8374382: (aio) AsynchronousFileChannel writes wrong content using heap ByteBuffer when position != 0

[AlanBateman]

On Windows only, if AsynchronousFileChannel is used with a heap ByteBuffer with a non-0 buffer position then the AsynchronousFileChannel read/write methods don't work correctly when the buffer is "substituted" for the underlying I/O operation.

This is a regression in JDK 26 after JDK-8357847, missed as we didn't have tests that exercise this scenario.

---

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Issue

• JDK-8374382: (aio) AsynchronousFileChannel writes wrong content using heap ByteBuffer when position != 0 (Bug - P3)

Reviewers

• Jaikiran Pai (@jaikiran - Reviewer)

Reviewing

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[bridgekeeper]

👋 Welcome back alanb! 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]

@AlanBateman 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:

8374382: (aio) AsynchronousFileChannel writes wrong content using heap ByteBuffer when position != 0

Reviewed-by: jpai

You can use pull request commands such as /summary, /contributor and /issue to adjust it as needed.

At the time when this comment was updated there had been 3 new commits pushed to the master branch:

• c6246d5: 8374383: Update the copyright year to 2025 in the remaining files under test/ where it was missed
• 36d2c27: 8374327: Update copyright year to 2025 for files in java.base added/updated by commits in 2025
• 3fd7bde: 8374378: Update copyright year to 2025 for jdk.internal.vm.ci in files where it was missed

Please see this link for an up-to-date comparison between the source branch of this pull request and the master branch.
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.

[openjdk]

@AlanBateman The following label will be automatically applied to this pull request:

• nio

When this pull request is ready to be reviewed, an "RFR" email will be sent to the corresponding mailing list. If you would like to change these labels, use the /label pull request command.

[mlbridge]

Webrevs

• 00: Full (4fa97fb2)

[jaikiran]

This looks good to me.

[AlanBateman]

/integrate

[openjdk]

Going to push as commit d9bd300.
Since your change was applied there have been 10 commits pushed to the master branch:

• 752f46d: 8374373: Typo in VirtualThreadSchedulerMXBean.setParallelism javadoc
• 96e5c27: 8373893: Refactor networking http server tests to use JUnit
• 481ef1d: 8374352: Update copyright year to 2025 for test/langtools/tools/javac/ in files where it was missed
• ... and 7 more: https://git.openjdk.org/jdk/compare/a6462d641cba004829f9136df22f3d953c0e0c5d...master

Your commit was automatically rebased without conflicts.

[openjdk]

@AlanBateman Pushed as commit d9bd300.

💡 You may see a message that your pull request was closed with unmerged commits. This can be safely ignored.

[AlanBateman]

/backport :jdk26

[openjdk]

@AlanBateman the backport was successfully created on the branch backport-AlanBateman-d9bd300c-jdk26 in my personal fork of openjdk/jdk. To create a pull request with this backport targeting openjdk/jdk:jdk26, just click the following link:

➡️ Create pull request

The title of the pull request is automatically filled in correctly and below you find a suggestion for the pull request body:

Hi all,

This pull request contains a backport of commit d9bd300c from the openjdk/jdk repository.

The commit being backported was authored by Alan Bateman on 1 Jan 2026 and was reviewed by Jaikiran Pai.

Thanks!

If you need to update the source branch of the pull then run the following commands in a local clone of your personal fork of openjdk/jdk:

$ git fetch https://github.com/openjdk-bots/jdk.git backport-AlanBateman-d9bd300c-jdk26:backport-AlanBateman-d9bd300c-jdk26
$ git checkout backport-AlanBateman-d9bd300c-jdk26
# make changes
$ git add paths/to/changed/files
$ git commit --message 'Describe additional changes made'
$ git push https://github.com/openjdk-bots/jdk.git backport-AlanBateman-d9bd300c-jdk26