8177107: Reduce memory footprint of java.lang.reflect.Constructor/Method

[cl4es]

As an alternative to #7667 I took a look at injecting an empty class array from the VM. Turns out we already do this for exception types - see https://github.com/openjdk/jdk/blob/master/src/hotspot/share/oops/method.cpp#L918 - and we can do similarly for the parameter types array. We still need to parse the signature for the return type, though.

I've verified by dumping and inspecting heaps that this means we are not allocating extra Class<?>[] on Method reflection.

---

Progress

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Issue

• JDK-8177107: Reduce memory footprint of java.lang.reflect.Constructor/Method

Reviewers

• Joe Darcy (@jddarcy - Reviewer)
• Aleksey Shipilev (@shipilev - Reviewer)
• Coleen Phillimore (@coleenp - Reviewer)

Reviewing

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

8177107: Reduce memory footprint of java.lang.reflect.Constructor/Method

Reviewed-by: darcy, shade, coleenp

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At the time when this comment was updated there had been 30 new commits pushed to the master branch:

• b9cc3bc: 8284067: jpackage'd launcher reports non-zero exit codes with error prompt
• bbe894f: 8284288: Use SVG images for FocusSpec.html and Modality.html
• e524107: 8280872: Reorder code cache segments to improve code density
• e18414a: 8284014: Menu items with submenus in JPopupMEnu are not spoken on macOS
• b56df28: 8283935: Parallel: Crash during pretouch after large pages allocation failure
• 0a67d68: 8284294: Create an automated regression test for RFE 4138746
• 955d61d: 8284369: TestFailedAllocationBadGraph fails with -XX:TieredStopAtLevel < 4
• 4ffe96a: 8282506: Clean up remaining references to TwoStacksPlain*SocketImpl
• 741be46: 8183390: Fix and re-enable post loop vectorization
• 500f9a5: 8283396: Null pointer dereference in loopnode.cpp:2851
• ... and 20 more: https://git.openjdk.java.net/jdk/compare/9d200d6e7a3399d2b5448c27e40eb3b4d14a02df...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.

[shipilev]

Looks fine. I would have thought to put assert(parameter_count > 0) near mirrors->obj_at_put(index++, mirror);, but I think it is fine as it is, since obj_at_put does its own bounds checking.

[cl4es]

Thanks for reviewing! As @shipilev point out obj_at_put would assert if we tried to put anything into an empty array, so it seems redundant to add more checks here. Perhaps a comment to point that out since it was brought up here.

Do I need a second reviewer for the hotspot changes?

[shipilev]

Do I need a second reviewer for the hotspot changes?

FWIW, I think hotspot changes are quite simple, so maybe no need for second reviewer?

[coleenp]

Looks good.

[cl4es]

Thanks!

/integrate

[openjdk]

Going to push as commit a385142.
Since your change was applied there have been 31 commits pushed to the master branch:

• ec205f6: 8284023: java.sun.awt.X11GraphicsDevice.getDoubleBufferVisuals() leaks XdbeScreenVisualInfo
• b9cc3bc: 8284067: jpackage'd launcher reports non-zero exit codes with error prompt
• bbe894f: 8284288: Use SVG images for FocusSpec.html and Modality.html
• e524107: 8280872: Reorder code cache segments to improve code density
• e18414a: 8284014: Menu items with submenus in JPopupMEnu are not spoken on macOS
• b56df28: 8283935: Parallel: Crash during pretouch after large pages allocation failure
• 0a67d68: 8284294: Create an automated regression test for RFE 4138746
• 955d61d: 8284369: TestFailedAllocationBadGraph fails with -XX:TieredStopAtLevel < 4
• 4ffe96a: 8282506: Clean up remaining references to TwoStacksPlain*SocketImpl
• 741be46: 8183390: Fix and re-enable post loop vectorization
• ... and 21 more: https://git.openjdk.java.net/jdk/compare/9d200d6e7a3399d2b5448c27e40eb3b4d14a02df...master

Your commit was automatically rebased without conflicts.

[openjdk]

@cl4es Pushed as commit a385142.

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