RFR: 8338596: Clarify handling of restricted and caller-sensitive methods

[Jorn Vernee]

On Wed, 18 Sep 2024 15:47:01 GMT, Maurizio Cimadamore <mcimadamore at openjdk.org> wrote:

> This PR moves the section on restricted methods from the the javadoc of `java.lang.foreign` package into a standalone static [javadoc page](https://cr.openjdk.org/~mcimadamore/jdk/restricted_javadoc_section/docs/api/java.base/java/lang/foreign/doc-files/RestrictedMethods.html).
> 
> This is because, after [JEP 472](https://openjdk.org/jeps/472), we now have restricted methods *outside* the foreign package, namely `System::loadLibrary`, `Runtime::loadLibrary` (and related methods). And, even before, we also had a restricted method in `ModuleLayer.Controller`.
> 
> The new static page contains some guidance of what happens when a restricted method is called when there's no Java frame on the stack (this can happen e.g. when upcalling into a restricted method from a native thread not known to the JVM) - that is, the call is treated as originating from an unnamed module.
> 
> The static page is linked from the restricted method banner in a restricted method javadoc. Here's an [example](https://cr.openjdk.org/~mcimadamore/jdk/restricted_javadoc_section/docs/api/java.base/java/lang/foreign/Linker.html#downcallHandle(java.lang.foreign.MemorySegment,java.lang.foreign.FunctionDescriptor,java.lang.foreign.Linker.Option...)).

Is the `java/lang/foreign` package still the right place for this? (Maybe it should be under `java/lang`).

src/java.base/share/classes/java/lang/foreign/doc-files/RestrictedMethods.html line 34:

> 32: 
> 33: Some methods in the Java SE API are considered <em>restricted</em>. Restricted methods
> 34: are typically used to bind native foreign data and/or functions to first-class

I feel like a short general description is warranted here as well. Maybe something like: 'Restricted methods are APIs that can, when used incorrectly, violate the integrity of the Java Virtual Machine, but are conditionally made available to users as they provide essential functionality'

src/java.base/share/classes/java/lang/foreign/doc-files/RestrictedMethods.html line 39:

> 37: can be used to create a fresh segment with the same address and temporal bounds, but with
> 38: the provided size. This can be useful to resize memory segments obtained when
> 39: interacting with native functions.

This example is now talking about 'segment'/'address'/'temporal bounds' without the context of the other text in the package-info file, which seems a bit confusing. I suggest removing the example here, as essentially the same example is given in the next paragraph as well.

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PR Review: https://git.openjdk.org/jdk/pull/21067#pullrequestreview-2313392631
PR Review Comment: https://git.openjdk.org/jdk/pull/21067#discussion_r1765490635
PR Review Comment: https://git.openjdk.org/jdk/pull/21067#discussion_r1765482794