RFR: 8282191: Implementation of Foreign Function & Memory API (Preview) [v37]

[ExE Boss]

On Tue, 3 May 2022 10:40:02 GMT, Maurizio Cimadamore <mcimadamore at openjdk.org> wrote:

>> This PR contains the API and implementation changes for JEP-424 [1]. A more detailed description of such changes, to avoid repetitions during the review process, is included as a separate comment.
>> 
>> [1] - https://openjdk.java.net/jeps/424
>
> Maurizio Cimadamore has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 57 commits:
> 
>  - Merge branch 'master' into foreign-preview
>  - Update src/java.base/share/classes/jdk/internal/misc/X-ScopedMemoryAccess.java.template
>    
>    Co-authored-by: ExE Boss <3889017+ExE-Boss at users.noreply.github.com>
>  - Tweak support for Linker lookup
>    Improve javadoc of SymbolLookup
>  - Tweak Addressable javadoc
>  - Downcall and upcall tests use wrong layout which is missing some trailing padding
>  - Simplify libraryLookup impl
>  - Address CSR comments
>  - Merge branch 'master' into foreign-preview
>  - Add ValueLayout changes
>  - Tweak support for array element var handle
>  - ... and 47 more: https://git.openjdk.java.net/jdk/compare/af1ee1cc...41d055ab

src/java.base/share/classes/java/lang/foreign/SymbolLookup.java line 116:

> 114:  * Linker nativeLinker = Linker.nativeLinker();
> 115:  * SymbolLookup stdlib = nativeLinker.defaultLookup();
> 116:  * MemorySegment malloc = stdlib.lookup("malloc");

This should be:
Suggestion:

 * Optional<MemorySegment> malloc = stdlib.lookup("malloc");

or
Suggestion:

 * MemorySegment malloc = stdlib.lookup("malloc").orElseThrow();

src/java.base/share/classes/java/lang/foreign/SymbolLookup.java line 153:

> 151:     static SymbolLookup loaderLookup() {
> 152:         Class<?> caller = Reflection.getCallerClass();
> 153:         ClassLoader loader = Objects.requireNonNull(caller.getClassLoader());

Shouldn’t this be changed to throw `IllegalCallerException` instead of throwing `NullPointerException` when the `caller`’s `ClassLoader` is `null`[^1] or when `caller` itself is `null`[^2]?

[^1]: This happens when `caller` is on the bootstrap classpath.
[^2]: This happens when `SymbolLookup.loaderLookup()` is called by native code and no **Java** code is on the call stack.

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PR: https://git.openjdk.java.net/jdk/pull/7888