8343426: ConcurrentSkipListMap.spliterator() can no longer split the stream

[satyenme]

Backporting JDK-8343426: ConcurrentSkipListMap.spliterator() can no longer split the stream. Since Java 10, the trySplit() method for spliterators for the ConcurrentSkipListMap always returned null, causing parallel streams to be broken for ConcurrentSkipListMap and ConcurrentSkipListSet since. This change fixes the logic for considering the head.node.next field in addition to head.node. Ran GHA Sanity Checks, local Tier 1 and 2, and new test directly. Patch is clean.

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Progress

• Change must not contain extraneous whitespace
• Commit message must refer to an issue
• JDK-8343426 needs maintainer approval

Issue

• JDK-8343426: ConcurrentSkipListMap.spliterator() can no longer split the stream (Bug - P3 - Rejected)

Reviewing

Using git

Checkout this PR locally:
$ git fetch https://git.openjdk.org/jdk21u-dev.git pull/1895/head:pull/1895
$ git checkout pull/1895

Update a local copy of the PR:
$ git checkout pull/1895
$ git pull https://git.openjdk.org/jdk21u-dev.git pull/1895/head

Using Skara CLI tools

Checkout this PR locally:
$ git pr checkout 1895

View PR using the GUI difftool:
$ git pr show -t 1895

Using diff file

Download this PR as a diff file:
https://git.openjdk.org/jdk21u-dev/pull/1895.diff

Using Webrev

Link to Webrev Comment

[bridgekeeper]

👋 Welcome back ssubramaniam! A progress list of the required criteria for merging this PR into master will be added to the body of your pull request. There are additional pull request commands available for use with this pull request.

[openjdk]

❗ This change is not yet ready to be integrated.
See the Progress checklist in the description for automated requirements.

[openjdk]

This backport pull request has now been updated with issue from the original commit.

[openjdk]

⚠️ @satyenme This change is now ready for you to apply for maintainer approval. This can be done directly in each associated issue or by using the /approval command.

[mlbridge]

Webrevs

• 00: Full (41f7f319)

[satyenme]

/approval request for backport of JDK-8343426: ConcurrentSkipListMap.spliterator() can no longer split the stream

Motivation: Without this change the trySplit() method for spliterators for ConcurrentSkipListMaps and ConcurrentSkipListSets using parallel streams will remain broken. With the change, the pre-Java 10 functionality will be restored, fixing the current buggy implementation. It's possible someone's written code that depends on the buggy implementation (which always returns null), but quite unlikely.

Risk: Low. Ran GHA Sanity Checks, local Tier 1 and 2, and new test directly. Patch is clean. Change has been present in tip since November, 2024.

[openjdk]

@satyenme
8343426: The approval request has been created successfully.

[GoeLin]

Hi @satyenme
can you please

• annotate the change that broke this issue in JBS (caused by link)
• do a dependent pull request for the follow-up bug fix?
• mention the dependent pull request in your fix request message
  Thanks for the good risk assessment.

[satyenme]

Took a look through the git history, having a hard time pinpointing the exact breaking change between Java 9 and 10. Planning to take a second look, in the meantime opened a PR for the referenced follow up issue: #1906. Will get that reviewed and re-create approval request here (and create one there)

[phohensee]

#1906 appears to include the JDK-8344253 backport. You can use "/issue add JDK-8344253" to update 1906 to include the 8344253 backport, then close this one in favor of 1906.