8267452: Delegate forEachRemaining in Spliterators.iterator()

[amaembo]

Sometimes, Spliterator::forEachRemaining has much more optimized implementation, compared to Spliterator::tryAdvance. For example, if a Stream::spliterator called for a stream that has intermediate operations, tryAdvance() may buffer intermediate elements while forEachRemaining() just delegates to the wrapAndCopyInto (see StreamSpliterators.AbstractWrappingSpliterator and its inheritors).

Spliterators::iterator methods (used in particular by Stream::iterator) provide adapter iterators that delegate to the supplied spliterator. Unfortunately, they don't have a specialized implementation for Iterator::forEachRemaining. As a result, a default implementation is used that delegates to hasNext/next, which in turn causes the delegation to tryAdvance. It's quite simple to implement Iterator::forEachRemaining here, taking advantage of possible spliterator optimizations if the iterator client decides to use forEachRemaining.

This patch implements Iterator::forEachRemaining in Spliterators::iterator methods. Also, I nullize the nextElement in Iterator::next to avoid accidental prolongation of the user's object lifetime when iteration is finished. Finally, a small cleanup: I added the final modifier where possible to private fields in Spliterators.

Test-wise, some scenarios are already covered by SpliteratorTraversingAndSplittingTest. However, the resulting iterator is always wrapped into Spliterators::spliterator, so usage scenarios are somewhat limited. In particular, calling hasNext (without next) before forEachRemaining was not covered there. I added more tests in IteratorFromSpliteratorTest to cover these scenarios. I checked that removing valueReady = false; or action.accept(t); lines from newly implemented forEachRemaining method causes new tests to fail (but old tests don't fail due to this).

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Issue

• JDK-8267452: Delegate forEachRemaining in Spliterators.iterator()

Reviewers

• Paul Sandoz (@PaulSandoz - Reviewer) ⚠️ Review applies to 9a5e0dd

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[mlbridge]

Webrevs

• 02: Full - Incremental (cc337995)
• 01: Full - Incremental (9a5e0dd2)
• 00: Full (5b05135f)

[PaulSandoz]

Changes look good.

Testing wise we have the combo test SpliteratorTraversingAndSplittingTest that includes a case that tests a Spliterator produced via Spliterator -> Iterator -> Spliterator, and operations on that under various actions. GIven that case do you still think we require explicit tests?

[amaembo]

@PaulSandoz thanks for review!

As for SpliteratorTraversingAndSplittingTest, I commented in the issue description above:

Test-wise, some scenarios are already covered by SpliteratorTraversingAndSplittingTest. However, the resulting iterator is always wrapped into Spliterators::spliterator, so usage scenarios are somewhat limited. In particular, calling hasNext (without next) before forEachRemaining was not covered there. I added more tests in IteratorFromSpliteratorTest to cover these scenarios. I checked that removing valueReady = false; or action.accept(t); lines from newly implemented forEachRemaining method causes new tests to fail (but old tests don't fail due to this).

In short, it doesn't pass manual mutation testing. New tests are capable to catch more possible regressions.

[PaulSandoz]

Oops i missed the bit about testing in the description. That's subtle, the hasNext occurs in the assert before the forEachRemaining. Could you add a comment that this is the primary purpose of the test since SpliteratorTraversingAndSplittingTest cannot do that for a spliterator wrapping an iterator?

[openjdk]

@amaembo This change now passes all automated pre-integration checks.

ℹ️ This project also has non-automated pre-integration requirements. Please see the file CONTRIBUTING.md for details.

After integration, the commit message for the final commit will be:

8267452: Delegate forEachRemaining in Spliterators.iterator()

Reviewed-by: psandoz

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At the time when this comment was updated there had been 74 new commits pushed to the master branch:

• d0d2ddc: 8267651: runtime/handshake/HandshakeTimeoutTest.java times out when dumping core
• a98e476: 8267311: vmTestbase/gc/gctests/StringInternGC/StringInternGC.java eventually OOMEs
• 5aa45f2: 8267403: tools/jpackage/share/FileAssociationsTest.java#id0 failed with "Error: Bundler "Mac PKG Package" (pkg) failed to produce a package"
• c20ca42: 8267691: Change table to obsolete CriticalJNINatives in JDK 18, not 17
• e751b7b: 8267683: rfc7301Grease8F value not displayed correctly in SSLParameters javadoc
• 0b77359: 8224243: Add implSpec's to AccessibleObject and seal Executable
• 594d454: 8267574: Dead code in HtmlStyle/HtmlDocletWriter
• 2ef2450: 8263445: Duplicate key compiler.err.expected.module in compiler.properties
• cc687fd: 8267575: Add new documentation group in HtmlStyle
• 5a5b807: 8267633: Clarify documentation of (Doc)TreeScanner
• ... and 64 more: https://git.openjdk.java.net/jdk/compare/726785b8d7c18569bddae6a08fa7f61d8d7bd2c4...master

As there are no conflicts, your changes will automatically be rebased on top of these commits when integrating. If you prefer to avoid this automatic rebasing, please check the documentation for the /integrate command for further details.

➡️ To integrate this PR with the above commit message to the master branch, type /integrate in a new comment.

[amaembo]

@PaulSandoz added a comment, thanks!

[amaembo]

/integrate

[openjdk]

@amaembo Since your change was applied there have been 74 commits pushed to the master branch:

• d0d2ddc: 8267651: runtime/handshake/HandshakeTimeoutTest.java times out when dumping core
• a98e476: 8267311: vmTestbase/gc/gctests/StringInternGC/StringInternGC.java eventually OOMEs
• 5aa45f2: 8267403: tools/jpackage/share/FileAssociationsTest.java#id0 failed with "Error: Bundler "Mac PKG Package" (pkg) failed to produce a package"
• c20ca42: 8267691: Change table to obsolete CriticalJNINatives in JDK 18, not 17
• e751b7b: 8267683: rfc7301Grease8F value not displayed correctly in SSLParameters javadoc
• 0b77359: 8224243: Add implSpec's to AccessibleObject and seal Executable
• 594d454: 8267574: Dead code in HtmlStyle/HtmlDocletWriter
• 2ef2450: 8263445: Duplicate key compiler.err.expected.module in compiler.properties
• cc687fd: 8267575: Add new documentation group in HtmlStyle
• 5a5b807: 8267633: Clarify documentation of (Doc)TreeScanner
• ... and 64 more: https://git.openjdk.java.net/jdk/compare/726785b8d7c18569bddae6a08fa7f61d8d7bd2c4...master

Your commit was automatically rebased without conflicts.

Pushed as commit ac36b7d.

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