8259032: MappedMemorySegmentImpl#makeMappedSegment() ignores Unmapper#pagePosition

[mcimadamore]

Hi,
this patch fixes an oversight where the address() method in FileChannelImpl.Unmapper does not take into account the value of pagePosition - this leads to a situation in which, effectively, the specified offset when mapping the segment is ignored by the runtime (because base address will always be aligned to some known quantity - which is OS/platform dependent).

To test this I had to break open into FileChannelImpl and ready the granularity.

---

Progress

• Change must not contain extraneous whitespace
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Issue

• JDK-8259032: MappedMemorySegmentImpl#makeMappedSegment() ignores Unmapper#pagePosition

Reviewers

• Alan Bateman (@AlanBateman - Reviewer) ⚠️ Review applies to 7a78d72

Contributors

• Uwe Schindler <uschindler@openjdk.org>

Download

$ git fetch https://git.openjdk.java.net/jdk16 pull/84/head:pull/84
$ git checkout pull/84

[bridgekeeper]

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[openjdk]

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[mlbridge]

Webrevs

• 02: Full (5f9ea44)
• 01: Full - Incremental (7a78d72)
• 00: Full (b58a381)

[AlanBateman]

Can you change java.base/sun.nio.ch to java.base/sun.nio.ch:+open instead? That would avoid the --illegal-access=permit.

[uschindler]

I am not sure if a test like this is really needed.
The alignment is pageSize on Linux and some arbitrary value (65536) on Windows. If you have some test file that writes like a few bytes (1, 2, 3, 4,...) To a file and then maps it with offsets other than zero, you just have to get the first byte and compare it to offset.

[uschindler]

In fact the new test only checks if everything is aligned like we expect, but it does not test that our mapping returns a memory segment with expected contents.

[uschindler]

So I tend to make a simple test without reflection that writes a defined sequence of bytes to a file and then maps it with various offsets, checking that the first byte in the mapped segment is from that sequence.

[mcimadamore]

Good suggestion!

[openjdk]

@mcimadamore this pull request can not be integrated into master due to one or more merge conflicts. To resolve these merge conflicts and update this pull request you can run the following commands in the local repository for your personal fork:

git checkout 8259032_pagepos
git fetch https://git.openjdk.java.net/jdk16 master
git merge FETCH_HEAD
# resolve conflicts and follow the instructions given by git merge
git commit -m "Merge master"
git push

[uschindler]

Hi,
The new test looks fine to me.
Uwe

[AlanBateman]

Good suggestion from Uwe.

[mcimadamore]

/integrate

[openjdk]

@mcimadamore This PR has not yet been marked as ready for integration.

[openjdk]

@mcimadamore 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:

8259032: MappedMemorySegmentImpl#makeMappedSegment() ignores Unmapper#pagePosition

Co-authored-by: Uwe Schindler <uschindler@openjdk.org>
Reviewed-by: alanb

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

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[mcimadamore]

/contributor add uschindler

[openjdk]

@mcimadamore
Contributor Uwe Schindler <uschindler@openjdk.org> successfully added.

[mcimadamore]

/integrate

[openjdk]

@mcimadamore Pushed as commit e66187d.

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