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List:       openjdk-hotspot-runtime-dev
Subject:    Re: RFR: 8331670: Deprecate the Memory-Access Methods in sun.misc.Unsafe for Removal [v2]
From:       Per Minborg <pminborg () openjdk ! org>
Date:       2024-05-16 13:15:06
Message-ID: qiaxu2DvEBGByMMMdQycO7U39iRa6qGadkSOAcDOpbs=.fb3c487e-d3be-43a6-a1cb-5cc07c3b2254 () github ! com
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On Thu, 16 May 2024 07:14:53 GMT, Alan Bateman <alanb@openjdk.org> wrote:

> > This is the implementation changes for JEP 471.
> > 
> > The methods in sun.misc.Unsafe for on-heap and off-heap access are deprecated for \
> > removal. This means a removal warning at compile time. No methods have been \
> > removed. A deprecated message is added to each of the methods but unlikely to be \
> > seen as the JDK does not generate or publish the API docs for this class. 
> > A new command line option --sun-misc-unsafe-memory-access=$value is introduced to \
> > allow or deny access to these methods. The default proposed for JDK 23 is "allow" \
> > so no change in behavior compared to JDK 22 or previous releases. 
> > A new test is added to test the command line option settings. The existing micros \
> > for FFM that use Unsafe are updated to suppress the removal warning at compile \
> > time. A new micro is introduced with a small sample of methods to ensure the \
> > changes doesn't cause any perf regressions. 
> > For now, the changes include the update to the man page for the "java" command. \
> > It might be that this has to be separated out so that it goes with other updates \
> > in the release.
> 
> Alan Bateman has updated the pull request with a new target base due to a merge or \
> a rebase. The incremental webrev excludes the unrelated changes brought in by the \
> merge/rebase. The pull request contains ten additional commits since the last \
> revision: 
> - Add removal to DISABLED_WARNINGS
> Fail at startup if bad value specified to option
> - Merge
> - Update man page
> - Update man page
> - Fix comment
> - Merge
> - Merge
> - Whitespace
> - Initial commit

Looks good. It appears the JVM will be able to constant-fold away the \
`beforeMemoryAcess()` checks but, it would be nice to see the output of the new \
benchmark for; before PR, `MemoryAccessOption.ALLOW` and `MemoryAccessOption.WARN`.

-------------

Marked as reviewed by pminborg (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/19174#pullrequestreview-2060709939


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