm sure using an Atomic Boolean will also work, but I'm not sure that Atomic Boolean is really necessary here since none of our sketches are thread safe anyway.

[leerho]

If you really need thread concurrency, you need to wrap the appropriate classes with a synchronized API. :)