RFR: 9999: Automatically open base module for accessing Unsafe on JDK 11+

[Gunnar Morling]

On Sun, 1 Nov 2020 10:00:41 GMT, Gunnar Morling <github.com+28612+gunnarmorling at openjdk.org> wrote:

>> So here's a fresh take on the `Unsafe` / `add-opens` issue for JMC Agent. This still is using `Unsafe`, but I'm using the instrumentation API for opening up the base module within the agent itself, instead of requiring the user to do so. Ideally, we'd still get away from `Unsafe`, but this make the agent easier to use. This is still a draft, would do some more polishing if you all think it's the right approach. Feedback welcome!
>
> Note that based on this I think it should also be possible to obtain a `MethodHandles.Lookup` with the private access in target packages which is required for using the publicly supported `MethodHandles` API instead of `Unsafe`.

@thegreystone, so that's ready for review from my PoV.

While not removing the need for `Unsafe` on JDK 11+ (there's my other WIP PR for that), it's a good intermediary improvement over the current situation, as it avoids the need for the user to specify the `--add-opens` option themselves. Could you log an issue so I can reference it in the commit message? Thanks!

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PR: https://git.openjdk.java.net/jmc/pull/152